refactor: Extract determine current overlay logic to a utility function

.changeset/eighty-singers-cover.md

@@ -0,0 +1,5 @@
+---
+"overlay-kit": patch
+---
+
+refactor: Extract determine current overlay logic to a utility function

packages/src/context/reducer.test.ts

@@ -0,0 +1,54 @@
+import { describe, expect, it } from 'vitest';
+import { determineCurrentOverlayId } from './reducer';
+
+describe('determineCurrentOverlayId', () => {
+  it('should return the previous overlay when closing the last overlay', () => {
+    const overlayOrderList = ['id1', 'id2', 'id3'];
+    const overlayData = {
+      id1: { id: 'id1', componentKey: 'key1', isOpen: true, controller: () => null },
+      id2: { id: 'id2', componentKey: 'key2', isOpen: true, controller: () => null },
+      id3: { id: 'id3', componentKey: 'key3', isOpen: true, controller: () => null },
+    };
+
+    const result = determineCurrentOverlayId(overlayOrderList, overlayData, 'id3');
+
+    expect(result).toBe('id2');
+  });
+
+  it('should return the last overlay when closing an intermediate overlay', () => {
+    const overlayOrderList = ['id1', 'id2', 'id3'];
+    const overlayData = {
+      id1: { id: 'id1', componentKey: 'key1', isOpen: true, controller: () => null },
+      id2: { id: 'id2', componentKey: 'key2', isOpen: true, controller: () => null },
+      id3: { id: 'id3', componentKey: 'key3', isOpen: true, controller: () => null },
+    };
+
+    const result = determineCurrentOverlayId(overlayOrderList, overlayData, 'id2');
+
+    expect(result).toBe('id3');
+  });
+
+  it('should skip closed overlays when determining the current overlay', () => {
+    const overlayOrderList = ['id1', 'id2', 'id3'];
+    const overlayData = {
+      id1: { id: 'id1', componentKey: 'key1', isOpen: true, controller: () => null },
+      id2: { id: 'id2', componentKey: 'key2', isOpen: false, controller: () => null },
+      id3: { id: 'id3', componentKey: 'key3', isOpen: true, controller: () => null },
+    };
+
+    const result = determineCurrentOverlayId(overlayOrderList, overlayData, 'id3');
+
+    expect(result).toBe('id1');
+  });
+
+  it('should return null when closing the only open overlay', () => {
+    const overlayOrderList = ['id1'];
+    const overlayData = {
+      id1: { id: 'id1', componentKey: 'key1', isOpen: true, controller: () => null },
+    };
+
+    const result = determineCurrentOverlayId(overlayOrderList, overlayData, 'id1');
+
+    expect(result).toBe(null);
+  });
+});

packages/src/context/reducer.ts

@@ -28,6 +28,38 @@ type OverlayReducerAction =
   | { type: 'CLOSE_ALL' }
   | { type: 'REMOVE_ALL' };
 
+/**
+ * Determines which overlay should become the current one when closing or removing an overlay.
+ *
+ * @description If closing the last overlay, specify the overlay before it.
+ * @description If closing intermediate overlays, specifies the last overlay.
+ *
+ * @example open - [1, 2, 3, 4]
+ * close 2 => current: 4
+ * close 4 => current: 3
+ * close 3 => current: 1
+ * close 1 => current: null
+ *
+ * @param overlayOrderList The ordered list of overlay IDs
+ * @param overlayData The map of overlay data
+ * @param targetOverlayId The ID of the overlay being closed or removed
+ * @returns The ID of the overlay that should become current, or null if none
+ */
+export const determineCurrentOverlayId = (
+  overlayOrderList: OverlayId[],
+  overlayData: Record<OverlayId, OverlayItem>,
+  targetOverlayId: OverlayId
+): OverlayId | null => {
+  const openedOverlayOrderList = overlayOrderList.filter(
+    (orderedOverlayId) => overlayData[orderedOverlayId].isOpen === true
+  );
+  const targetIndexInOpenedList = openedOverlayOrderList.findIndex((item) => item === targetOverlayId);
+
+  return targetIndexInOpenedList === openedOverlayOrderList.length - 1
+    ? openedOverlayOrderList[targetIndexInOpenedList - 1] ?? null
+    : openedOverlayOrderList.at(-1) ?? null;
+};
+
 export function overlayReducer(state: OverlayData, action: OverlayReducerAction): OverlayData {
   switch (action.type) {
     case 'ADD': {
@@ -78,25 +110,7 @@ export function overlayReducer(state: OverlayData, action: OverlayReducerAction)
         return state;
       }
 
-      const openedOverlayOrderList = state.overlayOrderList.filter(
-        (orderedOverlayId) => state.overlayData[orderedOverlayId].isOpen === true
-      );
-      const targetIndexInOpenedList = openedOverlayOrderList.findIndex((item) => item === action.overlayId);
-
-      /**
-       * @description If closing the last overlay, specify the overlay before it.
-       * @description If closing intermediate overlays, specifies the last overlay.
-       *
-       * @example open - [1, 2, 3, 4]
-       * close 2 => current: 4
-       * close 4 => current: 3
-       * close 3 => current: 1
-       * close 1 => current: null
-       */
-      const currentOverlayId =
-        targetIndexInOpenedList === openedOverlayOrderList.length - 1
-          ? openedOverlayOrderList[targetIndexInOpenedList - 1] ?? null
-          : openedOverlayOrderList.at(-1) ?? null;
+      const currentOverlayId = determineCurrentOverlayId(state.overlayOrderList, state.overlayData, action.overlayId);
 
       return {
         ...state,
@@ -126,25 +140,7 @@ export function overlayReducer(state: OverlayData, action: OverlayReducerAction)
       const copiedOverlayData = { ...state.overlayData };
       delete copiedOverlayData[action.overlayId];
 
-      const openedOverlayOrderList = state.overlayOrderList.filter(
-        (orderedOverlayId) => state.overlayData[orderedOverlayId].isOpen === true
-      );
-      const targetIndexInOpenedList = openedOverlayOrderList.findIndex((item) => item === action.overlayId);
-
-      /**
-       * @description If unmounting the last overlay, specify the overlay before it.
-       * @description If unmounting intermediate overlays, specifies the last overlay.
-       *
-       * @example open - [1, 2, 3, 4]
-       * unmount 2 => current: 4
-       * unmount 4 => current: 3
-       * unmount 3 => current: 1
-       * unmount 1 => current: null
-       */
-      const currentOverlayId =
-        targetIndexInOpenedList === openedOverlayOrderList.length - 1
-          ? openedOverlayOrderList[targetIndexInOpenedList - 1] ?? null
-          : openedOverlayOrderList.at(-1) ?? null;
+      const currentOverlayId = determineCurrentOverlayId(state.overlayOrderList, state.overlayData, action.overlayId);
 
       return {
         current: currentOverlayId,