ImageSharp/SixLabors.Fonts/Tables/TableLoader.cs

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

using SixLabors.Fonts.Tables.AdvancedTypographic;
using SixLabors.Fonts.Tables.AdvancedTypographic.Variations;
using SixLabors.Fonts.Tables.Cff;
using SixLabors.Fonts.Tables.General;
using SixLabors.Fonts.Tables.General.Colr;
using SixLabors.Fonts.Tables.General.Kern;
using SixLabors.Fonts.Tables.General.Name;
using SixLabors.Fonts.Tables.General.Post;
using SixLabors.Fonts.Tables.General.Svg;
using SixLabors.Fonts.Tables.TrueType;
using SixLabors.Fonts.Tables.TrueType.Glyphs;
using SixLabors.Fonts.Tables.TrueType.Hinting;
using System;
using System.Collections.Generic;

namespace SixLabors.Fonts.Tables {
  /// <summary>
  /// Provides registration and loading of font tables by tag or CLR type.
  /// Maps four-byte table tags (e.g. "cmap", "head") to their static <c>Load</c> factory methods.
  /// </summary>
  internal class TableLoader
  {
      private readonly Dictionary<string, Func<FontReader, Table?>> loaders = [];
      private readonly Dictionary<Type, string> types = [];
      private readonly Dictionary<Type, Func<FontReader, Table?>> typesLoaders = [];

      /// <summary>
      /// Initializes a new instance of the <see cref="TableLoader"/> class
      /// with all known table parsers registered.
      /// </summary>
      public TableLoader()
      {
          // We will hard code mapping registration in here for all the tables
          this.Register(NameTable.TableName, NameTable.Load);
          this.Register(CMapTable.TableName, CMapTable.Load);
          this.Register(HeadTable.TableName, HeadTable.Load);
          this.Register(HorizontalHeadTable.TableName, HorizontalHeadTable.Load);
          this.Register(HorizontalMetricsTable.TableName, HorizontalMetricsTable.Load);
          this.Register(VerticalHeadTable.TableName, VerticalHeadTable.Load);
          this.Register(VerticalMetricsTable.TableName, VerticalMetricsTable.Load);
          this.Register(MaximumProfileTable.TableName, MaximumProfileTable.Load);
          this.Register(OS2Table.TableName, OS2Table.Load);
          this.Register(IndexLocationTable.TableName, IndexLocationTable.Load);
          this.Register(GlyphTable.TableName, GlyphTable.Load);
          this.Register(KerningTable.TableName, KerningTable.Load);
          this.Register(ColrTable.TableName, ColrTable.Load);
          this.Register(CpalTable.TableName, CpalTable.Load);
          this.Register(GPosTable.TableName, GPosTable.Load);
          this.Register(GSubTable.TableName, GSubTable.Load);
          this.Register(CvtTable.TableName, CvtTable.Load);
          this.Register(FpgmTable.TableName, FpgmTable.Load);
          this.Register(PrepTable.TableName, PrepTable.Load);
          this.Register(GlyphDefinitionTable.TableName, GlyphDefinitionTable.Load);
          this.Register(PostTable.TableName, PostTable.Load);
          this.Register(Cff1Table.TableName, Cff1Table.Load);
          this.Register(Cff2Table.TableName, Cff2Table.Load);
          this.Register(AVarTable.TableName, AVarTable.Load);
          this.Register(GVarTable.TableName, GVarTable.Load);
          this.Register(FVarTable.TableName, FVarTable.Load);
          this.Register(HVarTable.TableName, HVarTable.Load);
          this.Register(VVarTable.TableName, VVarTable.Load);
          this.Register(MVarTable.TableName, MVarTable.Load);
          this.Register<CVarTable>(CVarTable.TableName, _ => null);
          this.Register(SvgTable.TableName, SvgTable.Load);
      }

      /// <summary>
      /// Gets the default shared <see cref="TableLoader"/> instance with all standard tables registered.
      /// </summary>
      public static TableLoader Default { get; } = new();

      /// <summary>
      /// Gets the four-byte tag string associated with the given table type.
      /// </summary>
      /// <param name="type">The CLR type of the table.</param>
      /// <returns>The tag string, or <see langword="null"/> if the type is not registered.</returns>
      public string? GetTag(Type type)
      {
          this.types.TryGetValue(type, out string? value);

          return value;
      }

      /// <summary>
      /// Gets the four-byte tag string associated with the given table type.
      /// </summary>
      /// <typeparam name="TType">The CLR type of the table.</typeparam>
      /// <returns>The tag string.</returns>
      public string GetTag<TType>()
      {
          this.types.TryGetValue(typeof(TType), out string? value);
          return value!;
      }

      /// <summary>
      /// Gets all registered table CLR types.
      /// </summary>
      internal IEnumerable<Type> RegisteredTypes() => this.types.Keys;

      /// <summary>
      /// Gets all registered four-byte table tags.
      /// </summary>
      internal IEnumerable<string> RegisteredTags() => this.types.Values;

      private void Register<T>(string tag, Func<FontReader, T?> createFunc)
          where T : Table
      {
          lock (this.loaders)
          {
              if (!this.loaders.ContainsKey(tag))
              {
                  this.loaders.Add(tag, createFunc);
                  this.types.Add(typeof(T), tag);
                  this.typesLoaders.Add(typeof(T), createFunc);
              }
          }
      }

      /// <summary>
      /// Loads a table by its four-byte tag string.
      /// Returns an <see cref="UnknownTable"/> if no parser is registered for the tag.
      /// </summary>
      /// <param name="tag">The four-byte table tag.</param>
      /// <param name="reader">The font reader.</param>
      /// <returns>The loaded table, or an <see cref="UnknownTable"/> for unrecognized tags.</returns>
      internal Table? Load(string tag, FontReader reader)

           // loader missing? register an unknown type loader and carry on
           => this.loaders.TryGetValue(tag, out Func<FontReader, Table?>? func)
              ? func.Invoke(reader)
              : new UnknownTable(tag);

      /// <summary>
      /// Loads a table by its CLR type.
      /// </summary>
      /// <typeparam name="TTable">The table type to load.</typeparam>
      /// <param name="reader">The font reader.</param>
      /// <returns>The loaded table instance, or <see langword="null"/>.</returns>
      /// <exception cref="MissingFontTableException">Thrown when the table type has not been registered.</exception>
      internal TTable? Load<TTable>(FontReader reader)
          where TTable : Table
      {
          // loader missing register an unknown type loader and carry on
          if (this.typesLoaders.TryGetValue(typeof(TTable), out Func<FontReader, Table?>? func))
          {
              return (TTable?)func.Invoke(reader);
          }

          throw new MissingFontTableException("Font table not registered.", nameof(TTable));
      }
  }
}