Link style indices mismatch

src/Mermaid.Flowcharts/Flowchart.cs

@@ -1,24 +1,25 @@
 using System.Text;
+using System.Runtime.CompilerServices;
 using Mermaid.Flowcharts.Links;
 using Mermaid.Flowcharts.Nodes;
 using Mermaid.Flowcharts.Styling;
 using Mermaid.Flowcharts.Subgraphs;
 
+[assembly: InternalsVisibleTo("Mermaid.Flowcharts.Tests")]
 namespace Mermaid.Flowcharts;
 
 public class Flowchart : IMermaidPrintable
 {
     private readonly List<INode> _nodes = [];
     private readonly List<Link> _links = [];
+    internal IEnumerable<INode> AllNodeChildren => _nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodeChildren));
+    internal IEnumerable<Node> AllNodes => Nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodes));
 
     public FlowchartTitle? Title { get; }
     public FlowchartDirection? Direction { get; }
     public IEnumerable<Node> Nodes => _nodes.OfType<Node>();
     public IEnumerable<Subgraph> Subgraphs => _nodes.OfType<Subgraph>();
     public IEnumerable<Link> Links => _links.AsReadOnly();
-    public IEnumerable<INode> AllNodeChildren => _nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodeChildren));
-    public IEnumerable<Node> AllNodes => Nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodes));
-    public IEnumerable<Link> AllLinks => Links.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllLinks));
 
     public Flowchart(FlowchartDirection? direction = null)
     {
@@ -59,7 +60,7 @@ public Flowchart AddLink(Link link)
     public override string ToString()
         => ToMermaidString();
 
-    public string ToMermaidString(int indentations = 0, string indentationText = "  ")
+    internal string ToMermaidStringWithOrderedLinks(int indentations, string indentationText, List<Link> linksInOrderOfOccurrence)
     {
         StringBuilder flowchartStringBuilder = new();
         if (Title is FlowchartTitle title)
@@ -68,26 +69,32 @@ public string ToMermaidString(int indentations = 0, string indentationText = "
         }
         flowchartStringBuilder.AppendLine($"flowchart {Direction ?? FlowchartDirection.TD}");
 
+        // Add node declarations
         foreach (Node node in Nodes)
         {
             flowchartStringBuilder.AppendLine(node.ToMermaidString(indentations + 1, indentationText));
         }
+
+        // Add subgraph declarations
         if (Subgraphs.Any())
         {
             flowchartStringBuilder.AppendLine();
         }
 
         foreach (Subgraph subgraph in Subgraphs)
         {
-            flowchartStringBuilder.AppendLine(subgraph.ToMermaidString(indentations + 1, indentationText));
+            flowchartStringBuilder.AppendLine(subgraph.ToMermaidStringWithOrderedLinks(indentations + 1, indentationText, linksInOrderOfOccurrence));
         }
+
+        // Add link declarations
         if (_links.Any())
         {
             flowchartStringBuilder.AppendLine();
         }
 
         foreach (Link link in _links)
         {
+            linksInOrderOfOccurrence.Add(link);
             flowchartStringBuilder.AppendLine(link.ToMermaidString(indentations + 1, indentationText));
         }
 
@@ -124,7 +131,7 @@ public string ToMermaidString(int indentations = 0, string indentationText = "
 
         // Group all link styles across flowchart and all subgraphs recursively together
         Dictionary<StyleClass, HashSet<int>> distinctLinkStyles = [];
-        foreach ((Link link, int index) in AllLinks.Select((l, i) => (l, i)))
+        foreach ((Link link, int index) in linksInOrderOfOccurrence.Select((l, i) => (l, i)))
         {
             if (link.LinkStyle is null)
             {
@@ -154,4 +161,7 @@ public string ToMermaidString(int indentations = 0, string indentationText = "
 
         return flowchartStringBuilder.ToString();
     }
+
+    public string ToMermaidString(int indentations = 0, string indentationText = "  ")
+        => ToMermaidStringWithOrderedLinks(indentations, indentationText, []);
 }

src/Mermaid.Flowcharts/Subgraphs/Subgraph.cs

@@ -9,16 +9,15 @@ public record Subgraph : INode<Subgraph>
 {
     private readonly List<INode> _nodes = [];
     private readonly List<Link> _links = [];
+    internal IEnumerable<INode> AllNodeChildren => _nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodeChildren));
+    internal IEnumerable<Node> AllNodes => Nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodes));
 
     public NodeIdentifier Id { get; }
     public INodeText Title { get; }
     public SubgraphDirection? Direction { get; }
     public IEnumerable<Node> Nodes => _nodes.OfType<Node>();
     public IEnumerable<Subgraph> Subgraphs => _nodes.OfType<Subgraph>();
     public IEnumerable<Link> Links => _links.AsReadOnly();
-    public IEnumerable<INode> AllNodeChildren => _nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodeChildren));
-    public IEnumerable<Node> AllNodes => Nodes.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllNodes));
-    public IEnumerable<Link> AllLinks => Links.Concat(Subgraphs.SelectMany(subgraph => subgraph.AllLinks));
 
     private Subgraph(NodeIdentifier id, INodeText title, SubgraphDirection? direction = null)
     {
@@ -78,7 +77,7 @@ public Subgraph AddLink(Link link)
     public override string ToString()
         => ToMermaidString();
 
-    public string ToMermaidString(int indentations = 0, string indentationText = "  ")
+    internal string ToMermaidStringWithOrderedLinks(int indentations, string indentationText, List<Link> linksInOrderOfOccurrence)
     {
         StringBuilder subgraphStringBuilder = new();
         string indent = indentationText.Repeat(indentations);
@@ -88,29 +87,38 @@ public string ToMermaidString(int indentations = 0, string indentationText = "
             subgraphStringBuilder.AppendLine($"{indent}{indentationText}direction {Direction.Value}");
         }
 
+        // Add node declarations
         foreach (Node node in Nodes)
         {
             subgraphStringBuilder.AppendLine(node.ToMermaidString(indentations + 1, indentationText));
         }
+
+        // Add subgraph declarations
         if (Subgraphs.Any())
         {
             subgraphStringBuilder.AppendLine();
         }
 
         foreach (Subgraph subgraph in Subgraphs)
         {
-            subgraphStringBuilder.AppendLine(subgraph.ToMermaidString(indentations + 1, indentationText));
+            subgraphStringBuilder.AppendLine(subgraph.ToMermaidStringWithOrderedLinks(indentations + 1, indentationText, linksInOrderOfOccurrence));
         }
+
+        // Add link declarations
         if (_links.Any())
         {
             subgraphStringBuilder.AppendLine();
         }
 
         foreach (Link link in _links)
         {
+            linksInOrderOfOccurrence.Add(link);
             subgraphStringBuilder.AppendLine(link.ToMermaidString(indentations + 1, indentationText));
         }
         subgraphStringBuilder.Append($"{indent}end");
         return subgraphStringBuilder.ToString();
     }
+
+    public string ToMermaidString(int indentations = 0, string indentationText = "  ")
+        => ToMermaidStringWithOrderedLinks(indentations, indentationText, []);
 }

tests/Mermaid.Flowcharts.Tests/FlowchartTests.cs

@@ -705,6 +705,153 @@ flowchart TD
         Assert.Equal(expected, actual);
     }
 
+    [Fact]
+    public void LinkStyleIndices_SubgraphLinkPrecedesFlowchartLink()
+    {
+        Flowchart flowchart = new();
+        Node a = Node.Create("a", "A");
+        Node b = Node.Create("b", "B");
+        Node c = Node.Create("c", "C");
+        Node d = Node.Create("d", "D");
+
+        Subgraph sg = Subgraph.Create("sg", "SG");
+        sg.AddNode(c).AddNode(d);
+        sg.AddLink(Link.Create(c, d, linkStyle: new StyleClass(Stroke: new Stroke(Color.FromHex("#00ff00")))));
+
+        flowchart
+            .AddNode(a)
+            .AddNode(b)
+            .AddNode(sg)
+            .AddLink(Link.Create(a, b, linkStyle: new StyleClass(Stroke: new Stroke(Color.FromHex("#ff0000")))));
+
+        string expected =
+            """
+            flowchart TD
+                a["A"]
+                b["B"]
+
+                subgraph sg ["SG"]
+                    c["C"]
+                    d["D"]
+
+                    c ---> d
+                end
+
+                a ---> b
+
+                linkStyle 0 stroke:#00ff00
+                linkStyle 1 stroke:#ff0000
+
+            """;
+
+        Assert.Equal(expected, flowchart.ToMermaidString(0, "    "));
+    }
+
+    [Fact]
+    public void LinkStyleIndices_SharedStyleAcrossSubgraphs_AndMultipleFlowchartLinks()
+    {
+        Flowchart flowchart = new();
+        Node a = Node.Create("a", "A");
+        Node b = Node.Create("b", "B");
+        Node c = Node.Create("c", "C");
+        Node d = Node.Create("d", "D");
+        Node e = Node.Create("e", "E");
+        Node g = Node.Create("g", "G");
+
+        StyleClass green = new(Stroke: new Stroke(Color.FromHex("#00ff00")));
+
+        Subgraph sg1 = Subgraph.Create("sg1", "SG1");
+        sg1.AddNode(c).AddNode(d);
+        sg1.AddLink(Link.Create(c, d, linkStyle: green));
+
+        Subgraph sg2 = Subgraph.Create("sg2", "SG2");
+        sg2.AddNode(e).AddNode(g);
+        sg2.AddLink(Link.Create(e, g, linkStyle: green));
+
+        flowchart
+            .AddNode(a)
+            .AddNode(b)
+            .AddNode(sg1)
+            .AddNode(sg2)
+            .AddLink(Link.Create(a, b, linkStyle: new StyleClass(Stroke: new Stroke(Color.FromHex("#ff0000")))))
+            .AddLink(Link.Create(b, a, linkStyle: new StyleClass(Stroke: new Stroke(Color.FromHex("#0000ff")))));
+
+        string expected =
+            """
+            flowchart TD
+                a["A"]
+                b["B"]
+
+                subgraph sg1 ["SG1"]
+                    c["C"]
+                    d["D"]
+
+                    c ---> d
+                end
+                subgraph sg2 ["SG2"]
+                    e["E"]
+                    g["G"]
+
+                    e ---> g
+                end
+
+                a ---> b
+                b ---> a
+
+                linkStyle 0,1 stroke:#00ff00
+                linkStyle 2 stroke:#ff0000
+                linkStyle 3 stroke:#0000ff
+
+            """;
+
+        Assert.Equal(expected, flowchart.ToMermaidString(0, "    "));
+    }
+
+    [Fact]
+    public void LinkStyleIndices_NestedSubgraph_InnerLinksRenderBeforeOuterOwnLinks()
+    {
+        Flowchart flowchart = new();
+        Node a = Node.Create("a", "A");
+        Node b = Node.Create("b", "B");
+        Node c = Node.Create("c", "C");
+        Node d = Node.Create("d", "D");
+
+        Subgraph inner = Subgraph.Create("inner", "Inner");
+        inner.AddNode(c).AddNode(d);
+        inner.AddLink(Link.Create(c, d, linkStyle: new StyleClass(Stroke: new Stroke(Color.FromHex("#00ff00")))));
+
+        Subgraph outer = Subgraph.Create("outer", "Outer");
+        outer.AddNode(a).AddNode(b).AddNode(inner);
+        outer.AddLink(Link.Create(a, b, linkStyle: new StyleClass(Stroke: new Stroke(Color.FromHex("#ff0000")))));
+
+        flowchart.AddNode(outer);
+
+        string expected =
+            """
+            flowchart TD
+
+                subgraph outer ["Outer"]
+                    a["A"]
+                    b["B"]
+
+                    subgraph inner ["Inner"]
+                        c["C"]
+                        d["D"]
+
+                        c ---> d
+                    end
+
+                    a ---> b
+                end
+
+                linkStyle 0 stroke:#00ff00
+                linkStyle 1 stroke:#ff0000
+
+            """;
+
+        Assert.Equal(expected, flowchart.ToMermaidString(0, "    "));
+    }
+
     [Fact]
     public void Flowchart_WhenNestedLinksParentToChild_ShouldNotAddDuplicateNodes()
     {