portfolio/packages/router/src/index.js

import { isFunction, isUndefined, Null, ObjectKeys } from 'trimkit';

const VARMATCH_RE = /:([^\/]+)/g;
const ROUTEELEMENT_RE = /^[^\/]+$/;
const nop = () => 1;
const digestRoutes = (routes, baseUrl) =>
	routes.map((route, i) => {
		const reg = route.path.replace(VARMATCH_RE, (m, varName) => {
			const varDef = route.vars || {};
			const regExStr = '' + (varDef[varName] || /[^\/]+/);
			return '(' + regExStr.substring(1, regExStr.lastIndexOf('/')) + ')';
		});

		return {
			matcher: new RegExp(`^${baseUrl}${reg}$`),
			_i: i,
			...route
		};
	});

export function Router(routes, baseUrl = '#') {
	let listening = false;
	let currentRoute = Null;
	let reEnterHook = Null;

	let routeMatcher = digestRoutes(routes, baseUrl);
	let routeByName = routeMatcher.reduce(
		(obj, route) => (route.name ? Object.assign(obj, { [route.name]: route }) : obj),
		{}
	);

	function goto(urlOrName, vars, fromLocation) {
		const url = urlOrName.startsWith(baseUrl) ? urlOrName : href(urlOrName, vars);

		if (listening && _location() !== url) {
			// If we're not there make the change and exit.
			location.hash = url;
			return;
		}

		if (currentRoute && currentRoute.path === url) {
			// This is only supposed to happen when recovering from a bad path.
			return;
		}

		let routeVars = {};

		const routeMatch = routeMatcher.find(({ matcher, path }) => {
			const match = url.match(matcher);
			if (!match) {
				return false;
			}

			if (path.indexOf(':') !== -1) {
				match.shift();
				path.replace(VARMATCH_RE, (_, varName) => {
					// We're abusing RegExp.replace here and it's awesome!
					routeVars[varName] = match.shift();
				});
			}

			return true;
		});

		if (routeMatch) {
			let newRoute = {
				name: routeMatch.name,
				vars: routeVars,
				path: url,
				_i: routeMatch._i
			};
			if (currentRoute && currentRoute._i === newRoute._i && isFunction(reEnterHook)) {
				const result = reEnterHook(newRoute);
				currentRoute = newRoute;
				return Promise.resolve(result);
			} else {
				let exit = currentRoute && currentRoute._i ? routes[currentRoute._i].exit || nop : nop;
				return Promise.resolve(exit(api, currentRoute, newRoute))
					.catch(() => {})
					.then(() => {
						reEnterHook = routes[routeMatch._i].enter(api, newRoute);
						currentRoute = newRoute;
					});
			}
		} else if (currentRoute && fromLocation) {
			// If we are listening and we receive an unmatched path, go back.
			location.hash = currentRoute.path;
			return;
		}
		// Either we received a goto call or a start call to in invalid path.
		throw new Error(`No route for "${url}"`);
	}

	function href(routeName, vars) {
		const route = routeByName[routeName];
		if (!route) {
			throw new Error(`Invalid route ${routeName}.`);
		}

		let path = '' + route.path;

		if (route.vars) {
			path = path.replace(VARMATCH_RE, (_, varName) => {
				let value = vars[varName];
				if ((route.vars[varName] || ROUTEELEMENT_RE).test(value)) {
					value = isUndefined(value) ? '' : '' + value;
					return value;
				}

				throw new Error(`Invalid value for route ${path} var ${varName}: ${value}.`);
			});
		}
		return `${baseUrl}${path}`;
	}

	function _location() {
		return location.hash;
	}

	function _handler() {
		goto(_location(), Null, true);
	}

	function start(initialRoute) {
		if (listening) {
			return;
		}

		self.addEventListener('hashchange', _handler, false);
		listening = true;
		goto(_location() || initialRoute);
	}

	function stop() {
		self.removeEventListener('hashchange', _handler);
	}

	function current() {
		return currentRoute;
	}

	const api = {
		goto,
		href,
		start,
		stop,
		current
	};

	return api;
}