ImageSharp/SixLabors.Fonts/Tables/Cff/CffOperator.cs

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

using System;
using System.Collections.Generic;

namespace SixLabors.Fonts.Tables.Cff {
  /// <summary>
  /// Represents a CFF DICT operator with its name and operand kind.
  /// Operators are registered in a static dictionary keyed by their byte encoding
  /// and looked up during DICT parsing.
  /// <see href="https://adobe-type-tools.github.io/font-tech-notes/pdfs/5176.CFF.pdf"/>
  /// </summary>
  internal sealed class CFFOperator
  {
      private static readonly Lazy<Dictionary<int, CFFOperator>> RegisteredOperators = new(CreateDictionary, true);

      /// <summary>
      /// Initializes a new instance of the <see cref="CFFOperator"/> class.
      /// </summary>
      /// <param name="name">The operator name.</param>
      /// <param name="operandKind">The expected operand format.</param>
      private CFFOperator(string name, OperatorOperandKind operandKind)
      {
          this.Name = name;
          this.OperandKind = operandKind;
      }

      /// <summary>
      /// Gets the name of the operator (e.g. "CharStrings", "FontMatrix", "Private").
      /// </summary>
      public string Name { get; }

      /// <summary>
      /// Gets the expected operand format for this operator.
      /// </summary>
      public OperatorOperandKind OperandKind { get; }

      /// <summary>
      /// Looks up a registered CFF operator by its one- or two-byte encoding.
      /// </summary>
      /// <param name="b0">The first byte of the operator.</param>
      /// <param name="b1">The second byte (0 for single-byte operators, or 12 prefix byte value).</param>
      /// <returns>The matching <see cref="CFFOperator"/>, or <see langword="null"/> if not found.</returns>
      public static CFFOperator GetOperatorByKey(byte b0, byte b1)
      {
          RegisteredOperators.Value.TryGetValue((b1 << 8) | b0, out CFFOperator? found);
          return found!;
      }

      /// <summary>
      /// Creates the dictionary of all registered CFF DICT operators, keyed by their byte encoding.
      /// </summary>
      /// <returns>The dictionary of registered operators.</returns>
      private static Dictionary<int, CFFOperator> CreateDictionary()
      {
          Dictionary<int, CFFOperator> dictionary = [];

          // Table 9: Top DICT Operator Entries
          Register(dictionary, 0, "version", OperatorOperandKind.SID);
          Register(dictionary, 1, "Notice", OperatorOperandKind.SID);
          Register(dictionary, 12, 0, "Copyright", OperatorOperandKind.SID);
          Register(dictionary, 2, "FullName", OperatorOperandKind.SID);
          Register(dictionary, 3, "FamilyName", OperatorOperandKind.SID);
          Register(dictionary, 4, "Weight", OperatorOperandKind.SID);
          Register(dictionary, 12, 1, "isFixedPitch", OperatorOperandKind.Boolean);
          Register(dictionary, 12, 2, "ItalicAngle", OperatorOperandKind.Number);
          Register(dictionary, 12, 3, "UnderlinePosition", OperatorOperandKind.Number);
          Register(dictionary, 12, 4, "UnderlineThickness", OperatorOperandKind.Number);
          Register(dictionary, 12, 5, "PaintType", OperatorOperandKind.Number);
          Register(dictionary, 12, 6, "CharstringType", OperatorOperandKind.Number); // default value 2
          Register(dictionary, 12, 7, "FontMatrix", OperatorOperandKind.Array);
          Register(dictionary, 13, "UniqueID", OperatorOperandKind.Number);
          Register(dictionary, 5, "FontBBox", OperatorOperandKind.Array);
          Register(dictionary, 12, 8, "StrokeWidth", OperatorOperandKind.Number);
          Register(dictionary, 14, "XUID", OperatorOperandKind.Array);
          Register(dictionary, 15, "charset", OperatorOperandKind.Number);
          Register(dictionary, 16, "Encoding", OperatorOperandKind.Number);
          Register(dictionary, 17, "CharStrings", OperatorOperandKind.Number);
          Register(dictionary, 18, "Private", OperatorOperandKind.NumberNumber);
          Register(dictionary, 12, 20, "SyntheticBase", OperatorOperandKind.Number);
          Register(dictionary, 12, 21, "PostScript", OperatorOperandKind.SID);
          Register(dictionary, 12, 22, "BaseFontName", OperatorOperandKind.SID);
          Register(dictionary, 12, 23, "BaseFontBlend", OperatorOperandKind.SID);

          // Table 10: CIDFont Operator Extensions
          Register(dictionary, 12, 30, "ROS", OperatorOperandKind.SID_SID_Number);
          Register(dictionary, 12, 31, "CIDFontVersion", OperatorOperandKind.Number);
          Register(dictionary, 12, 32, "CIDFontRevision", OperatorOperandKind.Number);
          Register(dictionary, 12, 33, "CIDFontType", OperatorOperandKind.Number);
          Register(dictionary, 12, 34, "CIDCount", OperatorOperandKind.Number);
          Register(dictionary, 12, 35, "UIDBase", OperatorOperandKind.Number);
          Register(dictionary, 12, 36, "FDArray", OperatorOperandKind.Number);
          Register(dictionary, 12, 37, "FDSelect", OperatorOperandKind.Number);
          Register(dictionary, 12, 38, "FontName", OperatorOperandKind.SID);

          // Table 23: Private DICT Operators
          Register(dictionary, 6, "BlueValues", OperatorOperandKind.Delta);
          Register(dictionary, 7, "OtherBlues", OperatorOperandKind.Delta);
          Register(dictionary, 8, "FamilyBlues", OperatorOperandKind.Delta);
          Register(dictionary, 9, "FamilyOtherBlues", OperatorOperandKind.Delta);
          Register(dictionary, 12, 9, "BlueScale", OperatorOperandKind.Number);
          Register(dictionary, 12, 10, "BlueShift", OperatorOperandKind.Number);
          Register(dictionary, 12, 11, "BlueFuzz", OperatorOperandKind.Number);
          Register(dictionary, 10, "StdHW", OperatorOperandKind.Number);
          Register(dictionary, 11, "StdVW", OperatorOperandKind.Number);
          Register(dictionary, 12, 12, "StemSnapH", OperatorOperandKind.Delta);
          Register(dictionary, 12, 13, "StemSnapV", OperatorOperandKind.Delta);
          Register(dictionary, 12, 14, "ForceBold", OperatorOperandKind.Boolean);

          // reserved 12 15
          // reserved 12 16
          Register(dictionary, 12, 17, "LanguageGroup", OperatorOperandKind.Number);
          Register(dictionary, 12, 18, "ExpansionFactor", OperatorOperandKind.Number);
          Register(dictionary, 12, 19, "initialRandomSeed", OperatorOperandKind.Number);

          Register(dictionary, 19, "Subrs", OperatorOperandKind.Number);
          Register(dictionary, 20, "defaultWidthX", OperatorOperandKind.Number);
          Register(dictionary, 21, "nominalWidthX", OperatorOperandKind.Number);

          // CFF2 operators
          Register(dictionary, 22, "vsindex", OperatorOperandKind.Number);
          Register(dictionary, 23, "blend", OperatorOperandKind.Number);
          Register(dictionary, 24, "vstore", OperatorOperandKind.Number);

          return dictionary;
      }

      /// <summary>
      /// Registers a two-byte CFF DICT operator.
      /// </summary>
      /// <param name="dictionary">The operator dictionary.</param>
      /// <param name="b0">The first byte of the operator (always 12 for two-byte operators).</param>
      /// <param name="b1">The second byte of the operator.</param>
      /// <param name="name">The operator name.</param>
      /// <param name="operandKind">The expected operand format.</param>
      private static void Register(Dictionary<int, CFFOperator> dictionary, byte b0, byte b1, string name, OperatorOperandKind operandKind)
          => dictionary.Add((b1 << 8) | b0, new CFFOperator(name, operandKind));

      /// <summary>
      /// Registers a single-byte CFF DICT operator.
      /// </summary>
      /// <param name="dictionary">The operator dictionary.</param>
      /// <param name="b0">The operator byte value.</param>
      /// <param name="name">The operator name.</param>
      /// <param name="operandKind">The expected operand format.</param>
      private static void Register(Dictionary<int, CFFOperator> dictionary, byte b0, string name, OperatorOperandKind operandKind)
          => dictionary.Add(b0, new CFFOperator(name, operandKind));

#if DEBUG
      /// <inheritdoc/>
      public override string ToString() => this.Name;
#endif
  }
}