use io;
use fmt;

type packet = []u8;
def PCKSZ: size = 4;

type packet_reader = struct {
	buf: [256]u8,
	good: []u8,
};

fn packet_reader_new() packet_reader = {
	let pr = packet_reader {
		buf = [0...],
		...
	};
	pr.good = pr.buf[0..0];
	return pr;

};

// call when input is ready. could block otherwise
fn packet_reader_read(pr: *packet_reader, sock: io::handle) (void | io::error | io::EOF) = {
	const remaining_amt = len(pr.good);
	const read_pos = if (remaining_amt > 0) {
		// still some unconsumed content in the buffer
		// move unconsumed stuff to start of buffer
		fmt::printfln("moving {} remaining bytes",remaining_amt)!;
		pr.buf[0..remaining_amt] = pr.good;
		yield remaining_amt;
	} else 0z;
	const nread = match(io::read(sock, pr.buf[read_pos..])?) {
		case io::EOF => return io::EOF;
		case let n: size => yield n;
	};
	fmt::printfln("read {} bytes",nread)!;
	const total_amt = read_pos + nread;
	pr.good = pr.buf[0..total_amt];
	fmt::printfln("now {} bytes in buffer",total_amt)!;
};


fn packet_reader_next(pr: *packet_reader) (packet | done) = {
	// either parse a full packet out of the front of good,
	// move good along that many bytes,
	// and return the packet,
	// or, ascertain there is no full packet, and return done
	if (len(pr.good) < PCKSZ) return done;
	const packet_bytes = pr.good[..PCKSZ];
	pr.good = pr.good[PCKSZ..];
	return packet_bytes;
};