#!/bin/bash
# Compare the merging function of stack_png with pamcomp.
#
# Note that temporary files are generated relative to current directory
# as opposed to the default place (usually /tmp).  This is needed because
# mingw can't access /tmp.

set -euo pipefail

if [[ $# -ne 4 ]]; then
   echo "$0 <stack_png.exe> <underlay.pgm> <overlay.pgm> <alpha.pgm>"
   exit 1
fi

STACK_PNG=$1
UNDERLAY=$2
OVERLAY=$3
ALPHA=$4

# Compose expected image with netpbm tools.
EXPECTED=$(mktemp -p .)
pamcomp -alpha="$ALPHA" "$OVERLAY" "$UNDERLAY" > "$EXPECTED"

INPUT1=$(mktemp -p .)
INPUT2=$(mktemp -p .)
ACTUAL=$(mktemp -p .)

# Compose image with the program we want to test.
pnmtopng "$UNDERLAY" > "$INPUT1"
pnmtopng -alpha="$ALPHA" "$OVERLAY" > "$INPUT2"
"./$STACK_PNG" "$INPUT1" "$INPUT2" > "$ACTUAL"

# Before checking that output pixels are as expected, try running the same
# program using stdin as input, and verify that output pixels are identical.
PIPED_OUTPUT=$(mktemp -p .)
cat "$INPUT1" | "./$STACK_PNG" - "$INPUT2" > "$PIPED_OUTPUT"
if ! ( diff -q "$ACTUAL" "$PIPED_OUTPUT" ); then
   rm -f "$INPUT1" "$INPUT2" "$EXPECTED" "$ACTUAL" "$PIPED_OUTPUT"
   echo "Failed to read first image from stdin"
   exit 1
fi
cat "$INPUT2" | "./$STACK_PNG" "$INPUT1" - > "$PIPED_OUTPUT"
if ! ( diff -q "$ACTUAL" "$PIPED_OUTPUT" ); then
   rm -f "$INPUT1" "$INPUT2" "$EXPECTED" "$ACTUAL" "$PIPED_OUTPUT"
   echo "Failed to read second image from stdin"
   exit 1
fi

DIFF=$(mktemp -p .)
pngtopnm "$ACTUAL" | pamarith -difference "$EXPECTED" - > "$DIFF"

# Check the output bytes in diff image, allowing for a bit of leeway in
# minute differences.  The differences are probably due to the slightly
# different floating point constants used for gamma correction.
if ! ( perl -e '
   $bytes = join "", <>;
   die "Unexpected difference\n" unless( $bytes =~ /^P\d+\s\d+\s\d+\s\d+\s[\x00-\x02]*$/s );
' "$DIFF" ) ; then
   rm -f "$INPUT1" "$INPUT2" "$EXPECTED" "$ACTUAL" "$PIPED_OUTPUT" "$DIFF"
   exit 1
fi

rm -f "$INPUT1" "$INPUT2" "$EXPECTED" "$ACTUAL" "$PIPED_OUTPUT" "$DIFF"
exit 0