/**
 * Use this class to ensure Google Maps API javascript is loaded before running any google map specific code.
 */
export class GoogleMapsApi {
	/**
	 * Constructor set up config.
	 */
	constructor() {
		// api key for google maps
		this.apiKey = 'APIKEY';

		// set a globally scoped callback if it doesn't already exist
		if (!window._GoogleMapsApi) {
			this.callbackName = '_GoogleMapsApi.mapLoaded';
			window._GoogleMapsApi = this;
			window._GoogleMapsApi.mapLoaded = this.mapLoaded.bind(this);
		}
	}

	/**
	 * Load the Google Maps API javascript
	 */
	load() {
		if (!this.promise) {
			this.promise = new Promise(resolve => {
				this.resolve = resolve;
				if (typeof window.google === 'undefined') {
					const script = document.createElement('script');
					script.src = `//maps.googleapis.com/maps/api/js?key=${this.apiKey}&callback=${this.callbackName}`;
					script.async = true;
					document.body.append(script);
				} else {
					this.resolve();
				}
			});
		}

		return this.promise;
	}

	/**
	 * Globally scoped callback for the map loaded
	 */
	mapLoaded() {
		if (this.resolve) {
			this.resolve();
		}
	}
}