/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 * 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 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 HOLDER 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.
 */

#pragma once

#include <AK/Types.h>
#include <AK/Vector.h>
#include <Kernel/Lock.h>

class DoubleBuffer {
public:
    DoubleBuffer()
        : m_write_buffer(&m_buffer1)
        , m_read_buffer(&m_buffer2)
    {
    }

    ssize_t write(const u8*, ssize_t);
    ssize_t read(u8*, ssize_t);

    bool is_empty() const { return m_empty; }

    // FIXME: Isn't this racy? What if we get interrupted between getting the buffer pointer and dereferencing it?
    ssize_t bytes_in_write_buffer() const { return (ssize_t)m_write_buffer->size(); }

private:
    void flip();
    void compute_emptiness();

    Vector<u8>* m_write_buffer { nullptr };
    Vector<u8>* m_read_buffer { nullptr };
    Vector<u8> m_buffer1;
    Vector<u8> m_buffer2;
    ssize_t m_read_buffer_index { 0 };
    bool m_empty { true };
    Lock m_lock { "DoubleBuffer" };
};