#!/bin/bash

if [ -z "${1}" ]; then
  echo 'No first input image path given.'
  exit 1
fi

if [ -z "${2}" ]; then
  echo 'No second input image path given.'
  exit 1
fi

ACTUAL="${1}"
EXPECTED="${2}"
DIFF_OUT="${3}"

if [ -n "${DIFF_OUT}" ]; then
  # When a debug diff image path is given, emit a side-by-side composite
  # of the actual, expected, and a red-highlighted pixel diff. The compare
  # command exits non-zero whenever the images differ, hence the trailing
  # `|| true` to keep the script flowing while still capturing the metric.
  TMP=$(mktemp -d)
  HIGHLIGHT="${TMP}/highlight.png"

  DIFF=$(compare -metric rmse "${ACTUAL}" "${EXPECTED}" "${HIGHLIGHT}" 2>&1 \
    | cut -d '(' -f2 \
    | tr -d ')')

  montage \
    -label 'actual'   "${ACTUAL}" \
    -label 'expected' "${EXPECTED}" \
    -label 'diff'     "${HIGHLIGHT}" \
    -tile 3x1 \
    -geometry '+8+8' \
    -background '#222222' \
    -fill '#ffffff' \
    "${DIFF_OUT}" >/dev/null 2>&1

  rm -rf "${TMP}"
else
  DIFF=$(compare -metric rmse "${ACTUAL}" "${EXPECTED}" /dev/null 2>&1 \
    | cut -d '(' -f2 \
    | tr -d ')')
fi

DIFF=$(perl -e "print ${DIFF} * 100")

if [ -z "${DIFF}" ]; then
  echo -1
  exit
fi

echo ${DIFF}