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jongallowayjongalloway
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Merge pull request #19 from jongalloway/mermaid-parser-facade
Refactor Mermaid parser into facade and flowchart subparser
2 parents 602045b + 066dc47 commit cb6a281

6 files changed

Lines changed: 411 additions & 295 deletions

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‎src/DiagramForge/Parsers/Mermaid/IMermaidDiagramParser.cs‎

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using DiagramForge.Models;
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namespace DiagramForge.Parsers.Mermaid;
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internal interface IMermaidDiagramParser
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{
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bool CanParse(MermaidDiagramKind kind);
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Diagram Parse(MermaidDocument document);
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}

‎src/DiagramForge/Parsers/Mermaid/MermaidDiagramKind.cs‎

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namespace DiagramForge.Parsers.Mermaid;
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internal enum MermaidDiagramKind
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{
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Unknown,
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Flowchart,
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}

‎src/DiagramForge/Parsers/Mermaid/MermaidDocument.cs‎

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using DiagramForge.Abstractions;
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namespace DiagramForge.Parsers.Mermaid;
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internal sealed class MermaidDocument
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{
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private MermaidDocument(MermaidDiagramKind kind, string headerLine, string[] lines)
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{
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Kind = kind;
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HeaderLine = headerLine;
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Lines = lines;
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}
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public MermaidDiagramKind Kind { get; }
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public string HeaderLine { get; }
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public string[] Lines { get; }
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public static bool TryParse(string diagramText, [System.Diagnostics.CodeAnalysis.NotNullWhen(true)] out MermaidDocument? document)
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{
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document = null;
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if (string.IsNullOrWhiteSpace(diagramText))
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return false;
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var lines = diagramText
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.Split('\n')
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.Select(line => line.Trim())
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.Where(line => !string.IsNullOrEmpty(line) && !line.StartsWith("%%", StringComparison.Ordinal))
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.ToArray();
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if (lines.Length == 0)
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return false;
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var headerLine = lines[0];
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if (!TryDetectKind(headerLine, out var kind))
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return false;
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document = new MermaidDocument(kind, headerLine, lines);
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return true;
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}
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// Known Mermaid diagram-type keywords (lowercased) that are recognized but not yet
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// supported by any registered IMermaidDiagramParser. Detecting them as Unknown lets
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// MermaidParser emit a specific "unsupported type" error instead of a generic one.
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private static readonly HashSet<string> KnownUnsupportedMermaidKeywords = new(StringComparer.Ordinal)
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{
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"sequencediagram",
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"classdiagram",
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"statediagram",
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"statediagram-v2",
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"erdiagram",
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"journey",
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"gantt",
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"pie",
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"gitgraph",
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"mindmap",
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"timeline",
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"quadrantchart",
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"requirementdiagram",
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"block-beta",
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"packet-beta",
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"architecture-beta",
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"kanban",
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"sankey-beta",
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"xychart-beta",
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"zenuml",
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};
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public static MermaidDocument Parse(string diagramText)
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{
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if (TryParse(diagramText, out var document))
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return document;
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if (string.IsNullOrWhiteSpace(diagramText))
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throw new DiagramParseException("Diagram text cannot be null or whitespace.");
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var firstContentLine = diagramText
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.Split('\n')
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.Select(line => line.Trim())
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.FirstOrDefault(line => !string.IsNullOrEmpty(line) && !line.StartsWith("%%", StringComparison.Ordinal));
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if (firstContentLine is null)
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throw new DiagramParseException("Diagram text cannot be empty or contain only comments.");
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throw new DiagramParseException($"Unsupported Mermaid diagram type '{firstContentLine}'.");
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}
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private static bool TryDetectKind(string headerLine, out MermaidDiagramKind kind)
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{
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var normalizedHeader = headerLine.Trim().ToLowerInvariant();
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if (normalizedHeader.StartsWith("graph ", StringComparison.Ordinal)
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|| normalizedHeader.StartsWith("flowchart ", StringComparison.Ordinal)
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|| normalizedHeader.Equals("graph", StringComparison.Ordinal)
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|| normalizedHeader.Equals("flowchart", StringComparison.Ordinal))
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{
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kind = MermaidDiagramKind.Flowchart;
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return true;
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}
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var spaceIndex = normalizedHeader.IndexOf(' ');
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var keyword = spaceIndex >= 0 ? normalizedHeader[..spaceIndex] : normalizedHeader;
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if (KnownUnsupportedMermaidKeywords.Contains(keyword))
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{
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kind = MermaidDiagramKind.Unknown;
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return true;
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}
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kind = default;
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return false;
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}
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}

‎src/DiagramForge/Parsers/Mermaid/MermaidFlowchartParser.cs‎

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using DiagramForge.Abstractions;
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using DiagramForge.Models;
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namespace DiagramForge.Parsers.Mermaid;
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internal sealed class MermaidFlowchartParser : IMermaidDiagramParser
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{
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public bool CanParse(MermaidDiagramKind kind) => kind == MermaidDiagramKind.Flowchart;
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public Diagram Parse(MermaidDocument document)
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{
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var builder = new DiagramSemanticModelBuilder()
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.WithSourceSyntax("mermaid")
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.WithDiagramType("flowchart");
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var direction = ParseDirection(document.HeaderLine.ToLowerInvariant());
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builder.WithLayoutHints(new LayoutHints { Direction = direction });
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var nodesSeen = new Dictionary<string, Node>(StringComparer.Ordinal);
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var groupStack = new Stack<(Group group, HashSet<string> members)>();
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int autoSubgraphId = 0;
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Node GetOrCreateNode(string id, string label)
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{
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if (!nodesSeen.TryGetValue(id, out var node))
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{
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node = new Node(id, label);
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nodesSeen[id] = node;
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builder.AddNode(node);
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}
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foreach (var frame in groupStack)
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frame.members.Add(id);
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return node;
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}
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void CloseGroup()
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{
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var (group, members) = groupStack.Pop();
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group.ChildNodeIds.AddRange(members.OrderBy(member => member, StringComparer.Ordinal));
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builder.AddGroup(group);
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}
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for (int i = 1; i < document.Lines.Length; i++)
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{
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var line = document.Lines[i];
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if (line.StartsWith("subgraph", StringComparison.OrdinalIgnoreCase)
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&& (line.Length == 8 || char.IsWhiteSpace(line[8])))
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{
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var (id, title) = ParseSubgraphHeader(line.Length > 8 ? line[8..] : string.Empty);
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id ??= $"__subgraph{autoSubgraphId++}";
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groupStack.Push((new Group(id, title), new HashSet<string>(StringComparer.Ordinal)));
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continue;
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}
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if (line.Equals("end", StringComparison.OrdinalIgnoreCase))
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{
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if (groupStack.Count > 0)
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CloseGroup();
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continue;
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}
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if (groupStack.Count > 0
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&& line.StartsWith("direction ", StringComparison.OrdinalIgnoreCase))
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continue;
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ParseLine(line, builder, GetOrCreateNode);
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}
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while (groupStack.Count > 0)
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CloseGroup();
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return builder.Build();
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}
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private static LayoutDirection ParseDirection(string headerLine)
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{
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if (headerLine.Contains(" lr", StringComparison.Ordinal)) return LayoutDirection.LeftToRight;
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if (headerLine.Contains(" rl", StringComparison.Ordinal)) return LayoutDirection.RightToLeft;
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if (headerLine.Contains(" bt", StringComparison.Ordinal)) return LayoutDirection.BottomToTop;
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return LayoutDirection.TopToBottom;
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}
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private static void ParseLine(
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string line,
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IDiagramSemanticModelBuilder builder,
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Func<string, string, Node> getOrCreate)
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{
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string[] edgeOps = ["--->", "-->>", "-.->", "==>", "===", "-->", "-.-", "---"];
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string? matchedOp = null;
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int opIndex = -1;
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foreach (var op in edgeOps)
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{
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int idx = line.IndexOf(op, StringComparison.Ordinal);
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if (idx >= 0 && (opIndex < 0 || idx < opIndex || (idx == opIndex && op.Length > matchedOp!.Length)))
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{
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opIndex = idx;
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matchedOp = op;
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}
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}
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if (matchedOp is not null)
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{
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var left = line[..opIndex].Trim();
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var right = line[(opIndex + matchedOp.Length)..].Trim();
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string? edgeLabel = null;
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int pipeIdx = left.IndexOf('|');
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if (pipeIdx >= 0)
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{
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edgeLabel = left[(pipeIdx + 1)..].TrimEnd('|').Trim();
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left = left[..pipeIdx].Trim();
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}
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else if (right.StartsWith('|'))
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{
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int endPipe = right.IndexOf('|', 1);
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if (endPipe > 0)
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{
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edgeLabel = right[1..endPipe].Trim();
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right = right[(endPipe + 1)..].Trim();
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}
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}
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var (srcId, srcLabel, srcShape) = ParseNodeDeclaration(left);
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var (tgtId, tgtLabel, tgtShape) = ParseNodeDeclaration(right);
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var srcNode = getOrCreate(srcId, srcLabel);
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if (srcShape.HasValue) srcNode.Shape = srcShape.Value;
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var tgtNode = getOrCreate(tgtId, tgtLabel);
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if (tgtShape.HasValue) tgtNode.Shape = tgtShape.Value;
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var edge = new Edge(srcId, tgtId);
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if (edgeLabel is not null)
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edge.Label = new Label(edgeLabel);
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edge.LineStyle = matchedOp.Contains('=') ? EdgeLineStyle.Thick
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: matchedOp.Contains('.') ? EdgeLineStyle.Dotted
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: EdgeLineStyle.Solid;
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edge.ArrowHead = matchedOp.Contains('>') ? ArrowHeadStyle.Arrow : ArrowHeadStyle.None;
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builder.AddEdge(edge);
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return;
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}
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var (id, label, shape) = ParseNodeDeclaration(line);
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if (!string.IsNullOrEmpty(id))
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{
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var node = getOrCreate(id, label);
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if (shape.HasValue) node.Shape = shape.Value;
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}
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}
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private static (string id, string label, Shape? shape) ParseNodeDeclaration(string token)
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{
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token = token.Trim();
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if (string.IsNullOrEmpty(token))
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return (string.Empty, string.Empty, null);
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int bracketStart = -1;
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for (int i = 0; i < token.Length; i++)
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{
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char c = token[i];
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if (c == '[' || c == '(' || c == '{' || c == '>')
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{
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bracketStart = i;
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break;
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}
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}
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if (bracketStart < 0)
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return (token, token, null);
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var id = token[..bracketStart].Trim();
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var rest = token[bracketStart..].Trim();
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Shape? shape = rest.StartsWith("((", StringComparison.Ordinal) ? Shape.Circle
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: rest[0] == '[' ? Shape.Rectangle
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: rest[0] == '(' ? Shape.RoundedRectangle
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: rest[0] == '{' ? Shape.Diamond
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: (Shape?)null;
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var label = rest
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.TrimStart('[', '(', '{', '>')
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.TrimEnd(']', ')', '}', '<')
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.Trim('"');
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return (id, string.IsNullOrEmpty(label) ? id : label, shape);
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}
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private static (string? id, string title) ParseSubgraphHeader(string remainder)
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{
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remainder = remainder.Trim();
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if (remainder.Length == 0)
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return (null, string.Empty);
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int sqStart = remainder.IndexOf('[');
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if (sqStart >= 0)
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{
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int sqEnd = remainder.LastIndexOf(']');
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if (sqEnd > sqStart)
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{
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string idPart = remainder[..sqStart].Trim();
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string title = remainder[(sqStart + 1)..sqEnd].Trim().Trim('"');
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return (idPart.Length > 0 ? idPart : null, title);
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}
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}
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if (remainder.Length >= 2 && remainder[0] == '"' && remainder[^1] == '"')
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return (null, remainder[1..^1]);
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if (!remainder.Any(char.IsWhiteSpace))
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return (remainder, remainder);
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return (null, remainder);
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}
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}

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