/*    Copyright 2014 MongoDB Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects
 *    for all of the code used other than as permitted herein. If you modify
 *    file(s) with this exception, you may extend this exception to your
 *    version of the file(s), but you are not obligated to do so. If you do not
 *    wish to do so, delete this exception statement from your version. If you
 *    delete this exception statement from all source files in the program,
 *    then also delete it in the license file.
 */

#pragma once

#include <cstring>
#include <type_traits>

#include "mongo/platform/endian.h"

namespace mongo {

    class ConstDataView {

    public:
        typedef const char* bytes_type;

        ConstDataView(bytes_type bytes)
            : _bytes(bytes) {
        }

        bytes_type view(std::size_t offset = 0) const {
            return _bytes + offset;
        }

        template<typename T>
        const ConstDataView& readNative(T* t, size_t offset = 0) const {
#if MONGO_HAVE_STD_IS_TRIVIALLY_COPYABLE
            static_assert(std::is_trivially_copyable<T>::value,
                          "Type for DataView::readNative must be trivially copyable");
#endif
            std::memcpy(t, view(offset), sizeof(*t));
            return *this;
        }

        template<typename T>
        T readNative(std::size_t offset = 0) const {
            T t;
            readNative(&t, offset);
            return t;
        }

        template<typename T>
        T readLE(std::size_t offset = 0) const {
            return endian::littleToNative(readNative<T>(offset));
        }

        template<typename T>
        T readBE(std::size_t offset = 0) const {
            return endian::bigToNative(readNative<T>(offset));
        }

    private:
        bytes_type _bytes;
    };

    class DataView : public ConstDataView {

    public:
        typedef char* bytes_type;

        DataView(bytes_type bytes)
            : ConstDataView(bytes) {
        }

        bytes_type view(std::size_t offset = 0) const {
            // It is safe to cast away const here since the pointer stored in our base class was
            // originally non-const by way of our constructor.
            return const_cast<bytes_type>(ConstDataView::view(offset));
        }

        template<typename T>
        DataView& writeNative(const T& value, std::size_t offset = 0) {
#if MONGO_HAVE_STD_IS_TRIVIALLY_COPYABLE
            static_assert(std::is_trivially_copyable<T>::value,
                          "Type for DataView::writeNative must be trivially copyable");
#endif
            std::memcpy(view(offset), &value, sizeof(value));
            return *this;
        }

        template<typename T>
        DataView& writeLE(const T& value, std::size_t offset = 0) {
            return writeNative(endian::nativeToLittle(value), offset);
        }

        template<typename T>
        DataView& writeBE(const T& value, std::size_t offset = 0) {
            return writeNative(endian::nativeToBig(value), offset);
        }
    };

} // namespace mongo