// SPDX-FileCopyrightText: Sam Nystrom <sam@samnystrom.dev>
// SPDX-License-Identifier: GPL-3.0-only

use bufio;
use encoding::utf8;
use getopt;
use io;
use fmt;
use fs;
use os;
use strconv;
use strings;
use time;
use unix::poll;
use unix::tty;

type segment = struct {
	index: uint,
	start: time::duration,
	end: time::duration,
	text: str,
};

export fn main() void = {
	let help: []getopt::help = [
		"Play a .srt subtitle file",
		"<file>",
	];
	let cmd = getopt::parse(os::args, help...);
	defer getopt::finish(&cmd);
	if (len(cmd.args) != 1) {
		getopt::printusage(os::stderr, os::args[0], help)!;
		os::exit(1);
	};

	let path = cmd.args[0];
	let mode = os::stat(path)!.mode;
	if (mode & fs::mode::DIR != 0) {
		fmt::fatalf("Error: '{}' is a directory\n", path);
	};
	let file = match (os::open(path)) {
	case let f: io::file =>
		yield f;
	case let err: fs::error =>
		fmt::fatalf("Error reading '{}': {}\n", path, fs::strerror(err));
	};

	let segments = parse_srt(file);
	defer free(segments);
	defer for (let i = 0z; i < len(segments); i += 1) {
		free(segments[i].text);
	};

	fmt::fprint(os::stdout_file, "\x1b[?25l")!;
	defer fmt::fprint(os::stdout_file, "\x1b[?25h")!;
	let termios = tty::termios_query(os::stdin_file)!;
	defer tty::termios_restore(&termios);
	tty::makeraw(&termios)!;

	let pollfds = [
		poll::pollfd {
			fd = os::stdin_file,
			events = poll::event::POLLIN,
			...
		},
	];

	let end: time::duration = 0;
	for (let i = 0z; i < len(segments); i += 1) {
		if (segments[i].end > end) {
			end = segments[i].end;
		};
	};
	let start = time::now(time::clock::REALTIME);
	let elapsed: time::duration = 0;
	let pause_start: (time::instant | void) = void;

	for (true) {
		let now = time::now(time::clock::REALTIME);
		match (pause_start) {
		case void =>
			elapsed = time::diff(start, now);
		case let inst: time::instant =>
			elapsed = time::diff(start, inst);
		};
		if (elapsed > end) break;

		fmt::printfln("\x1b[2J\x1b[;H{:02}:{:02}:{:02}{}\r",
			elapsed / time::HOUR,
			elapsed / time::MINUTE % 60,
			elapsed / time::SECOND % 60,
			if (pause_start is time::instant) " (PAUSED)" else "",
		)!;

		let timeout = end;

		for (let i = 0z; i < len(segments); i += 1) {
			let seg = segments[i];
			if (seg.start > elapsed && seg.start < timeout) {
				timeout = seg.start;
			};
			if (seg.end > elapsed && seg.end < timeout) {
				timeout = seg.end;
			};
			if (seg.start <= elapsed && elapsed <= seg.end) {
				fmt::println(seg.text)!;
			};
		};

		timeout -= elapsed;
		let next_second = time::SECOND - elapsed % time::SECOND;
		if (timeout > next_second) {
			timeout = next_second;
		};
		if (pause_start is time::instant) {
			timeout = poll::INDEF;
		};

		match (poll::poll(pollfds, timeout)) {
		case uint => void;
		case let err: poll::error =>
			fmt::errorln("Error polling for user input:", poll::strerror(err))!;
		};
		if (pollfds[0].revents & poll::event::POLLIN == 0) {
			continue;
		};

		static let buf: [os::BUFSIZ]u8 = [0...];
		let input = match (io::read(os::stdin_file, buf)) {
		case let x: size =>
			yield buf[..x];
		case io::EOF =>
			break;
		case let err: io::error =>
			fmt::errorln("Error reading user input:", io::strerror(err))!;
			continue;
		};
		let quit = false;
		for (let i = 0z; i < len(input); i += 1) {
			switch (input[i]) {
			case 'q' =>
				quit = true;
			case 'j' =>
				start = time::add(start, time::SECOND * 10);
			case 'l' =>
				start = time::add(start, -time::SECOND * 10);
			case 'k' =>
				match (pause_start) {
				case void =>
					pause_start = now;
				case let inst: time::instant =>
					pause_start = void;
					start = time::add(start, time::diff(inst, now));
				};
				
			case => void;
			};
		};
		if (quit) break;
	};
};

type state = enum {
	INDEX,
	TIMECODE,
	TEXT,
};

fn parse_srt(file: io::handle) []segment = {
	let segments: []segment = [];
	let current = segment { ... };
	let state = state::INDEX;

	for (let nr = 0; true; nr += 1) {
		let line = match (bufio::scanline(file)!) {
		case let line: []u8 =>
			yield match (strings::fromutf8(line)) {
			case let line: str =>
				yield line;
			case utf8::invalid =>
				fmt::fatal("Error: invalid UTF-8");
			};
		case io::EOF =>
			break;
		};
		defer free(line);

		switch (state) {
		case state::INDEX =>
			match (strconv::stou(line)) {
			case let index: uint =>
				current.index = index;
			case =>
				fmt::fatalf("Error on line {}: expected uint, found '{}'\n", nr, line);
			};
			state = state::TIMECODE;
		case state::TIMECODE =>
			match (parse_timecode(line)) {
			case let times: (time::duration, time::duration) =>
				current.start = times.0;
				current.end = times.1;
			case =>
				fmt::fatalf("Error on line {}: invalid timecode syntax\n", nr);
			};
			state = state::TEXT;
		case state::TEXT =>
			if (len(line) == 0) {
				state = state::INDEX;
				append(segments, current);
				current = segment { ... };
				continue;
			};
			let text = strings::concat(current.text, line, "\r\n");
			free(current.text);
			current.text = text;
		};
	};

	return segments;
};

fn parse_timecode(line: str) ((time::duration, time::duration) | strconv::invalid | strconv::overflow) = {
	let (start, end) = strings::cut(line, " --> ");
	let start = parse_part(start)?;
	let end = parse_part(end)?;
	return (start, end);
};

fn parse_part(text: str) (time::duration | strconv::invalid | strconv::overflow) = {
	let dur: time::duration = 0;

	let (text, ms) = strings::cut(text, ",");
	dur += strconv::stoi64(ms)? * time::MILLISECOND;
	let (hrs, text) = strings::cut(text, ":");
	dur += strconv::stoi64(hrs)? * time::HOUR;
	let (mins, secs) = strings::cut(text, ":");
	dur += strconv::stoi64(mins)? * time::MINUTE;
	dur += strconv::stoi64(secs)? * time::SECOND;

	return dur;
};