#!/usr/bin/env zsh
# export a clip from a video as a gif

local callstr="$0"

usage() {
	[[ "$1" != "" ]] && echo -e "\e[1;31merror:\e[0m $1\n"
	echo "Usage: $callstr [OPTIONS...] <infile> <outfile>"
	echo ""
	echo "description       option     default val"
	echo "start time        -s <time>  00:00:00"
	echo "length in seconds -t <int>   full length"
	echo "gif fps           -f <int>   10"
	echo "gif pixel width   -w <int>   480"
	echo "use subtitles     -b"
	echo "print this help   -h"
	exit 1
}

local start="00:00:00"
local length=""
local fps=10
local width=480
local subs=""

local timepat='^(([0-9][0-9]:){1,2}[0-9][0-9]|[0-9]+)$'
local intpat='^[0-9][0-9]*$'

local t=""

while getopts s:t:f:w:bh opt; do
	case "$opt" in
		s) 
			[[ ! $(echo $OPTARG | grep -oE "$timepat") ]] \
				&& usage "malformed start timestamp"
			start="$OPTARG"
			;;
		t)
			[[ ! $(echo $OPTARG | grep -oE "$intpat") ]] \
				&& usage "length must be an integer"
			length=$OPTARG
			t="-t"
			;;
		f)
			[[ ! $(echo $OPTARG | grep -oE "$intpat") ]] \
				&& usage "start time must be an integer"
			fps=$OPTARG
			;;
		w)
			[[ ! $(echo $OPTARG | grep -oE "$intpat") ]] \
				&& usage "fps must be an integer"
			width=$OPTARG
			;;
		b) subs=true ;;
		h) usage ;;
		[?]) usage ;;
	esac
done
shift $OPTIND-1

[[ ${#@} -gt 2 ]] && usage "trailing arguments detected"

[[ ${#@} -lt 2 ]] && usage "no output file specified"

[[ "${2:e}" != "gif" ]] && usage "output file must have a .gif file extension"

[[ ! -f "$1" ]] && usage "input file not found"


rm -f make-gif-palette.png
rm -f make-gif-in

ln -s "$1" make-gif-in

if [[ $subs ]]; then
	echo "pass 1..."
	ffmpeg -loglevel 16 -y -ss $start $t $length -i "$1" -copyts \
		-vf "subtitles=make-gif-in,fps=$fps,scale=$width:-1:flags=lanczos,palettegen" \
		make-gif-palette.png
	[[ $? -eq 0 ]] && echo "pass 2..." && ffmpeg -loglevel 24 \
		-ss $start $t $length -i "$1" -i make-gif-palette.png \
		-copyts -filter_complex \
		"subtitles=make-gif-in,fps=$fps,scale=$width:-1:flags=lanczos[x];[x][1:v]paletteuse" \
		out.gif
else
	echo "pass 1..."
	ffmpeg -loglevel 16 -y -ss "$start" $t $length -i "$1" \
		-vf "fps=$fps,scale=$width:-1:flags=lanczos,palettegen" \
		make-gif-palette.png
	[[ $? -eq 0 ]] && echo "pass 2..." && ffmpeg -loglevel 24 \
		-ss $start $t $length -i "$1" -i make-gif-palette.png -filter_complex \
		"fps=$fps,scale=$width:-1:flags=lanczos[x];[x][1:v]paletteuse" \
		out.gif
fi

rm -f make-gif-palette.png
rm -f make-gif-in