#!/bin/sh

if [ -z $1 ]; then
    CMD="git diff-index --raw --name-status HEAD"
else
    CMD="git diff --raw --name-status $1^ $1"
fi

echo_exit()
{
    echo $1
    exit
}

find_files()
{
    $CMD | grep '^\(A\|M\).*png$' | sed 's/^.\t//'
}

cd "$(git rev-parse --show-toplevel)"
[ $(find_files | wc -l) != 0 ] \
    || echo_exit "No changed .png files -- please 'git add' them first."
find_files | xargs -d "\n" optipng -o4 -i0 -fix
find_files | xargs -d "\n" advpng -z4