private void ResolveExplicitEmbeddingLevels()

in src/Avalonia.Base/Media/TextFormatting/Unicode/BiDiAlgorithm.cs [410:641]
180 lines of code
48 McCabe index (conditional complexity)

        private void ResolveExplicitEmbeddingLevels()
        {
            // Redundant?
            if (!_hasIsolates && !_hasEmbeddings)
            {
                return;
            }

            // Work variables
            _statusStack.Clear();
            var overflowIsolateCount = 0;
            var overflowEmbeddingCount = 0;
            var validIsolateCount = 0;

            // Constants
            const int maxStackDepth = 125;

            // Rule X1 - setup initial state
            _statusStack.Clear();

            // Neutral
            _statusStack.Push(new Status(_paragraphEmbeddingLevel, BidiClass.OtherNeutral, false));

            // Process all characters
            for (var i = 0; i < _originalClasses.Length; i++)
            {
                switch (_originalClasses[i])
                {
                    case BidiClass.RightToLeftEmbedding:
                    {
                        // Rule X2
                        var newLevel = (sbyte)((_statusStack.Peek().EmbeddingLevel + 1) | 1);
                        if (newLevel <= maxStackDepth && overflowIsolateCount == 0 && overflowEmbeddingCount == 0)
                        {
                            _statusStack.Push(new Status(newLevel, BidiClass.OtherNeutral, false));
                            _resolvedLevels[i] = newLevel;
                        }
                        else if (overflowIsolateCount == 0)
                        {
                            overflowEmbeddingCount++;
                        }

                        break;
                    }

                    case BidiClass.LeftToRightEmbedding:
                    {
                        // Rule X3
                        var newLevel = (sbyte)((_statusStack.Peek().EmbeddingLevel + 2) & ~1);
                        if (newLevel < maxStackDepth && overflowIsolateCount == 0 && overflowEmbeddingCount == 0)
                        {
                            _statusStack.Push(new Status(newLevel, BidiClass.OtherNeutral, false));
                            _resolvedLevels[i] = newLevel;
                        }
                        else if (overflowIsolateCount == 0)
                        {
                            overflowEmbeddingCount++;
                        }

                        break;
                    }

                    case BidiClass.RightToLeftOverride:
                    {
                        // Rule X4
                        var newLevel = (sbyte)((_statusStack.Peek().EmbeddingLevel + 1) | 1);
                        if (newLevel <= maxStackDepth && overflowIsolateCount == 0 && overflowEmbeddingCount == 0)
                        {
                            _statusStack.Push(new Status(newLevel, BidiClass.RightToLeft, false));
                            _resolvedLevels[i] = newLevel;
                        }
                        else if (overflowIsolateCount == 0)
                        {
                            overflowEmbeddingCount++;
                        }

                        break;
                    }

                    case BidiClass.LeftToRightOverride:
                    {
                        // Rule X5
                        var newLevel = (sbyte)((_statusStack.Peek().EmbeddingLevel + 2) & ~1);
                        if (newLevel <= maxStackDepth && overflowIsolateCount == 0 && overflowEmbeddingCount == 0)
                        {
                            _statusStack.Push(new Status(newLevel, BidiClass.LeftToRight, false));
                            _resolvedLevels[i] = newLevel;
                        }
                        else if (overflowIsolateCount == 0)
                        {
                            overflowEmbeddingCount++;
                        }

                        break;
                    }

                    case BidiClass.RightToLeftIsolate:
                    case BidiClass.LeftToRightIsolate:
                    case BidiClass.FirstStrongIsolate:
                    {
                        // Rule X5a, X5b and X5c
                        var resolvedIsolate = _originalClasses[i];

                        if (resolvedIsolate == BidiClass.FirstStrongIsolate)
                        {
                            if (!_isolatePairs.TryGetValue(i, out var endOfIsolate))
                            {
                                endOfIsolate = _originalClasses.Length;
                            }

                            // Rule X5c
                            if (ResolveEmbeddingLevel(_originalClasses.Slice(i + 1,endOfIsolate - (i + 1))) == 1)
                            {
                                resolvedIsolate = BidiClass.RightToLeftIsolate;
                            }
                            else
                            {
                                resolvedIsolate = BidiClass.LeftToRightIsolate;
                            }
                        }

                        // Replace RLI's level with current embedding level
                        var tos = _statusStack.Peek();
                        _resolvedLevels[i] = tos.EmbeddingLevel;

                        // Apply override
                        if (tos.OverrideStatus != BidiClass.OtherNeutral)
                        {
                            _workingClasses[i] = tos.OverrideStatus;
                        }

                        // Work out new level
                        sbyte newLevel;
                        if (resolvedIsolate == BidiClass.RightToLeftIsolate)
                        {
                            newLevel = (sbyte)((tos.EmbeddingLevel + 1) | 1);
                        }
                        else
                        {
                            newLevel = (sbyte)((tos.EmbeddingLevel + 2) & ~1);
                        }

                        // Valid?
                        if (newLevel <= maxStackDepth && overflowIsolateCount == 0 && overflowEmbeddingCount == 0)
                        {
                            validIsolateCount++;
                            _statusStack.Push(new Status(newLevel, BidiClass.OtherNeutral, true));
                        }
                        else
                        {
                            overflowIsolateCount++;
                        }

                        break;
                    }

                    case BidiClass.BoundaryNeutral:
                    {
                        // Mentioned in rule X6 - "for all types besides ..., BN, ..."
                        // no-op
                        break;
                    }

                    default:
                    {
                        // Rule X6
                        var tos = _statusStack.Peek();
                        _resolvedLevels[i] = tos.EmbeddingLevel;
                        if (tos.OverrideStatus != BidiClass.OtherNeutral)
                        {
                            _workingClasses[i] = tos.OverrideStatus;
                        }

                        break;
                    }

                    case BidiClass.PopDirectionalIsolate:
                    {
                        // Rule X6a
                        if (overflowIsolateCount > 0)
                        {
                            overflowIsolateCount--;
                        }
                        else if (validIsolateCount != 0)
                        {
                            overflowEmbeddingCount = 0;
                            while (!_statusStack.Peek().IsolateStatus)
                            {
                                _statusStack.Pop();
                            }

                            _statusStack.Pop();
                            validIsolateCount--;
                        }

                        var tos = _statusStack.Peek();
                        _resolvedLevels[i] = tos.EmbeddingLevel;
                        if (tos.OverrideStatus != BidiClass.OtherNeutral)
                        {
                            _workingClasses[i] = tos.OverrideStatus;
                        }

                        break;
                    }

                    case BidiClass.PopDirectionalFormat:
                    {
                        // Rule X7
                        if (overflowIsolateCount == 0)
                        {
                            if (overflowEmbeddingCount > 0)
                            {
                                overflowEmbeddingCount--;
                            }
                            else if (!_statusStack.Peek().IsolateStatus && _statusStack.Count >= 2)
                            {
                                _statusStack.Pop();
                            }
                        }

                        break;
                    }

                    case BidiClass.ParagraphSeparator:
                    {
                        // Rule X8
                        _resolvedLevels[i] = _paragraphEmbeddingLevel;
                        break;
                    }
                }
            }
        }