Refactor instance list fetcher

api/settings.js

@@ -2,7 +2,7 @@ const {render, redirect} = require("pinski/plugins")
 const db = require("../utils/db")
 const {getToken, getUser} = require("../utils/getuser")
 const constants = require("../utils/constants")
-const {getInstances} = require("../background/instances")
+const {instancesList} = require("../background/instances")
 const validate = require("../utils/validate")
 const V = validate.V
 
@@ -11,7 +11,7 @@ module.exports = [
 		route: "/settings", methods: ["GET"], code: async ({req}) => {
 			const user = getUser(req)
 			const settings = user.getSettings()
-			const instances = getInstances()
+			const instances = instancesList.get()
 			return render(200, "pug/settings.pug", {constants, user, settings, instances})
 		}
 	},

background/instances.js

@@ -1,23 +1,45 @@
 const {request} = require("../utils/request")
 
-let globalList = []
+class InstancesList {
+	constructor() {
+		this.list = []
+		this.inflight = null
+		this.update()
+		setInterval(() => {
+			this.update()
+		}, 60*60*1000)
+	}
 
-function execute() {
-	return request("https://api.invidious.io/instances.json?sort_by=health").then(res => res.json()).then(list => {
+	/**
+	 * Updates the list. Returns a promise of the new list. Called
+	 * automatically.
+	 */
+	update() {
+		return this.inflight = request("https://api.invidious.io/instances.json?sort_by=health").then(res => res.json()).then(list => {
 			list = list.filter(i => i[1].type === "https").map(i => i[1].uri.replace(/\/+$/, ""))
-		globalList = list
-	}).catch(error => {
-		console.error(error)
+			this.list = list
+			this.inflight = null
+			return this.list
 		})
+	}
+
+	/**
+	 * Return a promise of the list. If updates are in progress, wait
+	 * for them.
+	 */
+	fetch() {
+		if (this.inflight) return this.inflight
+		else return Promise.resolve(this.list)
+	}
+
+	/**
+	 * Return the current list, no matter whether it's been updated at all.
+	 */
+	get() {
+		return this.list
+	}
 }
 
-function getInstances() {
-	return globalList
-}
+const instancesList = new InstancesList()
 
-execute()
-setInterval(() => {
-	execute()
-}, 60*60*1000)
-
-module.exports.getInstances = getInstances
+module.exports.instancesList = instancesList