#!/usr/bin/env -S deno run -A

import { exists } from "https://deno.land/std@0.224.0/fs/exists.ts";
import { Command } from "https://deno.land/x/cliffy@v1.0.0-rc.4/command/mod.ts";
import { Channel, Constructible, InstanceOf } from "https://git.barnulf.net/mb/barnulf_ts/raw/branch/master/mod.ts";

async function main() {
	const { do_clear, command, extensions, files, strategy } = await parse_args();
	const channel = new Channel<Event>();
	files.map((path) => new Watcher(path, extensions).spin(channel));
	new Runner(command, strategy, do_clear).spin(channel);
}

async function parse_args() {
	const { args, options } = await new Command()
		.name("regar")
		.description("File watcher development utility.")
		.arguments("<command> [...files]")
		.option("-r, --hard", "Ends the child process by killing it.")
		.option("-s, --soft", "Ends the child process by sending an interuption and waiting for it to shut down.")
		.option("-w, --wait", "Wait for the child process to complete without terminating it. (default)")
		.option("-e, --extensions <extentions>", "Comma separated whitelist of extensions to whatch.")
		.option("-c, --clear", "Clear the terminal on restart").parse();
	const [command, ...files] = args;
	let strategy: ShutdownStrategy = new WaitStrategy();
	if (options.soft) strategy = new SoftStrategy();
	if (options.hard) strategy = new HardStrategy();
	if (options.wait) strategy = new WaitStrategy();
	const extensions = options.extensions?.split(",");
	const do_clear = options.clear ?? false;
	return { command, files, strategy, extensions, do_clear };
}

class Watcher {
	public constructor(
		private path: string,
		private extension_whitelist: string[] | undefined,
	) {}

	public async spin(channel: Channel<Event>) {
		const relevant_events: Deno.FsEvent["kind"][] = ["create", "modify", "remove", "rename"];
		for await (const event of Deno.watchFs(this.path, { recursive: true })) {
			if (!relevant_events.includes(event.kind)) continue;
			if (!this.matches_whitelist(event.paths[0])) continue;
			for (const path of event.paths) channel.send(new Event(path, Date.now()));
		}
	}

	private matches_whitelist(path: string) {
		if (this.extension_whitelist === undefined) return true;
		for (const ext of this.extension_whitelist) if (path.endsWith(ext)) return true;
		return false;
	}
}

class Runner {
	public constructor(
		private command: string,
		private strategy: ShutdownStrategy,
		private do_clear: boolean,
	) {}

	public async spin(channel: Channel<Event>) {
		this.could_clear();
		let process = this.launch();
		while (true) {
			const event = await channel.receive();
			if (this.debouncing(event)) continue;
			const shotdown = await this.strategy.shutdown(process);
			if (!shotdown) continue;
			this.could_clear();
			log("changed", event.path);
			process = this.launch();
		}
	}

	private launch() {
		const args = ["-c", this.command];
		log("running", this.command);
		const process = new Deno.Command("sh", { args }).spawn();
		process.status.then(this.on_end());
		return process;
	}

	private could_clear() {
		const clear_term_sequence = "\x1bc";
		if (this.do_clear) console.log(clear_term_sequence);
	}

	private last_event_date_ms = 0;
	private debouncing(event: Event) {
		const delay_ms = event.date_ms - this.last_event_date_ms;
		const threshold_ms = 100;
		if (delay_ms < threshold_ms) return true;
		this.last_event_date_ms = event.date_ms;
		return false;
	}

	private on_end() {
		const start_ms = Date.now();
		return () => {
			const end_ms = Date.now();
			const time_ms = end_ms - start_ms;
			const secs = time_ms / 1000;
			log("terminated", `${secs} s`);
		};
	}
}

interface ShutdownStrategy {
	// Returns wether the child has been shutdown.
	shutdown(process_: Deno.ChildProcess): Promise<boolean>;
}

class WaitStrategy implements ShutdownStrategy {
	async shutdown(process_: Deno.ChildProcess) {
		if (await process_exists(process_.pid)) return false;
		else return true;
	}
}

class SoftStrategy implements ShutdownStrategy {
	async shutdown(process_: Deno.ChildProcess) {
		try_signal(process_.pid, "SIGINT");
		await process_.output();
		return true;
	}
}

class HardStrategy implements ShutdownStrategy {
	async shutdown(process_: Deno.ChildProcess) {
		try_signal(process_.pid, "SIGKILL");
		return await true;
	}
}

class Event {
	constructor(
		public path: string,
		public date_ms: number,
	) {}
}

async function process_exists(pid: number) {
	return await exists(`/proc/${pid}`);
}

function try_signal(pid: number, sig: Deno.Signal) {
	catch_(
		() => Deno.kill(pid, sig),
		[Deno.errors.NotFound, "ignore"],
	);
}

// deno-lint-ignore no-explicit-any
type Catching<C extends Constructible<C, any>, R = void> = [
	exception: C,
	strategy: ((exc: InstanceOf<C>) => R) | "ignore",
];

// deno-lint-ignore no-explicit-any
function catch_<T, R, Cs extends Catching<any, R>[]>(op: () => T, ...catchings: Cs) {
	try {
		return op();
	} catch (exception) {
		for (const [kind, strategy] of catchings) {
			if (!(exception instanceof kind)) continue;
			if (strategy === "ignore") return;
			return strategy(exception);
		}
	}
}

function log(verb: string, value: unknown) {
	const yellow = "\x1b[0;33m";
	const bold = "\x1b[1m";
	const reset = "\x1b[0m";
	console.log(
		`` +
			`${yellow}${bold}${verb.padStart(12)}${reset}` +
			` ` +
			`${yellow}${value}${reset}`,
	);
}

if (import.meta.main) await main();