feat: add Embla initialization filters

Author: sunmorgn

docs/API.md

@@ -5,6 +5,37 @@ This block uses the **WordPress Interactivity API** to manage state and logic. Y
 ## Store Namespace
 `rt-carousel/carousel`
 
+## Embla Initialization Filters
+
+rtCarousel exposes JavaScript filters immediately before calling `EmblaCarousel( viewport, options, plugins )`, allowing runtime customization without changing saved block markup.
+
+```js
+import { addFilter } from '@wordpress/hooks';
+import AutoHeight from 'embla-carousel-auto-height';
+
+addFilter(
+    'rtcamp.carouselKit.emblaOptions',
+    'my-plugin/custom-options',
+    ( options ) => ( { ...options, duration: 40 } )
+);
+
+addFilter(
+    'rtcamp.carouselKit.emblaPlugins',
+    'my-plugin/auto-height',
+    ( plugins ) => [ ...plugins, AutoHeight() ]
+);
+```
+
+Both filters receive the carousel context object as the third argument. `rtcamp.carouselKit.emblaPlugins` also receives the filtered options on `options`.
+
+| Property | Type | Description |
+| :--- | :--- | :--- |
+| `context` | `CarouselContext` | Interactivity API context for the carousel. |
+| `root` | `HTMLElement` | Root `.rt-carousel` element. |
+| `viewport` | `HTMLElement` | Embla viewport element. |
+| `dynamicListContainer` | `HTMLElement \| null` | Query Loop or Terms Query template container when present. |
+| `options` | `EmblaOptionsType` | Only passed to `rtcamp.carouselKit.emblaPlugins`; contains filtered options. |
+
 ## Context (`CarouselContext`)
 
 The following properties are exposed in the Interactivity API context:

src/blocks/carousel/__tests__/view.test.ts

@@ -24,6 +24,14 @@ type EmblaViewportElement = HTMLElement & {
 	[EMBLA_KEY]?: EmblaCarouselType;
 };
 
+type HooksWindow = Window & {
+	wp?: {
+		hooks?: {
+			applyFilters?: jest.Mock;
+		};
+	};
+};
+
 import type { CarouselContext } from '../types';
 
 // Import view to trigger store registration
@@ -90,6 +98,20 @@ const createMockCarouselDOM = () => {
 	return { wrapper, viewport, button };
 };
 
+const mockVisibleViewport = ( viewport: HTMLElement ) => {
+	viewport.getBoundingClientRect = jest.fn( () => ( {
+		width: 100,
+		height: 0,
+		top: 0,
+		right: 0,
+		bottom: 0,
+		left: 0,
+		x: 0,
+		y: 0,
+		toJSON: () => ( {} ),
+	} ) );
+};
+
 /**
  * Helper to create mock Embla instance with all required methods.
  *
@@ -107,6 +129,8 @@ const createMockEmblaInstance = ( overrides = {} ) => ( {
 	canScrollNext: jest.fn( () => true ),
 	selectedScrollSnap: jest.fn( () => 0 ),
 	scrollSnapList: jest.fn( () => [ 0, 0.5, 1 ] ),
+	scrollProgress: jest.fn( () => 0 ),
+	slideNodes: jest.fn( () => [] ),
 	...overrides,
 } );
 
@@ -747,17 +771,7 @@ describe( 'Carousel View Module', () => {
 					return mockEmbla;
 				} );
 
-				viewport.getBoundingClientRect = jest.fn( () => ( {
-					width: 100,
-					height: 0,
-					top: 0,
-					right: 0,
-					bottom: 0,
-					left: 0,
-					x: 0,
-					y: 0,
-					toJSON: () => ( {} ),
-				} ) );
+				mockVisibleViewport( viewport );
 
 				( getContext as jest.Mock ).mockReturnValue( mockContext );
 				( getElement as jest.Mock ).mockReturnValue( { ref: wrapper } );
@@ -777,6 +791,64 @@ describe( 'Carousel View Module', () => {
 						originalIntersectionObserver;
 				}
 			} );
+
+			it( 'should filter Embla options and plugins before initialization', () => {
+				const mockContext = createMockContext( {
+					options: { duration: 25 },
+				} );
+				const { wrapper, viewport } = createMockCarouselDOM();
+				const mockEmbla = createMockEmblaInstance();
+				const originalIntersectionObserver = window.IntersectionObserver;
+				const extraPlugin = {
+					name: 'test-plugin',
+					options: {},
+					init: jest.fn(),
+					destroy: jest.fn(),
+				};
+
+				mockVisibleViewport( viewport );
+
+				const applyFilters = jest.fn( ( hookName, value ) => {
+					if ( hookName === 'rtcamp.carouselKit.emblaOptions' ) {
+						return { ...value, duration: 40 };
+					}
+					if ( hookName === 'rtcamp.carouselKit.emblaPlugins' ) {
+						return [ ...value, extraPlugin ];
+					}
+					return value;
+				} );
+
+				( window as HooksWindow ).wp = {
+					hooks: {
+						applyFilters,
+					},
+				};
+				( getContext as jest.Mock ).mockReturnValue( mockContext );
+				( getElement as jest.Mock ).mockReturnValue( { ref: wrapper } );
+				( EmblaCarousel as unknown as jest.Mock ).mockReturnValue( mockEmbla );
+				delete ( window as Window & { IntersectionObserver?: typeof IntersectionObserver } ).IntersectionObserver;
+
+				try {
+					storeConfig.callbacks.initCarousel();
+
+					expect( applyFilters ).toHaveBeenCalledTimes( 2 );
+					expect( applyFilters ).toHaveBeenNthCalledWith(
+						1,
+						'rtcamp.carouselKit.emblaOptions',
+						expect.objectContaining( { duration: 25 } ),
+						expect.objectContaining( { context: mockContext, root: wrapper, viewport } ),
+					);
+					expect( EmblaCarousel ).toHaveBeenCalledWith(
+						viewport,
+						expect.objectContaining( { duration: 40 } ),
+						[ extraPlugin ],
+					);
+				} finally {
+					( window as Window & { IntersectionObserver?: typeof IntersectionObserver } ).IntersectionObserver =
+						originalIntersectionObserver;
+					delete ( window as HooksWindow ).wp;
+				}
+			} );
 		} );
 	} );
 } );

src/blocks/carousel/block.json

@@ -90,5 +90,6 @@
 	"editorScript": "file:./index.js",
 	"editorStyle": "file:./index.css",
 	"style": "file:./style-index.css",
+	"viewScript": "wp-hooks",
 	"viewScriptModule": "file:./view.js"
-}
+}

src/blocks/carousel/view.ts

@@ -2,6 +2,7 @@ import { store, getContext, getElement } from '@wordpress/interactivity';
 import EmblaCarousel, {
 	type EmblaOptionsType,
 	type EmblaCarouselType,
+	type EmblaPluginType,
 } from 'embla-carousel';
 import Autoplay, { type AutoplayOptionsType } from 'embla-carousel-autoplay';
 import type { CarouselContext } from './types';
@@ -23,6 +24,40 @@ type EmblaViewportElement = HTMLElement & {
 
 export const emblaInstances = new WeakMap<HTMLElement, EmblaCarouselType>();
 
+type EmblaFilterContext = {
+	context: CarouselContext;
+	root: HTMLElement;
+	viewport: HTMLElement;
+	dynamicListContainer: HTMLElement | null;
+	options?: EmblaOptionsType;
+};
+
+type HooksWindow = Window & {
+	wp?: {
+		hooks?: {
+			applyFilters?: (
+				hookName: string,
+				value: unknown,
+				...args: unknown[]
+			) => unknown;
+		};
+	};
+};
+
+const applyEmblaFilter = <T>(
+	hookName: string,
+	value: T,
+	filterContext: EmblaFilterContext,
+): T => {
+	const applyFilters = ( window as HooksWindow ).wp?.hooks?.applyFilters;
+
+	if ( typeof applyFilters !== 'function' ) {
+		return value;
+	}
+
+	return applyFilters( hookName, value, filterContext ) as T;
+};
+
 const getElementRef = ( rawElement: unknown ): HTMLElement | null => {
 	if ( rawElement instanceof HTMLElement ) {
 		return rawElement;
@@ -263,13 +298,32 @@ store( 'rt-carousel/carousel', {
 						container: dynamicListContainer || null,
 					};
 
-					const plugins = [];
+					const plugins: EmblaPluginType[] = [];
 
 					if ( context.autoplay ) {
 						plugins.push( Autoplay( context.autoplay as AutoplayOptionsType ) );
 					}
 
-					const embla = EmblaCarousel( viewport, options, plugins );
+					const filterContext: EmblaFilterContext = {
+						context,
+						root: element,
+						viewport,
+						dynamicListContainer,
+					};
+
+					const filteredOptions = applyEmblaFilter(
+						'rtcamp.carouselKit.emblaOptions',
+						options,
+						filterContext,
+					);
+
+					const filteredPlugins = applyEmblaFilter(
+						'rtcamp.carouselKit.emblaPlugins',
+						plugins,
+						{ ...filterContext, options: filteredOptions },
+					);
+
+					const embla = EmblaCarousel( viewport, filteredOptions, filteredPlugins );
 
 					emblaInstances.set( viewport, embla );
 					viewport[ EMBLA_KEY ] = embla;