<?php
namespace GuzzleHttp\Promise;

/**
 * Get the global task queue used for promise resolution.
 *
 * This task queue MUST be run in an event loop in order for promises to be
 * settled asynchronously. It will be automatically run when synchronously
 * waiting on a promise.
 *
 * <code>
 * while ($eventLoop->isRunning()) {
 *     GuzzleHttp\Promise\queue()->run();
 * }
 * </code>
 *
 * @return TaskQueue
 */
function queue()
{
    static $queue;

    if (!$queue) {
        $queue = new TaskQueue();
    }

    return $queue;
}

/**
 * Adds a function to run in the task queue when it is next `run()` and returns
 * a promise that is fulfilled or rejected with the result.
 *
 * @param callable $task Task function to run.
 *
 * @return PromiseInterface
 */
function task(callable $task)
{
    $queue = queue();
    $promise = new Promise([$queue, 'run']);
    $queue->add(function () use ($task, $promise) {
        try {
            $promise->resolve($task());
        } catch (\Exception $e) {
            $promise->reject($e);
        }
    });

    return $promise;
}

/**
 * Creates a promise for a value if the value is not a promise.
 *
 * @param mixed $value Promise or value.
 *
 * @return PromiseInterface
 */
function promise_for($value)
{
    if ($value instanceof PromiseInterface) {
        return $value;
    }

    // Return a Guzzle promise that shadows the given promise.
    if (method_exists($value, 'then')) {
        $wfn = method_exists($value, 'wait') ? [$value, 'wait'] : null;
        $cfn = method_exists($value, 'cancel') ? [$value, 'cancel'] : null;
        $promise = new Promise($wfn, $cfn);
        $value->then([$promise, 'resolve'], [$promise, 'reject']);
        return $promise;
    }

    return new FulfilledPromise($value);
}

/**
 * Creates a rejected promise for a reason if the reason is not a promise. If
 * the provided reason is a promise, then it is returned as-is.
 *
 * @param mixed $reason Promise or reason.
 *
 * @return PromiseInterface
 */
function rejection_for($reason)
{
    if ($reason instanceof PromiseInterface) {
        return $reason;
    }

    return new RejectedPromise($reason);
}

/**
 * Create an exception for a rejected promise value.
 *
 * @param mixed $reason
 *
 * @return \Exception
 */
function exception_for($reason)
{
    return $reason instanceof \Exception
        ? $reason
        : new RejectionException($reason);
}

/**
 * Returns an iterator for the given value.
 *
 * @param mixed $value
 *
 * @return \Iterator
 */
function iter_for($value)
{
    if ($value instanceof \Iterator) {
        return $value;
    } elseif (is_array($value)) {
        return new \ArrayIterator($value);
    } else {
        return new \ArrayIterator([$value]);
    }
}

/**
 * Synchronously waits on a promise to resolve and returns an inspection state
 * array.
 *
 * Returns a state associative array containing a "state" key mapping to a
 * valid promise state. If the state of the promise is "fulfilled", the array
 * will contain a "value" key mapping to the fulfilled value of the promise. If
 * the promise is rejected, the array will contain a "reason" key mapping to
 * the rejection reason of the promise.
 *
 * @param PromiseInterface $promise Promise or value.
 *
 * @return array
 */
function inspect(PromiseInterface $promise)
{
    try {
        return [
            'state' => PromiseInterface::FULFILLED,
            'value' => $promise->wait()
        ];
    } catch (RejectionException $e) {
        return ['state' => PromiseInterface::REJECTED, 'reason' => $e->getReason()];
    } catch (\Exception $e) {
        return ['state' => PromiseInterface::REJECTED, 'reason' => $e];
    }
}

/**
 * Waits on all of the provided promises, but does not unwrap rejected promises
 * as thrown exception.
 *
 * Returns an array of inspection state arrays.
 *
 * @param PromiseInterface[] $promises Traversable of promises to wait upon.
 *
 * @return array
 * @see GuzzleHttp\Promise\inspect for the inspection state array format.
 */
function inspect_all($promises)
{
    $results = [];
    foreach ($promises as $key => $promise) {
        $results[$key] = inspect($promise);
    }

    return $results;
}

/**
 * Waits on all of the provided promises and returns the fulfilled values.
 *
 * Returns an array that contains the value of each promise (in the same order
 * the promises were provided). An exception is thrown if any of the promises
 * are rejected.
 *
 * @param mixed $promises Iterable of PromiseInterface objects to wait on.
 *
 * @return array
 * @throws \Exception on error
 */
function unwrap($promises)
{
    $results = [];
    foreach ($promises as $key => $promise) {
        $results[$key] = $promise->wait();
    }

    return $results;
}

/**
 * Given an array of promises, return a promise that is fulfilled when all the
 * items in the array are fulfilled.
 *
 * The promise's fulfillment value is an array with fulfillment values at
 * respective positions to the original array. If any promise in the array
 * rejects, the returned promise is rejected with the rejection reason.
 *
 * @param mixed $promises Promises or values.
 *
 * @return Promise
 */
function all($promises)
{
    $results = [];
    return each(
        $promises,
        function ($value, $idx) use (&$results) {
            $results[$idx] = $value;
        },
        function ($reason, $idx, Promise $aggregate) {
            $aggregate->reject($reason);
        }
    )->then(function () use (&$results) {
        ksort($results);
        return $results;
    });
}

/**
 * Initiate a competitive race between multiple promises or values (values will
 * become immediately fulfilled promises).
 *
 * When count amount of promises have been fulfilled, the returned promise is
 * fulfilled with an array that contains the fulfillment values of the winners
 * in order of resolution.
 *
 * This prommise is rejected with a {@see GuzzleHttp\Promise\AggregateException}
 * if the number of fulfilled promises is less than the desired $count.
 *
 * @param int   $count    Total number of promises.
 * @param mixed $promises Promises or values.
 *
 * @return Promise
 */
function some($count, $promises)
{
    $results = [];
    $rejections = [];

    return each(
        $promises,
        function ($value, $idx, PromiseInterface $p) use (&$results, $count) {
            if ($p->getState() !== PromiseInterface::PENDING) {
                return;
            }
            $results[$idx] = $value;
            if (count($results) >= $count) {
                $p->resolve(null);
            }
        },
        function ($reason) use (&$rejections) {
            $rejections[] = $reason;
        }
    )->then(
        function () use (&$results, &$rejections, $count) {
            if (count($results) !== $count) {
                throw new AggregateException(
                    'Not enough promises to fulfill count',
                    $rejections
                );
            }
            ksort($results);
            return array_values($results);
        }
    );
}

/**
 * Like some(), with 1 as count. However, if the promise fulfills, the
 * fulfillment value is not an array of 1 but the value directly.
 *
 * @param mixed $promises Promises or values.
 *
 * @return PromiseInterface
 */
function any($promises)
{
    return some(1, $promises)->then(function ($values) { return $values[0]; });
}

/**
 * Returns a promise that is fulfilled when all of the provided promises have
 * been fulfilled or rejected.
 *
 * The returned promise is fulfilled with an array of inspection state arrays.
 *
 * @param mixed $promises Promises or values.
 *
 * @return Promise
 * @see GuzzleHttp\Promise\inspect for the inspection state array format.
 */
function settle($promises)
{
    $results = [];

    return each(
        $promises,
        function ($value, $idx) use (&$results) {
            $results[$idx] = ['state' => PromiseInterface::FULFILLED, 'value' => $value];
        },
        function ($reason, $idx) use (&$results) {
            $results[$idx] = ['state' => PromiseInterface::REJECTED, 'reason' => $reason];
        }
    )->then(function () use (&$results) {
        ksort($results);
        return $results;
    });
}

/**
 * Given an iterator that yields promises or values, returns a promise that is
 * fulfilled with a null value when the iterator has been consumed or the
 * aggregate promise has been fulfilled or rejected.
 *
 * $onFulfilled is a function that accepts the fulfilled value, iterator
 * index, and the aggregate promise. The callback can invoke any necessary side
 * effects and choose to resolve or reject the aggregate promise if needed.
 *
 * $onRejected is a function that accepts the rejection reason, iterator
 * index, and the aggregate promise. The callback can invoke any necessary side
 * effects and choose to resolve or reject the aggregate promise if needed.
 *
 * @param mixed    $iterable    Iterator or array to iterate over.
 * @param callable $onFulfilled
 * @param callable $onRejected
 *
 * @return Promise
 */
function each(
    $iterable,
    callable $onFulfilled = null,
    callable $onRejected = null
) {
    return (new EachPromise($iterable, [
        'fulfilled' => $onFulfilled,
        'rejected'  => $onRejected
    ]))->promise();
}

/**
 * Like each, but only allows a certain number of outstanding promises at any
 * given time.
 *
 * $concurrency may be an integer or a function that accepts the number of
 * pending promises and returns a numeric concurrency limit value to allow for
 * dynamic a concurrency size.
 *
 * @param mixed        $iterable
 * @param int|callable $concurrency
 * @param callable     $onFulfilled
 * @param callable     $onRejected
 *
 * @return mixed
 */
function each_limit(
    $iterable,
    $concurrency,
    callable $onFulfilled = null,
    callable $onRejected = null
) {
    return (new EachPromise($iterable, [
        'fulfilled'   => $onFulfilled,
        'rejected'    => $onRejected,
        'concurrency' => $concurrency
    ]))->promise();
}

/**
 * Like each_limit, but ensures that no promise in the given $iterable argument
 * is rejected. If any promise is rejected, then the aggregate promise is
 * rejected with the encountered rejection.
 *
 * @param mixed        $iterable
 * @param int|callable $concurrency
 * @param callable     $onFulfilled
 *
 * @return mixed
 */
function each_limit_all(
    $iterable,
    $concurrency,
    callable $onFulfilled = null
) {
    return each_limit(
        $iterable,
        $concurrency,
        $onFulfilled,
        function ($reason, $idx, PromiseInterface $aggregate) {
            $aggregate->reject($reason);
        }
    );
}

/**
 * Returns true if a promise is fulfilled.
 *
 * @param PromiseInterface $promise
 *
 * @return bool
 */
function is_fulfilled(PromiseInterface $promise)
{
    return $promise->getState() === PromiseInterface::FULFILLED;
}

/**
 * Returns true if a promise is rejected.
 *
 * @param PromiseInterface $promise
 *
 * @return bool
 */
function is_rejected(PromiseInterface $promise)
{
    return $promise->getState() === PromiseInterface::REJECTED;
}

/**
 * Returns true if a promise is fulfilled or rejected.
 *
 * @param PromiseInterface $promise
 *
 * @return bool
 */
function is_settled(PromiseInterface $promise)
{
    return $promise->getState() !== PromiseInterface::PENDING;
}

/**
 * Creates a promise that is resolved using a generator that yields values or
 * promises (somewhat similar to C#'s async keyword).
 *
 * When called, the coroutine function will start an instance of the generator
 * and returns a promise that is fulfilled with its final yielded value.
 *
 * Control is returned back to the generator when the yielded promise settles.
 * This can lead to less verbose code when doing lots of sequential async calls
 * with minimal processing in between.
 *
 *     use GuzzleHttp\Promise;
 *
 *     function createPromise($value) {
 *         return new Promise\FulfilledPromise($value);
 *     }
 *
 *     $promise = Promise\coroutine(function () {
 *         $value = (yield createPromise('a'));
 *         try {
 *             $value = (yield createPromise($value . 'b'));
 *         } catch (\Exception $e) {
 *             // The promise was rejected.
 *         }
 *         yield $value . 'c';
 *     });
 *
 *     // Outputs "abc"
 *     $promise->then(function ($v) { echo $v; });
 *
 * @param callable $generatorFn Generator function to wrap into a promise.
 *
 * @return Promise
 * @link https://github.com/petkaantonov/bluebird/blob/master/API.md#generators inspiration
 */
function coroutine(callable $generatorFn)
{
    $generator = $generatorFn();
    return __next_coroutine($generator->current(), $generator)->then();
}

/** @internal */
function __next_coroutine($yielded, \Generator $generator)
{
    return promise_for($yielded)->then(
        function ($value) use ($generator) {
            $nextYield = $generator->send($value);
            return $generator->valid()
                ? __next_coroutine($nextYield, $generator)
                : $value;
        },
        function ($reason) use ($generator) {
            $nextYield = $generator->throw(exception_for($reason));
            // The throw was caught, so keep iterating on the coroutine
            return __next_coroutine($nextYield, $generator);
        }
    );
}