#!/bin/bash


# pdfdiff : perform a graphical diff on two similar pdf files, and highlight the differences
# Usage : pdfdiff SOURCE1 SOURCE2 [OUTPUT]
# 
# Dependencies: mutool (https://mupdf.com) ; ImageMagikc (imagemagick.org)

tmpdir=$(mktemp -d)

cp "${1}" "${tmpdir}/a.pdf"
cp "${2}" "${tmpdir}/b.pdf"

cd "${tmpdir}"

n=$(mutool info a.pdf | grep -im1 "Pages: " | cut -d " " -f 2)
m=$(mutool info b.pdf | grep -im1 "Pages: " | cut -d " " -f 2)

if test "${n}" != "${m}" ; then
	read -p "Warning: Source PDFs do not have the same number of pages. Continue ? [Y/n]"
	test "${REPLY}" = "n" || test "${REPLY}" = "N" && exit 0
	test "${n}" -gt "${m}" && n="${m}"
fi

mutool draw -F png -A 0 -N -o a-%d.png a.pdf
mutool draw -F png -A 0 -N -o b-%d.png b.pdf

for i in $(seq 1 "${n}") ; do
	compare "a-${i}.png" "b-${i}.png" -compose src "diff-${i}.png"
	montage "a-${i}.png" "diff-${i}.png" "b-${i}.png" -tile 3x1 -geometry +0+0 "out-${i}.png"
done

convert $(ls -v out*.png) out.pdf

cd -
mv "${tmpdir}/out.pdf" "${3:-./diff.pdf}"

rm -rf "${tmpdir}"