@wordpress/data/build-module/plugins/persistence/index.js

Data module for WordPress.

/**
 * External dependencies
 */
import { isPlainObject } from 'is-plain-object';
import deepmerge from 'deepmerge';

/**
 * Internal dependencies
 */
import defaultStorage from './storage/default';
import { combineReducers } from '../../';

/** @typedef {import('../../registry').WPDataRegistry} WPDataRegistry */

/** @typedef {import('../../registry').WPDataPlugin} WPDataPlugin */

/**
 * @typedef {Object} WPDataPersistencePluginOptions Persistence plugin options.
 *
 * @property {Storage} storage    Persistent storage implementation. This must
 *                                at least implement `getItem` and `setItem` of
 *                                the Web Storage API.
 * @property {string}  storageKey Key on which to set in persistent storage.
 */

/**
 * Default plugin storage.
 *
 * @type {Storage}
 */
const DEFAULT_STORAGE = defaultStorage;

/**
 * Default plugin storage key.
 *
 * @type {string}
 */
const DEFAULT_STORAGE_KEY = 'WP_DATA';

/**
 * Higher-order reducer which invokes the original reducer only if state is
 * inequal from that of the action's `nextState` property, otherwise returning
 * the original state reference.
 *
 * @param {Function} reducer Original reducer.
 *
 * @return {Function} Enhanced reducer.
 */
export const withLazySameState = reducer => (state, action) => {
  if (action.nextState === state) {
    return state;
  }
  return reducer(state, action);
};

/**
 * Creates a persistence interface, exposing getter and setter methods (`get`
 * and `set` respectively).
 *
 * @param {WPDataPersistencePluginOptions} options Plugin options.
 *
 * @return {Object} Persistence interface.
 */
export function createPersistenceInterface(options) {
  const {
    storage = DEFAULT_STORAGE,
    storageKey = DEFAULT_STORAGE_KEY
  } = options;
  let data;

  /**
   * Returns the persisted data as an object, defaulting to an empty object.
   *
   * @return {Object} Persisted data.
   */
  function getData() {
    if (data === undefined) {
      // If unset, getItem is expected to return null. Fall back to
      // empty object.
      const persisted = storage.getItem(storageKey);
      if (persisted === null) {
        data = {};
      } else {
        try {
          data = JSON.parse(persisted);
        } catch (error) {
          // Similarly, should any error be thrown during parse of
          // the string (malformed JSON), fall back to empty object.
          data = {};
        }
      }
    }
    return data;
  }

  /**
   * Merges an updated reducer state into the persisted data.
   *
   * @param {string} key   Key to update.
   * @param {*}      value Updated value.
   */
  function setData(key, value) {
    data = {
      ...data,
      [key]: value
    };
    storage.setItem(storageKey, JSON.stringify(data));
  }
  return {
    get: getData,
    set: setData
  };
}

/**
 * Data plugin to persist store state into a single storage key.
 *
 * @param {WPDataRegistry}                  registry      Data registry.
 * @param {?WPDataPersistencePluginOptions} pluginOptions Plugin options.
 *
 * @return {WPDataPlugin} Data plugin.
 */
function persistencePlugin(registry, pluginOptions) {
  const persistence = createPersistenceInterface(pluginOptions);

  /**
   * Creates an enhanced store dispatch function, triggering the state of the
   * given store name to be persisted when changed.
   *
   * @param {Function}       getState  Function which returns current state.
   * @param {string}         storeName Store name.
   * @param {?Array<string>} keys      Optional subset of keys to save.
   *
   * @return {Function} Enhanced dispatch function.
   */
  function createPersistOnChange(getState, storeName, keys) {
    let getPersistedState;
    if (Array.isArray(keys)) {
      // Given keys, the persisted state should by produced as an object
      // of the subset of keys. This implementation uses combineReducers
      // to leverage its behavior of returning the same object when none
      // of the property values changes. This allows a strict reference
      // equality to bypass a persistence set on an unchanging state.
      const reducers = keys.reduce((accumulator, key) => Object.assign(accumulator, {
        [key]: (state, action) => action.nextState[key]
      }), {});
      getPersistedState = withLazySameState(combineReducers(reducers));
    } else {
      getPersistedState = (state, action) => action.nextState;
    }
    let lastState = getPersistedState(undefined, {
      nextState: getState()
    });
    return () => {
      const state = getPersistedState(lastState, {
        nextState: getState()
      });
      if (state !== lastState) {
        persistence.set(storeName, state);
        lastState = state;
      }
    };
  }
  return {
    registerStore(storeName, options) {
      if (!options.persist) {
        return registry.registerStore(storeName, options);
      }

      // Load from persistence to use as initial state.
      const persistedState = persistence.get()[storeName];
      if (persistedState !== undefined) {
        let initialState = options.reducer(options.initialState, {
          type: '@@WP/PERSISTENCE_RESTORE'
        });
        if (isPlainObject(initialState) && isPlainObject(persistedState)) {
          // If state is an object, ensure that:
          // - Other keys are left intact when persisting only a
          //   subset of keys.
          // - New keys in what would otherwise be used as initial
          //   state are deeply merged as base for persisted value.
          initialState = deepmerge(initialState, persistedState, {
            isMergeableObject: isPlainObject
          });
        } else {
          // If there is a mismatch in object-likeness of default
          // initial or persisted state, defer to persisted value.
          initialState = persistedState;
        }
        options = {
          ...options,
          initialState
        };
      }
      const store = registry.registerStore(storeName, options);
      store.subscribe(createPersistOnChange(store.getState, storeName, options.persist));
      return store;
    }
  };
}
persistencePlugin.__unstableMigrate = () => {};
export default persistencePlugin;
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