#!/bin/bash

if (( $# == 0 )) ; then
    echo "Missing argument." >&2
    exit 1
fi

INFILE="$1" OUTFILE="$2"
if [[ ! -e "$INFILE" ]] ; then
    echo "File not found: '$INFILE'" >&2
    exit 1
fi
if [[ -z "$OUTFILE" ]] ; then
    OUTFILE="$(basename "$INFILE" .xcf).png"
fi

# taken from https://stackoverflow.com/a/5846727
gimp -n -i -b - <<EOF
(let* ( (infile "${INFILE}") (outfile "${OUTFILE}") (image 0) (layer 0) )
    (set! image (car (gimp-file-load RUN-NONINTERACTIVE infile infile)))
    (set! layer (car (gimp-image-merge-visible-layers image CLIP-TO-IMAGE)))
    (gimp-file-save RUN-NONINTERACTIVE image layer outfile outfile)
    (gimp-image-delete image)
  (gimp-quit 0)
  )
EOF