Initial import into Gitea

IntelligenceApi/Engines/EngineRouter.cs

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+using IntelligenceApi.Engines.Franchisee;
+using IntelligenceApi.Engines.Franchisor;
+using IntelligenceApi.Engines.General;
+
+namespace IntelligenceApi.Engines;
+
+/// <summary>
+/// Routes incoming spend distribution requests to the correct engine
+/// based on clientCategory.
+///
+/// ADDING A NEW ENGINE:
+///   1. Create a folder under Engines/ (e.g. Engines/FoodFranchisee/)
+///   2. Implement ISpendDistributionEngine
+///   3. Register in Program.cs
+///   4. Add the category string to the routing table below
+///
+/// The General engine is the fallback for any unrecognised category,
+/// ensuring existing clients are never broken by new category additions.
+/// </summary>
+public sealed class EngineRouter
+{
+    private readonly GeneralEngine _general;
+    private readonly FranchiseeEngine _franchisee;
+    private readonly FranchisorEngine _franchisor;
+    private readonly ILogger<EngineRouter> _logger;
+
+    public EngineRouter(
+        GeneralEngine general,
+        FranchiseeEngine franchisee,
+        FranchisorEngine franchisor,
+        ILogger<EngineRouter> logger)
+    {
+        _general    = general;
+        _franchisee = franchisee;
+        _franchisor = franchisor;
+        _logger     = logger;
+    }
+
+    public ISpendDistributionEngine Resolve(string? clientCategory)
+    {
+        var engine = (clientCategory ?? "General").Trim() switch
+        {
+            // ── Exact category matches ──────────────────────────────
+            "General"        => (ISpendDistributionEngine)_general,
+            "Franchisee"     => _franchisee,
+            "Franchisor"     => _franchisor,
+
+            // ── Future sub-categories route to their parent stub
+            //    until a dedicated engine is built.
+            //    e.g. "FoodFranchisee" => _foodFranchisee (not yet registered)
+            //    falls through to Franchisee as the nearest match.
+            var c when c.EndsWith("Franchisee", StringComparison.OrdinalIgnoreCase)
+                     => _franchisee,
+            var c when c.EndsWith("Franchisor", StringComparison.OrdinalIgnoreCase)
+                     => _franchisor,
+
+            // ── Unknown / unrecognised — safe fallback ──────────────
+            var c => LogAndFallback(c)
+        };
+
+        _logger.LogInformation(
+            "[EngineRouter] Category={Category} → Engine={Engine}",
+            clientCategory, engine.EngineName);
+
+        return engine;
+    }
+
+    private ISpendDistributionEngine LogAndFallback(string category)
+    {
+        _logger.LogWarning(
+            "[EngineRouter] Unrecognised category '{Category}' — falling back to GeneralEngine",
+            category);
+        return _general;
+    }
+}