use io;
use fmt;
use endian;
use drawing;

export type error = !str;

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

export fn new() packet_reader = {
	let pr = packet_reader {
		buf = alloc([0...],512*512*4*2), // ehhh
		...
	};
	pr.good = pr.buf[0..0];
	return pr;
};

export type packet_type = enum u8 {
	DRAW_OP,
	SEND_CHUNK,
};

export type packet_drawop = drawing::op;
export type packet_sendchunk = []u32;
export type packet = (packet_drawop | packet_sendchunk);

// call when input is ready. could block otherwise
export fn 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)!;
};

// packet format:
// u32 size
// u32 type
// [size-8]u8 data...
// size includes size of header (size and type fields)

export fn next(pr: *packet_reader) (packet | done | error) = {
	// 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) < size(u32)) return done;
	const packet_len = endian::legetu32(pr.good[0..4]);
	if (packet_len < 8) return "packet size field too small": error;
	if (len(pr.good) < packet_len) return done;

	const packet_bytes = pr.good[..packet_len];
	pr.good = pr.good[packet_len..];

	const ty = endian::legetu32(packet_bytes[4..8]): packet_type;
	switch (ty) {
	case packet_type::DRAW_OP =>
		const op = drawing::deser_op(packet_bytes[8..]);
		return op: packet_drawop;
	case packet_type::SEND_CHUNK =>
		// in an ideal world we would need no copies
		const totally_necessary_copy = alloc(packet_bytes[8..]...);
		return totally_necessary_copy: packet_sendchunk;
	};
};

export fn send_raw(sock: io::file, ty: packet_type, data: []u8) (void | io::error) = {
	// ehh
	const header: [8]u8 = [0...];
	endian::leputu32(header[0..4], 8u32 + len(data):u32);
	endian::leputu32(header[4..8], ty);
	io::writeall(sock, header)?;
	io::writeall(sock, data)?;
};

export fn send(sock: io::file, packet: packet) (void | io::error) = {
	match (packet) {
	case let op: packet_drawop =>
		const ser_op = drawing::ser_op(op);
		defer free(ser_op);
		send_raw(sock, packet_type::DRAW_OP, ser_op)?;
	case let chunkdata: packet_sendchunk =>
		abort("not implemented sendchunk yet");
	};
};