/**
 * External dependencies
 */
import isShallowEqual from '@wordpress/is-shallow-equal';

/**
 * Internal dependencies
 */
import { TYPES, DEFAULT_STATE, STATUS } from './constants';

const {
	SET_PRISTINE,
	SET_PROCESSING,
	SET_REDIRECT_URL,
	SET_COMPLETE,
	SET_HAS_ERROR,
	SET_NO_ERROR,
	INCREMENT_CALCULATING,
	DECREMENT_CALCULATING,
	SET_BILLING_DATA,
} = TYPES;

const { PRISTINE, IDLE, CALCULATING, PROCESSING, COMPLETE } = STATUS;

/**
 * Reducer for the checkout state
 *
 * @param {Object} state  Current state.
 * @param {Object} action Incoming action object.
 */
export const reducer = ( state = DEFAULT_STATE, { url, type, data } ) => {
	let status, nextStatus, newState;
	switch ( type ) {
		case SET_PRISTINE:
			newState = DEFAULT_STATE;
			break;
		case SET_REDIRECT_URL:
			newState =
				url !== state.url
					? {
							...state,
							redirectUrl: url,
					  }
					: state;
			break;
		case SET_COMPLETE:
			status = COMPLETE;
			nextStatus = state.status;
			if ( state.status === CALCULATING ) {
				status = CALCULATING;
				nextStatus = COMPLETE;
			}
			newState =
				status !== state.status
					? {
							...state,
							status,
							nextStatus,
					  }
					: state;
			break;
		case SET_PROCESSING:
			status = PROCESSING;
			nextStatus = state.status;
			if ( state.status === CALCULATING ) {
				status = CALCULATING;
				nextStatus = PROCESSING;
			}
			newState =
				status !== state.status
					? {
							...state,
							status,
							nextStatus,
							hasError: false,
					  }
					: state;
			// clear any error state.
			newState =
				newState.hasError === false
					? newState
					: { ...newState, hasError: false };
			break;
		case SET_HAS_ERROR:
			newState = state.hasError
				? state
				: {
						...state,
						hasError: true,
				  };
			newState =
				state.status === PROCESSING
					? {
							...newState,
							status: IDLE,
					  }
					: newState;
			break;
		case SET_NO_ERROR:
			newState = state.hasError
				? {
						...state,
						hasError: false,
				  }
				: state;
			break;
		case INCREMENT_CALCULATING:
			newState = {
				...state,
				status: CALCULATING,
				nextStatus: state.status,
				calculatingCount: state.calculatingCount + 1,
			};
			break;
		case DECREMENT_CALCULATING:
			status = CALCULATING;
			nextStatus = state.status;
			if ( state.calculatingCount <= 1 ) {
				status = state.nextStatus;
				nextStatus = IDLE;
			}
			newState = {
				...state,
				status,
				nextStatus,
				calculatingCount: Math.max( 0, state.calculatingCount - 1 ),
			};
			break;
		case SET_BILLING_DATA:
			newState = isShallowEqual( state.billingData, data )
				? state
				: {
						...state,
						billingData: {
							...data,
						},
				  };
			break;
	}
	// automatically update state to idle from pristine as soon as it
	// initially changes.
	if (
		newState !== state &&
		type !== SET_PRISTINE &&
		newState.status === PRISTINE
	) {
		newState.status = IDLE;
	}
	return newState;
};