/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2017 - ROLI Ltd.

   JUCE is an open source library subject to commercial or open-source
   licensing.

   The code included in this file is provided under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
   To use, copy, modify, and/or distribute this software for any purpose with or
   without fee is hereby granted provided that the above copyright notice and
   this permission notice appear in all copies.

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

//==============================================================================
/**
    Holds a list of ChangeListeners, and sends messages to them when instructed.

    @see ChangeListener

    @tags{Events}
*/
class JUCE_API  ChangeBroadcaster
{
public:
    //==============================================================================
    /** Creates an ChangeBroadcaster. */
    ChangeBroadcaster() noexcept;

    /** Destructor. */
    virtual ~ChangeBroadcaster();

    //==============================================================================
    /** Registers a listener to receive change callbacks from this broadcaster.
        Trying to add a listener that's already on the list will have no effect.
    */
    void addChangeListener (ChangeListener* listener);

    /** Unregisters a listener from the list.
        If the listener isn't on the list, this won't have any effect.
    */
    void removeChangeListener (ChangeListener* listener);

    /** Removes all listeners from the list. */
    void removeAllChangeListeners();

    //==============================================================================
    /** Causes an asynchronous change message to be sent to all the registered listeners.

        The message will be delivered asynchronously by the main message thread, so this
        method will return immediately. To call the listeners synchronously use
        sendSynchronousChangeMessage().
    */
    void sendChangeMessage();

    /** Sends a synchronous change message to all the registered listeners.

        This will immediately call all the listeners that are registered. For thread-safety
        reasons, you must only call this method on the main message thread.

        @see dispatchPendingMessages
    */
    void sendSynchronousChangeMessage();

    /** If a change message has been sent but not yet dispatched, this will call
        sendSynchronousChangeMessage() to make the callback immediately.

        For thread-safety reasons, you must only call this method on the main message thread.
    */
    void dispatchPendingMessages();

private:
    //==============================================================================
    class ChangeBroadcasterCallback  : public AsyncUpdater
    {
    public:
        ChangeBroadcasterCallback();
        void handleAsyncUpdate() override;

        ChangeBroadcaster* owner;
    };

    friend class ChangeBroadcasterCallback;
    ChangeBroadcasterCallback broadcastCallback;
    ListenerList <ChangeListener> changeListeners;

    std::atomic<bool> anyListeners { false };

    void callListeners();

    JUCE_DECLARE_NON_COPYABLE (ChangeBroadcaster)
};

} // namespace juce
