Rewrote the api rate limiter with promises instead of callbacks

lib/systems.js

@@ -0,0 +1,36 @@
+import * as api from './api.js';
+import * as db from '../database/systems.js';
+
+// Retrieves a list of waypoints that have a specific ctx.trait like a SHIPYARD or a MARKETPLACE in the system ctx.symbol
+export async function trait(ctx) {
+	const s = await getSystem(ctx);
+	return s.filter(s => s.traits.some(t => t.symbol === ctx.trait));
+}
+
+// Retrieves a list of waypoints that have a specific ctx.type like ASTEROID_FIELD in the system ctx.symbol
+export async function type(ctx, response) {
+	const s = await getSystem(ctx);
+	return s.filter(s => s.type === ctx.type);
+}
+
+// Retrieves the system's information for ctx.symbol and cache it in the database
+async function getSystem(ctx) {
+	let s = db.getSystem(ctx.symbol);
+	if (s === null) {
+		const response = await api.send({endpoint: `/systems/${ctx.symbol}/waypoints?limit=20&page=1`});
+		if (response.error !== undefined) {
+			switch(response.error.code) {
+			case 404:
+				throw `Error retrieving waypoints for system ${ctx.symbol}: ${response.error.message}`;
+			default: // yet unhandled error
+				throw response;
+			}
+		}
+		if (response.meta !== undefined && response.meta.total > response.meta.limit) {
+			throw `Error retrieving waypoints for system ${ctx.symbol}: Pagination is not implemented yet!`;
+		}
+		s = response.data;
+		db.setSystem(ctx.symbol, s);
+	}
+	return s;
+}