import fs = require("fs");

import { GeoCoordinates } from "../../types";

export abstract class Geocoder {

	private static cacheFile: string = __dirname + "/../../../geocoderCache.json";

	private cache: Map<string, GeoCoordinates>;

	public constructor() {
		// Load the cache from disk.
		if ( fs.existsSync( Geocoder.cacheFile ) ) {
			this.cache = new Map( JSON.parse( fs.readFileSync( Geocoder.cacheFile, "utf-8" ) ) );
		} else {
			this.cache = new Map();
		}

		// Write the cache to disk every 5 minutes.
		setInterval( () => {
			this.saveCache();
		}, 5 * 60 * 1000 );
	}

	private saveCache(): void {
		fs.writeFileSync( Geocoder.cacheFile, JSON.stringify( Array.from( this.cache.entries() ) ) );
	}

	/**
	 * Converts a location name to geographic coordinates.
	 * @param location A location name.
	 * @return A Promise that will be resolved with the GeoCoordinates of the specified location, or rejected with a
	 * CodedError.
	 */
	protected abstract geocodeLocation( location: string ): Promise<GeoCoordinates>;

	/**
	 * Converts a location name to geographic coordinates, first checking the cache and updating it if necessary.
	 */
	public async getLocation( location: string ): Promise<GeoCoordinates> {
		if ( this.cache.has( location ) ) {
			return this.cache.get( location );
		}

		const coords: GeoCoordinates = await this.geocodeLocation( location );
		this.cache.set( location, coords );
		return coords;
	}
}