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


#ifndef Foundation_AbstractCache_INCLUDED
#define Foundation_AbstractCache_INCLUDED


#include <cstddef>
#include <map>
#include <set>
#include "Poco/Delegate.h"
#include "Poco/EventArgs.h"
#include "Poco/Exception.h"
#include "Poco/FIFOEvent.h"
#include "Poco/KeyValueArgs.h"
#include "Poco/Mutex.h"
#include "Poco/SharedPtr.h"
#include "Poco/ValidArgs.h"


namespace Poco
{


template <class TKey, class TValue, class TStrategy, class TMutex = FastMutex, class TEventMutex = FastMutex>
class AbstractCache
/// An AbstractCache is the interface of all caches.
{
public:
    FIFOEvent<const KeyValueArgs<TKey, TValue>, TEventMutex> Add;
    FIFOEvent<const KeyValueArgs<TKey, TValue>, TEventMutex> Update;
    FIFOEvent<const TKey, TEventMutex> Remove;
    FIFOEvent<const TKey, TEventMutex> Get;
    FIFOEvent<const EventArgs, TEventMutex> Clear;

    typedef std::map<TKey, SharedPtr<TValue>> DataHolder;
    typedef typename DataHolder::iterator Iterator;
    typedef typename DataHolder::const_iterator ConstIterator;
    typedef std::set<TKey> KeySet;

    AbstractCache() { initialize(); }

    AbstractCache(const TStrategy & strategy) : _strategy(strategy) { initialize(); }

    virtual ~AbstractCache()
    {
        try
        {
            uninitialize();
        }
        catch (...)
        {
            poco_unexpected();
        }
    }

    void add(const TKey & key, const TValue & val)
    /// Adds the key value pair to the cache.
    /// If for the key already an entry exists, it will be overwritten.
    {
        typename TMutex::ScopedLock lock(_mutex);
        doAdd(key, val);
    }

    void update(const TKey & key, const TValue & val)
    /// Adds the key value pair to the cache. Note that adding a NULL SharedPtr will fail!
    /// If for the key already an entry exists, it will be overwritten.
    /// The difference to add is that no remove or add events are thrown in this case,
    /// just a simply silent update is performed
    /// If the key does not exist the behavior is equal to add, ie. an add event is thrown
    {
        typename TMutex::ScopedLock lock(_mutex);
        doUpdate(key, val);
    }

    void add(const TKey & key, SharedPtr<TValue> val)
    /// Adds the key value pair to the cache. Note that adding a NULL SharedPtr will fail!
    /// If for the key already an entry exists, it will be overwritten, ie. first a remove event
    /// is thrown, then a add event
    {
        typename TMutex::ScopedLock lock(_mutex);
        doAdd(key, val);
    }

    void update(const TKey & key, SharedPtr<TValue> val)
    /// Adds the key value pair to the cache. Note that adding a NULL SharedPtr will fail!
    /// If for the key already an entry exists, it will be overwritten.
    /// The difference to add is that no remove or add events are thrown in this case,
    /// just an Update is thrown
    /// If the key does not exist the behavior is equal to add, ie. an add event is thrown
    {
        typename TMutex::ScopedLock lock(_mutex);
        doUpdate(key, val);
    }

    void remove(const TKey & key)
    /// Removes an entry from the cache. If the entry is not found,
    /// the remove is ignored.
    {
        typename TMutex::ScopedLock lock(_mutex);
        Iterator it = _data.find(key);
        doRemove(it);
    }

    bool has(const TKey & key) const
    /// Returns true if the cache contains a value for the key.
    {
        typename TMutex::ScopedLock lock(_mutex);
        return doHas(key);
    }

    SharedPtr<TValue> get(const TKey & key)
    /// Returns a SharedPtr of the value. The SharedPointer will remain valid
    /// even when cache replacement removes the element.
    /// If for the key no value exists, an empty SharedPtr is returned.
    {
        typename TMutex::ScopedLock lock(_mutex);
        return doGet(key);
    }

    void clear()
    /// Removes all elements from the cache.
    {
        typename TMutex::ScopedLock lock(_mutex);
        doClear();
    }

    std::size_t size()
    /// Returns the number of cached elements
    {
        typename TMutex::ScopedLock lock(_mutex);
        doReplace();
        return _data.size();
    }

    void forceReplace()
    /// Forces cache replacement. Note that Poco's cache strategy use for efficiency reason no background thread
    /// which periodically triggers cache replacement. Cache Replacement is only started when the cache is modified
    /// from outside, i.e. add is called, or when a user tries to access an cache element via get.
    /// In some cases, i.e. expire based caching where for a long time no access to the cache happens,
    /// it might be desirable to be able to trigger cache replacement manually.
    {
        typename TMutex::ScopedLock lock(_mutex);
        doReplace();
    }

    std::set<TKey> getAllKeys()
    /// Returns a copy of all keys stored in the cache
    {
        typename TMutex::ScopedLock lock(_mutex);
        doReplace();
        ConstIterator it = _data.begin();
        ConstIterator itEnd = _data.end();
        std::set<TKey> result;
        for (; it != itEnd; ++it)
            result.insert(it->first);

        return result;
    }

protected:
    mutable FIFOEvent<ValidArgs<TKey>> IsValid;
    mutable FIFOEvent<KeySet> Replace;

    void initialize()
    /// Sets up event registration.
    {
        Add += Delegate<TStrategy, const KeyValueArgs<TKey, TValue>>(&_strategy, &TStrategy::onAdd);
        Update += Delegate<TStrategy, const KeyValueArgs<TKey, TValue>>(&_strategy, &TStrategy::onUpdate);
        Remove += Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onRemove);
        Get += Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onGet);
        Clear += Delegate<TStrategy, const EventArgs>(&_strategy, &TStrategy::onClear);
        IsValid += Delegate<TStrategy, ValidArgs<TKey>>(&_strategy, &TStrategy::onIsValid);
        Replace += Delegate<TStrategy, KeySet>(&_strategy, &TStrategy::onReplace);
    }

    void uninitialize()
    /// Reverts event registration.
    {
        Add -= Delegate<TStrategy, const KeyValueArgs<TKey, TValue>>(&_strategy, &TStrategy::onAdd);
        Update -= Delegate<TStrategy, const KeyValueArgs<TKey, TValue>>(&_strategy, &TStrategy::onUpdate);
        Remove -= Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onRemove);
        Get -= Delegate<TStrategy, const TKey>(&_strategy, &TStrategy::onGet);
        Clear -= Delegate<TStrategy, const EventArgs>(&_strategy, &TStrategy::onClear);
        IsValid -= Delegate<TStrategy, ValidArgs<TKey>>(&_strategy, &TStrategy::onIsValid);
        Replace -= Delegate<TStrategy, KeySet>(&_strategy, &TStrategy::onReplace);
    }

    void doAdd(const TKey & key, const TValue & val)
    /// Adds the key value pair to the cache.
    /// If for the key already an entry exists, it will be overwritten.
    {
        Iterator it = _data.find(key);
        doRemove(it);

        KeyValueArgs<TKey, TValue> args(key, val);
        Add.notify(this, args);
        _data.insert(std::make_pair(key, SharedPtr<TValue>(new TValue(val))));

        doReplace();
    }

    void doAdd(const TKey & key, SharedPtr<TValue> & val)
    /// Adds the key value pair to the cache.
    /// If for the key already an entry exists, it will be overwritten.
    {
        Iterator it = _data.find(key);
        doRemove(it);

        KeyValueArgs<TKey, TValue> args(key, *val);
        Add.notify(this, args);
        _data.insert(std::make_pair(key, val));

        doReplace();
    }

    void doUpdate(const TKey & key, const TValue & val)
    /// Adds the key value pair to the cache.
    /// If for the key already an entry exists, it will be overwritten.
    {
        KeyValueArgs<TKey, TValue> args(key, val);
        Iterator it = _data.find(key);
        if (it == _data.end())
        {
            Add.notify(this, args);
            _data.insert(std::make_pair(key, SharedPtr<TValue>(new TValue(val))));
        }
        else
        {
            Update.notify(this, args);
            it->second = SharedPtr<TValue>(new TValue(val));
        }

        doReplace();
    }

    void doUpdate(const TKey & key, SharedPtr<TValue> & val)
    /// Adds the key value pair to the cache.
    /// If for the key already an entry exists, it will be overwritten.
    {
        KeyValueArgs<TKey, TValue> args(key, *val);
        Iterator it = _data.find(key);
        if (it == _data.end())
        {
            Add.notify(this, args);
            _data.insert(std::make_pair(key, val));
        }
        else
        {
            Update.notify(this, args);
            it->second = val;
        }

        doReplace();
    }

    void doRemove(Iterator it)
    /// Removes an entry from the cache. If the entry is not found
    /// the remove is ignored.
    {
        if (it != _data.end())
        {
            Remove.notify(this, it->first);
            _data.erase(it);
        }
    }

    bool doHas(const TKey & key) const
    /// Returns true if the cache contains a value for the key
    {
        // ask the strategy if the key is valid
        ConstIterator it = _data.find(key);
        bool result = false;

        if (it != _data.end())
        {
            ValidArgs<TKey> args(key);
            IsValid.notify(this, args);
            result = args.isValid();
        }

        return result;
    }

    SharedPtr<TValue> doGet(const TKey & key)
    /// Returns a SharedPtr of the cache entry, returns 0 if for
    /// the key no value was found
    {
        Iterator it = _data.find(key);
        SharedPtr<TValue> result;

        if (it != _data.end())
        {
            // inform all strategies that a read-access to an element happens
            Get.notify(this, key);
            // ask all strategies if the key is valid
            ValidArgs<TKey> args(key);
            IsValid.notify(this, args);

            if (!args.isValid())
            {
                doRemove(it);
            }
            else
            {
                result = it->second;
            }
        }

        return result;
    }

    void doClear()
    {
        static EventArgs _emptyArgs;
        Clear.notify(this, _emptyArgs);
        _data.clear();
    }

    void doReplace()
    {
        std::set<TKey> delMe;
        Replace.notify(this, delMe);
        // delMe contains the to be removed elements
        typename std::set<TKey>::const_iterator it = delMe.begin();
        typename std::set<TKey>::const_iterator endIt = delMe.end();

        for (; it != endIt; ++it)
        {
            Iterator itH = _data.find(*it);
            doRemove(itH);
        }
    }

    TStrategy _strategy;
    mutable DataHolder _data;
    mutable TMutex _mutex;

private:
    AbstractCache(const AbstractCache & aCache);
    AbstractCache & operator=(const AbstractCache & aCache);
};


} // namespace Poco


#endif // Foundation_AbstractCache_INCLUDED