module msgpackrpc.client;
import core.atomic;

import std.array;
import std.concurrency : receiveOnly;
import std.exception;
import std.experimental.logger;
import std.traits;
import std.typecons;

import msgpack;

import vibe.core.concurrency;
import vibe.core.core;
import vibe.core.net;
import vibe.core.task;

import msgpackrpc.protocol;

/**
 * MessagePack RPC client
 */
class Client {
private:
	TCPConnection m_connection;
	shared int m_nextRequestId = 0;
	
	/// Map of sent request, mapping the requestId to a future.
	Tid[int] m_requests;
public:
	this(TCPConnection connection) {
		this.m_connection = connection;
		runTask(&receiveLoop);
	}
	
	/**
	 * Notifies the server, not waiting for a response. Although it waits for the request to be sent
	 *
	 * params:
	 *     method = The name of the method to be notified
	 *     arguments = The arguments to pass to the server
	 */
	void notify(Args...)(string method, Args arguments) {
		tracef("Notify '%s'", method);
		auto pack = packer(Appender!(ubyte[])());
		pack.beginArray(3).pack(MessageType.notify, method, pack.packArray(arguments));
		sendData(pack.stream.data);
	}
	
	/**
	 * Calls a method on the other side, awaiting a response.
	 *
	 * The difference between this and notify(string, Args) is that call expects a result from the
	 * other endpoint and will actually wait for it.
	 */
	R call(R, Args...)(string method, Args arguments) {
		R res = sendRequest!R(method, arguments).getResult();
		return res;
	}
	
	/**
	 * Calls a method on the other endpoint, but will not wait for a result. Instead, a Future!R is
	 * returned.
	 */
	Future!R callAsync(R, Args...)(string method, Args arguments) {
		return sendRequest!R(method, arguments);
	}
	
private:
	void receiveLoop() {
		StreamingUnpacker unpacker = StreamingUnpacker([]);
		while(m_connection.connected) {
			m_connection.waitForData();
			ubyte[] buf = new ubyte[m_connection.leastSize];
			m_connection.read(buf);
			unpacker.feed(buf);
			
			foreach(ref message; unpacker) {
				enforce!ProtocolException(message.length == 3 || message.length == 4, "Protocol error: incoming message size mismatch");
				immutable uint messageType = message[0].as!uint;
				switch(messageType) {
				case MessageType.response:
					enforce!ProtocolException(message.length == 4, "Protocol error: Response must be of size 4");
					immutable error = message[2];
					immutable result = message[3];
					onResponse(message[1].as!int, error, result);
					break;
				default:
					tracef("Received unhandled messageType %s", cast(MessageType) messageType);
					break;
				}
			}
		}
	}
	
	void onResponse(int id, immutable Value error, immutable Value result) {
		if (id in m_requests) {
			tracef("Reply for %d; Error: %s; Result: %s", id, error.type, result.type);
			send(m_requests[id], error, result);
			m_requests.remove(id);
		} else {
			warningf("No task for id %d", id);
		}
	}

	void sendData(T)(T data) {
		m_connection.write(data);
		m_connection.flush();
	}
	
	/**
	 * Sends a request and returns a future containing the result.
	 */
	Future!R sendRequest(R, Args...)(string method, Args arguments) {
		tracef("Call '%s'", method);
		auto pack = packer(Appender!(ubyte[])());
		immutable int requestId = atomicFetchAdd(m_nextRequestId, 1);
		pack.beginArray(4)
			.pack(MessageType.request, requestId, method)
			.packArray(arguments);
		
		sendData(pack.stream.data);
		
		return async(delegate R() {
			m_requests[requestId] = Task.getThis().tid;
			//     error            result
			Tuple!(immutable Value, immutable Value) reply = receiveOnly!(immutable Value, immutable Value);
			if (reply[0].type != Value.Type.nil) {
				throw new RPCException(reply[0]);
			}
			Value result = reply[1];
			return result.as!R;
		});
	}
}