#!/bin/sh
INPUT="$1"
FRAMES="$2"

die() {
	echo "$@"
	exit 1
}
check_command() {
	cmd="$1"
	command -v "$cmd" > /dev/null || die "command '$cmd' not found"
}

check_command magick
check_command identify
[ "$#" -eq 2 ] || die "usage: $0 <input image> <frame count>"
[ -e "$INPUT" ] || die "file not found: $INPUT"
[ "$FRAMES" -gt 0 ] || die "invalid frame count: $FRAMES"

tile_width=$(identify -format "%w" "$INPUT")
tile_height=$(identify -format "%h" "$INPUT")

OUTPUT="$INPUT.scroll.png"
magick -size "${tile_width}x$(( $tile_height * $FRAMES ))" 'xc:#ff00ff00' "$OUTPUT"

for i in $(seq 0 $(( $FRAMES - 1 ))); do
	offset_x=$(( $tile_width * $i / $FRAMES ))
	offset_y=$(( i * $tile_height ))

	magick "$OUTPUT" "$INPUT" -geometry "+${offset_x}+${offset_y}" -composite "$OUTPUT"
	magick "$OUTPUT" "$INPUT" -geometry "+$(( $offset_x - $tile_width ))+${offset_y}" -composite "$OUTPUT"
	echo "+${offset_x}+${offset_y}"
done

# magick -size ${total_width}x${sprite_height} xc:none canvas.png