reducer.js

/**
 * External dependencies
 */
import { get, omit, has } from 'lodash';
import EquivalentKeyMap from 'equivalent-key-map';

/**
 * Reducer function returning next state for selector resolution of
 * subkeys, object form:
 *
 *  reducerKey -> selectorName -> EquivalentKeyMap<Array,boolean>
 *
 * @param {Object} state  Current state.
 * @param {Object} action Dispatched action.
 *
 * @return {Object} Next state.
 */
export function isResolved( state = {}, action ) {
	switch ( action.type ) {
		case 'START_RESOLUTION':
		case 'FINISH_RESOLUTION': {
			const { reducerKey, selectorName, args } = action;
			const isStarting = action.type === 'START_RESOLUTION';
			const subState = get( state, [ reducerKey, selectorName ] );
			const nextSubState = new EquivalentKeyMap( subState );
			nextSubState.set( args, isStarting );
			return {
				...state,
				[ reducerKey ]: {
					...state[ reducerKey ],
					[ selectorName ]: nextSubState,
				},
			};
		}

		case 'INVALIDATE_RESOLUTION': {
			const { reducerKey, selectorName, args } = action;
			const subState = get( state, [ reducerKey, selectorName ] );
			const nextSubState = new EquivalentKeyMap( subState );
			nextSubState.delete( args );
			return {
				...state,
				[ reducerKey ]: {
					...state[ reducerKey ],
					[ selectorName ]: nextSubState,
				},
			};
		}

		case 'INVALIDATE_RESOLUTION_FOR_STORE':
			return has( state, action.reducerKey ) ?
				omit( state, [ action.reducerKey ] ) :
				state;

		case 'INVALIDATE_RESOLUTION_FOR_STORE_SELECTOR': {
			const { reducerKey, selectorName } = action;
			return has( state, [ reducerKey, selectorName ] ) ?
				{
					...state,
					[ reducerKey ]: omit(
						state[ reducerKey ],
						[ selectorName ]
					),
				} :
				state;
		}
	}

	return state;
}

export default isResolved;