extension: allow running without the backend if host set to empty string

relevant to #120

README.org

@@ -324,7 +324,7 @@ Visits have the following fields:
 
 - source (or indexer) is any function that extract visits from raw files and generates a stream of visits (i.e. =Iterable[Visit]=).
 - promnesia indexer goes through the sources, specified in config, collects the visits and puts in the database
-- promnesia server reads visits form the database, and them to the extension
+- promnesia server reads visits form the database, and sends them to the extension
 
 
 Now let's consider some *concrete* examples of different kinds of Visits:

extension/src/background.js

@@ -2,7 +2,7 @@
 
 import type {Locator, Src, Url, Second, JsonArray, JsonObject, AwareDate, NaiveDate} from './common';
 import {Visit, Visits, Blacklisted, unwrap, Methods, ldebug, linfo, lerror, lwarn} from './common';
-import {get_options_async, setOptions, THIS_BROWSER_TAG} from './options';
+import {get_options_async, getOptions, setOptions, THIS_BROWSER_TAG} from './options';
 import {chromeTabsExecuteScriptAsync, chromeTabsInsertCSS, chromeTabsQueryAsync, chromeRuntimeGetPlatformInfo, chromeTabsGet} from './async_chrome';
 import {showTabNotification, showBlackListedNotification, showIgnoredNotification, defensify, notify} from './notifications';
 import {Blacklist} from './blacklist'
@@ -64,7 +64,17 @@ function rawToVisits(vis: JsonObject): Visits {
 
 
 async function queryBackendCommon<R>(params, endp: string): Promise<R> {
-    const opts = await get_options_async();
+    const opts = await getOptions()
+    if (opts.host == '') {
+        // the user only wants to use browser visits?
+        // todo: won't work for all endpoints, but can think how to fix later..
+        if (endp == 'visits') {
+            return (({visits: []} : any): R)
+        } else {
+            throw Error(`'${endp}' isn't implemented without the backend yet. Please set host in the extension settings.`)
+        }
+    }
+
     const endpoint = `${opts.host}/${endp}`;
     // TODO cors mode?
     const response = await fetch(endpoint, {
@@ -91,6 +101,7 @@ async function getBackendVisits(u: Url): Promise<Visits> {
 
 
 // TODO include browser visits here too?
+// see /~https://github.com/karlicoss/promnesia/issues/120
 export async function searchVisits(u: Url): Promise<Visits> {
     return queryBackendCommon<JsonObject>({url: u}, 'search').then(rawToVisits);
 }

extension/src/options_page.html

@@ -18,7 +18,7 @@
 
         <table>
             <tr>
-                <td><label for="host_id">Host</label> </td>
+                <td><label for="host_id">Host (set to empty string if you want to use in-browser visits only)</label> </td>
                 <td><input type="URL" id="host_id">  </td>
             </tr>
             <!-- Warn about auth token being plaintext -->

extension/src/options_page.js

@@ -155,16 +155,15 @@ unwrap(document.getElementById('backend_status_id')).addEventListener('click', d
         },
     }, second).then(res => {
         if (!res.ok) {
-            throw `Backend error: ${res.status} ${res.statusText}` // TODO
+            throw `Backend error: ${res.status} ${res.statusText}`
         }
         return res;
     }).then(async res => {
         // TODO ugh. need to reject if ok is false...
         const resj = await res.json()
-        // TODO log debug?
         alert(`Success! ${JSON.stringify(resj)}`)
     }, err => {
-        alertError(err);
+        alertError(`${err}. See /~https://github.com/karlicoss/promnesia/blob/master/doc/TROUBLESHOOTING.org`);
     });
 }));