SlobViewer/Slob/StoreItemFileBased.cs

// Copyright (c) Dr. Dirk Lellinger. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.
using System.IO;
using System.Text;
using SlobViewer.Common;

namespace SlobViewer.Slob
{
  /// <summary>
  /// Part of a <see cref="SlobDictionaryFileBased"/>.
  /// A <see cref="StoreItemFileBased"/> holds the position where to find the contents in the file. After reading the SLOB file,
  /// the content is stored in compressed form. If the contents is accessed, it is decompressed.
  /// </summary>
  public class StoreItemFileBased : StoreItemBase
  {
    long _filePosition;


    public StoreItemFileBased(long filePosition)
    {
      _filePosition = filePosition;
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="StoreItemFileBased"/> class.
    /// </summary>
    /// <param name="contentIds">The array of content IDs.</param>
    /// <param name="compressedContent">Compressed content as retrieved from the SLOB file.</param>
    public StoreItemFileBased(byte[] contentIds, byte[] compressedContent)
    {
      _contentIds = contentIds;
      _compressedContent = compressedContent;
    }

    /// <summary>
    /// Get the content item with index <paramref name="idx"/>.
    /// </summary>
    /// <param name="idx">The index.</param>
    /// <returns>A tuple, consisting of the content and content id at index <paramref name="idx"/>.</returns>
    public (string Content, int ContentId) GetAt(int idx, Stream stream, Encoding encoding, string compression, byte[] buffer)
    {
      ReadCompressedContentFromStream(stream, buffer);

      // StoreCompressedContentForDebugging();

      if (null != _compressedContent)
      {
        DecompressContent(encoding, compression, buffer);

        _compressedContent = null;
      }

      return (_content[idx], _contentIds[idx]);
    }


    private void StoreCompressedContentForDebugging()
    {
      using (var s = new FileStream("C:\\TEMP\\CompressedContent.XXX", FileMode.Create, FileAccess.Write, FileShare.Read))
      {
        s.Write(_compressedContent, 0, _compressedContent.Length);
      }
    }



    private void ReadCompressedContentFromStream(Stream stream, byte[] buffer)
    {
      stream.Seek(_filePosition, SeekOrigin.Begin);
      stream.Read(buffer, 0, 4);
      uint count = BigEndianBitConverter.ToUInt32(buffer, 0);
      _contentIds = new byte[count];
      for (int k = 0; k < count; ++k)
      {
        _contentIds[k] = (byte)stream.ReadByte();
      }

      stream.Read(buffer, 0, 4);
      uint contentLen = BigEndianBitConverter.ToUInt32(buffer, 0);
      _compressedContent = new byte[contentLen];
      stream.Read(_compressedContent, 0, (int)contentLen);
    }
  }
}