#!/bin/env -S deno run --allow-read --allow-net

async function main() {
	const [program_path] = Deno.args;
	if (program_path === undefined) fail_with("Usage: host.ts <program_path>");
	const port = 1728;
	const server = Deno.listen({ port });
	console.log("listening on port", port);
	for await (const connection of server) handle(connection, program_path);
}

async function handle(connection: Deno.TcpConn, program_path: string) {
	console.log("serving");
	const file = await try_else(
		() => Deno.open(program_path, { read: true }),
		() => fail_with("Program at", program_path, "does not exists"),
	);
	await try_(() => file.readable.pipeTo(connection.writable));
}

function fail_with(...message: string[]) {
	console.error(...message);
	return Deno.exit(1);
}

async function try_else<T>(operation: () => T | Promise<T>, on_error: (error: unknown) => T | Promise<T>) {
	try {
		return await operation();
	} catch (error) {
		return await on_error(error);
	}
}

async function try_<T>(operation: () => T | Promise<T>) {
	return await try_else(operation, () => null);
}

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