feat: add Mermaid class diagram parser (#86)

Co-authored-by: jongalloway <68539+jongalloway@users.noreply.github.com>

Author: Copilot

src/DiagramForge/Parsers/Mermaid/MermaidClassDiagramParser.cs

@@ -0,0 +1,334 @@
+using DiagramForge.Abstractions;
+using DiagramForge.Models;
+
+namespace DiagramForge.Parsers.Mermaid;
+
+internal sealed class MermaidClassDiagramParser : IMermaidDiagramParser
+{
+    // Relationship operators sorted so that longer tokens are tried first when positions tie.
+    // Each entry: (token, relationshipType, isReversed).
+    // "isReversed" is not used for edge direction (we always keep source=left, target=right)
+    // but is stored in metadata for potential renderer use.
+    private static readonly (string Token, string RelType, bool IsReversed)[] RelOperators =
+    [
+        ("<|--", "inheritance", false),
+        ("--|>", "inheritance", true),
+        ("<|..", "realization", false),
+        ("..|>", "realization", true),
+        ("*--",  "composition", false),
+        ("--*",  "composition", true),
+        ("o--",  "aggregation", false),
+        ("--o",  "aggregation", true),
+        ("<..",  "dependency",  false),
+        ("..>",  "dependency",  true),
+        ("<--",  "association", true),
+        ("-->",  "association", false),
+        ("..",   "link",        false),
+        ("--",   "link",        false),
+    ];
+
+    public bool CanParse(MermaidDiagramKind kind) => kind == MermaidDiagramKind.ClassDiagram;
+
+    public Diagram Parse(MermaidDocument document)
+    {
+        var hints = new LayoutHints { Direction = LayoutDirection.TopToBottom };
+
+        var builder = new DiagramSemanticModelBuilder()
+            .WithSourceSyntax("mermaid")
+            .WithDiagramType("classdiagram")
+            .WithLayoutHints(hints);
+
+        var nodesSeen = new Dictionary<string, Node>(StringComparer.Ordinal);
+
+        Node GetOrCreateNode(string id)
+        {
+            if (!nodesSeen.TryGetValue(id, out var node))
+            {
+                node = new Node(id, id) { Shape = Shape.Rectangle };
+                node.Metadata["class:isClass"] = true;
+                nodesSeen[id] = node;
+                builder.AddNode(node);
+            }
+
+            return node;
+        }
+
+        // Current class whose {} block is being parsed (null = top-level).
+        Node? currentBlockNode = null;
+
+        for (int i = 1; i < document.Lines.Length; i++)
+        {
+            var line = document.Lines[i];
+
+            // ── Close brace ends a member block ─────────────────────────────
+            if (line == "}")
+            {
+                currentBlockNode = null;
+                continue;
+            }
+
+            // ── Lines inside a member block ──────────────────────────────────
+            if (currentBlockNode is not null)
+            {
+                AddMemberToNode(currentBlockNode, line);
+                continue;
+            }
+
+            // ── direction ────────────────────────────────────────────────────
+            if (line.StartsWith("direction ", StringComparison.OrdinalIgnoreCase))
+            {
+                hints.Direction = ParseDirection(line);
+                continue;
+            }
+
+            // ── Explicit class declaration: "class ClassName" or
+            //    "class ClassName[\"label\"]" or "class ClassName {"  ─────────
+            if (line.StartsWith("class ", StringComparison.Ordinal))
+            {
+                var rest = line[6..].Trim();
+                bool opensBrace = rest.EndsWith('{');
+                if (opensBrace)
+                    rest = rest[..^1].TrimEnd();
+
+                var (id, label) = ParseClassDeclaration(rest);
+                if (!string.IsNullOrEmpty(id))
+                {
+                    var node = GetOrCreateNode(id);
+                    if (label is not null)
+                        node.Label = new Label(label);
+
+                    if (opensBrace)
+                        currentBlockNode = node;
+                }
+
+                continue;
+            }
+
+            // ── ClassName { member block (no "class" keyword) ────────────────
+            if (line.EndsWith('{'))
+            {
+                var candidate = line[..^1].TrimEnd();
+                if (IsValidClassId(candidate) && FindRelationshipOp(candidate) is null)
+                {
+                    currentBlockNode = GetOrCreateNode(candidate);
+                    continue;
+                }
+            }
+
+            // ── Relationship line (try before colon-member to avoid false ────
+            //    positives on "ClassName : member" that looks like a target)   ─
+            if (TryParseRelationship(line, builder, GetOrCreateNode, hints))
+                continue;
+
+            // ── Colon-member: "ClassName : memberDefinition" ─────────────────
+            if (TryParseColonMember(line, GetOrCreateNode))
+                continue;
+        }
+
+        return builder.Build();
+    }
+
+    // ── Direction ─────────────────────────────────────────────────────────────
+
+    private static LayoutDirection ParseDirection(string line)
+    {
+        var lower = line.ToLowerInvariant();
+        if (lower.Contains(" lr", StringComparison.Ordinal)) return LayoutDirection.LeftToRight;
+        if (lower.Contains(" rl", StringComparison.Ordinal)) return LayoutDirection.RightToLeft;
+        if (lower.Contains(" bt", StringComparison.Ordinal)) return LayoutDirection.BottomToTop;
+        return LayoutDirection.TopToBottom;
+    }
+
+    // ── Class declaration parsing ─────────────────────────────────────────────
+
+    /// <summary>
+    /// Parses the part after "class ": returns (id, optionalLabel).
+    /// Handles both plain IDs and <c>ClassName["A label"]</c> form.
+    /// </summary>
+    private static (string Id, string? Label) ParseClassDeclaration(string token)
+    {
+        token = token.Trim();
+        int bracketStart = token.IndexOf('[');
+        if (bracketStart > 0 && token.EndsWith(']'))
+        {
+            var id = token[..bracketStart].Trim();
+            var labelRaw = token[(bracketStart + 1)..^1].Trim();
+            // Strip surrounding quotes that Mermaid allows: ["My Label"]
+            if (labelRaw.Length >= 2 && labelRaw[0] == '"' && labelRaw[^1] == '"')
+                labelRaw = labelRaw[1..^1];
+            return (id, labelRaw.Length > 0 ? labelRaw : null);
+        }
+
+        return (token, null);
+    }
+
+    // ── Member handling ───────────────────────────────────────────────────────
+
+    /// <summary>
+    /// Adds a single member line to the appropriate compartment of <paramref name="node"/>.
+    /// Methods (those containing <c>()</c>) go to the "methods" compartment;
+    /// everything else goes to the "attributes" compartment.
+    /// </summary>
+    private static void AddMemberToNode(Node node, string memberText)
+    {
+        if (string.IsNullOrWhiteSpace(memberText))
+            return;
+
+        memberText = memberText.Trim();
+        bool isMethod = memberText.Contains('(');
+        var kind = isMethod ? "methods" : "attributes";
+
+        var compartment = node.Compartments.FirstOrDefault(c => c.Kind == kind);
+        if (compartment is null)
+        {
+            compartment = new NodeCompartment(kind);
+            node.Compartments.Add(compartment);
+        }
+
+        compartment.Lines.Add(new Label(memberText));
+    }
+
+    // ── Colon-member syntax: "ClassName : member" ────────────────────────────
+
+    private static bool TryParseColonMember(string line, Func<string, Node> getOrCreate)
+    {
+        int colonIdx = line.IndexOf(':');
+        if (colonIdx <= 0)
+            return false;
+
+        var id = line[..colonIdx].Trim();
+        var member = line[(colonIdx + 1)..].Trim();
+
+        if (string.IsNullOrEmpty(id) || string.IsNullOrEmpty(member) || !IsValidClassId(id))
+            return false;
+
+        AddMemberToNode(getOrCreate(id), member);
+        return true;
+    }
+
+    // ── Relationship parsing ──────────────────────────────────────────────────
+
+    private static bool TryParseRelationship(
+        string line,
+        IDiagramSemanticModelBuilder builder,
+        Func<string, Node> getOrCreate,
+        LayoutHints hints)
+    {
+        var found = FindRelationshipOp(line);
+        if (found is null)
+            return false;
+
+        var (token, relType, isReversed, opIdx) = found.Value;
+
+        var leftRaw = line[..opIdx].Trim();
+        var rightRaw = line[(opIdx + token.Length)..].Trim();
+
+        // Extract relationship label: "ClassName : label" after the right class
+        string? label = null;
+        int labelColon = rightRaw.LastIndexOf(':');
+        if (labelColon >= 0)
+        {
+            var candidate = rightRaw[(labelColon + 1)..].Trim();
+            if (!string.IsNullOrEmpty(candidate))
+            {
+                label = candidate;
+                rightRaw = rightRaw[..labelColon].Trim();
+            }
+        }
+
+        // Strip cardinality tokens (quoted strings adjacent to class names)
+        var leftId = ExtractClassId(leftRaw);
+        var rightId = ExtractClassId(rightRaw);
+
+        if (string.IsNullOrEmpty(leftId) || string.IsNullOrEmpty(rightId))
+            return false;
+
+        getOrCreate(leftId);
+        getOrCreate(rightId);
+
+        var edge = new Edge(leftId, rightId);
+        if (label is not null)
+            edge.Label = new Label(label);
+
+        bool isDashed = token.Contains('.');
+        edge.LineStyle = isDashed ? EdgeLineStyle.Dashed : EdgeLineStyle.Solid;
+        edge.ArrowHead = MapArrowHead(relType);
+        edge.Metadata["class:relationshipType"] = relType;
+        edge.Metadata["class:operatorReversed"] = isReversed;
+
+        builder.AddEdge(edge);
+        return true;
+    }
+
+    /// <summary>
+    /// Extracts the class name from an endpoint token, stripping any adjacent
+    /// quoted cardinality strings (e.g., <c>Animal "1"</c> → <c>Animal</c>;
+    /// <c>"0..*" Zoo</c> → <c>Zoo</c>).
+    /// </summary>
+    private static string ExtractClassId(string part)
+    {
+        part = part.Trim();
+
+        // Leading quoted cardinality: "0..*" Zoo
+        if (part.StartsWith('"'))
+        {
+            int end = part.IndexOf('"', 1);
+            if (end >= 0)
+                part = part[(end + 1)..].Trim();
+        }
+
+        // Trailing quoted cardinality: Animal "1"
+        if (part.EndsWith('"'))
+        {
+            int start = part.LastIndexOf('"', part.Length - 2);
+            if (start >= 0)
+                part = part[..start].Trim();
+        }
+
+        return part;
+    }
+
+    private static ArrowHeadStyle MapArrowHead(string relType) =>
+        relType switch
+        {
+            "association" or "dependency" => ArrowHeadStyle.Arrow,
+            "composition" or "aggregation" => ArrowHeadStyle.Diamond,
+            _ => ArrowHeadStyle.None, // inheritance, realization, link
+        };
+
+    // ── Operator lookup ───────────────────────────────────────────────────────
+
+    private static (string Token, string RelType, bool IsReversed, int Index)?
+        FindRelationshipOp(string line)
+    {
+        (string Token, string RelType, bool IsReversed, int Index)? best = null;
+
+        foreach (var (token, relType, isReversed) in RelOperators)
+        {
+            int idx = line.IndexOf(token, StringComparison.Ordinal);
+            if (idx < 0)
+                continue;
+
+            if (best is null
+                || idx < best.Value.Index
+                || (idx == best.Value.Index && token.Length > best.Value.Token.Length))
+            {
+                best = (token, relType, isReversed, idx);
+            }
+        }
+
+        return best;
+    }
+
+    // ── Helpers ───────────────────────────────────────────────────────────────
+
+    /// <summary>
+    /// Returns <see langword="true"/> when <paramref name="s"/> looks like a valid
+    /// Mermaid class identifier (starts with a letter or underscore, contains only
+    /// letters, digits, or underscores).
+    /// </summary>
+    private static bool IsValidClassId(string s) =>
+        s.Length > 0
+        && (char.IsLetter(s[0]) || s[0] == '_')
+        && s.All(c => char.IsLetterOrDigit(c) || c == '_');
+}

src/DiagramForge/Parsers/Mermaid/MermaidDiagramKind.cs

@@ -12,4 +12,5 @@ internal enum MermaidDiagramKind
     Timeline,
     ArchitectureDiagram,
     XyChart,
+    ClassDiagram,
 }

src/DiagramForge/Parsers/Mermaid/MermaidDocument.cs

@@ -82,7 +82,6 @@ public static bool TryParse(string diagramText, [System.Diagnostics.CodeAnalysis
     // MermaidParser emit a specific "unsupported type" error instead of a generic one.
     private static readonly FrozenSet<string> KnownUnsupportedMermaidKeywords = new[]
     {
-        "classdiagram",
         "erdiagram",
         "journey",
         "gantt",
@@ -198,6 +197,11 @@ private static bool TryDetectKind(string headerLine, out MermaidDiagramKind kind
             kind = MermaidDiagramKind.XyChart;
             return true;
         }
+        if (normalizedHeader.Equals("classdiagram", StringComparison.OrdinalIgnoreCase))
+        {
+            kind = MermaidDiagramKind.ClassDiagram;
+            return true;
+        }
         var spaceIndex = normalizedHeader.IndexOf(' ');
         var keyword = spaceIndex >= 0 ? normalizedHeader[..spaceIndex] : normalizedHeader;
         if (KnownUnsupportedMermaidKeywords.Contains(keyword))

src/DiagramForge/Parsers/Mermaid/MermaidParser.cs

@@ -17,6 +17,7 @@ namespace DiagramForge.Parsers.Mermaid;
 ///   <item>Sequence diagram (sequenceDiagram)</item>
 ///   <item>Timeline</item>
 ///   <item>Architecture diagram (architecture-beta)</item>
+///   <item>Class diagram (classDiagram)</item>
 /// </list>
 /// </remarks>
 public sealed class MermaidParser : IDiagramParser
@@ -32,9 +33,10 @@ public sealed class MermaidParser : IDiagramParser
         new MermaidTimelineParser(),
         new MermaidArchitectureParser(),
         new MermaidXyChartParser(),
+        new MermaidClassDiagramParser(),
     ];
 
-    private static readonly string[] SupportedDiagramTypes = ["flowchart", "mindmap", "venn-beta", "statediagram", "block", "sequencediagram", "timeline", "architecture-beta", "xychart", "xychart-beta"];
+    private static readonly string[] SupportedDiagramTypes = ["flowchart", "mindmap", "venn-beta", "statediagram", "block", "sequencediagram", "timeline", "architecture-beta", "xychart", "xychart-beta", "classdiagram"];
 
     public string SyntaxId => "mermaid";