Add geocoder cache

routes/geocoders/Geocoder.ts

@@ -1,11 +1,49 @@
+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.
 	 */
-	public abstract geocodeLocation( location: string ): Promise<GeoCoordinates>;
+	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;
+	}
 }