/*

 * Copyright (c) 2021, Hunter Salyer <thefalsehonesty@gmail.com>

 * Copyright (c) 2022, Gregory Bertilson <zaggy1024@gmail.com>

 *

 * SPDX-License-Identifier: BSD-2-Clause

 */

#pragma once

#include <AK/BitStream.h>

#include <AK/Error.h>

#include <AK/Optional.h>

#include <AK/Types.h>

namespace Gfx {

// Can decode bitstreams encoded with VP8's and VP9's arithmetic boolean encoder.

class BooleanDecoder {

public:

    static ErrorOr<BooleanDecoder> initialize(ReadonlyBytes data);

    /* (9.2) */

    bool read_bool(u8 probability);

    u8 read_literal(u8 bits);

    ErrorOr<void> finish_decode();

private:

    using ValueType = size_t;

    static constexpr u8 reserve_bytes = sizeof(ValueType) - 1;

    static constexpr u8 reserve_bits = reserve_bytes * 8;

    BooleanDecoder(u8 const* data, u64 bytes_left)

        : m_data(data + 1)

        , m_bytes_left(bytes_left - 1)

        , m_range(255)

        , m_value(static_cast<ValueType>(*data) << reserve_bits)

        , m_value_bits_left(8)

    {

        fill_reservoir();

    }

    void fill_reservoir();

    u8 const* m_data;

    size_t m_bytes_left { 0 };

    bool m_overread { false };

    // This value will never exceed 255. If this is a u8, the compiler will generate a truncation in read_bool().

    u32 m_range { 0 };

    ValueType m_value { 0 };

    // Like above, this will never exceed reserve_bits, but will truncate if it is a u8.

    u32 m_value_bits_left { 0 };

};

}