/*
** Copyright 2015, Mohamed Naufal
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
**     http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/

package com.reactlibrary;

import android.util.Log;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.ConcurrentLinkedQueue;

import com.reactlibrary.TCB.TCBStatus;

public class TCPInput implements Runnable
{
    private static final String TAG = TCPInput.class.getSimpleName();
    private static final int HEADER_SIZE = Packet.IP4_HEADER_SIZE + Packet.TCP_HEADER_SIZE;

    private ConcurrentLinkedQueue<ByteBuffer> outputQueue;
    private Selector selector;

    public TCPInput(ConcurrentLinkedQueue<ByteBuffer> outputQueue, Selector selector)
    {
        this.outputQueue = outputQueue;
        this.selector = selector;
    }

    @Override
    public void run()
    {
        try
        {
            Log.d(TAG, "Started");
            while (!Thread.interrupted())
            {
                int readyChannels = selector.select();

                if (readyChannels == 0) {
                    Thread.sleep(10);
                    continue;
                }

                Set<SelectionKey> keys = selector.selectedKeys();
                Iterator<SelectionKey> keyIterator = keys.iterator();

                while (keyIterator.hasNext() && !Thread.interrupted())
                {
                    SelectionKey key = keyIterator.next();
                    if (key.isValid())
                    {
                        if (key.isConnectable())
                            processConnect(key, keyIterator);
                        else if (key.isReadable())
                            processInput(key, keyIterator);
                    }
                }
            }
        }
        catch (InterruptedException e)
        {
            Log.i(TAG, "Stopping");
        }
        catch (IOException e)
        {
            Log.w(TAG, e.toString(), e);
        }
    }

    private void processConnect(SelectionKey key, Iterator<SelectionKey> keyIterator)
    {
        TCB tcb = (TCB) key.attachment();
        Packet referencePacket = tcb.referencePacket;
        try
        {
            if (tcb.channel.finishConnect())
            {
                keyIterator.remove();
                tcb.status = TCBStatus.SYN_RECEIVED;

                // TODO: Set MSS for receiving larger packets from the device
                ByteBuffer responseBuffer = ByteBufferPool.acquire();
                referencePacket.updateTCPBuffer(responseBuffer, (byte) (Packet.TCPHeader.SYN | Packet.TCPHeader.ACK),
                        tcb.mySequenceNum, tcb.myAcknowledgementNum, 0);
                outputQueue.offer(responseBuffer);

                tcb.mySequenceNum++; // SYN counts as a byte
                key.interestOps(SelectionKey.OP_READ);
            }
        }
        catch (IOException e)
        {
            Log.e(TAG, "Connection error: " + tcb.ipAndPort, e);
            ByteBuffer responseBuffer = ByteBufferPool.acquire();
            referencePacket.updateTCPBuffer(responseBuffer, (byte) Packet.TCPHeader.RST, 0, tcb.myAcknowledgementNum, 0);
            outputQueue.offer(responseBuffer);
            TCB.closeTCB(tcb);
        }
    }

    private void processInput(SelectionKey key, Iterator<SelectionKey> keyIterator)
    {
        keyIterator.remove();
        ByteBuffer receiveBuffer = ByteBufferPool.acquire();
        // Leave space for the header
        receiveBuffer.position(HEADER_SIZE);

        TCB tcb = (TCB) key.attachment();
        synchronized (tcb)
        {
            Packet referencePacket = tcb.referencePacket;
            SocketChannel inputChannel = (SocketChannel) key.channel();
            int readBytes;
            try
            {
                readBytes = inputChannel.read(receiveBuffer);
            }
            catch (IOException e)
            {
                Log.e(TAG, "Network read error: " + tcb.ipAndPort, e);
                referencePacket.updateTCPBuffer(receiveBuffer, (byte) Packet.TCPHeader.RST, 0, tcb.myAcknowledgementNum, 0);
                outputQueue.offer(receiveBuffer);
                TCB.closeTCB(tcb);
                return;
            }

            if (readBytes == -1)
            {
                // End of stream, stop waiting until we push more data
                key.interestOps(0);
                tcb.waitingForNetworkData = false;

                if (tcb.status != TCBStatus.CLOSE_WAIT)
                {
                    ByteBufferPool.release(receiveBuffer);
                    return;
                }

                tcb.status = TCBStatus.LAST_ACK;
                referencePacket.updateTCPBuffer(receiveBuffer, (byte) Packet.TCPHeader.FIN, tcb.mySequenceNum, tcb.myAcknowledgementNum, 0);
                tcb.mySequenceNum++; // FIN counts as a byte
            }
            else
            {
                // XXX: We should ideally be splitting segments by MTU/MSS, but this seems to work without
                referencePacket.updateTCPBuffer(receiveBuffer, (byte) (Packet.TCPHeader.PSH | Packet.TCPHeader.ACK),
                        tcb.mySequenceNum, tcb.myAcknowledgementNum, readBytes);
                tcb.mySequenceNum += readBytes; // Next sequence number
                receiveBuffer.position(HEADER_SIZE + readBytes);
            }
        }
        outputQueue.offer(receiveBuffer);
    }
}