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

local callstr="$0"
local hasgsic=$(whence gifsicle)

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 "    use subtitle track  -n <int>   0"
	[[ $hasgsic ]] && echo "optimise with gifsicle  -g"
	echo "       print this help  -h"
	exit 1
}

local start="00:00:00"
local length=""
local fps=10
local width=480
local subs=""
local strack=0
local gsic=""

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

# tmp var used to old '-t' if length is used
local t=""

# really annoying, but no other good way to do this
if [[ $hasgsic ]]; then
	while getopts s:t:f:w:bhn:g opt; do
		case "$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 ;;
			n)
				[[ ! $(echo $OPTARG | grep -oE "$intpat") ]] \
					&& usage "sub track specifier must be an integer"
				strack=$OPTARG
				;;
			g) gsic=true ;;
			h) usage ;;
			[?]) usage ;;
		esac
	done
else
	while getopts s:t:f:w:bhn: opt; do
		case "$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 ;;
			n)
				[[ ! $(echo $OPTARG | grep -oE "$intpat") ]] \
					&& usage "sub track specifier must be an integer"
				strack=$OPTARG
				;;
			h) usage ;;
			[?]) usage ;;
		esac
	done
fi
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"

local paltmp="make-gif"
while [[ -f "${paltmp}-palette.png" ]] || [[ -f "${paltmp}-in" ]]; do
	paltmp="${paltmp}-1"
done

ln -s "$1" "${paltmp}-in"

local fferr

if [[ $subs ]]; then
	echo "pass 1..."
	ffmpeg -loglevel 16 -y -ss $start $t $length -i "$1" -copyts \
		-vf "subtitles=${paltmp}-in:si=$strack,fps=$fps,scale=$width:-1:flags=lanczos,palettegen" \
		${paltmp}-palette.png
	[[ $? -ne 0 ]] && fferr=true
	[[ ! $fferr ]] && echo "pass 2..." && ffmpeg -loglevel 24 \
		-ss $start $t $length -i "$1" -i ${paltmp}-palette.png \
		-copyts -filter_complex \
		"subtitles=${paltmp}-in:si=$strack,fps=$fps,scale=$width:-1:flags=lanczos[x];[x][1:v]paletteuse" \
		"$2"
else
	echo "pass 1..."
	ffmpeg -loglevel 16 -y -ss "$start" $t $length -i "$1" \
		-vf "fps=$fps,scale=$width:-1:flags=lanczos,palettegen" \
		${paltmp}-palette.png
	[[ $? -ne 0 ]] && fferr=true
	[[ ! $fferr ]] && echo "pass 2..." && ffmpeg -loglevel 24 \
		-ss $start $t $length -i "$1" -i ${paltmp}-palette.png -filter_complex \
		"fps=$fps,scale=$width:-1:flags=lanczos[x];[x][1:v]paletteuse" \
		"$2"
fi

rm -f ${paltmp}-palette.png
rm -f ${paltmp}-in

if [[ -f "$2" ]] && [[ ! $fferr ]]; then
	if [[ $gsic ]]; then
		local gsictmp="$2.out"
		while [[ -f "$gsictmp" ]]; do
			gsictmp="$gsictmp.out"
		done
		echo "optimising..."
		gifsicle -O3 -i "$2" -o "$gsictmp"
		[[ $? -eq 0 ]] && rm -f "$2" && mv "$gsictmp" "$2"
	fi
fi