Added a popup system

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

@@ -0,0 +1,51 @@
+using System;
+using UnityEngine;
+
+namespace Jovian.PopupSystem {
+    public sealed class FadePopupAnimator : IPopupAnimator {
+        private CanvasGroup target;
+        private float duration;
+        private float elapsed;
+        private float startAlpha;
+        private float endAlpha;
+        private Action onComplete;
+
+        public bool IsAnimating => target != null;
+
+        public void Show(CanvasGroup canvasGroup, float duration, Action onComplete) {
+            target = canvasGroup;
+            this.duration = Mathf.Max(duration, 0.001f);
+            elapsed = 0f;
+            startAlpha = 0f;
+            endAlpha = 1f;
+            this.onComplete = onComplete;
+            canvasGroup.alpha = 0f;
+        }
+
+        public void Hide(CanvasGroup canvasGroup, float duration, Action onComplete) {
+            target = canvasGroup;
+            this.duration = Mathf.Max(duration, 0.001f);
+            elapsed = 0f;
+            startAlpha = canvasGroup.alpha;
+            endAlpha = 0f;
+            this.onComplete = onComplete;
+        }
+
+        public void Tick(float deltaTime) {
+            if(target == null) {
+                return;
+            }
+
+            elapsed += deltaTime;
+            var t = Mathf.Clamp01(elapsed / duration);
+            target.alpha = Mathf.Lerp(startAlpha, endAlpha, t);
+
+            if(t >= 1f) {
+                var callback = onComplete;
+                target = null;
+                onComplete = null;
+                callback?.Invoke();
+            }
+        }
+    }
+}