Major updates to the HUD and selectable objects

Assets/_Project/Scripts/Gameplay/ISelectable.cs

@@ -0,0 +1,46 @@
+// Assets/_Project/Scripts/Gameplay/ISelectable.cs
+using UnityEngine;
+
+namespace TD.Gameplay
+{
+    /// <summary>
+    /// Categorizes the kind of selectable object so HUD can decide which command
+    /// buttons (tower-build vs upgrade/sell vs none) to show without doing
+    /// type-tests against every concrete component.
+    /// </summary>
+    public enum SelectableKind
+    {
+        Builder,
+        Tower,
+        Enemy,
+        BuildSite,   // tower in queued / constructing / paused / shelved state
+    }
+
+    /// <summary>
+    /// Anything the local player can click to select. Implementers expose a
+    /// display name for the HUD portrait, a kind for context-aware UI, and the
+    /// position + size hints the <see cref="SelectionVisualizer"/> needs to draw
+    /// the selection ring.
+    /// </summary>
+    /// <remarks>
+    /// Selection is a local UI concept — implementers don't need to be
+    /// NetworkBehaviours (though Builder and TowerInstance happen to be).
+    /// </remarks>
+    public interface ISelectable
+    {
+        string DisplayName { get; }
+        SelectableKind Kind { get; }
+
+        /// <summary>Transform whose XZ position the scene-wide selection ring
+        /// follows. The visualizer projects Y to the buildable plane regardless
+        /// of where this transform sits, so implementers can simply return
+        /// <c>this.transform</c>.</summary>
+        Transform SelectionTransform { get; }
+
+        /// <summary>Half-width of the selection ring in world units. The visualizer
+        /// scales its base 1-unit-diameter ring mesh to <c>2 * SelectionRadius</c>.
+        /// Computed on every selection change, so implementers may derive it from
+        /// runtime state (e.g., tower footprint, collider bounds).</summary>
+        float SelectionRadius { get; }
+    }
+}