added documentation, fixed some bugs

Packages/com.jovian.popup-system/Runtime/FadePopupAnimator.cs

@@ -2,33 +2,37 @@ using System;
 using UnityEngine;
 
 namespace Jovian.PopupSystem {
+    /// <summary>
+    /// Default popup animator that fades CanvasGroup alpha. Each category gets its own instance
+    /// so concurrent show/hide animations don't corrupt each other.
+    /// </summary>
     public sealed class FadePopupAnimator : IPopupAnimator {
         private CanvasGroup target;
-        private float duration;
+        private float timer;
         private float elapsed;
         private float startAlpha;
         private float endAlpha;
-        private Action onComplete;
+        private Action onFinish;
 
         public bool IsAnimating => target != null;
 
         public void Show(CanvasGroup canvasGroup, float duration, Action onComplete) {
             target = canvasGroup;
-            this.duration = Mathf.Max(duration, 0.001f);
+            timer = Mathf.Max(duration, 0.001f);
             elapsed = 0f;
             startAlpha = 0f;
             endAlpha = 1f;
-            this.onComplete = onComplete;
+            onFinish = onComplete;
             canvasGroup.alpha = 0f;
         }
 
         public void Hide(CanvasGroup canvasGroup, float duration, Action onComplete) {
             target = canvasGroup;
-            this.duration = Mathf.Max(duration, 0.001f);
+            timer = Mathf.Max(duration, 0.001f);
             elapsed = 0f;
             startAlpha = canvasGroup.alpha;
             endAlpha = 0f;
-            this.onComplete = onComplete;
+            onFinish = onComplete;
         }
 
         public void Tick(float deltaTime) {
@@ -37,15 +41,16 @@ namespace Jovian.PopupSystem {
             }
 
             elapsed += deltaTime;
-            var t = Mathf.Clamp01(elapsed / duration);
+            var t = Mathf.Clamp01(elapsed / timer);
             target.alpha = Mathf.Lerp(startAlpha, endAlpha, t);
 
-            if(t >= 1f) {
-                var callback = onComplete;
-                target = null;
-                onComplete = null;
-                callback?.Invoke();
+            if(!(t >= 1f)) {
+                return;
             }
+            var callback = onFinish;
+            target = null;
+            onFinish = null;
+            callback?.Invoke();
         }
     }
 }