#!/bin/bash

if [[ -z "$1" || -z "$2" ]]; then
    echo "Usage: $0 <pdf1> <pdf2>"
    exit 1
fi

TMP=$(mktemp --suffix=.png)
echo "Comparing [$1] to [$2]"
echo "Saving difference in $TMP"
echo

DENSITY=100

# this supports both simple file names and page indexed file names like:
# file[0] file[1] - will either return one line for each page, or a single
# line if a single page is specified
PAGES1=$(magick identify "$1" | wc -l)
PAGES2=$(magick identify "$2" | wc -l)

if (( PAGES1 != PAGES2 )); then
    echo "Number of pages between documents does not match: $PAGES1 != $PAGES2"
    echo "Only comparing the first page."

    magick compare -density "$DENSITY" -background white "$1[0]" "$2[0]" "$TMP"
    PHASH_DIFF=$(~/bin/pdf-compare-phash "$1[0]" "$2[0]")
elif (( PAGES1 > 5 )); then
    echo "Too many pages ($PAGES1 > 5) to create hyper-image with all pages."
    echo "Only comparing first page."
    magick compare -density "$DENSITY" -background white "$1[0]" "$2[0]" "$TMP"
    PHASH_DIFF=$(~/bin/pdf-compare-phash "$1[0]" "$2[0]")
else
    # convert the PDFs into a single image with the pages vertically stacked
    ALL1=$(mktemp --suffix=.png)
    magick convert -density "$DENSITY" "$1" -append "$ALL1"
    ALL2=$(mktemp --suffix=.png)
    magick convert -density "$DENSITY" "$2" -append "$ALL2"

    magick compare -density "$DENSITY" -background white "$ALL1" "$ALL2" "$TMP"
    PHASH_DIFF=$(~/bin/pdf-compare-phash "$ALL1" "$ALL2")
fi

if [ "$TERM_PROGRAM" = "iTerm.app" ]; then
    echo "Visual difference between images:"
    echo "--------------------------------"
    imgcat-small "$TMP"
    echo "--------------------------------"
else
    open "$TMP"
fi

echo "Perceptual hash difference (0 is exactly the same): $PHASH_DIFF"