/*
 * Copyright (c) Contributors to the Open 3D Engine Project.
 * For complete copyright and license terms please see the LICENSE at the root of this distribution.
 *
 * SPDX-License-Identifier: Apache-2.0 OR MIT
 *
 */


#ifndef CRYINCLUDE_CRYSYSTEM_HUFFMAN_H
#define CRYINCLUDE_CRYSYSTEM_HUFFMAN_H
#pragma once


class HuffmanCoder
{
private:
    struct HuffmanTreeNode
    {
        uint32 count;
        uint32 savedCount;
        int child0;
        int child1;
    };

    struct HuffmanSymbolCode
    {
        uint32 value;
        uint32 numBits;
    };

    struct BitStreamBuilder
    {
        enum EModes
        {
            eM_WRITE,
            eM_READ
        };
        union buf_ptr
        {
            uint8* ptr;
            const uint8* const_ptr;
        };
        EModes m_mode;
        uint8 m_mask;
        buf_ptr m_pBufferStart;
        buf_ptr m_pBufferCursor;
        buf_ptr m_pBufferEnd;       //Pointer to the last byte in the buffer

        BitStreamBuilder(uint8* pBufferStart, uint8* pBufferEnd)
            : m_mode(eM_WRITE)
            , m_mask(0x80)
        {
            m_pBufferStart.ptr = pBufferStart;
            m_pBufferCursor.ptr = pBufferStart;
            m_pBufferEnd.ptr = pBufferEnd;
        }
        BitStreamBuilder(const uint8* pBufferStart, const uint8* pBufferEnd)
            : m_mode(eM_READ)
            , m_mask(0x80)
        {
            m_pBufferStart.const_ptr = pBufferStart;
            m_pBufferCursor.const_ptr = pBufferStart;
            m_pBufferEnd.const_ptr = pBufferEnd;
        }

        void AddBits(uint32 value, uint32 numBits);
        void AddBits(uint8 value, uint32 numBits);
        //Returns 1 or 0 for valid values. Returns 2 if the buffer has run out or is the wrong type of builder.
        uint8 GetBit();
    };

    const static int MAX_SYMBOL_VALUE = (255);
    const static int MAX_NUM_SYMBOLS = (MAX_SYMBOL_VALUE + 1);
    const static int END_OF_STREAM = (MAX_NUM_SYMBOLS);
    const static int MAX_NUM_CODES = (MAX_NUM_SYMBOLS + 1);
    const static int MAX_NUM_NODES = (MAX_NUM_CODES * 2);
    const static int MAX_NODE = (MAX_NUM_NODES - 1);

    enum EHuffmanCoderState
    {
        eHCS_NEW,       //Has been created, Init not called
        eHCS_OPEN,      //Init has been called, tree not yet constructed. Can accept new data.
        eHCS_FINAL      //Finalize has been called. Can no longer accept data, but can encode/decode.
    };

    HuffmanTreeNode* m_TreeNodes;
    HuffmanSymbolCode* m_Codes;
    uint32* m_Counts;
    int m_RootNode;
    uint32 m_RefCount;
    EHuffmanCoderState m_State;

public:
    HuffmanCoder()
        : m_TreeNodes(NULL)
        , m_Codes(NULL)
        , m_Counts(NULL)
        , m_State(eHCS_NEW)
        , m_RootNode(0)
        , m_RefCount(0) {}
    ~HuffmanCoder()
    {
        SAFE_DELETE_ARRAY(m_TreeNodes);
        SAFE_DELETE_ARRAY(m_Codes);
        SAFE_DELETE_ARRAY(m_Counts);
    }

    //A bit like an MD5 generator, has three phases.
    //Clears the existing data
    void Init();
    //Adds the values of an array of chars to the counts
    void Update(const uint8* const pSource, const size_t numBytes);
    //Construct the coding tree using the counts
    void Finalize();

    //We typically create a Huffman Coder per localized string table loaded. Since we can and do unload strings at runtime, it's useful to keep a ref count of each coder.
    inline void AddRef() { m_RefCount++; }
    inline void DecRef() { m_RefCount = m_RefCount > 0 ? m_RefCount - 1 : 0; }
    inline uint32 RefCount() { return m_RefCount; }

    void CompressInput(const uint8* const pInput, const size_t numBytes, uint8* const pOutput, size_t* const outputSize);
    size_t UncompressInput(const uint8* const pInput, const size_t numBytes, uint8* const pOutput, const size_t maxOutputSize);

private:
    void ScaleCountsAndUpdateNodes();
    int BuildTree();
    void ConvertTreeToCode(const HuffmanTreeNode* const pNodes, HuffmanSymbolCode* const pCodes, const unsigned int value, const unsigned int numBits, const int node);
};

#endif // CRYINCLUDE_CRYSYSTEM_HUFFMAN_H