module doap.client.client;

import std.socket : Socket, Address, SocketType, ProtocolType, getAddress, parseAddress, InternetAddress, SocketShutdown;
import doap.client.messaging;
import doap.protocol;
import doap.client.request : CoapRequestBuilder, CoapRequest, CoapRequestFuture, RequestState;
import doap.client.exceptions : RequestTimeoutException;
import core.sync.mutex : Mutex;
import core.sync.condition : Condition;
import std.container.slist : SList;
import core.thread : dur, Duration, Thread;
import std.datetime.stopwatch : StopWatch, AutoStart;
import doap.utils : findNextFree;

/** 
 * A CoAP client
 */
public class CoapClient
{
    /** 
     * CoAP server endpoint
     */
    package Address address;

    /** 
     * Running status
     */
    package bool running;

    /** 
     * The messaging layer which provides
     * request-response message match-ups
     */
    private CoapMessagingLayer messaging;

    /** 
     * The request-response match list
     */
    private SList!(CoapRequest) outgoingRequests;

    /** 
     * The lock for the request-response match list
     */
    private Mutex requestsLock;

    /** 
     * Message IDs and lifetime map
     */
    private StopWatch[ushort] mids;

    /** 
     * Lock for the above
     */
    private Mutex midsLock;

    /** 
     * Creates a new CoAP client to the
     * provided endpoint address
     *
     * Params:
     *   address = the CoAP server endpoint
     */
    this(Address address)
    {
        this.address = address;

        import doap.client.messaging.udp : UDPMessaging;
        this.messaging = new UDPMessaging(this); //UDP transport

        this.requestsLock = new Mutex();
        this.midsLock = new Mutex();

        // FIXME: Change to algorithmic later
        this.setExchangeLifetime(dur!("seconds")(5));

        init();
    }

    /** 
     * Maximum lifetime of a message ID before
     * it is considered for re-use
     */
    private Duration EXCHANGE_LIFETIME = dur!("msecs")(180);

    /** 
     * Sets the exchange lifetime. In other words
     * the duration of time that must pass before
     * a message ID is considered free-for-use again
     *
     * Params:
     *   lifetime = the lifetime duration
     */
    public void setExchangeLifetime(Duration lifetime)
    {
        this.EXCHANGE_LIFETIME = lifetime;
    }

    /** 
     * Generates a new message ID
     *
     * Returns: the next message id
     */
    private final ushort newMid2()
    {
        // Lock rolling counter
        this.midsLock.lock();

        scope(exit)
        {
            // Unlock rolling counter
            this.midsLock.unlock();
        }

        // Message IDs which are in use
        ushort[] inUse;

        foreach(ushort occupied; this.mids.keys())
        {
            // Peek the value of the stopwatch
            if(this.mids[occupied].peek() >= EXCHANGE_LIFETIME)
            {
                // It's expired, so we can use it (first reset the time)
                this.mids[occupied].reset();

                return occupied;
            }
            else
            {
                inUse ~= occupied;
            }
        }

        // If none was available for re-use then find next available
        // ... free and use that (also don't forget to register it)
        ushort newMid;
        bool gotAvailable = findNextFree(inUse, newMid);

        // FIXME: Add a thing which does something
        // ... if `gotAvailable` is false

        this.mids[newMid] = StopWatch(AutoStart.yes);

        return newMid;
    }

    /** 
     * Constructs a new CoAP client to the
     * provided endpoint address and port.
     *
     * This constructor provided name
     * resolution on the host part.
     *
     * Params:
     *   host = the CoAP host
     *   port = the CoAP port
     */
    this(string host, ushort port)
    {
        this(new InternetAddress(host, port));
    }

    /** 
     * Sets up a new datagram socket,
     * sets the running status to `true`
     * and then starts the messaging
     * layer
     */
    private void init()
    {
        // Set status to running
        this.running = true;

        // Start the messaging layer
        this.messaging.begin();
    }

    /** 
     * Stops this client
     *
     * This results in closing down the
     * messaging layer and ensuring that
     * no new datagrams may arrive on
     * our source port.
     */
    public void close()
    {
        // Set status to not running
        this.running = false;

        // Shutdown the messaging layer
        this.messaging.close();
        
        // Cancel all active request futures
        this.requestsLock.lock();
        foreach(CoapRequest curReq; outgoingRequests)
        {
            curReq.future.cancel();
        }
        this.requestsLock.unlock();
    }

    /** 
     * Creates a new CoAP request builder
     *
     * Returns: a new `CoapRequestBuilder`
     */
    public CoapRequestBuilder newRequestBuilder()
    {
        return new CoapRequestBuilder(this);
    }

    /** 
     * Given the builder this will extract the details required
     * to encode the CoAP packet into its byte form, register
     * a coap request internally and return a future for this
     * request.
     *
     * Params:
     *   requestBuilder = the request builder
     * Returns: the future
     */
    package CoapRequestFuture doRequest(CoapRequestBuilder requestBuilder)
    {
        // Encode the packet
        CoapPacket requestPacket = new CoapPacket();
        requestPacket.setCode(requestBuilder.requestCode);
        requestPacket.setPayload(requestBuilder.pyld);
        requestPacket.setToken(requestBuilder.tkn);
        requestPacket.setMessageId(newMid2());

        // Create the future
        CoapRequestFuture future = new CoapRequestFuture();

        // Link the CoapRequest to the future so it can be signalled
        CoapRequest request = new CoapRequest(requestPacket, future);

        // Store the request
        storeRequest(request);

        // Transmit the request
        transmitRequest(request);

        return future;
    }

    /** 
     * Stores the request
     *
     * Params:
     *   request = the `CoapRequest` to store in the
     * tracking list
     */
    private void storeRequest(CoapRequest request)
    {
        // Store the request
        requestsLock.lock();
        outgoingRequests.insertAfter(outgoingRequests[], request);
        requestsLock.unlock();
    }

    /** 
     * Given a packet this will try and find an active
     * request with a matching token and return it.
     *
     * This will also remove it from the requests queue.
     *
     * Params:
     *   packet = the packet received
     * Returns: the original `CoapRequest` if a match
     * is found, otherwise `null`
     */
    package CoapRequest yankRequest(CoapPacket packet)
    {
        CoapRequest foundRequest = null;

        requestsLock.lock();

        foreach(CoapRequest request; outgoingRequests)
        {
            if(request.getMid() == packet.getMessageId())
            {
                foundRequest = request;
                outgoingRequests.linearRemoveElement(foundRequest);
                break;
            }
        }

        requestsLock.unlock();

        return foundRequest;
    }

    /** 
     * Transmits the given request's associated
     * packet to the underlying transport
     *
     * Params:
     *   request = the `CoapRequest` to put into
     * flight
     */
    private void transmitRequest(CoapRequest request)
    {
        // Encode the request packet and send it
        this.messaging.send(request.getRequestPacket());

        // Now start ticking the timer
        request.startTime();
    }

    // private Duration sweepInterval;
    private Duration retransmitTimeout;

    /** 
     * The intention of this method is that
     * some kind-of `CoapMessagingLayer`
     * can call this when it has no new
     * messages to process.
     *
     * This then let's the client handle
     * the checking of potentially timed
     * out requests, and the re-issueing
     * of them to the messaging layer.
     */
    package void onNoNewMessages()
    {
        requestsLock.lock();
        foreach(CoapRequest curReq; outgoingRequests)
        {
            if(curReq.hasTimedOut(retransmitTimeout))
            {
                // TODO: Retransmit
            }
        }
        requestsLock.unlock();
    }
}

/**
 * Tests the client
 *
 * In the future dogfooding should be
 * used and we should test against our
 * own server too.
 */
unittest
{
    // Address[] resolved = getAddress("coap.me");
    // resolved[0].po
    Address addr = new InternetAddress("coap.me", 5683);
    // CoapClient client = new CoapClient(addr);

    // client.resource("/hello");

    // client.connect();

    // Test sending something
    CoapPacket packet = new CoapPacket();
    packet.setCode(Code.POST);
    packet.setToken([69]);
    packet.setPayload(cast(ubyte[])"My custom payload");
    packet.setType(MessageType.CONFIRMABLE);
    packet.setMessageId(257);

    // client.socket.send(packet.getBytes());

}

version(unittest)
{
    import std.stdio : writeln;
}

/**
 * Client testing
 *
 * Tests the rolling of the message id,
 * here I configure the `EXCHANGE_LIFETIME`
 * to be a value high enough to not have
 * them quickly expire.
 *
 * NOTE: In the future it may be calculated
 * in relation to other variables and we may
 * need a private method accessible here that
 * can override it
 */
unittest
{
    CoapClient client = new CoapClient("coap.me", 5683);

    
    CoapRequestFuture future = client.newRequestBuilder()
                              .payload(cast(ubyte[])"First message")
                              .token([69])
                              .post();


    // Set it to something high enough (TODO: Change this later)
    client.setExchangeLifetime(dur!("msecs")(300));

    writeln("Future start (first)");
    CoapPacket response = future.get();
    writeln("Future done (first)");
    writeln("Got response (first): ", response);
    assert(response.getMessageId() == 0);

    future = client.newRequestBuilder()
                              .payload(cast(ubyte[])"Second message")
                              .token([69])
                              .post();


    writeln("Future start (second)");
    response = future.get();
    writeln("Future done (second)");
    writeln("Got response (second): ", response);
    assert(response.getMessageId() == 1);




    client.close();
}



/**
 * Client testing
 *
 * This tests building of a request using the builder,
 * finalizing through the client and then waiting on
 * the returned future for a result.
 *
 * We test the blocking example here therefore, i.e.
 * a blocking `get()`.
 *
 * This therefore tests the entire `messaging` module
 * and `client` module.
 */
unittest
{
    CoapClient client = new CoapClient("coap.me", 5683);

    
    CoapRequestFuture future = client.newRequestBuilder()
                              .payload(cast(ubyte[])"Hello this is Tristan!")
                              .token([69])
                              .post();


    writeln("Future start");
    CoapPacket response  = future.get();
    writeln("Future done");
    writeln("Got response: ", response);

    client.close();
}

version(unittest)
{
    import core.time : dur;
    // import doap.client.exceptions : RequestTimeoutException;
    // import doap.client.request : CoapRequestFuture, RequestState;
}

/**
 * Client testing
 *
 * See above except we test a timeout-based
 * request future here.
 *
 * This test DOES time out
 */
unittest
{
    CoapClient client = new CoapClient("coap.me", 5683);

    
    CoapRequestFuture future = client.newRequestBuilder()
                              .payload(cast(ubyte[])"Hello this is Tristan!")
                              .token([69])
                              .post();

    try
    {
        writeln("Future start");
        CoapPacket response  = future.get(dur!("msecs")(10));

        // We should timeout and NOT get here
        assert(false);
    }
    catch(RequestTimeoutException e)
    {
        // Ensure that we have the correct state
        assert(future.getState() == RequestState.TIMEDOUT);

        // We SHOULD time out
        assert(true);
    }

    client.close();
}

/**
 * Client testing
 *
 * See above except we test a timeout-based
 * request future here.
 *
 * This test DOES NOT time out (it tests
 * with a high-enough threshold)
 */
unittest
{
    CoapClient client = new CoapClient("coap.me", 5683);

    
    CoapRequestFuture future = client.newRequestBuilder()
                              .payload(cast(ubyte[])"Hello this is Tristan!")
                              .token([69])
                              .post();

    try
    {
        writeln("Future start");
        CoapPacket response  = future.get(dur!("msecs")(400));

        // Ensure that we have the correct state
        assert(future.getState() == RequestState.COMPLETED);

        // We SHOULD get here
        assert(true);
    }
    catch(RequestTimeoutException e)
    {
        // We should NOT time out
        assert(false);
    }

    client.close();
}