/*
  Copyright 2017 Larry Gritz and the other authors and contributors.
  All Rights Reserved.

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:
  * Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
  * 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.
  * Neither the name of the software's owners nor the names of its
    contributors may be used to endorse or promote products derived from
    this software without specific prior written permission.
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
  OWNER OR 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.

  (This is the Modified BSD License)
*/

// Portions of the code in this file is a derived work based on the
// FunctionRef class in LLVM:
//
// University of Illinois/NCSA Open Source License
//
// Copyright (c) 2003-2018 University of Illinois at Urbana-Champaign.
// All rights reserved.
//
// Developed by:
//   LLVM Team, University of Illinois at Urbana-Champaign, http://llvm.org
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal with
// the Software without restriction, including without limitation the rights to
// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do
// so, subject to the following conditions:
//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimers.
//     * Redistributions in binary form must reproduce the above copyright notice,
//       this list of conditions and the following disclaimers in the
//       documentation and/or other materials provided with the distribution.
//     * Neither the names of the LLVM Team, University of Illinois at
//       Urbana-Champaign, nor the names of its contributors may be used to
//       endorse or promote products derived from this Software without specific
//       prior written permission.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// CONTRIBUTORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS WITH THE
// SOFTWARE.


#pragma once

#include <functional>
#include <type_traits>

#include <OpenImageIO/export.h>
#include <OpenImageIO/oiioversion.h>
#include <OpenImageIO/platform.h>


OIIO_NAMESPACE_BEGIN


/// function_view<R(T...)> is a lightweight non-owning generic callable
/// object view, similar to a std::function<R(T...)>, but with much less
/// overhead.
///
/// A function_view invocation should have the same cost as a function
/// pointer (which it basically is underneath). Similar in spirit to a
/// string_view or span, the function-like object that the function_view
/// refers to MUST have a lifetime that outlasts any use of the
/// function_view.
///
/// In contrast, a full std::function<> is an owning container for a
/// callable object. It's more robust, especially with restpect to object
/// lifetimes, but the call overhead is quite high. So use a function_view
/// when you can.
///
/// This implementation comes from LLVM:
/// https://github.com/llvm-mirror/llvm/blob/master/include/llvm/ADT/STLExtras.h

template<typename Fn> class function_view;

template<typename Ret, typename... Params> class function_view<Ret(Params...)> {
    Ret (*callback)(intptr_t callable, Params... params) = nullptr;
    intptr_t callable;

    template<typename Callable>
    static Ret callback_fn(intptr_t callable, Params... params)
    {
        return (*reinterpret_cast<Callable*>(callable))(
            std::forward<Params>(params)...);
    }

public:
    function_view() = default;
    function_view(std::nullptr_t) {}

    template<typename Callable>
    function_view(
        Callable&& callable,
        typename std::enable_if<
            !std::is_same<typename std::remove_reference<Callable>::type,
                          function_view>::value>::type* = nullptr)
        : callback(callback_fn<typename std::remove_reference<Callable>::type>)
        , callable(reinterpret_cast<intptr_t>(&callable))
    {
    }

    Ret operator()(Params... params) const
    {
        return callback(callable, std::forward<Params>(params)...);
    }

    operator bool() const { return callback; }
};


OIIO_NAMESPACE_END