<?php  // $Id: questionlib.php,v 1.119.2.29 2010/02/05 16:36:59 tjhunt Exp $
/**
 * Code for handling and processing questions
 *
 * This is code that is module independent, i.e., can be used by any module that
 * uses questions, like quiz, lesson, ..
 * This script also loads the questiontype classes
 * Code for handling the editing of questions is in {@link question/editlib.php}
 *
 * TODO: separate those functions which form part of the API
 *       from the helper functions.
 *
 * @author Martin Dougiamas and many others. This has recently been completely
 *         rewritten by Alex Smith, Julian Sedding and Gustav Delius as part of
 *         the Serving Mathematics project
 *         {@link http://maths.york.ac.uk/serving_maths}
 * @license http://www.gnu.org/copyleft/gpl.html GNU Public License
 * @package question
 */

/// CONSTANTS ///////////////////////////////////

/**#@+
 * The different types of events that can create question states
 */
define('QUESTION_EVENTOPEN', '0');      // The state was created by Moodle
define('QUESTION_EVENTNAVIGATE', '1');  // The responses were saved because the student navigated to another page (this is not currently used)
define('QUESTION_EVENTSAVE', '2');      // The student has requested that the responses should be saved but not submitted or validated
define('QUESTION_EVENTGRADE', '3');     // Moodle has graded the responses. A SUBMIT event can be changed to a GRADE event by Moodle.
define('QUESTION_EVENTDUPLICATE', '4'); // The responses submitted were the same as previously
define('QUESTION_EVENTVALIDATE', '5');  // The student has requested a validation. This causes the responses to be saved as well, but not graded.
define('QUESTION_EVENTCLOSEANDGRADE', '6'); // Moodle has graded the responses. A CLOSE event can be changed to a CLOSEANDGRADE event by Moodle.
define('QUESTION_EVENTSUBMIT', '7');    // The student response has been submitted but it has not yet been marked
define('QUESTION_EVENTCLOSE', '8');     // The response has been submitted and the session has been closed, either because the student requested it or because Moodle did it (e.g. because of a timelimit). The responses have not been graded.
define('QUESTION_EVENTMANUALGRADE', '9');   // Grade was entered by teacher

define('QUESTION_EVENTS_GRADED', QUESTION_EVENTGRADE.','.
                    QUESTION_EVENTCLOSEANDGRADE.','.
                    QUESTION_EVENTMANUALGRADE);
/**#@-*/

/**#@+
 * The core question types.
 */
define("SHORTANSWER",   "shortanswer");
define("TRUEFALSE",     "truefalse");
define("MULTICHOICE",   "multichoice");
define("RANDOM",        "random");
define("MATCH",         "match");
define("RANDOMSAMATCH", "randomsamatch");
define("DESCRIPTION",   "description");
define("NUMERICAL",     "numerical");
define("MULTIANSWER",   "multianswer");
define("CALCULATED",    "calculated");
define("ESSAY",         "essay");
/**#@-*/

/**
 * Constant determines the number of answer boxes supplied in the editing
 * form for multiple choice and similar question types.
 */
define("QUESTION_NUMANS", "10");

/**
 * Constant determines the number of answer boxes supplied in the editing
 * form for multiple choice and similar question types to start with, with
 * the option of adding QUESTION_NUMANS_ADD more answers.
 */
define("QUESTION_NUMANS_START", 3);

/**
 * Constant determines the number of answer boxes to add in the editing
 * form for multiple choice and similar question types when the user presses
 * 'add form fields button'.
 */
define("QUESTION_NUMANS_ADD", 3);

/**
 * The options used when popping up a question preview window in Javascript.
 */
define('QUESTION_PREVIEW_POPUP_OPTIONS', 'scrollbars=yes,resizable=yes,width=700,height=540');

/**#@+
 * Option flags for ->optionflags
 * The options are read out via bitwise operation using these constants
 */
/**
 * Whether the questions is to be run in adaptive mode. If this is not set then
 * a question closes immediately after the first submission of responses. This
 * is how question is Moodle always worked before version 1.5
 */
define('QUESTION_ADAPTIVE', 1);

/**
 * options used in forms that move files.
 *
 */
define('QUESTION_FILENOTHINGSELECTED', 0);
define('QUESTION_FILEDONOTHING', 1);
define('QUESTION_FILECOPY', 2);
define('QUESTION_FILEMOVE', 3);
define('QUESTION_FILEMOVELINKSONLY', 4);

/**#@-*/

/// QTYPES INITIATION //////////////////
// These variables get initialised via calls to question_register_questiontype
// as the question type classes are included.
global $QTYPES, $QTYPE_MANUAL, $QTYPE_EXCLUDE_FROM_RANDOM;
/**
 * Array holding question type objects
 */
$QTYPES = array();
/**
 * String in the format "'type1','type2'" that can be used in SQL clauses like
 * "WHERE q.type IN ($QTYPE_MANUAL)".
 */
$QTYPE_MANUAL = '';
/**
 * String in the format "'type1','type2'" that can be used in SQL clauses like
 * "WHERE q.type NOT IN ($QTYPE_EXCLUDE_FROM_RANDOM)".
 */
$QTYPE_EXCLUDE_FROM_RANDOM = '';

/**
 * Add a new question type to the various global arrays above.
 *
 * @param object $qtype An instance of the new question type class.
 */
function question_register_questiontype($qtype) {
    global $QTYPES, $QTYPE_MANUAL, $QTYPE_EXCLUDE_FROM_RANDOM;

    $name = $qtype->name();
    $QTYPES[$name] = $qtype;
    if ($qtype->is_manual_graded()) {
        if ($QTYPE_MANUAL) {
            $QTYPE_MANUAL .= ',';
        }
        $QTYPE_MANUAL .= "'$name'";
    }
    if (!$qtype->is_usable_by_random()) {
        if ($QTYPE_EXCLUDE_FROM_RANDOM) {
            $QTYPE_EXCLUDE_FROM_RANDOM .= ',';
        }
        $QTYPE_EXCLUDE_FROM_RANDOM .= "'$name'";
    }
}

require_once("$CFG->dirroot/question/type/questiontype.php");

// Load the questiontype.php file for each question type
// These files in turn call question_register_questiontype()
// with a new instance of each qtype class.
$qtypenames= get_list_of_plugins('question/type');
foreach($qtypenames as $qtypename) {
    // Instanciates all plug-in question types
    $qtypefilepath= "$CFG->dirroot/question/type/$qtypename/questiontype.php";

    // echo "Loading $qtypename<br/>"; // Uncomment for debugging
    if (is_readable($qtypefilepath)) {
        require_once($qtypefilepath);
    }
}

/**
 * An array of question type names translated to the user's language, suitable for use when
 * creating a drop-down menu of options.
 *
 * Long-time Moodle programmers will realise that this replaces the old $QTYPE_MENU array.
 * The array returned will only hold the names of all the question types that the user should
 * be able to create directly. Some internal question types like random questions are excluded.
 *
 * @return array an array of question type names translated to the user's language.
 */
function question_type_menu() {
    global $QTYPES;
    static $menu_options = null;
    if (is_null($menu_options)) {
        $menu_options = array();
        foreach ($QTYPES as $name => $qtype) {
            $menuname = $qtype->menu_name();
            if ($menuname) {
                $menu_options[$name] = $menuname;
            }
        }
    }
    return $menu_options;
}

/// OTHER CLASSES /////////////////////////////////////////////////////////

/**
 * This holds the options that are set by the course module
 */
class cmoptions {
    /**
    * Whether a new attempt should be based on the previous one. If true
    * then a new attempt will start in a state where all responses are set
    * to the last responses from the previous attempt.
    */
    var $attemptonlast = false;

    /**
    * Various option flags. The flags are accessed via bitwise operations
    * using the constants defined in the CONSTANTS section above.
    */
    var $optionflags = QUESTION_ADAPTIVE;

    /**
    * Determines whether in the calculation of the score for a question
    * penalties for earlier wrong responses within the same attempt will
    * be subtracted.
    */
    var $penaltyscheme = true;

    /**
    * The maximum time the user is allowed to answer the questions withing
    * an attempt. This is measured in minutes so needs to be multiplied by
    * 60 before compared to timestamps. If set to 0 no timelimit will be applied
    */
    var $timelimit = 0;

    /**
    * Timestamp for the closing time. Responses submitted after this time will
    * be saved but no credit will be given for them.
    */
    var $timeclose = 9999999999;

    /**
    * The id of the course from withing which the question is currently being used
    */
    var $course = SITEID;

    /**
    * Whether the answers in a multiple choice question should be randomly
    * shuffled when a new attempt is started.
    */
    var $shuffleanswers = true;

    /**
    * The number of decimals to be shown when scores are printed
    */
    var $decimalpoints = 2;
}


/// FUNCTIONS //////////////////////////////////////////////////////

/**
 * Returns an array of names of activity modules that use this question
 *
 * @param object $questionid
 * @return array of strings
 */
function question_list_instances($questionid) {
    global $CFG;
    $instances = array();
    $modules = get_records('modules');
    foreach ($modules as $module) {
        $fullmod = $CFG->dirroot . '/mod/' . $module->name;
        if (file_exists($fullmod . '/lib.php')) {
            include_once($fullmod . '/lib.php');
            $fn = $module->name.'_question_list_instances';
            if (function_exists($fn)) {
                $instances = $instances + $fn($questionid);
            }
        }
    }
    return $instances;
}

/**
 * Determine whether there arey any questions belonging to this context, that is whether any of its
 * question categories contain any questions. This will return true even if all the questions are
 * hidden.
 *
 * @param mixed $context either a context object, or a context id.
 * @return boolean whether any of the question categories beloning to this context have
 *         any questions in them.
 */
function question_context_has_any_questions($context) {
    global $CFG;
    if (is_object($context)) {
        $contextid = $context->id;
    } else if (is_numeric($context)) {
        $contextid = $context;
    } else {
        print_error('invalidcontextinhasanyquestions', 'question');
    }
    return record_exists_sql('SELECT * FROM ' . $CFG->prefix . 'question q ' .
            'JOIN ' . $CFG->prefix . 'question_categories qc ON qc.id = q.category ' .
            "WHERE qc.contextid = $contextid AND q.parent = 0");
}

/**
 * Returns list of 'allowed' grades for grade selection
 * formatted suitably for dropdown box function
 * @return object ->gradeoptionsfull full array ->gradeoptions +ve only
 */
function get_grade_options() {
    // define basic array of grades
    $grades = array(
        1.00,
        0.90,
        0.83333,
        0.80,
        0.75,
        0.70,
        0.66666,
        0.60,
        0.50,
        0.40,
        0.33333,
        0.30,
        0.25,
        0.20,
        0.16666,
        0.142857,
        0.125,
        0.11111,
        0.10,
        0.05,
        0);

    // iterate through grades generating full range of options
    $gradeoptionsfull = array();
    $gradeoptions = array();
    foreach ($grades as $grade) {
        $percentage = 100 * $grade;
        $neggrade = -$grade;
        $gradeoptions["$grade"] = "$percentage %";
        $gradeoptionsfull["$grade"] = "$percentage %";
        $gradeoptionsfull["$neggrade"] = -$percentage." %";
    }
    $gradeoptionsfull["0"] = $gradeoptions["0"] = get_string("none");

    // sort lists
    arsort($gradeoptions, SORT_NUMERIC);
    arsort($gradeoptionsfull, SORT_NUMERIC);

    // construct return object
    $grades = new stdClass;
    $grades->gradeoptions = $gradeoptions;
    $grades->gradeoptionsfull = $gradeoptionsfull;

    return $grades;
}

/**
 * match grade options
 * if no match return error or match nearest
 * @param array $gradeoptionsfull list of valid options
 * @param int $grade grade to be tested
 * @param string $matchgrades 'error' or 'nearest'
 * @return mixed either 'fixed' value or false if erro
 */
function match_grade_options($gradeoptionsfull, $grade, $matchgrades='error') {
    // if we just need an error...
    if ($matchgrades=='error') {
        foreach($gradeoptionsfull as $value => $option) {
            // slightly fuzzy test, never check floats for equality :-)
            if (abs($grade-$value)<0.00001) {
                return $grade;
            }
        }
        // didn't find a match so that's an error
        return false;
    }
    // work out nearest value
    else if ($matchgrades=='nearest') {
        $hownear = array();
        foreach($gradeoptionsfull as $value => $option) {
            if ($grade==$value) {
                return $grade;
            }
            $hownear[ $value ] = abs( $grade - $value );
        }
        // reverse sort list of deltas and grab the last (smallest)
        asort( $hownear, SORT_NUMERIC );
        reset( $hownear );
        return key( $hownear );
    }
    else {
        return false;
    }
}

/**
 * Tests whether a category is in use by any activity module
 *
 * @return boolean
 * @param integer $categoryid
 * @param boolean $recursive Whether to examine category children recursively
 */
function question_category_isused($categoryid, $recursive = false) {

    //Look at each question in the category
    if ($questions = get_records('question', 'category', $categoryid)) {
        foreach ($questions as $question) {
            if (count(question_list_instances($question->id))) {
                return true;
            }
        }
    }

    //Look under child categories recursively
    if ($recursive) {
        if ($children = get_records('question_categories', 'parent', $categoryid)) {
            foreach ($children as $child) {
                if (question_category_isused($child->id, $recursive)) {
                    return true;
                }
            }
        }
    }

    return false;
}

/**
 * Deletes all data associated to an attempt from the database
 *
 * @param integer $attemptid The id of the attempt being deleted
 */
function delete_attempt($attemptid) {
    global $QTYPES;

    $states = get_records('question_states', 'attempt', $attemptid);
    if ($states) {
        $stateslist = implode(',', array_keys($states));

        // delete question-type specific data
        foreach ($QTYPES as $qtype) {
            $qtype->delete_states($stateslist);
        }
    }

    // delete entries from all other question tables
    // It is important that this is done only after calling the questiontype functions
    delete_records("question_states", "attempt", $attemptid);
    delete_records("question_sessions", "attemptid", $attemptid);
    delete_records("question_attempts", "id", $attemptid);
}

/**
 * Deletes question and all associated data from the database
 *
 * It will not delete a question if it is used by an activity module
 * @param object $question  The question being deleted
 */
function delete_question($questionid) {
    global $QTYPES;

    if (!$question = get_record('question', 'id', $questionid)) {
        // In some situations, for example if this was a child of a
        // Cloze question that was previously deleted, the question may already
        // have gone. In this case, just do nothing.
        return;
    }

    // Do not delete a question if it is used by an activity module
    if (count(question_list_instances($questionid))) {
        return;
    }

    // delete questiontype-specific data
    question_require_capability_on($question, 'edit');
    if ($question) {
        if (isset($QTYPES[$question->qtype])) {
            $QTYPES[$question->qtype]->delete_question($questionid);
        }
    } else {
        echo "Question with id $questionid does not exist.<br />";
    }

    if ($states = get_records('question_states', 'question', $questionid)) {
        $stateslist = implode(',', array_keys($states));

        // delete questiontype-specific data
        foreach ($QTYPES as $qtype) {
            $qtype->delete_states($stateslist);
        }
    }

    // delete entries from all other question tables
    // It is important that this is done only after calling the questiontype functions
    delete_records("question_answers", "question", $questionid);
    delete_records("question_states", "question", $questionid);
    delete_records("question_sessions", "questionid", $questionid);

    // Now recursively delete all child questions
    if ($children = get_records('question', 'parent', $questionid)) {
        foreach ($children as $child) {
            if ($child->id != $questionid) {
                delete_question($child->id);
            }
        }
    }

    // Finally delete the question record itself
    delete_records('question', 'id', $questionid);

    return;
}

/**
 * All question categories and their questions are deleted for this course.
 *
 * @param object $mod an object representing the activity
 * @param boolean $feedback to specify if the process must output a summary of its work
 * @return boolean
 */
function question_delete_course($course, $feedback=true) {
    //To store feedback to be showed at the end of the process
    $feedbackdata   = array();

    //Cache some strings
    $strcatdeleted = get_string('unusedcategorydeleted', 'quiz');
    $coursecontext = get_context_instance(CONTEXT_COURSE, $course->id);
    $categoriescourse = get_records('question_categories', 'contextid', $coursecontext->id, 'parent', 'id, parent, name');

    if ($categoriescourse) {

        //Sort categories following their tree (parent-child) relationships
        //this will make the feedback more readable
        $categoriescourse = sort_categories_by_tree($categoriescourse);

        foreach ($categoriescourse as $category) {

            //Delete it completely (questions and category itself)
            //deleting questions
            if ($questions = get_records("question", "category", $category->id)) {
                foreach ($questions as $question) {
                    delete_question($question->id);
                }
                delete_records("question", "category", $category->id);
            }
            //delete the category
            delete_records('question_categories', 'id', $category->id);

            //Fill feedback
            $feedbackdata[] = array($category->name, $strcatdeleted);
        }
        //Inform about changes performed if feedback is enabled
        if ($feedback) {
            $table = new stdClass;
            $table->head = array(get_string('category','quiz'), get_string('action'));
            $table->data = $feedbackdata;
            print_table($table);
        }
    }
    return true;
}

/**
 * Category is about to be deleted,
 * 1/ All question categories and their questions are deleted for this course category.
 * 2/ All questions are moved to new category
 *
 * @param object $category course category object
 * @param object $newcategory empty means everything deleted, otherwise id of category where content moved
 * @param boolean $feedback to specify if the process must output a summary of its work
 * @return boolean
 */
function question_delete_course_category($category, $newcategory, $feedback=true) {
    $context = get_context_instance(CONTEXT_COURSECAT, $category->id);
    if (empty($newcategory)) {
        $feedbackdata   = array(); // To store feedback to be showed at the end of the process
        $rescueqcategory = null; // See the code around the call to question_save_from_deletion.
        $strcatdeleted = get_string('unusedcategorydeleted', 'quiz');

        // Loop over question categories.
        if ($categories = get_records('question_categories', 'contextid', $context->id, 'parent', 'id, parent, name')) {
            foreach ($categories as $category) {

                // Deal with any questions in the category.
                if ($questions = get_records('question', 'category', $category->id)) {

                    // Try to delete each question.
                    foreach ($questions as $question) {
                        delete_question($question->id);
                    }

                    // Check to see if there were any questions that were kept because they are
                    // still in use somehow, even though quizzes in courses in this category will
                    // already have been deteted. This could happen, for example, if questions are
                    // added to a course, and then that course is moved to another category (MDL-14802).
                    $questionids = get_records_select_menu('question', 'category = ' . $category->id, '', 'id,1');
                    if (!empty($questionids)) {
                        if (!$rescueqcategory = question_save_from_deletion(implode(',', array_keys($questionids)),
                                get_parent_contextid($context), print_context_name($context), $rescueqcategory)) {
                            return false;
                       }
                       $feedbackdata[] = array($category->name, get_string('questionsmovedto', 'question', $rescueqcategory->name));
                    }
                }

                // Now delete the category.
                if (!delete_records('question_categories', 'id', $category->id)) {
                    return false;
                }
                $feedbackdata[] = array($category->name, $strcatdeleted);

            } // End loop over categories.
        }

        // Output feedback if requested.
        if ($feedback and $feedbackdata) {
            $table = new stdClass;
            $table->head = array(get_string('questioncategory','question'), get_string('action'));
            $table->data = $feedbackdata;
            print_table($table);
        }

    } else {
        // Move question categories ot the new context.
        if (!$newcontext = get_context_instance(CONTEXT_COURSECAT, $newcategory->id)) {
            return false;
        }
        if (!set_field('question_categories', 'contextid', $newcontext->id, 'contextid', $context->id)) {
            return false;
        }
        if ($feedback) {
            $a = new stdClass;
            $a->oldplace = print_context_name($context);
            $a->newplace = print_context_name($newcontext);
            notify(get_string('movedquestionsandcategories', 'question', $a), 'notifysuccess');
        }
    }

    return true;
}

/**
 * Enter description here...
 *
 * @param string $questionids list of questionids
 * @param object $newcontext the context to create the saved category in.
 * @param string $oldplace a textual description of the think being deleted, e.g. from get_context_name
 * @param object $newcategory
 * @return mixed false on
 */
function question_save_from_deletion($questionids, $newcontextid, $oldplace, $newcategory = null) {
    // Make a category in the parent context to move the questions to.
    if (is_null($newcategory)) {
        $newcategory = new object();
        $newcategory->parent = 0;
        $newcategory->contextid = $newcontextid;
        $newcategory->name = addslashes(get_string('questionsrescuedfrom', 'question', $oldplace));
        $newcategory->info = addslashes(get_string('questionsrescuedfrominfo', 'question', $oldplace));
        $newcategory->sortorder = 999;
        $newcategory->stamp = make_unique_id_code();
        if (!$newcategory->id = insert_record('question_categories', $newcategory)) {
            return false;
        }
    }

    // Move any remaining questions to the 'saved' category.
    if (!question_move_questions_to_category($questionids, $newcategory->id)) {
        return false;
    }
    return $newcategory;
}

/**
 * All question categories and their questions are deleted for this activity.
 *
 * @param object $cm the course module object representing the activity
 * @param boolean $feedback to specify if the process must output a summary of its work
 * @return boolean
 */
function question_delete_activity($cm, $feedback=true) {
    //To store feedback to be showed at the end of the process
    $feedbackdata   = array();

    //Cache some strings
    $strcatdeleted = get_string('unusedcategorydeleted', 'quiz');
    $modcontext = get_context_instance(CONTEXT_MODULE, $cm->id);
    if ($categoriesmods = get_records('question_categories', 'contextid', $modcontext->id, 'parent', 'id, parent, name')){
        //Sort categories following their tree (parent-child) relationships
        //this will make the feedback more readable
        $categoriesmods = sort_categories_by_tree($categoriesmods);

        foreach ($categoriesmods as $category) {

            //Delete it completely (questions and category itself)
            //deleting questions
            if ($questions = get_records("question", "category", $category->id)) {
                foreach ($questions as $question) {
                    delete_question($question->id);
                }
                delete_records("question", "category", $category->id);
            }
            //delete the category
            delete_records('question_categories', 'id', $category->id);

            //Fill feedback
            $feedbackdata[] = array($category->name, $strcatdeleted);
        }
        //Inform about changes performed if feedback is enabled
        if ($feedback) {
            $table = new stdClass;
            $table->head = array(get_string('category','quiz'), get_string('action'));
            $table->data = $feedbackdata;
            print_table($table);
        }
    }
    return true;
}

/**
 * This function should be considered private to the question bank, it is called from
 * question/editlib.php question/contextmoveq.php and a few similar places to to the work of
 * acutally moving questions and associated data. However, callers of this function also have to
 * do other work, which is why you should not call this method directly from outside the questionbank.
 *
 * @param string $questionids a comma-separated list of question ids.
 * @param integer $newcategory the id of the category to move to.
 */
function question_move_questions_to_category($questionids, $newcategory) {
    $result = true;

    // Move the questions themselves.
    $result = $result && set_field_select('question', 'category', $newcategory, "id IN ($questionids)");

    // Move any subquestions belonging to them.
    $result = $result && set_field_select('question', 'category', $newcategory, "parent IN ($questionids)");

    // TODO Deal with datasets.

    return $result;
}

/**
 * @param array $row tab objects
 * @param question_edit_contexts $contexts object representing contexts available from this context
 * @param string $querystring to append to urls
 * */
function questionbank_navigation_tabs(&$row, $contexts, $querystring) {
    global $CFG, $QUESTION_EDITTABCAPS;
    $tabs = array(
            'questions' =>array("$CFG->wwwroot/question/edit.php?$querystring", get_string('questions', 'quiz'), get_string('editquestions', 'quiz')),
            'categories' =>array("$CFG->wwwroot/question/category.php?$querystring", get_string('categories', 'quiz'), get_string('editqcats', 'quiz')),
            'import' =>array("$CFG->wwwroot/question/import.php?$querystring", get_string('import', 'quiz'), get_string('importquestions', 'quiz')),
            'export' =>array("$CFG->wwwroot/question/export.php?$querystring", get_string('export', 'quiz'), get_string('exportquestions', 'quiz')));
    foreach ($tabs as $tabname => $tabparams){
        if ($contexts->have_one_edit_tab_cap($tabname)) {
            $row[] = new tabobject($tabname, $tabparams[0], $tabparams[1], $tabparams[2]);
        }
    }
}

/**
 * Private function to factor common code out of get_question_options().
 *
 * @param object $question the question to tidy.
 * @return boolean true if successful, else false.
 */
function _tidy_question(&$question) {
    global $QTYPES;
    if (!array_key_exists($question->qtype, $QTYPES)) {
        $question->qtype = 'missingtype';
        $question->questiontext = '<p>' . get_string('warningmissingtype', 'quiz') . '</p>' . $question->questiontext;
    }
    $question->name_prefix = question_make_name_prefix($question->id);
    return $QTYPES[$question->qtype]->get_question_options($question);
}

/**
 * Updates the question objects with question type specific
 * information by calling {@link get_question_options()}
 *
 * Can be called either with an array of question objects or with a single
 * question object.
 *
 * @param mixed $questions Either an array of question objects to be updated
 *         or just a single question object
 * @return bool Indicates success or failure.
 */
function get_question_options(&$questions) {
    if (is_array($questions)) { // deal with an array of questions
        foreach ($questions as $i => $notused) {
            if (!_tidy_question($questions[$i])) {
                return false;
            }
        }
        return true;
    } else { // deal with single question
        return _tidy_question($questions);
    }
}

/**
* Loads the most recent state of each question session from the database
* or create new one.
*
* For each question the most recent session state for the current attempt
* is loaded from the question_states table and the question type specific data and
* responses are added by calling {@link restore_question_state()} which in turn
* calls {@link restore_session_and_responses()} for each question.
* If no states exist for the question instance an empty state object is
* created representing the start of a session and empty question
* type specific information and responses are created by calling
* {@link create_session_and_responses()}.
*
* @return array           An array of state objects representing the most recent
*                         states of the question sessions.
* @param array $questions The questions for which sessions are to be restored or
*                         created.
* @param object $cmoptions
* @param object $attempt  The attempt for which the question sessions are
*                         to be restored or created.
* @param mixed either the id of a previous attempt, if this attmpt is
*                         building on a previous one, or false for a clean attempt.
*/
function get_question_states(&$questions, $cmoptions, $attempt, $lastattemptid = false) {
    global $CFG, $QTYPES;

    // get the question ids
    $ids = array_keys($questions);
    $questionlist = implode(',', $ids);

    // The question field must be listed first so that it is used as the
    // array index in the array returned by get_records_sql
    $statefields = 'n.questionid as question, s.*, n.sumpenalty, n.manualcomment';
    // Load the newest states for the questions
    $sql = "SELECT $statefields".
           "  FROM {$CFG->prefix}question_states s,".
           "       {$CFG->prefix}question_sessions n".
           " WHERE s.id = n.newest".
           "   AND n.attemptid = '$attempt->uniqueid'".
           "   AND n.questionid IN ($questionlist)";
    $states = get_records_sql($sql);

    // Load the newest graded states for the questions
    $sql = "SELECT $statefields".
           "  FROM {$CFG->prefix}question_states s,".
           "       {$CFG->prefix}question_sessions n".
           " WHERE s.id = n.newgraded".
           "   AND n.attemptid = '$attempt->uniqueid'".
           "   AND n.questionid IN ($questionlist)";
    $gradedstates = get_records_sql($sql);

    // loop through all questions and set the last_graded states
    foreach ($ids as $i) {
        if (isset($states[$i])) {
            restore_question_state($questions[$i], $states[$i]);
            if (isset($gradedstates[$i])) {
                restore_question_state($questions[$i], $gradedstates[$i]);
                $states[$i]->last_graded = $gradedstates[$i];
            } else {
                $states[$i]->last_graded = clone($states[$i]);
            }
        } else {
            if ($lastattemptid) {
                // If the new attempt is to be based on this previous attempt.
                // Find the responses from the previous attempt and save them to the new session

                // Load the last graded state for the question
                $statefields = 'n.questionid as question, s.*, n.sumpenalty';
                $sql = "SELECT $statefields".
                       "  FROM {$CFG->prefix}question_states s,".
                       "       {$CFG->prefix}question_sessions n".
                       " WHERE s.id = n.newest".
                       "   AND n.attemptid = '$lastattemptid'".
                       "   AND n.questionid = '$i'";
                if (!$laststate = get_record_sql($sql)) {
                    // Only restore previous responses that have been graded
                    continue;
                }
                // Restore the state so that the responses will be restored
                restore_question_state($questions[$i], $laststate);
                $states[$i] = clone($laststate);
                unset($states[$i]->id);
            } else {
                // create a new empty state
                $states[$i] = new object;
                $states[$i]->question = $i;
                $states[$i]->responses = array('' => '');
                $states[$i]->raw_grade = 0;
            }

            // now fill/overide initial values
            $states[$i]->attempt = $attempt->uniqueid;
            $states[$i]->seq_number = 0;
            $states[$i]->timestamp = $attempt->timestart;
            $states[$i]->event = ($attempt->timefinish) ? QUESTION_EVENTCLOSE : QUESTION_EVENTOPEN;
            $states[$i]->grade = 0;
            $states[$i]->penalty = 0;
            $states[$i]->sumpenalty = 0;
            $states[$i]->manualcomment = '';

            // Prevent further changes to the session from incrementing the
            // sequence number
            $states[$i]->changed = true;

            if ($lastattemptid) {
                // prepare the previous responses for new processing
                $action = new stdClass;
                $action->responses = $laststate->responses;
                $action->timestamp = $laststate->timestamp;
                $action->event = QUESTION_EVENTSAVE; //emulate save of questions from all pages MDL-7631

                // Process these responses ...
                question_process_responses($questions[$i], $states[$i], $action, $cmoptions, $attempt);

                // Fix for Bug #5506: When each attempt is built on the last one,
                // preserve the options from any previous attempt.
                if ( isset($laststate->options) ) {
                    $states[$i]->options = $laststate->options;
                }
            } else {
                // Create the empty question type specific information
                if (!$QTYPES[$questions[$i]->qtype]->create_session_and_responses(
                        $questions[$i], $states[$i], $cmoptions, $attempt)) {
                    return false;
                }
            }
            $states[$i]->last_graded = clone($states[$i]);
        }
    }
    return $states;
}


/**
* Creates the run-time fields for the states
*
* Extends the state objects for a question by calling
* {@link restore_session_and_responses()}
* @param object $question The question for which the state is needed
* @param object $state The state as loaded from the database
* @return boolean Represents success or failure
*/
function restore_question_state(&$question, &$state) {
    global $QTYPES;

    // initialise response to the value in the answer field
    $state->responses = array('' => addslashes($state->answer));
    unset($state->answer);
    $state->manualcomment = isset($state->manualcomment) ? addslashes($state->manualcomment) : '';

    // Set the changed field to false; any code which changes the
    // question session must set this to true and must increment
    // ->seq_number. The save_question_session
    // function will save the new state object to the database if the field is
    // set to true.
    $state->changed = false;

    // Load the question type specific data
    return $QTYPES[$question->qtype]
            ->restore_session_and_responses($question, $state);

}

/**
* Saves the current state of the question session to the database
*
* The state object representing the current state of the session for the
* question is saved to the question_states table with ->responses[''] saved
* to the answer field of the database table. The information in the
* question_sessions table is updated.
* The question type specific data is then saved.
* @return mixed           The id of the saved or updated state or false
* @param object $question The question for which session is to be saved.
* @param object $state    The state information to be saved. In particular the
*                         most recent responses are in ->responses. The object
*                         is updated to hold the new ->id.
*/
function save_question_session(&$question, &$state) {
    global $QTYPES;
    // Check if the state has changed
    if (!$state->changed && isset($state->id)) {
        return $state->id;
    }
    // Set the legacy answer field
    $state->answer = isset($state->responses['']) ? $state->responses[''] : '';

    // Save the state
    if (!empty($state->update)) { // this forces the old state record to be overwritten
        update_record('question_states', $state);
    } else {
        if (!$state->id = insert_record('question_states', $state)) {
            unset($state->id);
            unset($state->answer);
            return false;
        }
    }

    // create or update the session
    if (!$session = get_record('question_sessions', 'attemptid',
            $state->attempt, 'questionid', $question->id)) {
        $session->attemptid = $state->attempt;
        $session->questionid = $question->id;
        $session->newest = $state->id;
        // The following may seem weird, but the newgraded field needs to be set
        // already even if there is no graded state yet.
        $session->newgraded = $state->id;
        $session->sumpenalty = $state->sumpenalty;
        $session->manualcomment = $state->manualcomment;
        if (!insert_record('question_sessions', $session)) {
            error('Could not insert entry in question_sessions');
        }
    } else {
        $session->newest = $state->id;
        if (question_state_is_graded($state) or $state->event == QUESTION_EVENTOPEN) {
            // this state is graded or newly opened, so it goes into the lastgraded field as well
            $session->newgraded = $state->id;
            $session->sumpenalty = $state->sumpenalty;
            $session->manualcomment = $state->manualcomment;
        } else {
            $session->manualcomment = addslashes($session->manualcomment);
        }
        update_record('question_sessions', $session);
    }

    unset($state->answer);

    // Save the question type specific state information and responses
    if (!$QTYPES[$question->qtype]->save_session_and_responses(
     $question, $state)) {
        return false;
    }
    // Reset the changed flag
    $state->changed = false;
    return $state->id;
}

/**
* Determines whether a state has been graded by looking at the event field
*
* @return boolean         true if the state has been graded
* @param object $state
*/
function question_state_is_graded($state) {
    $gradedevents = explode(',', QUESTION_EVENTS_GRADED);
    return (in_array($state->event, $gradedevents));
}

/**
* Determines whether a state has been closed by looking at the event field
*
* @return boolean         true if the state has been closed
* @param object $state
*/
function question_state_is_closed($state) {
    return ($state->event == QUESTION_EVENTCLOSE
        or $state->event == QUESTION_EVENTCLOSEANDGRADE
        or $state->event == QUESTION_EVENTMANUALGRADE);
}


/**
 * Extracts responses from submitted form
 *
 * This can extract the responses given to one or several questions present on a page
 * It returns an array with one entry for each question, indexed by question id
 * Each entry is an object with the properties
 *  ->event     The event that has triggered the submission. This is determined by which button
 *               the user has pressed.
 *  ->responses An array holding the responses to an individual question, indexed by the
 *               name of the corresponding form element.
 *  ->timestamp A unix timestamp
 * @return array            array of action objects, indexed by question ids.
 * @param array $questions  an array containing at least all questions that are used on the form
 * @param array $formdata   the data submitted by the form on the question page
 * @param integer $defaultevent  the event type used if no 'mark' or 'validate' is submitted
 */
function question_extract_responses($questions, $formdata, $defaultevent=QUESTION_EVENTSAVE) {

    $time = time();
    $actions = array();
    foreach ($formdata as $key => $response) {
        // Get the question id from the response name
        if (false !== ($quid = question_get_id_from_name_prefix($key))) {
            // check if this is a valid id
            if (!isset($questions[$quid])) {
                error('Form contained question that is not in questionids');
            }

            // Remove the name prefix from the name
            //decrypt trying
            $key = substr($key, strlen($questions[$quid]->name_prefix));
            if (false === $key) {
                $key = '';
            }
            // Check for question validate and mark buttons & set events
            if ($key === 'validate') {
                $actions[$quid]->event = QUESTION_EVENTVALIDATE;
            } else if ($key === 'submit') {
                $actions[$quid]->event = QUESTION_EVENTSUBMIT;
            } else {
                $actions[$quid]->event = $defaultevent;
            }

            // Update the state with the new response
            $actions[$quid]->responses[$key] = $response;

            // Set the timestamp
            $actions[$quid]->timestamp = $time;
        }
    }
    foreach ($actions as $quid => $notused) {
        ksort($actions[$quid]->responses);
    }
    return $actions;
}


/**
 * Returns the html for question feedback image.
 * @param float   $fraction  value representing the correctness of the user's
 *                           response to a question.
 * @param boolean $selected  whether or not the answer is the one that the
 *                           user picked.
 * @return string
 */
function question_get_feedback_image($fraction, $selected=true) {

    global $CFG;

    if ($fraction >= 1.0) {
        if ($selected) {
            $feedbackimg = '<img src="'.$CFG->pixpath.'/i/tick_green_big.gif" '.
                            'alt="'.get_string('correct', 'quiz').'" class="icon" />';
        } else {
            $feedbackimg = '<img src="'.$CFG->pixpath.'/i/tick_green_small.gif" '.
                            'alt="'.get_string('correct', 'quiz').'" class="icon" />';
        }
    } else if ($fraction > 0.0 && $fraction < 1.0) {
        if ($selected) {
            $feedbackimg = '<img src="'.$CFG->pixpath.'/i/tick_amber_big.gif" '.
                            'alt="'.get_string('partiallycorrect', 'quiz').'" class="icon" />';
        } else {
            $feedbackimg = '<img src="'.$CFG->pixpath.'/i/tick_amber_small.gif" '.
                            'alt="'.get_string('partiallycorrect', 'quiz').'" class="icon" />';
        }
    } else {
        if ($selected) {
            $feedbackimg = '<img src="'.$CFG->pixpath.'/i/cross_red_big.gif" '.
                            'alt="'.get_string('incorrect', 'quiz').'" class="icon" />';
        } else {
            $feedbackimg = '<img src="'.$CFG->pixpath.'/i/cross_red_small.gif" '.
                            'alt="'.get_string('incorrect', 'quiz').'" class="icon" />';
        }
    }
    return $feedbackimg;
}


/**
 * Returns the class name for question feedback.
 * @param float  $fraction  value representing the correctness of the user's
 *                          response to a question.
 * @return string
 */
function question_get_feedback_class($fraction) {

    global $CFG;

    if ($fraction >= 1.0) {
        $class = 'correct';
    } else if ($fraction > 0.0 && $fraction < 1.0) {
        $class = 'partiallycorrect';
    } else {
        $class = 'incorrect';
    }
    return $class;
}


/**
* For a given question in an attempt we walk the complete history of states
* and recalculate the grades as we go along.
*
* This is used when a question is changed and old student
* responses need to be marked with the new version of a question.
*
* TODO: Make sure this is not quiz-specific
*
* @return boolean            Indicates whether the grade has changed
* @param object  $question   A question object
* @param object  $attempt    The attempt, in which the question needs to be regraded.
* @param object  $cmoptions
* @param boolean $verbose    Optional. Whether to print progress information or not.
*/
function regrade_question_in_attempt($question, $attempt, $cmoptions, $verbose=false) {

    // load all states for this question in this attempt, ordered in sequence
    if ($states = get_records_select('question_states',
            "attempt = '{$attempt->uniqueid}' AND question = '{$question->id}'",
            'seq_number ASC')) {
        $states = array_values($states);

        // Subtract the grade for the latest state from $attempt->sumgrades to get the
        // sumgrades for the attempt without this question.
        $attempt->sumgrades -= $states[count($states)-1]->grade;

        // Initialise the replaystate
        $state = clone($states[0]);
        $state->manualcomment = get_field('question_sessions', 'manualcomment', 'attemptid',
                $attempt->uniqueid, 'questionid', $question->id);
        restore_question_state($question, $state);
        $state->sumpenalty = 0.0;
        $replaystate = clone($state);
        $replaystate->last_graded = $state;

        $changed = false;
        for($j = 1; $j < count($states); $j++) {
            restore_question_state($question, $states[$j]);
            $action = new stdClass;
            $action->responses = $states[$j]->responses;
            $action->timestamp = $states[$j]->timestamp;

            // Change event to submit so that it will be reprocessed
            if (QUESTION_EVENTCLOSE == $states[$j]->event
                    or QUESTION_EVENTGRADE == $states[$j]->event
                    or QUESTION_EVENTCLOSEANDGRADE == $states[$j]->event) {
                $action->event = QUESTION_EVENTSUBMIT;

            // By default take the event that was saved in the database
            } else {
                $action->event = $states[$j]->event;
            }

            if ($action->event == QUESTION_EVENTMANUALGRADE) {
                // Ensure that the grade is in range - in the past this was not checked,
                // but now it is (MDL-14835) - so we need to ensure the data is valid before
                // proceeding.
                if ($states[$j]->grade < 0) {
                    $states[$j]->grade = 0;
                } else if ($states[$j]->grade > $question->maxgrade) {
                    $states[$j]->grade = $question->maxgrade;
                }
                $error = question_process_comment($question, $replaystate, $attempt,
                        $replaystate->manualcomment, $states[$j]->grade);
                if (is_string($error)) {
                     notify($error);
                }
            } else {

                // Reprocess (regrade) responses
                if (!question_process_responses($question, $replaystate,
                        $action, $cmoptions, $attempt)) {
                    $verbose && notify("Couldn't regrade state #{$state->id}!");
                }
            }

            // We need rounding here because grades in the DB get truncated
            // e.g. 0.33333 != 0.3333333, but we want them to be equal here
            if ((round((float)$replaystate->raw_grade, 5) != round((float)$states[$j]->raw_grade, 5))
                    or (round((float)$replaystate->penalty, 5) != round((float)$states[$j]->penalty, 5))
                    or (round((float)$replaystate->grade, 5) != round((float)$states[$j]->grade, 5))) {
                $changed = true;
            }

            $replaystate->id = $states[$j]->id;
            $replaystate->changed = true;
            $replaystate->update = true; // This will ensure that the existing database entry is updated rather than a new one created
            save_question_session($question, $replaystate);
        }
        if ($changed) {
            // TODO, call a method in quiz to do this, where 'quiz' comes from
            // the question_attempts table.
            update_record('quiz_attempts', $attempt);
        }

        return $changed;
    }
    return false;
}

/**
* Processes an array of student responses, grading and saving them as appropriate
*
* @param object $question Full question object, passed by reference
* @param object $state    Full state object, passed by reference
* @param object $action   object with the fields ->responses which
*                         is an array holding the student responses,
*                         ->action which specifies the action, e.g., QUESTION_EVENTGRADE,
*                         and ->timestamp which is a timestamp from when the responses
*                         were submitted by the student.
* @param object $cmoptions
* @param object $attempt  The attempt is passed by reference so that
*                         during grading its ->sumgrades field can be updated
* @return boolean         Indicates success/failure
*/
function question_process_responses(&$question, &$state, $action, $cmoptions, &$attempt) {
    global $QTYPES;

    // if no responses are set initialise to empty response
    if (!isset($action->responses)) {
        $action->responses = array('' => '');
    }

    // make sure these are gone!
    unset($action->responses['submit'], $action->responses['validate']);

    // Check the question session is still open
    if (question_state_is_closed($state)) {
        return true;
    }

    // If $action->event is not set that implies saving
    if (! isset($action->event)) {
        debugging('Ambiguous action in question_process_responses.' , DEBUG_DEVELOPER);
        $action->event = QUESTION_EVENTSAVE;
    }
    // If submitted then compare against last graded
    // responses, not last given responses in this case
    if (question_isgradingevent($action->event)) {
        $state->responses = $state->last_graded->responses;
    }

    // Check for unchanged responses (exactly unchanged, not equivalent).
    // We also have to catch questions that the student has not yet attempted
    $sameresponses = $QTYPES[$question->qtype]->compare_responses($question, $action, $state);
    if (!empty($state->last_graded) && $state->last_graded->event == QUESTION_EVENTOPEN &&
            question_isgradingevent($action->event)) {
        $sameresponses = false;
    }

    // If the response has not been changed then we do not have to process it again
    // unless the attempt is closing or validation is requested
    if ($sameresponses and QUESTION_EVENTCLOSE != $action->event
            and QUESTION_EVENTVALIDATE != $action->event) {
        return true;
    }

    // Roll back grading information to last graded state and set the new
    // responses
    $newstate = clone($state->last_graded);
    $newstate->responses = $action->responses;
    $newstate->seq_number = $state->seq_number + 1;
    $newstate->changed = true; // will assure that it gets saved to the database
    $newstate->last_graded = clone($state->last_graded);
    $newstate->timestamp = $action->timestamp;
    $state = $newstate;

    // Set the event to the action we will perform. The question type specific
    // grading code may override this by setting it to QUESTION_EVENTCLOSE if the
    // attempt at the question causes the session to close
    $state->event = $action->event;

    if (!question_isgradingevent($action->event)) {
        // Grade the response but don't update the overall grade
        if (!$QTYPES[$question->qtype]->grade_responses($question, $state, $cmoptions)) {
            return false;
        }

        // Temporary hack because question types are not given enough control over what is going
        // on. Used by Opaque questions.
        // TODO fix this code properly.
        if (!empty($state->believeevent)) {
            // If the state was graded we need to ...
            if (question_state_is_graded($state)) {
                question_apply_penalty_and_timelimit($question, $state, $attempt, $cmoptions);

                // update the attempt grade
                $attempt->sumgrades -= (float)$state->last_graded->grade;
                $attempt->sumgrades += (float)$state->grade;

                // and update the last_graded field.
                unset($state->last_graded);
                $state->last_graded = clone($state);
                unset($state->last_graded->changed);
            }
        } else {
            // Don't allow the processing to change the event type
            $state->event = $action->event;
        }

    } else { // grading event

        // Unless the attempt is closing, we want to work out if the current responses
        // (or equivalent responses) were already given in the last graded attempt.
        if(QUESTION_EVENTCLOSE != $action->event && QUESTION_EVENTOPEN != $state->last_graded->event &&
                $QTYPES[$question->qtype]->compare_responses($question, $state, $state->last_graded)) {
            $state->event = QUESTION_EVENTDUPLICATE;
        }

        // If we did not find a duplicate or if the attempt is closing, perform grading
        if ((!$sameresponses and QUESTION_EVENTDUPLICATE != $state->event) or
                QUESTION_EVENTCLOSE == $action->event) {
            if (!$QTYPES[$question->qtype]->grade_responses($question, $state, $cmoptions)) {
                return false;
            }

            // Calculate overall grade using correct penalty method
            question_apply_penalty_and_timelimit($question, $state, $attempt, $cmoptions);
        }

        // If the state was graded we need to ...
        if (question_state_is_graded($state)) {
            // update the attempt grade
            $attempt->sumgrades -= (float)$state->last_graded->grade;
            $attempt->sumgrades += (float)$state->grade;

            // and update the last_graded field.
            unset($state->last_graded);
            $state->last_graded = clone($state);
            unset($state->last_graded->changed);
        }
    }
    $attempt->timemodified = $action->timestamp;

    return true;
}

/**
* Determine if event requires grading
*/
function question_isgradingevent($event) {
    return (QUESTION_EVENTSUBMIT == $event || QUESTION_EVENTCLOSE == $event);
}

/**
* Applies the penalty from the previous graded responses to the raw grade
* for the current responses
*
* The grade for the question in the current state is computed by subtracting the
* penalty accumulated over the previous graded responses at the question from the
* raw grade. If the timestamp is more than 1 minute beyond the end of the attempt
* the grade is set to zero. The ->grade field of the state object is modified to
* reflect the new grade but is never allowed to decrease.
* @param object $question The question for which the penalty is to be applied.
* @param object $state    The state for which the grade is to be set from the
*                         raw grade and the cumulative penalty from the last
*                         graded state. The ->grade field is updated by applying
*                         the penalty scheme determined in $cmoptions to the ->raw_grade and
*                         ->last_graded->penalty fields.
* @param object $cmoptions  The options set by the course module.
*                           The ->penaltyscheme field determines whether penalties
*                           for incorrect earlier responses are subtracted.
*/
function question_apply_penalty_and_timelimit(&$question, &$state, $attempt, $cmoptions) {
    // TODO. Quiz dependancy. The fact that the attempt that is passed in here
    // is from quiz_attempts, and we use things like $cmoptions->timelimit.

    // deal with penalty
    if ($cmoptions->penaltyscheme) {
        $state->grade = $state->raw_grade - $state->sumpenalty;
        $state->sumpenalty += (float) $state->penalty;
    } else {
        $state->grade = $state->raw_grade;
    }

    // deal with timelimit
    if ($cmoptions->timelimit) {
        // We allow for 5% uncertainty in the following test
        if ($state->timestamp - $attempt->timestart > $cmoptions->timelimit * 63) {
            $cm = get_coursemodule_from_instance('quiz', $cmoptions->id);
            if (!has_capability('mod/quiz:ignoretimelimits', get_context_instance(CONTEXT_MODULE, $cm->id),
                    $attempt->userid, false)) {
                $state->grade = 0;
            }
        }
    }

    // deal with closing time
    if ($cmoptions->timeclose and $state->timestamp > ($cmoptions->timeclose + 60) // allowing 1 minute lateness
             and !$attempt->preview) { // ignore closing time for previews
        $state->grade = 0;
    }

    // Ensure that the grade does not go down
    $state->grade = max($state->grade, $state->last_graded->grade);
}

/**
* Print the icon for the question type
*
* @param object $question  The question object for which the icon is required
* @param boolean $return   If true the functions returns the link as a string
*/
function print_question_icon($question, $return = false) {
    global $QTYPES, $CFG;

    if (array_key_exists($question->qtype, $QTYPES)) {
        $namestr = $QTYPES[$question->qtype]->menu_name();
    } else {
        $namestr = 'missingtype';
    }
    $html = '<img src="' . $CFG->wwwroot . '/question/type/' .
            $question->qtype . '/icon.gif" alt="' .
            $namestr . '" title="' . $namestr . '" />';
    if ($return) {
        return $html;
    } else {
        echo $html;
    }
}

/**
* Returns a html link to the question image if there is one
*
* @return string The html image tag or the empy string if there is no image.
* @param object $question The question object
*/
function get_question_image($question) {

    global $CFG;
    $img = '';

    if (!$category = get_record('question_categories', 'id', $question->category)){
        error('invalid category id '.$question->category);
    }
    $coursefilesdir = get_filesdir_from_context(get_context_instance_by_id($category->contextid));

    if ($question->image) {

        if (substr(strtolower($question->image), 0, 7) == 'http://') {
            $img .= $question->image;

        } else {
            require_once($CFG->libdir .'/filelib.php');
            $img = get_file_url("$coursefilesdir/{$question->image}");
        }      
    }
    return $img;
}

function question_print_comment_box($question, $state, $attempt, $url) {
    global $CFG, $QTYPES;

    $prefix = 'response';
    $usehtmleditor = can_use_richtext_editor();
    if (!question_state_is_graded($state) && $QTYPES[$question->qtype]->is_question_manual_graded($question, $attempt->layout)) {
        $grade = '';
    } else {
        $grade = round($state->last_graded->grade, 3);
    }
    echo '<form method="post" action="'.$url.'">';
    include($CFG->dirroot.'/question/comment.html');
    echo '<input type="hidden" name="attempt" value="'.$attempt->uniqueid.'" />';
    echo '<input type="hidden" name="question" value="'.$question->id.'" />';
    echo '<input type="hidden" name="sesskey" value="'.sesskey().'" />';
    echo '<input type="submit" name="submit" value="'.get_string('save', 'quiz').'" />';
    echo '</form>';

    if ($usehtmleditor) {
        use_html_editor();
    }
}

/**
 * Process a manual grading action. That is, use $comment and $grade to update
 * $state and $attempt. The attempt and the comment text are stored in the
 * database. $state is only updated in memory, it is up to the call to store
 * that, if appropriate.
 *
 * @param object $question the question
 * @param object $state the state to be updated.
 * @param object $attempt the attempt the state belongs to, to be updated.
 * @param string $comment the new comment from the teacher.
 * @param mixed $grade the grade the teacher assigned, or '' to not change the grade.
 * @return mixed true on success, a string error message if a problem is detected
 *         (for example score out of range).
 */
function question_process_comment($question, &$state, &$attempt, $comment, $grade) {
    $grade = trim($grade);
    if ($grade < 0 || $grade > $question->maxgrade) {
        $a = new stdClass;
        $a->grade = $grade;
        $a->maxgrade = $question->maxgrade;
        $a->name = $question->name;
        return get_string('errormanualgradeoutofrange', 'question', $a);
    }

    // Update the comment and save it in the database
    $comment = trim($comment);
    $state->manualcomment = $comment;
    if (!set_field('question_sessions', 'manualcomment', $comment, 'attemptid', $attempt->uniqueid, 'questionid', $question->id)) {
        return get_string('errorsavingcomment', 'question', $question);
    }

    // Update the attempt if the score has changed.
    if ($grade !== '' && (abs($state->last_graded->grade - $grade) > 0.002 || $state->last_graded->event != QUESTION_EVENTMANUALGRADE)) {
        $attempt->sumgrades = $attempt->sumgrades - $state->last_graded->grade + $grade;
        $attempt->timemodified = time();
        if (!update_record('quiz_attempts', $attempt)) {
            return get_string('errorupdatingattempt', 'question', $attempt);
        }

        // We want to update existing state (rather than creating new one) if it
        // was itself created by a manual grading event.
        $state->update = $state->event == QUESTION_EVENTMANUALGRADE;

        // Update the other parts of the state object.
        $state->raw_grade = $grade;
        $state->grade = $grade;
        $state->penalty = 0;
        $state->timestamp = time();
        $state->seq_number++;
        $state->event = QUESTION_EVENTMANUALGRADE;

        // Update the last graded state (don't simplify!)
        unset($state->last_graded);
        $state->last_graded = clone($state);

        // We need to indicate that the state has changed in order for it to be saved.
        $state->changed = 1;
    }

    return true;
}

/**
* Construct name prefixes for question form element names
*
* Construct the name prefix that should be used for example in the
* names of form elements created by questions.
* This is called by {@link get_question_options()}
* to set $question->name_prefix.
* This name prefix includes the question id which can be
* extracted from it with {@link question_get_id_from_name_prefix()}.
*
* @return string
* @param integer $id  The question id
*/
function question_make_name_prefix($id) {
    return 'resp' . $id . '_';
}

/**
* Extract question id from the prefix of form element names
*
* @return integer      The question id
* @param string $name  The name that contains a prefix that was
*                      constructed with {@link question_make_name_prefix()}
*/
function question_get_id_from_name_prefix($name) {
    if (!preg_match('/^resp([0-9]+)_/', $name, $matches))
        return false;
    return (integer) $matches[1];
}

/**
 * Returns the unique id for a new attempt
 *
 * Every module can keep their own attempts table with their own sequential ids but
 * the question code needs to also have a unique id by which to identify all these
 * attempts. Hence a module, when creating a new attempt, calls this function and
 * stores the return value in the 'uniqueid' field of its attempts table.
 */
function question_new_attempt_uniqueid($modulename='quiz') {
    global $CFG;
    $attempt = new stdClass;
    $attempt->modulename = $modulename;
    if (!$id = insert_record('question_attempts', $attempt)) {
        error('Could not create new entry in question_attempts table');
    }
    return $id;
}

/**
 * Creates a stamp that uniquely identifies this version of the question
 *
 * In future we want this to use a hash of the question data to guarantee that
 * identical versions have the same version stamp.
 *
 * @param object $question
 * @return string A unique version stamp
 */
function question_hash($question) {
    return make_unique_id_code();
}


/// FUNCTIONS THAT SIMPLY WRAP QUESTIONTYPE METHODS //////////////////////////////////
/**
 * Get the HTML that needs to be included in the head tag when the
 * questions in $questionlist are printed in the gives states.
 *
 * @param array $questionlist a list of questionids of the questions what will appear on this page.
 * @param array $questions an array of question objects, whose keys are question ids.
 *      Must contain all the questions in $questionlist
 * @param array $states an array of question state objects, whose keys are question ids.
 *      Must contain the state of all the questions in $questionlist
 *
 * @return string some HTML code that can go inside the head tag.
 */
function get_html_head_contributions(&$questionlist, &$questions, &$states) {
    global $QTYPES;

    $contributions = array();
    foreach ($questionlist as $questionid) {
        $question = $questions[$questionid];
        $contributions = array_merge($contributions,
                $QTYPES[$question->qtype]->get_html_head_contributions(
                $question, $states[$questionid]));
    }
    return implode("\n", array_unique($contributions));
}

/**
 * Like @see{get_html_head_contributions} but for the editing page
 * question/question.php.
 *
 * @param $question A question object. Only $question->qtype is used.
 * @return string some HTML code that can go inside the head tag.
 */
function get_editing_head_contributions($question) {
    global $QTYPES;
    $contributions = $QTYPES[$question->qtype]->get_editing_head_contributions();
    return implode("\n", array_unique($contributions));
}

/**
 * Prints a question
 *
 * Simply calls the question type specific print_question() method.
 * @param object $question The question to be rendered.
 * @param object $state    The state to render the question in.
 * @param integer $number  The number for this question.
 * @param object $cmoptions  The options specified by the course module
 * @param object $options  An object specifying the rendering options.
 */
function print_question(&$question, &$state, $number, $cmoptions, $options=null) {
    global $QTYPES;
    $QTYPES[$question->qtype]->print_question($question, $state, $number, $cmoptions, $options);
}
/**
 * Saves question options
 *
 * Simply calls the question type specific save_question_options() method.
 */
function save_question_options($question) {
    global $QTYPES;

    $QTYPES[$question->qtype]->save_question_options($question);
}

/**
* Gets all teacher stored answers for a given question
*
* Simply calls the question type specific get_all_responses() method.
*/
// ULPGC ecastro
function get_question_responses($question, $state) {
    global $QTYPES;
    $r = $QTYPES[$question->qtype]->get_all_responses($question, $state);
    return $r;
}


/**
* Gets the response given by the user in a particular state
*
* Simply calls the question type specific get_actual_response() method.
*/
// ULPGC ecastro
function get_question_actual_response($question, $state) {
    global $QTYPES;

    $r = $QTYPES[$question->qtype]->get_actual_response($question, $state);
    return $r;
}

/**
* TODO: document this
*/
// ULPGc ecastro
function get_question_fraction_grade($question, $state) {
    global $QTYPES;

    $r = $QTYPES[$question->qtype]->get_fractional_grade($question, $state);
    return $r;
}


/// CATEGORY FUNCTIONS /////////////////////////////////////////////////////////////////

/**
 * returns the categories with their names ordered following parent-child relationships
 * finally it tries to return pending categories (those being orphaned, whose parent is
 * incorrect) to avoid missing any category from original array.
 */
function sort_categories_by_tree(&$categories, $id = 0, $level = 1) {
    $children = array();
    $keys = array_keys($categories);

    foreach ($keys as $key) {
        if (!isset($categories[$key]->processed) && $categories[$key]->parent == $id) {
            $children[$key] = $categories[$key];
            $categories[$key]->processed = true;
            $children = $children + sort_categories_by_tree($categories, $children[$key]->id, $level+1);
        }
    }
    //If level = 1, we have finished, try to look for non processed categories (bad parent) and sort them too
    if ($level == 1) {
        foreach ($keys as $key) {
            //If not processed and it's a good candidate to start (because its parent doesn't exist in the course)
            if (!isset($categories[$key]->processed) && !record_exists('question_categories', 'course', $categories[$key]->course, 'id', $categories[$key]->parent)) {
                $children[$key] = $categories[$key];
                $categories[$key]->processed = true;
                $children = $children + sort_categories_by_tree($categories, $children[$key]->id, $level+1);
            }
        }
    }
    return $children;
}

/**
 * Private method, only for the use of add_indented_names().
 *
 * Recursively adds an indentedname field to each category, starting with the category
 * with id $id, and dealing with that category and all its children, and
 * return a new array, with those categories in the right order.
 *
 * @param array $categories an array of categories which has had childids
 *          fields added by flatten_category_tree(). Passed by reference for
 *          performance only. It is not modfied.
 * @param int $id the category to start the indenting process from.
 * @param int $depth the indent depth. Used in recursive calls.
 * @return array a new array of categories, in the right order for the tree.
 */
function flatten_category_tree(&$categories, $id, $depth = 0, $nochildrenof = -1) {

    // Indent the name of this category.
    $newcategories = array();
    $newcategories[$id] = $categories[$id];
    $newcategories[$id]->indentedname = str_repeat('&nbsp;&nbsp;&nbsp;', $depth) . $categories[$id]->name;

    // Recursively indent the children.
    foreach ($categories[$id]->childids as $childid) {
        if ($childid != $nochildrenof){
            $newcategories = $newcategories + flatten_category_tree($categories, $childid, $depth + 1, $nochildrenof);
        }
    }

    // Remove the childids array that were temporarily added.
    unset($newcategories[$id]->childids);

    return $newcategories;
}

/**
 * Format categories into an indented list reflecting the tree structure.
 *
 * @param array $categories An array of category objects, for example from the.
 * @return array The formatted list of categories.
 */
function add_indented_names($categories, $nochildrenof = -1) {

    // Add an array to each category to hold the child category ids. This array will be removed
    // again by flatten_category_tree(). It should not be used outside these two functions.
    foreach (array_keys($categories) as $id) {
        $categories[$id]->childids = array();
    }

    // Build the tree structure, and record which categories are top-level.
    // We have to be careful, because the categories array may include published
    // categories from other courses, but not their parents.
    $toplevelcategoryids = array();
    foreach (array_keys($categories) as $id) {
        if (!empty($categories[$id]->parent) && array_key_exists($categories[$id]->parent, $categories)) {
            $categories[$categories[$id]->parent]->childids[] = $id;
        } else {
            $toplevelcategoryids[] = $id;
        }
    }

    // Flatten the tree to and add the indents.
    $newcategories = array();
    foreach ($toplevelcategoryids as $id) {
        $newcategories = $newcategories + flatten_category_tree($categories, $id, 0, $nochildrenof);
    }

    return $newcategories;
}

/**
 * Output a select menu of question categories.
 *
 * Categories from this course and (optionally) published categories from other courses
 * are included. Optionally, only categories the current user may edit can be included.
 *
 * @param integer $courseid the id of the course to get the categories for.
 * @param integer $published if true, include publised categories from other courses.
 * @param integer $only_editable if true, exclude categories this user is not allowed to edit.
 * @param integer $selected optionally, the id of a category to be selected by default in the dropdown.
 */
function question_category_select_menu($contexts, $top = false, $currentcat = 0, $selected = "", $nochildrenof = -1) {
    $categoriesarray = question_category_options($contexts, $top, $currentcat, false, $nochildrenof);
    if ($selected) {
        $nothing = '';
    } else {
        $nothing = 'choose';
    }
    choose_from_menu_nested($categoriesarray, 'category', $selected, $nothing);
}

/**
* Gets the default category in the most specific context.
* If no categories exist yet then default ones are created in all contexts.
*
* @param array $contexts  The context objects for this context and all parent contexts.
* @return object The default category - the category in the course context
*/
function question_make_default_categories($contexts) {
    static $preferredlevels = array(
        CONTEXT_COURSE => 4,
        CONTEXT_MODULE => 3,
        CONTEXT_COURSECAT => 2,
        CONTEXT_SYSTEM => 1,
    );
    $toreturn = null;
    $preferredness = 0;
    // If it already exists, just return it.
    foreach ($contexts as $key => $context) {
        if (!$categoryrs = get_recordset_select("question_categories", "contextid = '{$context->id}'", 'sortorder, name', '*', '', 1)) {
            error('error getting category record');
        } else {
            if (!$category = rs_fetch_record($categoryrs)){
                // Otherwise, we need to make one
                $category = new stdClass;
                $contextname = print_context_name($context, false, true);
                $category->name = addslashes(get_string('defaultfor', 'question', $contextname));
                $category->info = addslashes(get_string('defaultinfofor', 'question', $contextname));
                $category->contextid = $context->id;
                $category->parent = 0;
                $category->sortorder = 999; // By default, all categories get this number, and are sorted alphabetically.
                $category->stamp = make_unique_id_code();
                if (!$category->id = insert_record('question_categories', $category)) {
                    error('Error creating a default category for context '.print_context_name($context));
                }
            }
        }
        if ($preferredlevels[$context->contextlevel] > $preferredness &&
                has_any_capability(array('moodle/question:usemine', 'moodle/question:useall'), $context)) {
            $toreturn = $category;
            $preferredness = $preferredlevels[$context->contextlevel];
        }
    }

    if (!is_null($toreturn)) {
        $toreturn = clone($toreturn);
    }
    return $toreturn;
}

/**
 * Get all the category objects, including a count of the number of questions in that category,
 * for all the categories in the lists $contexts.
 *
 * @param mixed $contexts either a single contextid, or a comma-separated list of context ids.
 * @param string $sortorder used as the ORDER BY clause in the select statement.
 * @return array of category objects.
 */
function get_categories_for_contexts($contexts, $sortorder = 'parent, sortorder, name ASC') {
    global $CFG;
    return get_records_sql("
            SELECT c.*, (SELECT count(1) FROM {$CFG->prefix}question q
                    WHERE c.id = q.category AND q.hidden='0' AND q.parent='0') as questioncount
            FROM {$CFG->prefix}question_categories c
            WHERE c.contextid IN ($contexts)
            ORDER BY $sortorder");
}

/**
 * Output an array of question categories.
 */
function question_category_options($contexts, $top = false, $currentcat = 0, $popupform = false, $nochildrenof = -1) {
    global $CFG;
    $pcontexts = array();
    foreach($contexts as $context){
        $pcontexts[] = $context->id;
    }
    $contextslist = join($pcontexts, ', ');

    $categories = get_categories_for_contexts($contextslist);

    $categories = question_add_context_in_key($categories);

    if ($top){
        $categories = question_add_tops($categories, $pcontexts);
    }
    $categories = add_indented_names($categories, $nochildrenof);

    //sort cats out into different contexts
    $categoriesarray = array();
    foreach ($pcontexts as $pcontext){
        $contextstring = print_context_name(get_context_instance_by_id($pcontext), true, true);
        foreach ($categories as $category) {
            if ($category->contextid == $pcontext){
                $cid = $category->id;
                if ($currentcat!= $cid || $currentcat==0) {
                    $countstring = (!empty($category->questioncount))?" ($category->questioncount)":'';
                    $categoriesarray[$contextstring][$cid] = $category->indentedname.$countstring;
                }
            }
        }
    }
    if ($popupform){
        $popupcats = array();
        foreach ($categoriesarray as $contextstring => $optgroup){
            $popupcats[] = '--'.$contextstring;
            $popupcats = array_merge($popupcats, $optgroup);
            $popupcats[] = '--';
        }
        return $popupcats;
    } else {
        return $categoriesarray;
    }
}

function question_add_context_in_key($categories){
    $newcatarray = array();
    foreach ($categories as $id => $category) {
        $category->parent = "$category->parent,$category->contextid";
        $category->id = "$category->id,$category->contextid";
        $newcatarray["$id,$category->contextid"] = $category;
    }
    return $newcatarray;
}
function question_add_tops($categories, $pcontexts){
    $topcats = array();
    foreach ($pcontexts as $context){
        $newcat = new object();
        $newcat->id = "0,$context";
        $newcat->name = get_string('top');
        $newcat->parent = -1;
        $newcat->contextid = $context;
        $topcats["0,$context"] = $newcat;
    }
    //put topcats in at beginning of array - they'll be sorted into different contexts later.
    return array_merge($topcats, $categories);
}

/**
 * Returns a comma separated list of ids of the category and all subcategories
 */
function question_categorylist($categoryid) {
    // returns a comma separated list of ids of the category and all subcategories
    $categorylist = $categoryid;
    if ($subcategories = get_records('question_categories', 'parent', $categoryid, 'sortorder ASC', 'id, 1 AS notused')) {
        foreach ($subcategories as $subcategory) {
            $categorylist .= ','. question_categorylist($subcategory->id);
        }
    }
    return $categorylist;
}


//===========================
// Import/Export Functions
//===========================

/**
 * Get list of available import or export formats
 * @param string $type 'import' if import list, otherwise export list assumed
 * @return array sorted list of import/export formats available
**/
function get_import_export_formats( $type ) {

    global $CFG;
    $fileformats = get_list_of_plugins("question/format");

    $fileformatname=array();
    require_once( "{$CFG->dirroot}/question/format.php" );
    foreach ($fileformats as $key => $fileformat) {
        $format_file = $CFG->dirroot . "/question/format/$fileformat/format.php";
        if (file_exists( $format_file ) ) {
            require_once( $format_file );
        }
        else {
            continue;
        }
        $classname = "qformat_$fileformat";
        $format_class = new $classname();
        if ($type=='import') {
            $provided = $format_class->provide_import();
        }
        else {
            $provided = $format_class->provide_export();
        }
        if ($provided) {
            $formatname = get_string($fileformat, 'quiz');
            if ($formatname == "[[$fileformat]]") {
                $formatname = get_string($fileformat, 'qformat_'.$fileformat);
                if ($formatname == "[[$fileformat]]") {
                    $formatname = $fileformat;  // Just use the raw folder name
                }
            }
            $fileformatnames[$fileformat] = $formatname;
        }
    }
    natcasesort($fileformatnames);

    return $fileformatnames;
}


/**
* Create default export filename
*
* @return string   default export filename
* @param object $course
* @param object $category
*/
function default_export_filename($course,$category) {
    //Take off some characters in the filename !!
    $takeoff = array(" ", ":", "/", "\\", "|");
    $export_word = str_replace($takeoff,"_",moodle_strtolower(get_string("exportfilename","quiz")));
    //If non-translated, use "export"
    if (substr($export_word,0,1) == "[") {
        $export_word= "export";
    }

    //Calculate the date format string
    $export_date_format = str_replace(" ","_",get_string("exportnameformat","quiz"));
    //If non-translated, use "%Y%m%d-%H%M"
    if (substr($export_date_format,0,1) == "[") {
        $export_date_format = "%%Y%%m%%d-%%H%%M";
    }

    //Calculate the shortname
    $export_shortname = clean_filename($course->shortname);
    if (empty($export_shortname) or $export_shortname == '_' ) {
        $export_shortname = $course->id;
    }

    //Calculate the category name
    $export_categoryname = clean_filename($category->name);

    //Calculate the final export filename
    //The export word
    $export_name = $export_word."-";
    //The shortname
    $export_name .= moodle_strtolower($export_shortname)."-";
    //The category name
    $export_name .= moodle_strtolower($export_categoryname)."-";
    //The date format
    $export_name .= userdate(time(),$export_date_format,99,false);
    //Extension is supplied by format later.

    return $export_name;
}
class context_to_string_translator{
    /**
     * @var array used to translate between contextids and strings for this context.
     */
    var $contexttostringarray = array();

    function context_to_string_translator($contexts){
        $this->generate_context_to_string_array($contexts);
    }

    function context_to_string($contextid){
        return $this->contexttostringarray[$contextid];
    }

    function string_to_context($contextname){
        $contextid = array_search($contextname, $this->contexttostringarray);
        return $contextid;
    }

    function generate_context_to_string_array($contexts){
        if (!$this->contexttostringarray){
            $catno = 1;
            foreach ($contexts as $context){
                switch  ($context->contextlevel){
                    case CONTEXT_MODULE :
                        $contextstring = 'module';
                        break;
                    case CONTEXT_COURSE :
                        $contextstring = 'course';
                        break;
                    case CONTEXT_COURSECAT :
                        $contextstring = "cat$catno";
                        $catno++;
                        break;
                    case CONTEXT_SYSTEM :
                        $contextstring = 'system';
                        break;
                }
                $this->contexttostringarray[$context->id] = $contextstring;
            }
        }
    }

}

/**
 * Check capability on category
 * @param mixed $question object or id
 * @param string $cap 'add', 'edit', 'view', 'use', 'move'
 * @param integer $cachecat useful to cache all question records in a category
 * @return boolean this user has the capability $cap for this question $question?
 */
function question_has_capability_on($question, $cap, $cachecat = -1){
    global $USER;
    // nicolasconnault@gmail.com In some cases I get $question === false. Since no such object exists, it can't be deleted, we can safely return true
    if ($question === false) {
        return true;
    }

    // these are capabilities on existing questions capabilties are
    //set per category. Each of these has a mine and all version. Append 'mine' and 'all'
    $question_questioncaps = array('edit', 'view', 'use', 'move');
    static $questions = array();
    static $categories = array();
    static $cachedcat = array();
    if ($cachecat != -1 && (array_search($cachecat, $cachedcat)===FALSE)){
        $questions += get_records('question', 'category', $cachecat);
        $cachedcat[] = $cachecat;
    }
    if (!is_object($question)){
        if (!isset($questions[$question])){
            if (!$questions[$question] = get_record('question', 'id', $question)){
                print_error('questiondoesnotexist', 'question');
            }
        }
        $question = $questions[$question];
    }
    if (!isset($categories[$question->category])){
        if (!$categories[$question->category] = get_record('question_categories', 'id', $question->category)){
            print_error('invalidcategory', 'quiz');
        }
    }
    $category = $categories[$question->category];

    if (array_search($cap, $question_questioncaps)!== FALSE){
        if (!has_capability('moodle/question:'.$cap.'all', get_context_instance_by_id($category->contextid))){
            if ($question->createdby == $USER->id){
                return has_capability('moodle/question:'.$cap.'mine', get_context_instance_by_id($category->contextid));
            } else {
                return false;
            }
        } else {
            return true;
        }
    } else {
        return has_capability('moodle/question:'.$cap, get_context_instance_by_id($category->contextid));
    }

}

/**
 * Require capability on question.
 */
function question_require_capability_on($question, $cap){
    if (!question_has_capability_on($question, $cap)){
        print_error('nopermissions', '', '', $cap);
    }
    return true;
}

function question_file_links_base_url($courseid){
    global $CFG;
    $baseurl = preg_quote("$CFG->wwwroot/file.php", '!');
    $baseurl .= '('.preg_quote('?file=', '!').')?';//may or may not
                                     //be using slasharguments, accept either
    $baseurl .= "/$courseid/";//course directory
    return $baseurl;
}

/*
 * Find all course / site files linked to in a piece of html.
 * @param string html the html to search
 * @param int course search for files for courseid course or set to siteid for
 *              finding site files.
 * @return array files with keys being files.
 */
function question_find_file_links_from_html($html, $courseid){
    global $CFG;
    $baseurl = question_file_links_base_url($courseid);
    $searchfor = '!'.
                   '(<\s*(a|img)\s[^>]*(href|src)\s*=\s*")'.$baseurl.'([^"]*)"'.
                   '|'.
                   '(<\s*(a|img)\s[^>]*(href|src)\s*=\s*\')'.$baseurl.'([^\']*)\''.
                  '!i';
    $matches = array();
    $no = preg_match_all($searchfor, $html, $matches);
    if ($no){
        $rawurls = array_filter(array_merge($matches[5], $matches[10]));//array_filter removes empty elements
        //remove any links that point somewhere they shouldn't
        foreach (array_keys($rawurls) as $rawurlkey){
            if (!$cleanedurl = question_url_check($rawurls[$rawurlkey])){
                unset($rawurls[$rawurlkey]);
            } else {
                $rawurls[$rawurlkey] = $cleanedurl;
            }

        }
        $urls = array_flip($rawurls);// array_flip removes duplicate files
                                            // and when we merge arrays will continue to automatically remove duplicates
    } else {
        $urls = array();
    }
    return $urls;
}
/*
 * Check that url doesn't point anywhere it shouldn't
 *
 * @param $url string relative url within course files directory
 * @return mixed boolean false if not OK or cleaned URL as string if OK
 */
function question_url_check($url){
    global $CFG;
    if ((substr(strtolower($url), 0, strlen($CFG->moddata)) == strtolower($CFG->moddata)) ||
            (substr(strtolower($url), 0, 10) == 'backupdata')){
        return false;
    } else {
        return clean_param($url, PARAM_PATH);
    }
}

/*
 * Find all course / site files linked to in a piece of html.
 * @param string html the html to search
 * @param int course search for files for courseid course or set to siteid for
 *              finding site files.
 * @return array files with keys being files.
 */
function question_replace_file_links_in_html($html, $fromcourseid, $tocourseid, $url, $destination, &$changed){
    global $CFG;
    require_once($CFG->libdir .'/filelib.php');
    $tourl = get_file_url("$tocourseid/$destination");
    $fromurl = question_file_links_base_url($fromcourseid).preg_quote($url, '!');
    $searchfor = array('!(<\s*(a|img)\s[^>]*(href|src)\s*=\s*")'.$fromurl.'(")!i',
                   '!(<\s*(a|img)\s[^>]*(href|src)\s*=\s*\')'.$fromurl.'(\')!i');
    $newhtml = preg_replace($searchfor, '\\1'.$tourl.'\\5', $html);
    if ($newhtml != $html){
        $changed = true;
    }
    return $newhtml;
}

function get_filesdir_from_context($context){
    switch ($context->contextlevel){
        case CONTEXT_COURSE :
            $courseid = $context->instanceid;
            break;
        case CONTEXT_MODULE :
            $courseid = get_field('course_modules', 'course', 'id', $context->instanceid);
            break;
        case CONTEXT_COURSECAT :
        case CONTEXT_SYSTEM :
            $courseid = SITEID;
            break;
        default :
            error('Unsupported contextlevel in category record!');
    }
    return $courseid;
}
?>