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

   This file is part of the JUCE library.
   Copyright (c) 2016 - ROLI Ltd.

   Permission is granted to use this software 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.

   THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH REGARD
   TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
   FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT,
   OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
   TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
   OF THIS SOFTWARE.

   -----------------------------------------------------------------------------

   To release a closed-source product which uses other parts of JUCE not
   licensed under the ISC terms, commercial licenses are available: visit
   www.juce.com for more information.

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

#ifndef JUCE_ASYNCUPDATER_H_INCLUDED
#define JUCE_ASYNCUPDATER_H_INCLUDED


//==============================================================================
/**
    Has a callback method that is triggered asynchronously.

    This object allows an asynchronous callback function to be triggered, for
    tasks such as coalescing multiple updates into a single callback later on.

    Basically, one or more calls to the triggerAsyncUpdate() will result in the
    message thread calling handleAsyncUpdate() as soon as it can.
*/
class JUCE_API  AsyncUpdater
{
public:
    //==============================================================================
    /** Creates an AsyncUpdater object. */
    AsyncUpdater();

    /** Destructor.
        If there are any pending callbacks when the object is deleted, these are lost.
    */
    virtual ~AsyncUpdater();

    //==============================================================================
    /** Causes the callback to be triggered at a later time.

        This method returns immediately, having made sure that a callback
        to the handleAsyncUpdate() method will occur as soon as possible.

        If an update callback is already pending but hasn't happened yet, calls
        to this method will be ignored.

        It's thread-safe to call this method from any number of threads without
        needing to worry about locking.
    */
    void triggerAsyncUpdate();

    /** This will stop any pending updates from happening.

        If called after triggerAsyncUpdate() and before the handleAsyncUpdate()
        callback happens, this will cancel the handleAsyncUpdate() callback.

        Note that this method simply cancels the next callback - if a callback is already
        in progress on a different thread, this won't block until the callback finishes, so
        there's no guarantee that the callback isn't still running when the method returns.
    */
    void cancelPendingUpdate() noexcept;

    /** If an update has been triggered and is pending, this will invoke it
        synchronously.

        Use this as a kind of "flush" operation - if an update is pending, the
        handleAsyncUpdate() method will be called immediately; if no update is
        pending, then nothing will be done.

        Because this may invoke the callback, this method must only be called on
        the main event thread.
    */
    void handleUpdateNowIfNeeded();

    /** Returns true if there's an update callback in the pipeline. */
    bool isUpdatePending() const noexcept;

    //==============================================================================
    /** Called back to do whatever your class needs to do.

        This method is called by the message thread at the next convenient time
        after the triggerAsyncUpdate() method has been called.
    */
    virtual void handleAsyncUpdate() = 0;

private:
    //==============================================================================
    class AsyncUpdaterMessage;
    friend class ReferenceCountedObjectPtr<AsyncUpdaterMessage>;
    ReferenceCountedObjectPtr<AsyncUpdaterMessage> activeMessage;

    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (AsyncUpdater)
};


#endif   // JUCE_ASYNCUPDATER_H_INCLUDED
