Refactored and fixed:

- Refactored, linted, fixed potential problems, enabled 'use strict'

Fixed:
- Added "Enable plugin synchronization" option
(Plugins and settings had been run always)

Implemented:
- Sync preset implemented.
- "Check integrity on saving" implemented.
- "Sanity check" implemented
It's mainly for debugging.

src/utils_couchdb.ts

@@ -0,0 +1,70 @@
+import { Logger } from "./logger";
+import { LOG_LEVEL, VER, VERSIONINFO_DOCID, EntryVersionInfo, EntryDoc } from "./types";
+import { resolveWithIgnoreKnownError } from "./utils";
+import { PouchDB } from "../pouchdb-browser-webpack/dist/pouchdb-browser.js";
+
+export const isValidRemoteCouchDBURI = (uri: string): boolean => {
+    if (uri.startsWith("https://")) return true;
+    if (uri.startsWith("http://")) return true;
+    return false;
+};
+export const connectRemoteCouchDB = async (uri: string, auth: { username: string; password: string }): Promise<string | { db: PouchDB.Database<EntryDoc>; info: PouchDB.Core.DatabaseInfo }> => {
+    if (!isValidRemoteCouchDBURI(uri)) return "Remote URI is not valid";
+    const db: PouchDB.Database<EntryDoc> = new PouchDB<EntryDoc>(uri, {
+        auth,
+    });
+    try {
+        const info = await db.info();
+        return { db: db, info: info };
+    } catch (ex) {
+        let msg = `${ex.name}:${ex.message}`;
+        if (ex.name == "TypeError" && ex.message == "Failed to fetch") {
+            msg += "\n**Note** This error caused by many reasons. The only sure thing is you didn't touch the server.\nTo check details, open inspector.";
+        }
+        Logger(ex, LOG_LEVEL.VERBOSE);
+        return msg;
+    }
+};
+// check the version of remote.
+// if remote is higher than current(or specified) version, return false.
+export const checkRemoteVersion = async (db: PouchDB.Database, migrate: (from: number, to: number) => Promise<boolean>, barrier: number = VER): Promise<boolean> => {
+    try {
+        const versionInfo = (await db.get(VERSIONINFO_DOCID)) as EntryVersionInfo;
+        if (versionInfo.type != "versioninfo") {
+            return false;
+        }
+
+        const version = versionInfo.version;
+        if (version < barrier) {
+            const versionUpResult = await migrate(version, barrier);
+            if (versionUpResult) {
+                await bumpRemoteVersion(db);
+                return true;
+            }
+        }
+        if (version == barrier) return true;
+        return false;
+    } catch (ex) {
+        if (ex.status && ex.status == 404) {
+            if (await bumpRemoteVersion(db)) {
+                return true;
+            }
+            return false;
+        }
+        throw ex;
+    }
+};
+export const bumpRemoteVersion = async (db: PouchDB.Database, barrier: number = VER): Promise<boolean> => {
+    const vi: EntryVersionInfo = {
+        _id: VERSIONINFO_DOCID,
+        version: barrier,
+        type: "versioninfo",
+    };
+    const versionInfo = (await resolveWithIgnoreKnownError(db.get(VERSIONINFO_DOCID), vi)) as EntryVersionInfo;
+    if (versionInfo.type != "versioninfo") {
+        return false;
+    }
+    vi._rev = versionInfo._rev;
+    await db.put(vi);
+    return true;
+};