shared variables for checker attributes

SimpleHttpServer/Types/BaseEndpointCheckAttribute.cs

@@ -1,13 +1,103 @@
 using System.Net;
+using System.Reflection;
 
 namespace SimpleHttpServer.Types;
 
 public abstract class InternalEndpointCheckAttribute : Attribute {
+    public InternalEndpointCheckAttribute() {
+        CheckSharedVariables();
+    }
+
+    private void CheckSharedVariables() {
+        foreach (var f in GetType().GetRuntimeFields()) {
+            if (f.FieldType.IsAssignableTo(typeof(SharedVariable))) {
+                if (!f.IsInitOnly) {
+                    throw new Exception($"Found non-readonly global field {f}!");
+                }
+                if (f.GetValue(this) == null) {
+                    throw new Exception("Global fields must be assigned in the CCTOR!");
+                }
+            }
+        }
+    }
+
+    private void Initialize(object? instance, Dictionary<FieldInfo, List<(InternalEndpointCheckAttribute, SharedVariable)>> globals) {
+        SetInstance(instance);
+        foreach (var f in GetType().GetRuntimeFields()) {
+            if (f.FieldType.IsAssignableTo(typeof(SharedVariable))) {
+                SharedVariable origVal = (SharedVariable) f.GetValue(this)!;
+                if (globals.TryGetValue(f, out var options)) {
+                    bool foundMatch = false;
+                    foreach ((var checker, var gv) in options) {
+                        if (Match(checker)) {
+                            foundMatch = true;
+                            // we need to unify their global variables
+                            f.SetValue(this, gv);
+                        }
+                    }
+                    if (!foundMatch) {
+                        options.Add((this, origVal));
+                    }
+                } else {
+                    globals.Add(f, new List<(InternalEndpointCheckAttribute, SharedVariable)>() { (this, origVal) });
+                }
+            }
+        }
+    }
+
+    public static void Initialize(object? instance, IEnumerable<InternalEndpointCheckAttribute> endPointChecks) {
+        Dictionary<FieldInfo, List<(InternalEndpointCheckAttribute, SharedVariable)>> globals = new();
+        foreach (var check in endPointChecks) {
+            check.Initialize(instance, globals);
+        }
+    }
+
+    private interface SharedVariable {
+        // Tagging interface
+    }
+
+    /// <summary>
+    /// Represents a Mutable Shared Variable. Fields of this type need to be initialized in the CCtor.
+    /// </summary>
+    protected sealed class MSV<V> : SharedVariable {
+        private readonly V __default;
+
+        public V Val { get; set; } = default!;
+
+        public MSV() : this(default!) { }
+
+        public MSV(V _default) {
+            __default = _default;
+        }
+
+        public static implicit operator V(MSV<V> v) => v.Val;
+    }
+
+    /// <summary>
+    /// Represents an Immutable Shared Variable. Fields of this type need to be initialized in the CCtor.
+    /// </summary>
+    protected sealed class ISV<V> : SharedVariable {
+        private readonly V __default;
+
+        public V Val { get; } = default!;
+
+        public ISV() : this(default!) { }
+
+        public ISV(V _default) {
+            __default = _default;
+        }
+
+        public static implicit operator V(ISV<V> v) => v.Val;
+    }
+
     /// <summary>
     /// Executed when the endpoint is invoked. The endpoint invocation is skipped if any of the checks fail.
     /// </summary>
     /// <returns>True to allow invocation, false to prevent.</returns>
     public abstract bool Check(HttpListenerRequest req);
+
+    protected virtual bool Match(InternalEndpointCheckAttribute other) => true;
+
     internal abstract void SetInstance(object? instance);
 }
 
@@ -18,7 +108,9 @@ public abstract class BaseEndpointCheckAttribute<T> : InternalEndpointCheckAttri
     /// Will be null iff an class factory was passed in <see cref="HttpServer.RegisterEndpointsFromType{T}(Func{T}?)"/>.
     /// </summary>
     protected internal T? EndpointClassInstance { get; internal set; } = default;
-    public BaseEndpointCheckAttribute() { }
+
+    public BaseEndpointCheckAttribute() : base() { }
+
     internal override void SetInstance(object? instance) {
         if (instance != null)
             EndpointClassInstance = (T?) instance;