/*
 *  Copyright (c) 2011-2015 The original author or authors
 *  ------------------------------------------------------
 *  All rights reserved. This program and the accompanying materials
 *  are made available under the terms of the Eclipse Public License v1.0
 *  and Apache License v2.0 which accompanies this distribution.
 *
 *       The Eclipse Public License is available at
 *       http://www.eclipse.org/legal/epl-v10.html
 *
 *       The Apache License v2.0 is available at
 *       http://www.opensource.org/licenses/apache2.0.php
 *
 *  You may elect to redistribute this code under either of these licenses.
 */

package io.vertx.ext.stomp.impl;

import io.vertx.core.Vertx;
import io.vertx.ext.stomp.Destination;
import io.vertx.ext.stomp.Frame;
import io.vertx.ext.stomp.StompServerConnection;
import io.vertx.ext.stomp.utils.Headers;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import java.util.stream.Collectors;

Implementation of Destination dispatching messages to a single subscriber. It dispatches the messages using a round-robin strategy. 
Author:
Clement Escoffier/**
 * Implementation of {@link Destination} dispatching messages to a single subscriber. It dispatches
 * the messages using a round-robin strategy.
 *
 * @author <a href="http://escoffier.me">Clement Escoffier</a>
 */
public class Queue implements Destination {

  private final String destination;

  private final List<Subscription> subscriptions = new ArrayList<>();
  private final Vertx vertx;
  private int lastUsedSubscriptions = -1;

  public Queue(Vertx vertx, String destination) {
    this.destination = destination;
    this.vertx = vertx;
  }

  
Returns:
the destination address./**
   * @return the destination address.
   */
  @Override
  public String destination() {
    return destination;
  }

  
Dispatches the given frame.
Params:
connection – the connection
frame –  the frame (SEND frame).
Returns:
the current instance of Destination/**
   * Dispatches the given frame.
   *
   * @param connection the connection
   * @param frame      the frame ({@code SEND} frame).
   * @return the current instance of {@link Destination}
   */
  @Override
  public synchronized Destination dispatch(StompServerConnection connection, Frame frame) {
    if (subscriptions.isEmpty()) {
      lastUsedSubscriptions = -1;
      return this;
    }
    Subscription subscription = getNextSubscription();
    String messageId = UUID.randomUUID().toString();
    Frame message = transform(frame, subscription, messageId);
    subscription.connection.write(message);
    return this;
  }

  private Subscription getNextSubscription() {
    lastUsedSubscriptions = lastUsedSubscriptions + 1;
    if (lastUsedSubscriptions >= subscriptions.size()) {
      lastUsedSubscriptions = 0;
    }
    return subscriptions.get(lastUsedSubscriptions);
  }

  public static Frame transform(Frame frame, Subscription subscription, String messageId) {
    final Headers headers = Headers.create(frame.getHeaders())
        // Destination already set in the input headers.
        .add(Frame.SUBSCRIPTION, subscription.id)
        .add(Frame.MESSAGE_ID, messageId);
    if (!subscription.ackMode.equals("auto")) {
      // We reuse the message Id as ack Id
      headers.add(Frame.ACK, messageId);
    }
    return new Frame(Frame.Command.MESSAGE,
        headers,
        frame.getBody());
  }

  
Handles a subscription request to the current Destination. All check about the frame format and unicity of the id should have been done beforehand. 
Params:
connection – the connection
frame –  the SUBSCRIBE frame
Returns:
the current instance of Destination/**
   * Handles a subscription request to the current {@link Destination}. All check about the frame format and unicity
   * of the id should have been done beforehand.
   *
   * @param connection the connection
   * @param frame      the {@code SUBSCRIBE} frame
   * @return the current instance of {@link Destination}
   */
  @Override
  public synchronized Destination subscribe(StompServerConnection connection, Frame frame) {
    Subscription subscription = new Subscription(connection, frame);
    subscriptions.add(subscription);
    return this;
  }

  
Handles a un-subscription request to the current Destination. 
Params:
connection – the connection
frame –  the UNSUBSCRIBE frame
Returns:
true if the un-subscription has been handled, false otherwise./**
   * Handles a un-subscription request to the current {@link Destination}.
   *
   * @param connection the connection
   * @param frame      the {@code UNSUBSCRIBE} frame
   * @return {@code true} if the un-subscription has been handled, {@code false} otherwise.
   */
  @Override
  public synchronized boolean unsubscribe(StompServerConnection connection, Frame frame) {
    boolean r = false;
    for (Subscription subscription : subscriptions) {
      if (subscription.connection.equals(connection) && subscription.id.equals(frame.getId())) {
        r = subscriptions.remove(subscription);
        // Subscription id are unique for a connection.
        break;
      }
    }
    if (subscriptions.isEmpty()) {
      vertx.sharedData().getLocalMap("stomp.destinations").remove(this);
    }
    return r;
  }

  
Removes all subscriptions of the given connection
Params:
connection – the connection
Returns:
the current instance of Destination/**
   * Removes all subscriptions of the given connection
   *
   * @param connection the connection
   * @return the current instance of {@link Destination}
   */
  @Override
  public synchronized Destination unsubscribeConnection(StompServerConnection connection) {
    new ArrayList<>(subscriptions)
        .stream()
        .filter(subscription -> subscription.connection.equals(connection))
        .forEach(subscriptions::remove);

    if (subscriptions.isEmpty()) {
      vertx.sharedData().getLocalMap("stomp.destinations").remove(this);
    }
    return this;
  }

  
Handles a ACK frame. 
Params:
connection – the connection
frame –  the ACK frame
Returns:
true if the destination has handled the frame (meaning it has sent the message with id)/**
   * Handles a {@code ACK} frame.
   *
   * @param connection the connection
   * @param frame      the {@code ACK} frame
   * @return {@code true} if the destination has handled the frame (meaning it has sent the message with id)
   */
  @Override
  public synchronized boolean ack(StompServerConnection connection, Frame frame) {
    return false;
  }

  
Handles a NACK frame. 
Params:
connection – the connection
frame –  the NACK frame
Returns:
true if the destination has handled the frame (meaning it has sent the message with id)/**
   * Handles a {@code NACK} frame.
   *
   * @param connection the connection
   * @param frame      the {@code NACK} frame
   * @return {@code true} if the destination has handled the frame (meaning it has sent the message with id)
   */
  @Override
  public synchronized boolean nack(StompServerConnection connection, Frame frame) {
    return false;
  }

  
Gets all subscription ids for the given destination hold by the given client
Params:
connection – the connection (client)
Returns:
the list of subscription id, empty if none/**
   * Gets all subscription ids for the given destination hold by the given client
   *
   * @param connection the connection (client)
   * @return the list of subscription id, empty if none
   */
  @Override
  public synchronized List<String> getSubscriptions(StompServerConnection connection) {
    return subscriptions.stream()
        .filter(subscription -> subscription.connection.equals(connection))
        .map(s -> s.id)
        .collect(Collectors.toList());
  }

  
Gets the number of subscriptions attached to the current Destination. 
Returns:
the number of subscriptions./**
   * Gets the number of subscriptions attached to the current {@link Destination}.
   *
   * @return the number of subscriptions.
   */
  @Override
  public synchronized int numberOfSubscriptions() {
    return subscriptions.size();
  }

  
Checks whether or not the given address matches with the current destination.
Params:
address – the address
Returns:
true if it matches, false otherwise./**
   * Checks whether or not the given address matches with the current destination.
   *
   * @param address the address
   * @return {@code true} if it matches, {@code false} otherwise.
   */
  @Override
  public boolean matches(String address) {
    return this.destination.equals(address);
  }

  private class Subscription {
    private final StompServerConnection connection;
    private final String id;
    private final String ackMode;

    private Subscription(StompServerConnection connection, Frame frame) {
      this.connection = connection;
      this.ackMode = frame.getAck() != null ? frame.getAck() : "auto";
      this.id = frame.getId();
    }
  }

}