#!/bin/bash
# Author: Cesar FUGUET
# Date  : Novembre 2013

clusters=65536
sector_size=512
sectors_per_cluster=8
reserved_sectors=4096

# FAT32 SPEC: The first two clusters are not present in the data region but
# they are used in the computation of the FAT sectors
data_region_clusters=$clusters-2

let "data_sectors = data_region_clusters * sectors_per_cluster"
let "fat_sectors  = (clusters * 4) / 512"

# The disk image contains:
#   - MBR sector : this sector is removed by this script as it will be copied
#                  after)
#   - Reserved region sectors (usually 32)
#   - FAT region sectors
#   - DATA region sectors
let "sectors      = data_sectors + fat_sectors + reserved_sectors + 1" 

platform=`uname`
echo "Detected platform: $platform"

if [[ $platform == "Darwin" ]]; then
	case $1 in
		create )
			# Create disk image
			# -fs        <fs>   : use filesystem <fs>
			# -volname   <name> : use volume name <name>
			# -srcfolder <src>  : copy every file in <src> into image
			# -format    <fmt>  : format of image. UDRW (UDIF read/write image)
			# -sectors   <sect> : size of image in 512-byte sectors
			# -ov				: overwrite existing image file
			# -fargs	 <args> : additional args to pass to newfs program 
			#			     -F : FAT type (FAT32)
			#				 -c : sector per cluster
			#				 -n : number of FAT

			if [[ -z $2 ]]; then
				echo "Create action need second argument: <disk_image>"
				exit 1;
			fi;

			# -F FAT type = 32 (FAT32)
			# -c sectors/cluster
			# -n number of FATs
			# -r reserved sectors
			# -k backup boot sector (VBR and FS INFO) = 0xffff (no backup)
			echo "Creating empty disk image: $2.dmg"
			fsargs="-F32 -c $sectors_per_cluster -n 1 -r $reserved_sectors -k 0xffff"

			# -layout = NONE (No partition scheme. Hence no Master Boot Record)
			hdiutil create \
				-fs MS-DOS \
				-volname virtualdisk \
				-layout NONE \
				-sectors $sectors \
				-ov \
				-fsargs "$fsargs" \
				-type "UDIF" \
				$2; 
			;;

		attach )
			# Attach created disk image to the system and mount it
			hdiutil attach $2
			;;

		detach )
			# Detach attached device. Must pass as parameter the /dev/<device>
			hdiutil detach $2
			;;

		info )
			hdiutil imageinfo $2
			;;

		* )
			echo "Pass the command as the first parameter: "
			echo "  - create: create disk image"
			echo "  - attach: attach created disk image to the system and "
			echo "            mount it (arg: path to disk_image)"
			echo "  - detach: detach specified device "
			echo "            (arg: path to /dev/<device>)"
			echo "  - info  : print information about created disk image"
			echo "            (arg: path to disk_image)"
			echo ""
			echo "EXAMPLES:"
			echo " ./create_diskimage.sh create disk_image"
			echo " ./create_diskimage.sh attach /path/to/disk_image.dmg"
			echo " ./create_diskimage.sh detach /dev/disk5"
			echo " ./create_diskimage.sh info   /path/to/disk_image.dmg"
			;;
	esac;

elif [[ $platform == "Linux" ]]; then
	case $1 in
		create )

			if [[ -z $2 ]]; then
				echo "Create action need second argument: <disk_image>"
				exit 1;
			fi;

			echo "Creating empty disk image: $2"
			let "sectors = (sectors - 1) / 2" 

			CREATE_DISK=$(command -v mkfs.vfat ||\
				      command -v /sbin/mkfs.vfat ||\
				      command -v /usr/sbin/mkfs.vfat ||\
				      command -v /usr/local/sbin/mkfs.vfat)

			if [ -z ${CREATE_DISK} ]; then
				echo "error: command mkfs.vfat not found";
				exit 1;
			fi;

			${CREATE_DISK} \
				-C \
				-F32 \
				-f 1 \
				-R $reserved_sectors \
				-S $sector_size \
				-s $sectors_per_cluster \
				-v \
				$2.dmg $sectors
			;;

		* )
			echo "Pass the command as the first parameter: "
			echo "  - create: create disk image"
			echo ""
			echo "EXAMPLES:"
			echo " ./create_diskimage.sh create disk_image"
			;;
	esac;

else
	echo "Your platform is not supported: $platform"
fi;