/*
 * Copyright (C) 2016 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <memory>
#include <wtf/FastMalloc.h>

namespace WTF {

template<typename> class Function;

template <typename Out, typename... In>
class Function<Out(In...)> {
public:
    Function() = default;
    Function(std::nullptr_t) { }

    template<typename CallableType, class = typename std::enable_if<std::is_rvalue_reference<CallableType&&>::value>::type>
    Function(CallableType&& callable)
        : m_callableWrapper(std::make_unique<CallableWrapper<CallableType>>(WTFMove(callable)))
    {
    }

    Out operator()(In... in) const
    {
        if (m_callableWrapper)
            return m_callableWrapper->call(std::forward<In>(in)...);
        return Out();
    }

    explicit operator bool() const { return !!m_callableWrapper; }

    template<typename CallableType, class = typename std::enable_if<std::is_rvalue_reference<CallableType&&>::value>::type>
    Function& operator=(CallableType&& callable)
    {
        m_callableWrapper = std::make_unique<CallableWrapper<CallableType>>(WTFMove(callable));
        return *this;
    }

    Function& operator=(std::nullptr_t)
    {
        m_callableWrapper = nullptr;
        return *this;
    }

private:
    class CallableWrapperBase {
        WTF_MAKE_FAST_ALLOCATED;
    public:
        virtual ~CallableWrapperBase() { }

        virtual Out call(In...) = 0;
    };

    template<typename CallableType>
    class CallableWrapper : public CallableWrapperBase {
    public:
        explicit CallableWrapper(CallableType&& callable)
            : m_callable(WTFMove(callable))
        {
        }

        CallableWrapper(const CallableWrapper&) = delete;
        CallableWrapper& operator=(const CallableWrapper&) = delete;

        Out call(In... in) final { return m_callable(std::forward<In>(in)...); }

    private:
        CallableType m_callable;
    };

    std::unique_ptr<CallableWrapperBase> m_callableWrapper;
};

} // namespace WTF

using WTF::Function;
