// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

using System.IO;

namespace SixLabors.Fonts.Tables.Woff {
  /// <summary>
  /// Represents a table directory entry in a WOFF1 font file.
  /// Each entry describes a single font table within the WOFF container,
  /// including its compressed and original lengths.
  /// See: <see href="https://www.w3.org/TR/WOFF/#TableDirectory"/>.
  /// </summary>
  internal sealed class WoffTableHeader : TableHeader
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="WoffTableHeader"/> class.
      /// </summary>
      /// <param name="tag">The 4-byte sfnt table identifier.</param>
      /// <param name="offset">The offset to the data from the beginning of the WOFF file.</param>
      /// <param name="compressedLength">The length of the compressed table data, excluding padding.</param>
      /// <param name="origLength">The length of the uncompressed table data, excluding padding.</param>
      /// <param name="checkSum">The checksum of the uncompressed table data.</param>
      public WoffTableHeader(string tag, uint offset, uint compressedLength, uint origLength, uint checkSum)
          : base(tag, checkSum, offset, origLength)
          => this.CompressedLength = compressedLength;

      /// <summary>
      /// Gets the length of the compressed table data, excluding padding.
      /// </summary>
      public uint CompressedLength { get; }

      /// <summary>
      /// Creates a <see cref="BigEndianBinaryReader"/> for the table data, decompressing with zlib if necessary.
      /// </summary>
      /// <param name="stream">The stream containing the WOFF font data.</param>
      /// <returns>A <see cref="BigEndianBinaryReader"/> positioned at the start of the uncompressed table data.</returns>
      public override BigEndianBinaryReader CreateReader(Stream stream)
      {
          // Stream is not compressed.
          if (this.Length == this.CompressedLength)
          {
              return base.CreateReader(stream);
          }

          // Read all data from the compressed stream.
          stream.Seek(this.Offset, SeekOrigin.Begin);
          using var compressedStream = new IO.ZlibInflateStream(stream);
          byte[] uncompressedBytes = new byte[this.Length];
          int totalBytesRead = 0;
          int bytesLeftToRead = uncompressedBytes.Length;
          while (totalBytesRead < this.Length)
          {
              int bytesRead = compressedStream.Read(uncompressedBytes, totalBytesRead, bytesLeftToRead);
              if (bytesRead <= 0)
              {
                  throw new InvalidFontFileException($"Could not read compressed data! Expected bytes: {this.Length}, bytes read: {totalBytesRead}");
              }

              totalBytesRead += bytesRead;
              bytesLeftToRead -= bytesRead;
          }

          var memoryStream = new MemoryStream(uncompressedBytes);
          return new BigEndianBinaryReader(memoryStream, false);
      }

      // WOFF TableDirectoryEntry
      // UInt32 | tag          | 4-byte sfnt table identifier.
      // UInt32 | offset       | Offset to the data, from beginning of WOFF file.
      // UInt32 | compLength   | Length of the compressed data, excluding padding.
      // UInt32 | origLength   | Length of the uncompressed table, excluding padding.
      // UInt32 | origChecksum | Checksum of the uncompressed table.

      /// <summary>
      /// Reads a <see cref="WoffTableHeader"/> from the given reader.
      /// </summary>
      /// <param name="reader">The big-endian binary reader.</param>
      /// <returns>The parsed <see cref="WoffTableHeader"/>.</returns>
      public static new WoffTableHeader Read(BigEndianBinaryReader reader) =>
          new WoffTableHeader(
              reader.ReadTag(),
              reader.ReadUInt32(),
              reader.ReadUInt32(),
              reader.ReadUInt32(),
              reader.ReadUInt32());
  }
}