# reduce quality of a jpeg file to reach target file size
# by grepper

(($# != 2)) && echo \
Usage: $0 [target size in bytes] [in file] && exit 1

target_size=$1
infile=$2
q=99
insize=$(identify -format '%b' "$2")

spin()
{
    # Print spaces to overwrite previous line
    echo -ne "\r                                                            "
    echo -ne "\r$@ "
}

echo $2 is $insize and target_size is $target_size
while ((insize > target_size)); do
    spin "Trying -quality $q"
    tmpname=$(tempfile)
    outname=$(tempfile -s .jpg)
    convert "$infile" -quality $q "$outname"
    if (( $(identify -format '%b' "$outname") <= target_size )); then
        echo
        echo Success using -quality $q !
        echo
        echo Output file is "${infile%.*}-${q}.jpg"
        mv  "$outname" "${infile%.*}-${q}.jpg"
        insize=$target_size
    else
    rm -f "$outname"
    fi
    ((q--))
done