#!/bin/bash

set -euo pipefail


usage()
{
    echo "Usage: $0 [<options>] <file1> <file2>"
    echo
    echo "Options:"
    echo "  -h         Print this help."
    echo "  -c <color> Highlight differences with this color; defaults to red."
    echo "  -e         Show Exif differences only; don't compare the image data."
    echo "  -f <fuzz>  Use the specified percentage of fuzz.  Defaults to "
    echo "                 5% for JPEGs, zero otherwise."
    echo "  -n <name>  The name to give the first file."
    echo "  -N <name>  The name to give the second file."
    echo
}


color=
exif_only=false
fuzz=
name1=
name2=
while getopts "hc:ef:n:N:" opt
do
    case "$opt" in
    h)
        usage
        exit 0
        ;;
    c)
        color="$OPTARG"
        ;;
    e)
        exif_only=true
        ;;
    f)
        fuzz="$OPTARG"
        ;;
    n)
        name1="$OPTARG"
        ;;
    N)
        name2="$OPTARG"
        ;;
    esac
done
shift $(( OPTIND - 1 ))


if [ -z "${1-}" ] || [ -z "${2-}" ]
then
    usage
    exit 1
fi

f1="$1"
f2="$2"

if [[ "$f1" != '/dev/null' ]] && [[ ! -f "$f1" ]]
then
    echo "$f1: No such file." >&2
    exit 1
fi

if [[ "$f2" != '/dev/null' ]] && [[ ! -f "$f2" ]]
then
    echo "$f2: No such file." >&2
    usage
    exit 1
fi

if [[ -z "$name1" ]]
then
    name1="$f1"
fi
if [[ -z "$name2" ]]
then
    name1="$f2"
fi

ext="${name1##*.}"


if diff "$f1" "$f2" >/dev/null
then
  exit 0
fi


exif()
{
    if [[ "$1" = /dev/null ]]
    then
        echo /dev/null
        return
    fi

    local b="$(basename "$1")"
    local d="$(mktemp -t "$b.XXXXXX")"

    exiftool "$1" | grep -v 'File Name' | \
                    grep -v 'Directory' | \
                    grep -v 'ExifTool Version Number' | \
                    grep -v 'File Inode Change' | \
                    grep -v 'File Access Date/Time' | \
                    grep -v 'File Modification Date/Time' | \
                    grep -v 'File Permissions' | \
                    grep -v 'File Type Extension' \
        >"$d"
    echo "$d"
}


diff_clean_names()
{
    diff -u "$1" --label "$name1" "$2" --label "$name2" || true
}


if which exiftool > /dev/null
then
  d1="$(exif "$f1")"
  d2="$(exif "$f2")"
  diff_clean_names "$d1" "$d2"
else
  diff_clean_names "$f1" "$f2"
fi

if $exif_only
then
    exit 0
fi

if \
    ! which compare > /dev/null || \
    ! which montage > /dev/null
then
    echo 'ImageMagick is not installed.' >&2
    exit 1
fi

if compare "$f1" "$f2" /dev/null
then
    exit 0
fi

bn="$(basename "$f1")"
destfile="$(mktemp -t "$bn.XXXXXX").png"

if [ -z "$fuzz" ] && ( [ "$ext" = "jpeg" ] || [ "$ext" = "jpg" ] )
then
    fuzz='5'
fi

color_flag=
if [ -n "$color" ]
then
    color_flag="-highlight-color $color"
fi

fuzz_flag=
if [ -n "$fuzz" ]
then
    fuzz_flag="-fuzz $fuzz%"
fi

compare $color_flag $fuzz_flag "$f1" "$f2" png:- | \
    montage -geometry +4+4 "$f1" - "$f2" png:- >"$destfile" 2>/dev/null || true
if which xdg-open > /dev/null
then
    xdg-open "$destfile"
else
    open "$destfile"
fi