/**
 * WordPress dependencies
 */
import { combineReducers } from '@wordpress/data';
/**
 * Internal dependencies
 */
import type { StoreState, WPPreferencesPersistenceLayer } from './types';
import type { AvailableActions } from './actions';

/**
 * Reducer returning the defaults for user preferences.
 *
 * This is kept intentionally separate from the preferences
 * themselves so that defaults are not persisted.
 *
 * @param state  Current state.
 * @param action Dispatched action.
 *
 * @return Updated state.
 */
export function defaults(
	state: StoreState[ 'defaults' ] = {},
	action: AvailableActions
): StoreState[ 'defaults' ] {
	if ( action.type === 'SET_PREFERENCE_DEFAULTS' ) {
		const { scope, defaults: values } = action;
		return {
			...state,
			[ scope ]: {
				...state[ scope ],
				...values,
			},
		};
	}

	return state;
}

type PreferencesReducer = (
	state: StoreState[ 'preferences' ],
	action: AvailableActions
) => StoreState[ 'preferences' ];

/**
 * Higher order reducer that does the following:
 * - Merges any data from the persistence layer into the state when the
 *   `SET_PERSISTENCE_LAYER` action is received.
 * - Passes any preferences changes to the persistence layer.
 *
 * @param reducer The preferences reducer.
 *
 * @return The enhanced reducer.
 */
function withPersistenceLayer( reducer: PreferencesReducer ) {
	let persistenceLayer: WPPreferencesPersistenceLayer< any >;

	return ( state: StoreState[ 'preferences' ], action: AvailableActions ) => {
		// Set up the persistence layer, and return the persisted data
		// as the state.
		if ( action.type === 'SET_PERSISTENCE_LAYER' ) {
			const { persistenceLayer: persistence, persistedData } = action;
			persistenceLayer = persistence;
			return persistedData;
		}

		const nextState = reducer( state, action );
		if ( action.type === 'SET_PREFERENCE_VALUE' ) {
			persistenceLayer?.set( nextState );
		}

		return nextState;
	};
}

/**
 * Reducer returning the user preferences.
 *
 * @param {Object} state  Current state.
 * @param {Object} action Dispatched action.
 *
 * @return {Object} Updated state.
 */
export const preferences = withPersistenceLayer( ( state = {}, action ) => {
	if ( action.type === 'SET_PREFERENCE_VALUE' ) {
		const { scope, name, value } = action;
		return {
			...state,
			[ scope ]: {
				...state[ scope ],
				[ name ]: value,
			},
		};
	}

	return state;
} );

export default combineReducers( {
	defaults,
	preferences,
} );