ImageSharp/SixLabors.Fonts/Unicode/BidiData.cs

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

using System;
using System.Collections.Generic;

namespace SixLabors.Fonts.Unicode {
  /// <summary>
  /// Represents a unicode string and all associated attributes
  /// for each character required for the Bidi algorithm
  /// </summary>
  internal class BidiData
  {
      private ArrayBuilder<BidiCharacterType> types;
      private ArrayBuilder<BidiPairedBracketType> pairedBracketTypes;
      private ArrayBuilder<int> pairedBracketValues;
      private ArrayBuilder<BidiCharacterType> savedTypes;
      private ArrayBuilder<BidiPairedBracketType> savedPairedBracketTypes;
      private ArrayBuilder<sbyte> tempLevelBuffer;
      private readonly List<int> paragraphPositions = new();

      public sbyte ParagraphEmbeddingLevel { get; private set; }

      public bool HasBrackets { get; private set; }

      public bool HasEmbeddings { get; private set; }

      public bool HasIsolates { get; private set; }

      /// <summary>
      /// Gets the length of the data held by the BidiData
      /// </summary>
      public int Length => this.types.Length;

      /// <summary>
      /// Gets the bidi character type of each code point
      /// </summary>
      public ArraySlice<BidiCharacterType> Types { get; private set; }

      /// <summary>
      /// Gets the paired bracket type for each code point
      /// </summary>
      public ArraySlice<BidiPairedBracketType> PairedBracketTypes { get; private set; }

      /// <summary>
      /// Gets the paired bracket value for code point
      /// </summary>
      /// <remarks>
      /// The paired bracket values are the code points
      /// of each character where the opening code point
      /// is replaced with the closing code point for easier
      /// matching.  Also, bracket code points are mapped
      /// to their canonical equivalents
      /// </remarks>
      public ArraySlice<int> PairedBracketValues { get; private set; }

      /// <summary>
      /// Initialize with a text value.
      /// </summary>
      /// <param name="text">The text to process.</param>
      /// <param name="paragraphEmbeddingLevel">The paragraph embedding level</param>
      public void Init(ReadOnlySpan<char> text, sbyte paragraphEmbeddingLevel)
      {
          // Set working buffer sizes
          // TODO: This allocates more than it should for some arrays.
          int length = CodePoint.GetCodePointCount(text);
          this.types.Length = length;
          this.pairedBracketTypes.Length = length;
          this.pairedBracketValues.Length = length;

          this.paragraphPositions.Clear();
          this.ParagraphEmbeddingLevel = paragraphEmbeddingLevel;

          // Resolve the BidiCharacterType, paired bracket type and paired
          // bracket values for all code points
          this.HasBrackets = false;
          this.HasEmbeddings = false;
          this.HasIsolates = false;

          int i = 0;
          var codePointEnumerator = new SpanCodePointEnumerator(text);
          while (codePointEnumerator.MoveNext())
          {
              CodePoint codePoint = codePointEnumerator.Current;
              BidiClass bidi = CodePoint.GetBidiClass(codePoint);

              // Look up BidiCharacterType
              BidiCharacterType dir = bidi.CharacterType;
              this.types[i] = dir;

              switch (dir)
              {
                  case BidiCharacterType.LeftToRightEmbedding:
                  case BidiCharacterType.LeftToRightOverride:
                  case BidiCharacterType.RightToLeftEmbedding:
                  case BidiCharacterType.RightToLeftOverride:
                  case BidiCharacterType.PopDirectionalFormat:
                      this.HasEmbeddings = true;
                      break;

                  case BidiCharacterType.LeftToRightIsolate:
                  case BidiCharacterType.RightToLeftIsolate:
                  case BidiCharacterType.FirstStrongIsolate:
                  case BidiCharacterType.PopDirectionalIsolate:
                      this.HasIsolates = true;
                      break;
              }

              // Lookup paired bracket types
              BidiPairedBracketType pbt = bidi.PairedBracketType;
              this.pairedBracketTypes[i] = pbt;

              if (pbt == BidiPairedBracketType.Open)
              {
                  // Opening bracket types can never have a null pairing.
                  bidi.TryGetPairedBracket(out CodePoint paired);
                  this.pairedBracketValues[i] = CodePoint.GetCanonicalType(paired).Value;

                  this.HasBrackets = true;
              }
              else if (pbt == BidiPairedBracketType.Close)
              {
                  this.pairedBracketValues[i] = CodePoint.GetCanonicalType(codePoint).Value;
                  this.HasBrackets = true;
              }

              i++;
          }

          // Create slices on work buffers
          this.Types = this.types.AsSlice();
          this.PairedBracketTypes = this.pairedBracketTypes.AsSlice();
          this.PairedBracketValues = this.pairedBracketValues.AsSlice();
      }

      /// <summary>
      /// Save the Types and PairedBracketTypes of this bididata
      /// </summary>
      /// <remarks>
      /// This is used when processing embedded style runs with
      /// BidiCharacterType overrides.  TextLayout saves the data,
      /// overrides the style runs to neutral, processes the bidi
      /// data for the entire paragraph and then restores this data
      /// before processing the embedded runs.
      /// </remarks>
      public void SaveTypes()
      {
          // Capture the types data
          this.savedTypes.Clear();
          this.savedTypes.Add(this.types.AsSlice());
          this.savedPairedBracketTypes.Clear();
          this.savedPairedBracketTypes.Add(this.pairedBracketTypes.AsSlice());
      }

      /// <summary>
      /// Restore the data saved by SaveTypes
      /// </summary>
      public void RestoreTypes()
      {
          this.types.Clear();
          this.types.Add(this.savedTypes.AsSlice());
          this.pairedBracketTypes.Clear();
          this.pairedBracketTypes.Add(this.savedPairedBracketTypes.AsSlice());
      }

      /// <summary>
      /// Gets a temporary level buffer. Used by TextLayout when
      /// resolving style runs with different BidiCharacterType.
      /// </summary>
      /// <param name="length">Length of the required ExpandableBuffer</param>
      /// <returns>An uninitialized level ExpandableBuffer</returns>
      public ArraySlice<sbyte> GetTempLevelBuffer(int length)
      {
          this.tempLevelBuffer.Clear();
          return this.tempLevelBuffer.Add(length, false);
      }
  }
}