#!/bin/bash 
#
# This script generates a partitioned image blob for use with ARM systems that
# require a filesystem + MBR partition table. It takes in a FAT filesystem blob
#
# Parts of this script lifted from post-boot-armel+dove in debian-cd
#
# Copyright (C) 2011 Canonical
# Authors: Michael Casadevall <michael.casadevall@canonical.com>

set -e

FAT_IMAGE="$1"
IMAGE="$2"
OFFSET="${3:-512}"


log() {
    echo "$*" >&2
}

die() {
    log "$@"
    exit 1
}

file_length() {
    stat -c %s "$1"
}

# Make sure we have our input
if [ ! -e $FAT_IMAGE ]; then
    die "no file found"
fi

IMAGE_SIZE="$(file_length "$FAT_IMAGE")"

# round size to next block; note we add 512 for MBR + partition table; also
# note we assume blocks of 512 B
IMG_SIZE_BLOCKS="$(((512 + $IMAGE_SIZE + $OFFSET - 1) / 512))"

# create the blank disk image (and this is a sparse file)
dd if=/dev/zero of="$IMAGE" bs=512 count=0 seek="$IMG_SIZE_BLOCKS" 2>/dev/null

log "initializing disk label (MBR and partition table) ..."
parted -s "$IMAGE" mklabel msdos

# outputs actual partition start offset, end offset, and length, suffixed with
# B
get_part_data() {
    local n="$1"
    LANG=C parted -s "$IMAGE" unit B print | awk "/^ $n / { print \$2 \" \" \$3 \" \" \$4 }"
}

# create partition for the VFAT
log "creating VFAT partition..."
parted -s "$IMAGE" "mkpart primary fat32 ${OFFSET}B -1s"

VFAT_START_B="`(set -- $(get_part_data 1); echo "$1")`"
log "writing vfat contents..."
dd conv=notrunc bs="${VFAT_START_B%B}" if="$FAT_IMAGE" of="$IMAGE" seek=1 2>/dev/null
parted -s "$IMAGE" set 1 boot on