// /***************************************************************************
// Aaru Data Preservation Suite
// ----------------------------------------------------------------------------
//
// Filename       : ADC.cs
// Author(s)      : Natalia Portillo <claunia@claunia.com>
//
// Component      : Compression algorithms.
//
// --[ Description ] ----------------------------------------------------------
//
//     Decompresses Apple Data Compression.
//
// --[ License ] --------------------------------------------------------------
//
//     Permission is hereby granted, free of charge, to any person obtaining a
//     copy of this software and associated documentation files (the "Software"),
//     to deal in 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:
//
//     The above copyright notice and this permission notice shall be included in
//     all copies or substantial portions of the Software.
//
//     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
//     AUTHORS 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 IN
//     THE SOFTWARE.
//
// ----------------------------------------------------------------------------
// Copyright © 2016-2025 Natalia Portillo
// ****************************************************************************/

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace Aaru.Compression;

/// <summary>Implements the Apple version of RLE</summary>

// ReSharper disable once InconsistentNaming
public static partial class ADC
{
    const int PLAIN      = 1;
    const int TWO_BYTE   = 2;
    const int THREE_BYTE = 3;

    /// <summary>Set to <c>true</c> if this algorithm is supported, <c>false</c> otherwise.</summary>
    public static bool IsSupported => true;

    [LibraryImport("libAaru.Compression.Native", SetLastError = true)]
    private static partial int AARU_adc_decode_buffer(byte[] dstBuffer, int dstSize, byte[] srcBuffer, int srcSize);

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static int GetChunkType(byte byt) => (byt & 0x80) == 0x80
                                             ? PLAIN
                                             : (byt & 0x40) == 0x40
                                                 ? THREE_BYTE
                                                 : TWO_BYTE;

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static int GetChunkSize(byte byt) => GetChunkType(byt) switch
                                         {
                                             PLAIN      => (byt & 0x7F)        + 1,
                                             TWO_BYTE   => ((byt & 0x3F) >> 2) + 3,
                                             THREE_BYTE => (byt & 0x3F)        + 4,
                                             _          => -1
                                         };

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static int GetOffset(ReadOnlySpan<byte> chunk) => GetChunkType(chunk[0]) switch
                                                      {
                                                          PLAIN      => 0,
                                                          TWO_BYTE   => ((chunk[0] & 0x03) << 8) + chunk[1],
                                                          THREE_BYTE => (chunk[1]          << 8) + chunk[2],
                                                          _          => -1
                                                      };

    /// <summary>Decompresses a byte buffer that's compressed with ADC</summary>
    /// <param name="source">Compressed buffer</param>
    /// <param name="destination">Buffer to hold decompressed data</param>
    /// <returns>How many bytes are stored on <paramref name="destination" /></returns>
    [MethodImpl(MethodImplOptions.AggressiveOptimization)]
    public static int DecodeBuffer(byte[] source, byte[] destination)
    {
        if(Native.IsSupported) return AARU_adc_decode_buffer(destination, destination.Length, source, source.Length);

        var        inputPosition = 0;
        var        outPosition   = 0;
        Span<byte> temp          = stackalloc byte[3];

        while(inputPosition < source.Length)
        {
            byte readByte = source[inputPosition++];

            int chunkType = GetChunkType(readByte);

            int chunkSize;

            int offset;

            switch(chunkType)
            {
                case PLAIN:
                    chunkSize = GetChunkSize(readByte);

                    if(outPosition + chunkSize > destination.Length) goto finished;

                    Array.Copy(source, inputPosition, destination, outPosition, chunkSize);
                    outPosition   += chunkSize;
                    inputPosition += chunkSize;

                    break;
                case TWO_BYTE:
                    chunkSize = GetChunkSize(readByte);
                    temp[0]   = readByte;
                    temp[1]   = source[inputPosition++];
                    offset    = GetOffset(temp);

                    if(outPosition + chunkSize > destination.Length) goto finished;

                    if(offset == 0)
                    {
                        byte lastByte = destination[outPosition - 1];

                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = lastByte;
                            outPosition++;
                        }
                    }
                    else
                    {
                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = destination[outPosition - offset - 1];
                            outPosition++;
                        }
                    }

                    break;
                case THREE_BYTE:
                    chunkSize = GetChunkSize(readByte);
                    temp[0]   = readByte;
                    temp[1]   = source[inputPosition++];
                    temp[2]   = source[inputPosition++];
                    offset    = GetOffset(temp);

                    if(outPosition + chunkSize > destination.Length) goto finished;

                    if(offset == 0)
                    {
                        byte lastByte = destination[outPosition - 1];

                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = lastByte;
                            outPosition++;
                        }
                    }
                    else
                    {
                        for(var i = 0; i < chunkSize; i++)
                        {
                            destination[outPosition] = destination[outPosition - offset - 1];
                            outPosition++;
                        }
                    }

                    break;
            }
        }

    finished:

        return outPosition;
    }
}