index.js

/**
 * WordPress dependencies
 */
import { createQueue } from '@wordpress/priority-queue';
import {
	useRef,
	useCallback,
	useMemo,
	useSyncExternalStore,
	useDebugValue,
} from '@wordpress/element';
import isShallowEqual from '@wordpress/is-shallow-equal';

/**
 * Internal dependencies
 */
import useRegistry from '../registry-provider/use-registry';
import useAsyncMode from '../async-mode-provider/use-async-mode';

const renderQueue = createQueue();

/**
 * @typedef {import('../../types').StoreDescriptor<C>} StoreDescriptor
 * @template {import('../../types').AnyConfig} C
 */
/**
 * @typedef {import('../../types').ReduxStoreConfig<State,Actions,Selectors>} ReduxStoreConfig
 * @template State
 * @template {Record<string,import('../../types').ActionCreator>} Actions
 * @template Selectors
 */
/** @typedef {import('../../types').MapSelect} MapSelect */
/**
 * @typedef {import('../../types').UseSelectReturn<T>} UseSelectReturn
 * @template {MapSelect|StoreDescriptor<any>} T
 */

function Store( registry, suspense ) {
	const select = suspense ? registry.suspendSelect : registry.select;
	const queueContext = {};
	let lastMapSelect;
	let lastMapResult;
	let lastMapResultValid = false;
	let lastIsAsync;
	let subscriber;
	let didWarnUnstableReference;
	const storeStatesOnMount = new Map();

	function getStoreState( name ) {
		// If there's no store property (custom generic store), return an empty
		// object. When comparing the state, the empty objects will cause the
		// equality check to fail, setting `lastMapResultValid` to false.
		return registry.stores[ name ]?.store?.getState?.() ?? {};
	}

	const createSubscriber = ( stores ) => {
		// The set of stores the `subscribe` function is supposed to subscribe to. Here it is
		// initialized, and then the `updateStores` function can add new stores to it.
		const activeStores = [ ...stores ];

		// The `subscribe` function, which is passed to the `useSyncExternalStore` hook, could
		// be called multiple times to establish multiple subscriptions. That's why we need to
		// keep a set of active subscriptions;
		const activeSubscriptions = new Set();

		function subscribe( listener ) {
			// Maybe invalidate the value right after subscription was created.
			// React will call `getValue` after subscribing, to detect store
			// updates that happened in the interval between the `getValue` call
			// during render and creating the subscription, which is slightly
			// delayed. We need to ensure that this second `getValue` call will
			// compute a fresh value only if any of the store states have
			// changed in the meantime.
			if ( lastMapResultValid ) {
				for ( const name of activeStores ) {
					if (
						storeStatesOnMount.get( name ) !== getStoreState( name )
					) {
						lastMapResultValid = false;
					}
				}
			}

			storeStatesOnMount.clear();

			const onStoreChange = () => {
				// Invalidate the value on store update, so that a fresh value is computed.
				lastMapResultValid = false;
				listener();
			};

			const onChange = () => {
				if ( lastIsAsync ) {
					renderQueue.add( queueContext, onStoreChange );
				} else {
					onStoreChange();
				}
			};

			const unsubs = [];
			function subscribeStore( storeName ) {
				unsubs.push( registry.subscribe( onChange, storeName ) );
			}

			for ( const storeName of activeStores ) {
				subscribeStore( storeName );
			}

			activeSubscriptions.add( subscribeStore );

			return () => {
				activeSubscriptions.delete( subscribeStore );

				for ( const unsub of unsubs.values() ) {
					// The return value of the subscribe function could be undefined if the store is a custom generic store.
					unsub?.();
				}
				// Cancel existing store updates that were already scheduled.
				renderQueue.cancel( queueContext );
			};
		}

		// Check if `newStores` contains some stores we're not subscribed to yet, and add them.
		function updateStores( newStores ) {
			for ( const newStore of newStores ) {
				if ( activeStores.includes( newStore ) ) {
					continue;
				}

				// New `subscribe` calls will subscribe to `newStore`, too.
				activeStores.push( newStore );

				// Add `newStore` to existing subscriptions.
				for ( const subscription of activeSubscriptions ) {
					subscription( newStore );
				}
			}
		}

		return { subscribe, updateStores };
	};

	return ( mapSelect, isAsync ) => {
		function updateValue() {
			// If the last value is valid, and the `mapSelect` callback hasn't changed,
			// then we can safely return the cached value. The value can change only on
			// store update, and in that case value will be invalidated by the listener.
			if ( lastMapResultValid && mapSelect === lastMapSelect ) {
				return lastMapResult;
			}

			const listeningStores = { current: null };
			const mapResult = registry.__unstableMarkListeningStores(
				() => mapSelect( select, registry ),
				listeningStores
			);

			if ( process.env.NODE_ENV === 'development' ) {
				if ( ! didWarnUnstableReference ) {
					const secondMapResult = mapSelect( select, registry );
					if ( ! isShallowEqual( mapResult, secondMapResult ) ) {
						// eslint-disable-next-line no-console
						console.warn(
							`The 'useSelect' hook returns different values when called with the same state and parameters. This can lead to unnecessary rerenders.`
						);
						didWarnUnstableReference = true;
					}
				}
			}

			if ( ! subscriber ) {
				for ( const name of listeningStores.current ) {
					storeStatesOnMount.set( name, getStoreState( name ) );
				}
				subscriber = createSubscriber( listeningStores.current );
			} else {
				subscriber.updateStores( listeningStores.current );
			}

			// If the new value is shallow-equal to the old one, keep the old one so
			// that we don't trigger unwanted updates that do a `===` check.
			if ( ! isShallowEqual( lastMapResult, mapResult ) ) {
				lastMapResult = mapResult;
			}
			lastMapSelect = mapSelect;
			lastMapResultValid = true;
		}

		function getValue() {
			// Update the value in case it's been invalidated or `mapSelect` has changed.
			updateValue();
			return lastMapResult;
		}

		// When transitioning from async to sync mode, cancel existing store updates
		// that have been scheduled, and invalidate the value so that it's freshly
		// computed. It might have been changed by the update we just cancelled.
		if ( lastIsAsync && ! isAsync ) {
			lastMapResultValid = false;
			renderQueue.cancel( queueContext );
		}

		updateValue();

		lastIsAsync = isAsync;

		// Return a pair of functions that can be passed to `useSyncExternalStore`.
		return { subscribe: subscriber.subscribe, getValue };
	};
}

function useStaticSelect( storeName ) {
	return useRegistry().select( storeName );
}

function useMappingSelect( suspense, mapSelect, deps ) {
	const registry = useRegistry();
	const isAsync = useAsyncMode();
	const store = useMemo(
		() => Store( registry, suspense ),
		[ registry, suspense ]
	);

	// These are "pass-through" dependencies from the parent hook,
	// and the parent should catch any hook rule violations.
	// eslint-disable-next-line react-hooks/exhaustive-deps
	const selector = useCallback( mapSelect, deps );
	const { subscribe, getValue } = store( selector, isAsync );
	const result = useSyncExternalStore( subscribe, getValue, getValue );
	useDebugValue( result );
	return result;
}

/**
 * Custom react hook for retrieving props from registered selectors.
 *
 * In general, this custom React hook follows the
 * [rules of hooks](https://react.dev/reference/rules/rules-of-hooks).
 *
 * @template {MapSelect | StoreDescriptor<any>} T
 * @param {T}         mapSelect Function called on every state change. The returned value is
 *                              exposed to the component implementing this hook. The function
 *                              receives the `registry.select` method on the first argument
 *                              and the `registry` on the second argument.
 *                              When a store key is passed, all selectors for the store will be
 *                              returned. This is only meant for usage of these selectors in event
 *                              callbacks, not for data needed to create the element tree.
 * @param {unknown[]} deps      If provided, this memoizes the mapSelect so the same `mapSelect` is
 *                              invoked on every state change unless the dependencies change.
 *
 * @example
 * ```js
 * import { useSelect } from '@wordpress/data';
 * import { store as myCustomStore } from 'my-custom-store';
 *
 * function HammerPriceDisplay( { currency } ) {
 *   const price = useSelect( ( select ) => {
 *     return select( myCustomStore ).getPrice( 'hammer', currency );
 *   }, [ currency ] );
 *   return new Intl.NumberFormat( 'en-US', {
 *     style: 'currency',
 *     currency,
 *   } ).format( price );
 * }
 *
 * // Rendered in the application:
 * // <HammerPriceDisplay currency="USD" />
 * ```
 *
 * In the above example, when `HammerPriceDisplay` is rendered into an
 * application, the price will be retrieved from the store state using the
 * `mapSelect` callback on `useSelect`. If the currency prop changes then
 * any price in the state for that currency is retrieved. If the currency prop
 * doesn't change and other props are passed in that do change, the price will
 * not change because the dependency is just the currency.
 *
 * When data is only used in an event callback, the data should not be retrieved
 * on render, so it may be useful to get the selectors function instead.
 *
 * **Don't use `useSelect` this way when calling the selectors in the render
 * function because your component won't re-render on a data change.**
 *
 * ```js
 * import { useSelect } from '@wordpress/data';
 * import { store as myCustomStore } from 'my-custom-store';
 *
 * function Paste( { children } ) {
 *   const { getSettings } = useSelect( myCustomStore );
 *   function onPaste() {
 *     // Do something with the settings.
 *     const settings = getSettings();
 *   }
 *   return <div onPaste={ onPaste }>{ children }</div>;
 * }
 * ```
 * @return {UseSelectReturn<T>} A custom react hook.
 */
export default function useSelect( mapSelect, deps ) {
	// On initial call, on mount, determine the mode of this `useSelect` call
	// and then never allow it to change on subsequent updates.
	const staticSelectMode = typeof mapSelect !== 'function';
	const staticSelectModeRef = useRef( staticSelectMode );

	if ( staticSelectMode !== staticSelectModeRef.current ) {
		const prevMode = staticSelectModeRef.current ? 'static' : 'mapping';
		const nextMode = staticSelectMode ? 'static' : 'mapping';
		throw new Error(
			`Switching useSelect from ${ prevMode } to ${ nextMode } is not allowed`
		);
	}

	/* eslint-disable react-hooks/rules-of-hooks */
	// `staticSelectMode` is not allowed to change during the hook instance's,
	// lifetime, so the rules of hooks are not really violated.
	return staticSelectMode
		? useStaticSelect( mapSelect )
		: useMappingSelect( false, mapSelect, deps );
	/* eslint-enable react-hooks/rules-of-hooks */
}

/**
 * A variant of the `useSelect` hook that has the same API, but is a compatible
 * Suspense-enabled data source.
 *
 * @template {MapSelect} T
 * @param {T}     mapSelect Function called on every state change. The
 *                          returned value is exposed to the component
 *                          using this hook. The function receives the
 *                          `registry.suspendSelect` method as the first
 *                          argument and the `registry` as the second one.
 * @param {Array} deps      A dependency array used to memoize the `mapSelect`
 *                          so that the same `mapSelect` is invoked on every
 *                          state change unless the dependencies change.
 *
 * @throws {Promise} A suspense Promise that is thrown if any of the called
 * selectors is in an unresolved state.
 *
 * @return {ReturnType<T>} Data object returned by the `mapSelect` function.
 */
export function useSuspenseSelect( mapSelect, deps ) {
	return useMappingSelect( true, mapSelect, deps );
}