//
// AbstractEvent.h
//
// Library: Foundation
// Package: Events
// Module:  AbstractEvent
//
// Definition of the AbstractEvent class.
//
// Copyright (c) 2006-2011, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_AbstractFoundation_INCLUDED
#define Foundation_AbstractFoundation_INCLUDED


#include "Poco/ActiveMethod.h"
#include "Poco/ActiveResult.h"
#include "Poco/Foundation.h"
#include "Poco/Mutex.h"
#include "Poco/SharedPtr.h"
#include "Poco/SingletonHolder.h"


namespace Poco
{


template <class TArgs, class TStrategy, class TDelegate, class TMutex = FastMutex>
class AbstractEvent
/// An AbstractEvent is the base class of all events.
/// It works similar to the way C# handles notifications (aka events in C#).
///
/// Events can be used to send information to a set of delegates
/// which are registered with the event. The type of the data is specified with
/// the template parameter TArgs. The TStrategy parameter must be a subclass
/// of NotificationStrategy. The parameter TDelegate can either be a subclass of AbstractDelegate
/// or of AbstractPriorityDelegate.
///
/// Note that AbstractEvent should never be used directly. One ought to use
/// one of its subclasses which set the TStrategy and TDelegate template parameters
/// to fixed values. For most use-cases the BasicEvent template will be sufficient:
///
///     #include "Poco/BasicEvent.h"
///     #include "Poco/Delegate.h"
///
/// Note that as of release 1.4.2, the behavior of BasicEvent equals that of FIFOEvent,
/// so the FIFOEvent class is no longer necessary and provided for backwards compatibility
/// only.
///
/// BasicEvent works with a standard delegate. They allow one object to register
/// one or more delegates with an event. In contrast, a PriorityDelegate comes with an attached priority value
/// and allows one object to register for one priority value one or more delegates. Note that PriorityDelegates
/// only work with PriorityEvents:
///
///     #include "Poco/PriorityEvent.h"
///     #include "Poco/PriorityDelegate.h"
///
/// Use events by adding them as public members to the object which is throwing notifications:
///
///     class MyData
///     {
///     public:
///         Poco::BasicEvent<int> dataChanged;
///
///         MyData();
///         ...
///         void setData(int i);
///         ...
///     private:
///         int _data;
///     };
///
/// Firing the event is done either by calling the event's notify() or notifyAsync() method:
///
///     void MyData::setData(int i)
///     {
///         this->_data = i;
///         dataChanged.notify(this, this->_data);
///     }
///
/// Alternatively, instead of notify(), operator () can be used.
///
///     void MyData::setData(int i)
///     {
///         this->_data = i;
///         dataChanged(this, this->_data);
///     }
///
/// Note that operator (), notify() and notifyAsync() do not catch exceptions, i.e. in case a
/// delegate throws an exception, notifying is immediately aborted and the exception is propagated
/// back to the caller.
///
/// Delegates can register methods at the event. In the case of a BasicEvent
/// the Delegate template is used, in case of an PriorityEvent a PriorityDelegate is used.
/// Mixing of delegates, e.g. using a PriorityDelegate with a BasicEvent is not allowed and
/// can lead to compile-time and/or run-time errors. The standalone delegate() functions
/// can be used to construct Delegate objects.
///
/// Events require the observers to have one of the following method signatures:
///
///     void onEvent(const void* pSender, TArgs& args);
///     void onEvent(TArgs& args);
///     static void onEvent(const void* pSender, TArgs& args);
///     static void onEvent(void* pSender, TArgs& args);
///     static void onEvent(TArgs& args);
///
/// For performance reasons arguments are always sent by reference. This also allows observers
/// to modify the event argument. To prevent that, use <[const TArg]> as template
/// parameter. A non-conformant method signature leads to compile errors.
///
/// Assuming that the observer meets the method signature requirement, it can register
/// this method with the += operator:
///
///     class MyController
///     {
///     protected:
///         MyData _data;
///
///         void onDataChanged(void* pSender, int& data);
///         ...
///     };
///
///     MyController::MyController()
///     {
///         _data.dataChanged += delegate(this, &MyController::onDataChanged);
///     }
///
/// In some cases it might be desirable to work with automatically expiring registrations. Simply add
/// to delegate as 3rd parameter a expireValue (in milliseconds):
///
///     _data.dataChanged += delegate(this, &MyController::onDataChanged, 1000);
///
/// This will add a delegate to the event which will automatically be removed in 1000 millisecs.
///
/// Unregistering happens via the -= operator. Forgetting to unregister a method will lead to
/// segmentation faults later, when one tries to send a notify to a no longer existing object.
///
///     MyController::~MyController()
///     {
///         _data.dataChanged -= delegate(this, &MyController::onDataChanged);
///     }
///
/// Working with PriorityDelegate's as similar to working with BasicEvent.
/// Instead of delegate(), the priorityDelegate() function must be used
/// to create the PriorityDelegate.
{
public:
    typedef TDelegate * DelegateHandle;
    typedef TArgs Args;

    AbstractEvent() : _executeAsync(this, &AbstractEvent::executeAsyncImpl), _enabled(true) { }

    AbstractEvent(const TStrategy & strategy) : _executeAsync(this, &AbstractEvent::executeAsyncImpl), _strategy(strategy), _enabled(true)
    {
    }

    virtual ~AbstractEvent() { }

    void operator+=(const TDelegate & aDelegate)
    /// Adds a delegate to the event.
    ///
    /// Exact behavior is determined by the TStrategy.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.add(aDelegate);
    }

    void operator-=(const TDelegate & aDelegate)
    /// Removes a delegate from the event.
    ///
    /// If the delegate is not found, this function does nothing.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.remove(aDelegate);
    }

    DelegateHandle add(const TDelegate & aDelegate)
    /// Adds a delegate to the event.
    ///
    /// Exact behavior is determined by the TStrategy.
    ///
    /// Returns a DelegateHandle which can be used in call to
    /// remove() to remove the delegate.
    {
        typename TMutex::ScopedLock lock(_mutex);
        return _strategy.add(aDelegate);
    }

    void remove(DelegateHandle delegateHandle)
    /// Removes a delegate from the event using a DelegateHandle
    /// returned by add().
    ///
    /// If the delegate is not found, this function does nothing.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.remove(delegateHandle);
    }

    void operator()(const void * pSender, TArgs & args)
    /// Shortcut for notify(pSender, args);
    {
        notify(pSender, args);
    }

    void operator()(TArgs & args)
    /// Shortcut for notify(args).
    {
        notify(0, args);
    }

    void notify(const void * pSender, TArgs & args)
    /// Sends a notification to all registered delegates. The order is
    /// determined by the TStrategy. This method is blocking. While executing,
    /// the list of delegates may be modified. These changes don't
    /// influence the current active notifications but are activated with
    /// the next notify. If a delegate is removed during a notify(), the
    /// delegate will no longer be invoked (unless it has already been
    /// invoked prior to removal). If one of the delegates throws an exception,
    /// the notify method is immediately aborted and the exception is propagated
    /// to the caller.
    {
        Poco::ScopedLockWithUnlock<TMutex> lock(_mutex);

        if (!_enabled)
            return;

        // thread-safeness:
        // copy should be faster and safer than blocking until
        // execution ends
        TStrategy strategy(_strategy);
        lock.unlock();
        strategy.notify(pSender, args);
    }

    bool hasDelegates() const { return !empty(); }

    ActiveResult<TArgs> notifyAsync(const void * pSender, const TArgs & args)
    /// Sends a notification to all registered delegates. The order is
    /// determined by the TStrategy. This method is not blocking and will
    /// immediately return. The delegates are invoked in a separate thread.
    /// Call activeResult.wait() to wait until the notification has ended.
    /// While executing, other objects can change the delegate list. These changes don't
    /// influence the current active notifications but are activated with
    /// the next notify. If a delegate is removed during a notify(), the
    /// delegate will no longer be invoked (unless it has already been
    /// invoked prior to removal). If one of the delegates throws an exception,
    /// the execution is aborted and the exception is propagated to the caller.
    {
        NotifyAsyncParams params(pSender, args);
        {
            typename TMutex::ScopedLock lock(_mutex);

            // thread-safeness:
            // copy should be faster and safer than blocking until
            // execution ends
            // make a copy of the strategy here to guarantee that
            // between notifyAsync and the execution of the method no changes can occur

            params.ptrStrat = SharedPtr<TStrategy>(new TStrategy(_strategy));
            params.enabled = _enabled;
        }
        ActiveResult<TArgs> result = _executeAsync(params);
        return result;
    }

    void enable()
    /// Enables the event.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _enabled = true;
    }

    void disable()
    /// Disables the event. notify and notifyAsnyc will be ignored,
    /// but adding/removing delegates is still allowed.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _enabled = false;
    }

    bool isEnabled() const
    {
        typename TMutex::ScopedLock lock(_mutex);
        return _enabled;
    }

    void clear()
    /// Removes all delegates.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.clear();
    }

    bool empty() const
    /// Checks if any delegates are registered at the delegate.
    {
        typename TMutex::ScopedLock lock(_mutex);
        return _strategy.empty();
    }

protected:
    struct NotifyAsyncParams
    {
        SharedPtr<TStrategy> ptrStrat;
        const void * pSender;
        TArgs args;
        bool enabled;

        NotifyAsyncParams(const void * pSend, const TArgs & a) : ptrStrat(), pSender(pSend), args(a), enabled(true)
        /// Default constructor reduces the need for TArgs to have an empty constructor, only copy constructor is needed.
        {
        }
    };

    ActiveMethod<TArgs, NotifyAsyncParams, AbstractEvent> _executeAsync;

    TArgs executeAsyncImpl(const NotifyAsyncParams & par)
    {
        if (!par.enabled)
        {
            return par.args;
        }

        NotifyAsyncParams params = par;
        TArgs retArgs(params.args);
        params.ptrStrat->notify(params.pSender, retArgs);
        return retArgs;
    }

    TStrategy _strategy; /// The strategy used to notify observers.
    bool _enabled; /// Stores if an event is enabled. Notfies on disabled events have no effect
        /// but it is possible to change the observers.
    mutable TMutex _mutex;

private:
    AbstractEvent(const AbstractEvent & other);
    AbstractEvent & operator=(const AbstractEvent & other);
};


template <class TStrategy, class TDelegate, class TMutex>
class AbstractEvent<void, TStrategy, TDelegate, TMutex>
{
public:
    typedef TDelegate * DelegateHandle;

    AbstractEvent() : _executeAsync(this, &AbstractEvent::executeAsyncImpl), _enabled(true) { }

    AbstractEvent(const TStrategy & strategy) : _executeAsync(this, &AbstractEvent::executeAsyncImpl), _strategy(strategy), _enabled(true)
    {
    }

    virtual ~AbstractEvent() { }

    void operator+=(const TDelegate & aDelegate)
    /// Adds a delegate to the event.
    ///
    /// Exact behavior is determined by the TStrategy.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.add(aDelegate);
    }

    void operator-=(const TDelegate & aDelegate)
    /// Removes a delegate from the event.
    ///
    /// If the delegate is not found, this function does nothing.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.remove(aDelegate);
    }

    DelegateHandle add(const TDelegate & aDelegate)
    /// Adds a delegate to the event.
    ///
    /// Exact behavior is determined by the TStrategy.
    ///
    /// Returns a DelegateHandle which can be used in call to
    /// remove() to remove the delegate.
    {
        typename TMutex::ScopedLock lock(_mutex);
        return _strategy.add(aDelegate);
    }

    void remove(DelegateHandle delegateHandle)
    /// Removes a delegate from the event using a DelegateHandle
    /// returned by add().
    ///
    /// If the delegate is not found, this function does nothing.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.remove(delegateHandle);
    }

    void operator()(const void * pSender)
    /// Shortcut for notify(pSender, args);
    {
        notify(pSender);
    }

    void operator()()
    /// Shortcut for notify(args).
    {
        notify(0);
    }

    void notify(const void * pSender)
    /// Sends a notification to all registered delegates. The order is
    /// determined by the TStrategy. This method is blocking. While executing,
    /// the list of delegates may be modified. These changes don't
    /// influence the current active notifications but are activated with
    /// the next notify. If a delegate is removed during a notify(), the
    /// delegate will no longer be invoked (unless it has already been
    /// invoked prior to removal). If one of the delegates throws an exception,
    /// the notify method is immediately aborted and the exception is propagated
    /// to the caller.
    {
        Poco::ScopedLockWithUnlock<TMutex> lock(_mutex);

        if (!_enabled)
            return;

        // thread-safeness:
        // copy should be faster and safer than blocking until
        // execution ends
        TStrategy strategy(_strategy);
        lock.unlock();
        strategy.notify(pSender);
    }

    ActiveResult<void> notifyAsync(const void * pSender)
    /// Sends a notification to all registered delegates. The order is
    /// determined by the TStrategy. This method is not blocking and will
    /// immediately return. The delegates are invoked in a separate thread.
    /// Call activeResult.wait() to wait until the notification has ended.
    /// While executing, other objects can change the delegate list. These changes don't
    /// influence the current active notifications but are activated with
    /// the next notify. If a delegate is removed during a notify(), the
    /// delegate will no longer be invoked (unless it has already been
    /// invoked prior to removal). If one of the delegates throws an exception,
    /// the execution is aborted and the exception is propagated to the caller.
    {
        NotifyAsyncParams params(pSender);
        {
            typename TMutex::ScopedLock lock(_mutex);

            // thread-safeness:
            // copy should be faster and safer than blocking until
            // execution ends
            // make a copy of the strategy here to guarantee that
            // between notifyAsync and the execution of the method no changes can occur

            params.ptrStrat = SharedPtr<TStrategy>(new TStrategy(_strategy));
            params.enabled = _enabled;
        }
        ActiveResult<void> result = _executeAsync(params);
        return result;
    }

    void enable()
    /// Enables the event.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _enabled = true;
    }

    void disable()
    /// Disables the event. notify and notifyAsnyc will be ignored,
    /// but adding/removing delegates is still allowed.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _enabled = false;
    }

    bool isEnabled() const
    {
        typename TMutex::ScopedLock lock(_mutex);
        return _enabled;
    }

    void clear()
    /// Removes all delegates.
    {
        typename TMutex::ScopedLock lock(_mutex);
        _strategy.clear();
    }

    bool empty() const
    /// Checks if any delegates are registered at the delegate.
    {
        typename TMutex::ScopedLock lock(_mutex);
        return _strategy.empty();
    }

protected:
    struct NotifyAsyncParams
    {
        SharedPtr<TStrategy> ptrStrat;
        const void * pSender;
        bool enabled;

        NotifyAsyncParams(const void * pSend) : ptrStrat(), pSender(pSend), enabled(true)
        /// Default constructor reduces the need for TArgs to have an empty constructor, only copy constructor is needed.
        {
        }
    };

    ActiveMethod<void, NotifyAsyncParams, AbstractEvent> _executeAsync;

    void executeAsyncImpl(const NotifyAsyncParams & par)
    {
        if (!par.enabled)
        {
            return;
        }

        NotifyAsyncParams params = par;
        params.ptrStrat->notify(params.pSender);
        return;
    }

    TStrategy _strategy; /// The strategy used to notify observers.
    bool _enabled; /// Stores if an event is enabled. Notfies on disabled events have no effect
        /// but it is possible to change the observers.
    mutable TMutex _mutex;

private:
    AbstractEvent(const AbstractEvent & other);
    AbstractEvent & operator=(const AbstractEvent & other);
};


} // namespace Poco


#endif // Foundation_AbstractFoundation_INCLUDED