#!/bin/bash
#write a file to /dev/mmcblk0 making sure it is unmounted first.
#Functions:
#Unmount all partitions on the device
unmount_partitions() {
    RET=0
    for i in $(grep $1 /proc/mounts | awk '{print $1}')
    do
        echo unmounting $i >&2
        sudo umount $i
        if [ $? -ne 0 ]; then
            RET=$?
            echo Failed to unmount $i >&2
        fi
    done
    return $RET
}
#Write the image to the SD card calling xzcat or zcat, or just plain cat 
#as needed.
write_image() {
    FILE=$1
    DEVICE=$2
    case $(file -b $FILE | awk -F, '{print $1}') in
        compress*)
            echo "old style UNIX compress(1) format detected" >&2;
            CAT=zcat;;
       gzip*)
            echo "gzip detected" >&2;
            CAT=zcat;;
       XZ*)
           echo "XZ detected" >&2;
           CAT=xzcat;;
       bzip2*)
           echo "bzip2 detected" >&2;
           CAT=bzcat;;
       *)
           echo "uncompressed or unsupported compression methods detected using cat" >&2;
           CAT=cat;;
    esac
echo -n Calculating image size: >&2
SIZE=$($CAT $FILE | wc -c)
echo "$SIZE bytes" >&2
$CAT $FILE | pv -pterb -s $SIZE | sudo dd of=$DEVICE
}
#Main
if [ "x$2" = "x" ]; then
   DEVICE=/dev/mmcblk0
else
    DEVICE="$2"
fi 
if [ -b $DEVICE ]; then
    if [ ! -f $1 ]; then
        echo cannot open $1! >&2
        exit 1
    fi
    unmount_partitions $DEVICE
    if [ $? -ne 0 ]; then
        echo "Couldn't unmount all partitions on $DEVICE" >&2
        exit 1
    fi
    echo -n "Are you sure you want to erase $DEVICE and write $1? (y/n):" >&2
    read yn
    if [ "x$yn" = "xy" ];then
       echo "writing to $DEVICE in 5 seconds" >&2
       sleep 5
   else
       echo "ABORTING!" >&2
       exit 1
   fi
    which blkdiscard >/dev/null 
    if [ $? -eq 0 ]; then 
        sudo blkdiscard -v $DEVICE
    fi
    write_image $1 $DEVICE
    if [ $? -ne 0 ]; then
        echo "Something went wrong write_image returned $?" >&2
        exit 1
    else
        echo "Image was written successfully"
        sync
    fi
else
    echo block device $DEVICE does not exist! >&2
    exit 1
fi