66 lines
1.9 KiB
TypeScript
66 lines
1.9 KiB
TypeScript
import fs = require("fs");
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import { GeoCoordinates } from "../../types";
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import { CodedError, ErrorCode } from "../../errors";
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export abstract class Geocoder {
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private static cacheFile: string = __dirname + "/../../../geocoderCache.json";
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private cache: Map<string, GeoCoordinates>;
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public constructor() {
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// Load the cache from disk.
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if ( fs.existsSync( Geocoder.cacheFile ) ) {
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this.cache = new Map( JSON.parse( fs.readFileSync( Geocoder.cacheFile, "utf-8" ) ) );
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} else {
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this.cache = new Map();
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}
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// Write the cache to disk every 5 minutes.
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setInterval( () => {
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this.saveCache();
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}, 5 * 60 * 1000 );
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}
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private saveCache(): void {
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fs.writeFileSync( Geocoder.cacheFile, JSON.stringify( Array.from( this.cache.entries() ) ) );
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}
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/**
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* Converts a location name to geographic coordinates.
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* @param location A location name.
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* @return A Promise that will be resolved with the GeoCoordinates of the specified location, or rejected with a
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* CodedError.
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*/
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protected abstract geocodeLocation( location: string ): Promise<GeoCoordinates>;
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/**
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* Converts a location name to geographic coordinates, first checking the cache and updating it if necessary.
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*/
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public async getLocation( location: string ): Promise<GeoCoordinates> {
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if ( this.cache.has( location ) ) {
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const coords: GeoCoordinates = this.cache.get( location );
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if ( coords == null ) {
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// Throw an error if there are no results for this location.
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throw new CodedError( ErrorCode.NoLocationFound );
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} else {
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return coords;
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}
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}
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try {
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const coords: GeoCoordinates = await this.geocodeLocation( location );
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this.cache.set( location, coords );
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return coords;
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} catch ( ex ) {
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if ( ex instanceof CodedError && ex.errCode == ErrorCode.NoLocationFound ) {
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// Store in the cache the fact that this location has no results.
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this.cache.set( location, null );
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}
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throw ex;
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}
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}
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}
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