Usecases created for mermaid.js diagram exporter

RackPeek.Domain/UseCases/Mermaid/MermaidDiagramExportUseCase.cs

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+using RackPeek.Domain.Persistence;
+using RackPeek.Domain.Resources;
+
+namespace RackPeek.Domain.UseCases.Mermaid;
+
+public class MermaidDiagramExportUseCase(IResourceCollection repository) : IUseCase {
+    public async Task<MermaidExportResult?> ExecuteAsync(MermaidExportOptions options) {
+        IReadOnlyList<Resource> resources = await repository.GetAllOfTypeAsync<Resource>();
+        return resources.ToMermaidDiagram(options);
+    }
+}

RackPeek.Domain/UseCases/Mermaid/MermaidDiagramGenerator.cs

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+using System.Text;
+using RackPeek.Domain.Resources;
+
+namespace RackPeek.Domain.UseCases.Mermaid;
+
+public static class MermaidDiagramGenerator
+{
+    public static MermaidExportResult ToMermaidDiagram(
+        this IReadOnlyList<Resource> resources,
+        MermaidExportOptions? options = null)
+    {
+        MermaidExportOptions resolvedOptions = options ?? new MermaidExportOptions();
+
+        var sb = new StringBuilder();
+        var warnings = new List<string>();
+
+        sb.AppendLine(resolvedOptions.DiagramType);
+
+        foreach (Resource r in resources.OrderBy(x => x.Name))
+        {
+            if (resolvedOptions.IncludeTags.Any())
+            {
+                var tags = r.Tags ?? Array.Empty<string>();
+
+                var match = resolvedOptions
+                    .IncludeTags
+                    .Any(t => tags.Contains(t, StringComparer.OrdinalIgnoreCase));
+
+                if (!match)
+                    continue;
+            }
+
+            var nodeId = SanitizeId(r.Name);
+            var label = BuildNodeLabel(r, resolvedOptions);
+
+            sb.AppendLine($"    {nodeId}[\"{label}\"]");
+        }
+
+        if (sb.Length == 0)
+            warnings.Add("No Mermaid diagram entries generated.");
+
+        return new MermaidExportResult(sb.ToString().TrimEnd(), warnings);
+    }
+
+    private static string BuildNodeLabel(Resource r, MermaidExportOptions options)
+    {
+        if (!options.IncludeLabels || r.Labels.Count == 0)
+            return r.Name;
+
+        IEnumerable<KeyValuePair<string, string>> filtered;
+
+        if (options.LabelWhitelist is null)
+        {
+            filtered = r.Labels;
+        }
+        else
+        {
+            filtered = r.Labels.Where(kvp =>
+                options.LabelWhitelist.Contains(kvp.Key, StringComparer.OrdinalIgnoreCase));
+        }
+
+        var labelParts = filtered
+            .Select(kvp => $"{kvp.Key}: {kvp.Value}")
+            .ToList();
+
+        if (labelParts.Count == 0)
+            return r.Name;
+
+        return $"{r.Name}\\n{string.Join("\\n", labelParts)}";
+    }
+
+    private static string SanitizeId(string name)
+    {
+        var sb = new StringBuilder();
+
+        foreach (var ch in name.Trim().ToLowerInvariant())
+        {
+            if (char.IsLetterOrDigit(ch) || ch == '_')
+            {
+                sb.Append(ch);
+            }
+            else if (ch == '-' || ch == '.' || ch == ' ')
+            {
+                sb.Append('_');
+            }
+        }
+
+        return sb.Length == 0 ? "node" : sb.ToString();
+    }
+}

RackPeek.Domain/UseCases/Mermaid/MermaidExportOptions.cs

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+namespace RackPeek.Domain.UseCases.Mermaid;
+
+public sealed record MermaidExportOptions {
+    /// <summary>
+    /// Only include resources with these tags (optional)
+    /// </summary>
+    public IReadOnlyList<string> IncludeTags { get; init; } = [];
+
+    /// <summary>
+    /// Diagram type: "flowchart", "sequence", "class", "er", etc.
+    /// Default: flowchart TD
+    /// </summary>
+    public string DiagramType { get; init; } = "flowchart TD";
+
+    /// <summary>
+    /// Whether to include resource labels as annotations
+    /// </summary>
+    public bool IncludeLabels { get; init; } = true;
+
+    /// <summary>
+    /// Whether to include relationships (edges)
+    /// </summary>
+    public bool IncludeEdges { get; init; } = true;
+
+    /// <summary>
+    /// Optional label keys to include (null = include all)
+    /// </summary>
+    public IReadOnlyList<string>? LabelWhitelist { get; init; }
+}
+
+public sealed record MermaidExportResult(
+    string DiagramText,
+    IReadOnlyList<string> Warnings);