feat: add index parameter to customAnimation (#735)

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<!-- GitHub: Fixes #0, Relates to #1, etc. -->

### Description

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#709

### Review

- [ ] I self-reviewed this PR

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### Testing

- [ ] I added/updated tests
- [ ] I manually tested

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Author: dohooo

.changeset/modern-carpets-sleep.md

@@ -0,0 +1,5 @@
+---
+"react-native-reanimated-carousel": patch
+---
+
+This PR updates the customAnimation function signature to include an index parameter, allowing users to apply custom animations based on the item’s index.

src/components/Carousel.test.tsx

@@ -2,7 +2,7 @@ import type { FC } from "react";
 import React from "react";
 import type { PanGesture } from "react-native-gesture-handler";
 import { Gesture, State } from "react-native-gesture-handler";
-import Animated, { useDerivedValue, useSharedValue } from "react-native-reanimated";
+import Animated, { interpolate, useDerivedValue, useSharedValue } from "react-native-reanimated";
 import type { ReactTestInstance } from "react-test-renderer";
 
 import { act, render, waitFor } from "@testing-library/react-native";
@@ -301,7 +301,11 @@ describe("Test the real swipe behavior of Carousel to ensure it's working as exp
 
       fireGestureHandler<PanGesture>(getByGestureTestId(gestureTestId), [
         { state: State.BEGAN, translationX: 0, velocityX: -5 },
-        { state: State.ACTIVE, translationX: -slideWidth * 0.15, velocityX: -5 },
+        {
+          state: State.ACTIVE,
+          translationX: -slideWidth * 0.15,
+          velocityX: -5,
+        },
         { state: State.END, translationX: -slideWidth * 0.25, velocityX: -5 },
       ]);
 
@@ -314,8 +318,16 @@ describe("Test the real swipe behavior of Carousel to ensure it's working as exp
 
       fireGestureHandler<PanGesture>(getByGestureTestId(gestureTestId), [
         { state: State.BEGAN, translationX: 0, velocityX: -1000 },
-        { state: State.ACTIVE, translationX: -slideWidth * 0.15, velocityX: -1000 },
-        { state: State.END, translationX: -slideWidth * 0.25, velocityX: -1000 },
+        {
+          state: State.ACTIVE,
+          translationX: -slideWidth * 0.15,
+          velocityX: -1000,
+        },
+        {
+          state: State.END,
+          translationX: -slideWidth * 0.25,
+          velocityX: -1000,
+        },
       ]);
 
       await waitFor(() => expect(progress.current).toBe(1));
@@ -441,6 +453,45 @@ describe("Test the real swipe behavior of Carousel to ensure it's working as exp
     }
   });
 
+  it("`customAnimation` prop: should apply the custom animation", async () => {
+    const progress = { current: 0 };
+    const indexes: Record<number, number> = {};
+    const Wrapper = createCarousel(progress);
+    const { getByTestId } = render(
+      <Wrapper
+        customAnimation={(value: number, index: number) => {
+          "worklet";
+
+          indexes[index] = index;
+
+          const zIndex = interpolate(value, [-1, 0, 1], [10, 20, 30]);
+          const translateX = interpolate(value, [-2, 0, 1], [-slideWidth, 0, slideWidth]);
+
+          return {
+            transform: [{ translateX }],
+            zIndex,
+          };
+        }}
+      />
+    );
+
+    await verifyInitialRender(getByTestId);
+
+    swipeToLeftOnce();
+    await waitFor(() => {
+      expect(progress.current).toBe(1);
+
+      expect(indexes).toMatchInlineSnapshot(`
+        {
+          "0": 0,
+          "1": 1,
+          "2": 2,
+          "3": 3,
+        }
+      `);
+    });
+  });
+
   it("`overscrollEnabled` prop: should respect overscrollEnabled=false and prevent scrolling beyond bounds", async () => {
     const containerWidth = slideWidth;
     const containerHeight = containerWidth / 2;

src/components/ItemLayout.tsx

@@ -3,13 +3,14 @@ import type { ViewStyle } from "react-native";
 import type { SharedValue } from "react-native-reanimated";
 import Animated, { useAnimatedStyle, useDerivedValue } from "react-native-reanimated";
 
+import { TCarouselProps } from "src/types";
 import type { IOpts } from "../hooks/useOffsetX";
 import { useOffsetX } from "../hooks/useOffsetX";
 import type { IVisibleRanges } from "../hooks/useVisibleRanges";
 import type { ILayoutConfig } from "../layouts/stack";
 import { useGlobalState } from "../store";
 
-export type TAnimationStyle = (value: number) => ViewStyle;
+export type TAnimationStyle = NonNullable<TCarouselProps["customAnimation"]>;
 
 export const ItemLayout: React.FC<{
   index: number;
@@ -56,8 +57,8 @@ export const ItemLayout: React.FC<{
   const x = useOffsetX(offsetXConfig, visibleRanges);
   const animationValue = useDerivedValue(() => x.value / size, [x, size]);
   const animatedStyle = useAnimatedStyle<ViewStyle>(
-    () => animationStyle(x.value / size),
-    [animationStyle]
+    () => animationStyle(x.value / size, index),
+    [animationStyle, index]
   );
 
   // TODO: For dynamic dimension in the future

src/components/ItemRenderer.tsx

@@ -24,7 +24,7 @@ interface Props {
   handlerOffset: SharedValue<number>;
   layoutConfig: TAnimationStyle;
   renderItem: CarouselRenderItem<any>;
-  customAnimation?: (value: number) => ViewStyle;
+  customAnimation?: (value: number, index: number) => ViewStyle;
 }
 
 export const ItemRenderer: FC<Props> = (props) => {

src/types.ts

@@ -187,8 +187,9 @@ export type TCarouselProps<T = any> = {
   /**
    * Custom animations.
    * Must use `worklet`, Details: https://docs.swmansion.com/react-native-reanimated/docs/2.2.0/worklets/
+   * @test_coverage ✅ tested in Carousel.test.tsx > should apply the custom animation
    */
-  customAnimation?: (value: number) => ViewStyle;
+  customAnimation?: (value: number, index: number) => ViewStyle;
   /**
    * Render carousel item.
    * @test_coverage ✅ tested in Carousel.test.tsx > should render items correctly