Add awareness of 'api/capabilities', see #880

Logic/Osm/OsmConnection.ts

@@ -28,6 +28,8 @@ export default class UserDetails {
     }
 }
 
+export type OsmServiceState = "online" | "readonly" | "offline" | "unknown" | "unreachable"
+
 export class OsmConnection {
     public static readonly oauth_configs = {
         osm: {
@@ -46,6 +48,13 @@ export class OsmConnection {
     public auth
     public userDetails: UIEventSource<UserDetails>
     public isLoggedIn: Store<boolean>
+    public gpxServiceIsOnline: UIEventSource<OsmServiceState> = new UIEventSource<OsmServiceState>(
+        "unknown"
+    )
+    public apiIsOnline: UIEventSource<OsmServiceState> = new UIEventSource<OsmServiceState>(
+        "unknown"
+    )
+
     public loadingStatus = new UIEventSource<"not-attempted" | "loading" | "error" | "logged-in">(
         "not-attempted"
     )
@@ -94,7 +103,13 @@ export class OsmConnection {
             ud.totalMessages = 42
         }
         const self = this
-        this.isLoggedIn = this.userDetails.map((user) => user.loggedIn)
+        this.UpdateCapabilities()
+        this.isLoggedIn = this.userDetails.map(
+            (user) =>
+                user.loggedIn &&
+                (self.apiIsOnline.data === "unknown" || self.apiIsOnline.data === "online"),
+            [this.apiIsOnline]
+        )
         this.isLoggedIn.addCallback((isLoggedIn) => {
             if (self.userDetails.data.loggedIn == false && isLoggedIn == true) {
                 // We have an inconsistency: the userdetails say we _didn't_ log in, but this actor says we do
@@ -160,11 +175,17 @@ export class OsmConnection {
         this.loadingStatus.setData("not-attempted")
     }
 
+    /**
+     * The backend host, without path or trailing '/'
+     *
+     * new OsmConnection().Backend() // => "https://www.openstreetmap.org"
+     */
     public Backend(): string {
         return this._oauth_config.url
     }
 
     public AttemptLogin() {
+        this.UpdateCapabilities()
         this.loadingStatus.setData("loading")
         if (this.fakeUser) {
             this.loadingStatus.setData("logged-in")
@@ -504,4 +525,26 @@ export class OsmConnection {
             }
         })
     }
+
+    private UpdateCapabilities(): void {
+        const self = this
+        this.FetchCapabilities().then(({ api, gpx }) => {
+            self.apiIsOnline.setData(api)
+            self.gpxServiceIsOnline.setData(gpx)
+        })
+    }
+
+    private async FetchCapabilities(): Promise<{ api: OsmServiceState; gpx: OsmServiceState }> {
+        const result = await Utils.downloadAdvanced(this.Backend() + "/api/0.6/capabilities")
+        if (result["content"] === undefined) {
+            console.log("Something went wrong:", result)
+            return { api: "unreachable", gpx: "unreachable" }
+        }
+        const xmlRaw = result["content"]
+        const parsed = new DOMParser().parseFromString(xmlRaw, "text/xml")
+        const statusEl = parsed.getElementsByTagName("status")[0]
+        const api = <OsmServiceState>statusEl.getAttribute("api")
+        const gpx = <OsmServiceState>statusEl.getAttribute("gpx")
+        return { api, gpx }
+    }
 }