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

using SixLabors.Fonts.Tables.AdvancedTypographic.Variations;
using System;

namespace SixLabors.Fonts.Tables.Cff {
  /// <summary>
  /// Represents the Compact Font Format (CFF) version 1 table.
  /// <see href="https://adobe-type-tools.github.io/font-tech-notes/pdfs/5176.CFF.pdf"/>
  /// </summary>
  internal sealed class Cff1Table : Table, ICffTable
  {
      internal const string TableName = "CFF "; // 4 chars

      private readonly CffGlyphData[] glyphs;

      /// <summary>
      /// Initializes a new instance of the <see cref="Cff1Table"/> class.
      /// </summary>
      /// <param name="cff1Font">The parsed CFF1 font.</param>
      public Cff1Table(CffFont cff1Font) => this.glyphs = cff1Font.Glyphs;

      /// <inheritdoc/>
      public int GlyphCount => this.glyphs.Length;

      /// <inheritdoc/>
      public ItemVariationStore? ItemVariationStore => null;

      /// <inheritdoc/>
      public CffGlyphData GetGlyph(int index)
          => this.glyphs[index];

      /// <summary>
      /// Loads the CFF1 table from the specified font reader.
      /// </summary>
      /// <param name="fontReader">The font reader.</param>
      /// <returns>The <see cref="Cff1Table"/>, or <see langword="null"/> if the table is not present.</returns>
      public static Cff1Table? Load(FontReader fontReader)
      {
          if (!fontReader.TryGetReaderAtTablePosition(TableName, out BigEndianBinaryReader? binaryReader))
          {
              return null;
          }

          using (binaryReader)
          {
              return Load(binaryReader);
          }
      }

      /// <summary>
      /// Loads the CFF1 table from the specified binary reader.
      /// </summary>
      /// <param name="reader">The big-endian binary reader positioned at the CFF1 table header.</param>
      /// <returns>The <see cref="Cff1Table"/>.</returns>
      public static Cff1Table Load(BigEndianBinaryReader reader)
      {
          // +------+---------------+----------------------------------------+
          // | Type | Name          | Description                            |
          // +======+===============+========================================+
          // | byte | majorVersion  | Format major version. Set to 1.        |
          // +------+---------------+----------------------------------------+
          // | byte | minorVersion  | Format minor version. Set to zero.     |
          // +------+---------------+----------------------------------------+
          // | byte | headerSize    | Header size (bytes).                   |
          // +------+---------------+----------------------------------------+
          // | byte | topDictLength | Length of Top DICT structure in bytes. |
          // +------+---------------+----------------------------------------+
          long position = reader.BaseStream.Position;
          byte[] header = reader.ReadBytes(4);
          byte major = header[0];
          byte minor = header[1];
          byte hdrSize = header[2];
          byte offSize = header[3];

          switch (major)
          {
              case 1:
                  Cff1Parser parser = new();
                  return new(parser.Load(reader, position));

              default:
                  throw new NotSupportedException();
          }
      }
  }
}