/*
	MMO Client/Server Framework using ASIO
	"Happy Birthday Mrs Javidx9!" - javidx9

	Videos:
	Part #1: https://youtu.be/2hNdkYInj4g
	Part #2: https://youtu.be/UbjxGvrDrbw

	License (OLC-3)
	~~~~~~~~~~~~~~~

	Copyright 2018 - 2020 OneLoneCoder.com

	Redistribution and use in source and binary forms, with or without
	modification, are permitted provided that the following conditions
	are met:

	1. Redistributions or derivations of source code must retain the above
	copyright notice, this list of conditions and the following disclaimer.

	2. Redistributions or derivative works in binary form must reproduce
	the above copyright notice. This list of conditions and the following
	disclaimer must be reproduced in the documentation and/or other
	materials provided with the distribution.

	3. Neither the name of the copyright holder nor the names of its
	contributors may be used to endorse or promote products derived
	from this software without specific prior written permission.

	THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	Links
	~~~~~
	YouTube:	https://www.youtube.com/javidx9
	Discord:	https://discord.gg/WhwHUMV
	Twitter:	https://www.twitter.com/javidx9
	Twitch:		https://www.twitch.tv/javidx9
	GitHub:		https://www.github.com/onelonecoder
	Homepage:	https://www.onelonecoder.com

	Author
	~~~~~~
	David Barr, aka javidx9, ŠOneLoneCoder 2019, 2020

*/

#pragma once

#include "net_common.h"
#include "net_dequeue_ts.h"
#include "net_message.h"



namespace net
{
	template<typename T>
	class Connection : public std::enable_shared_from_this<Connection<T>>
	{
	public:
		// A connection is "owned" by either a server or a client, and its
		// behaviour is slightly different bewteen the two.
		enum class Owner
		{
			SERVER,
			CLIENT
		};

	public:
		// Constructor: Specify Owner, connect to context, transfer the socket
		//				Provide reference to incoming message queue
        Connection(Owner parent, asio::io_context& asioContext, asio::ip::tcp::socket socket, ts_dequeue<OwnedMessage<T>>& qIn)
            : m_socket(std::move(socket)), m_asioContext(asioContext), m_qMessagesIn(qIn)
		{
			m_nOwnerType = parent;
		}

		virtual ~Connection()
		{}

		// This ID is used system wide - its how clients will understand other clients
		// exist across the whole system.
		uint32_t GetID() const
		{
			return id;
		}

	public:
		void ConnectToClient(uint32_t uid = 0)
		{
			if (m_nOwnerType == Owner::SERVER)
			{
				if (m_socket.is_open())
				{
					id = uid;
					ReadHeader();
				}
			}
		}

		void ConnectToServer(const asio::ip::tcp::resolver::results_type& endpoints)
		{
			// Only clients can connect to servers
			if (m_nOwnerType == Owner::CLIENT)
			{
				// Request asio attempts to connect to an endpoint
				asio::async_connect(m_socket, endpoints,
					[this](std::error_code ec, asio::ip::tcp::endpoint endpoint)
					{
						if (!ec)
						{
							ReadHeader();
						}
					});
			}
		}


		void Disconnect()
		{
			if (IsConnected())
				asio::post(m_asioContext, [this]() { m_socket.close(); });
		}

		bool IsConnected() const
		{
			return m_socket.is_open();
		}

		// Prime the connection to wait for incoming messages
		void StartListening()
		{
				
		}

	public:
		// ASYNC - Send a message, connections are one-to-one so no need to specifiy
		// the target, for a client, the target is the server and vice versa
		void Send(const Message<T>& msg)
		{
			asio::post(m_asioContext,
				[this, msg]()
				{
					// If the queue has a message in it, then we must 
					// assume that it is in the process of asynchronously being written.
					// Either way add the message to the queue to be output. If no messages
					// were available to be written, then start the process of writing the
					// message at the front of the queue.
					bool bWritingMessage = !m_qMessagesOut.empty();
					m_qMessagesOut.push_back(msg);
					if (!bWritingMessage)
					{
						WriteHeader();
					}
				});
		}



	private:
		// ASYNC - Prime context to write a message header
		void WriteHeader()
		{
			// If this function is called, we know the outgoing message queue must have 
			// at least one message to send. So allocate a transmission buffer to hold
			// the message, and issue the work - asio, send these bytes
			asio::async_write(m_socket, asio::buffer(&m_qMessagesOut.front().header, sizeof(MessageHeader<T>)),
				[this](std::error_code ec, std::size_t length)
				{
					// asio has now sent the bytes - if there was a problem
					// an error would be available...
					if (!ec)
					{
						// ... no error, so check if the message header just sent also
						// has a message body...
						if (m_qMessagesOut.front().body.size() > 0)
						{
							// ...it does, so issue the task to write the body bytes
							WriteBody();
						}
						else
						{
							// ...it didnt, so we are done with this message. Remove it from 
							// the outgoing message queue
							m_qMessagesOut.pop_front();

							// If the queue is not empty, there are more messages to send, so
							// make this happen by issuing the task to send the next header.
							if (!m_qMessagesOut.empty())
							{
								WriteHeader();
							}
						}
					}
					else
					{
						// ...asio failed to write the message, we could analyse why but 
						// for now simply assume the connection has died by closing the
						// socket. When a future attempt to write to this client fails due
						// to the closed socket, it will be tidied up.
						std::cout << "[" << id << "] Write Header Fail.\n";
						m_socket.close();
					}
				});
		}

		// ASYNC - Prime context to write a message body
		void WriteBody()
		{
			// If this function is called, a header has just been sent, and that header
			// indicated a body existed for this message. Fill a transmission buffer
			// with the body data, and send it!
			asio::async_write(m_socket, asio::buffer(m_qMessagesOut.front().body.data(), m_qMessagesOut.front().body.size()),
				[this](std::error_code ec, std::size_t length)
				{
					if (!ec)
					{
						// Sending was successful, so we are done with the message
						// and remove it from the queue
						m_qMessagesOut.pop_front();

						// If the queue still has messages in it, then issue the task to 
						// send the next messages' header.
						if (!m_qMessagesOut.empty())
						{
							WriteHeader();
						}
					}
					else
					{
						// Sending failed, see WriteHeader() equivalent for description :P
						std::cout << "[" << id << "] Write Body Fail.\n";
						m_socket.close();
					}
				});
		}

		// ASYNC - Prime context ready to read a message header
		void ReadHeader()
		{
			// asio to waits until it receives
			// enough bytes to form a header of a message. We know the headers are a fixed
			// size, so allocate a transmission buffer large enough to store it.
			//Call this function to set up an asynchronous listener for a certain Connection
			asio::async_read(m_socket, asio::buffer(&m_msgTemporaryIn.header, sizeof(MessageHeader<T>)),
				[this](std::error_code ec, std::size_t length)
				{						
					if (!ec)
					{
						//Full header readed
						//Check for message body
						if (m_msgTemporaryIn.header.size > 0)
						{
							//Allocate storage
							m_msgTemporaryIn.body.resize(m_msgTemporaryIn.header.size);
							//Read if available
							ReadBody();
						}
						else
						{
							//Bodyless message, add to queue
							AddToIncomingMessageQueue();
						}
					}
					else
					{
						//Failure, probably a disconnection
						std::cout << "[" << id << "] Error: " << ec.message() << std::endl;
						m_socket.close();
					}
				});
		}

		// ASYNC - Prime context to read a message body
		void ReadBody()
		{
			//Called after header has been read successfully
			//Read the body in the pre allocated storage
			asio::async_read(m_socket, asio::buffer(m_msgTemporaryIn.body.data(), m_msgTemporaryIn.body.size()),
				[this](std::error_code ec, std::size_t length)
				{						
					if (!ec)
					{
						// Complete message, add to queue
						AddToIncomingMessageQueue();
					}
					else
					{
						//Failure, probably a disconnection
						std::cout << "[" << id << "] Error reading body: " << ec.message() << std::endl;
						m_socket.close();
					}
				});
		}

		// Add a complete message to the incoming queue,  with or without body
		void AddToIncomingMessageQueue()
		{				
			//Put it in the queue, put a owner to the object to let the server know who send the message (which connection)
			if(m_nOwnerType == Owner::SERVER)
				m_qMessagesIn.push_back({ this->shared_from_this(), m_msgTemporaryIn });
			else
				m_qMessagesIn.push_back({ nullptr, m_msgTemporaryIn });

			//Done queueing the message, now initialize a new async read to wait for next message
			ReadHeader();
		}

	protected:
		// unique socket to a remote 
		asio::ip::tcp::socket m_socket;

		// This context is shared with the whole asio instance
		asio::io_context& m_asioContext;

		// This queue holds all messages to be sent to the remote side
		// of this connection
        ts_dequeue<Message<T>> m_qMessagesOut;

		// This references the incoming queue of the parent object
        ts_dequeue<OwnedMessage<T>>& m_qMessagesIn;

		// Incoming messages are constructed asynchronously, so we will
		// store the part assembled message here, until it is ready
		Message<T> m_msgTemporaryIn;

		// The "owner" decides how some of the connection behaves
		Owner m_nOwnerType = Owner::SERVER;

		uint32_t id = 0;

	};
}