refactor: remove nested subscription (#36)

client/lib/patch-db.ts

@@ -1,4 +1,5 @@
-import { merge, Observable, ReplaySubject, Subject, Subscription } from 'rxjs'
+import { merge, Observable, ReplaySubject, Subject } from 'rxjs'
+import { switchMap } from 'rxjs/operators'
 import { Store } from './store'
 import { DBCache, Http } from './types'
 import { RPCError } from './source/ws-source'
@@ -10,15 +11,14 @@ export class PatchDB<T> {
   public rpcError$ = new Subject<RPCError>()
   public cache$ = new ReplaySubject<DBCache<T>>(1)
 
-  private updatesSub?: Subscription
-  private sourcesSub = this.sources$.subscribe(sources => {
-    this.updatesSub = merge(...sources.map(s => s.watch$(this.store))).subscribe({
+  private sub = this.sources$.pipe(
+    switchMap(sources => merge(...sources.map(s => s.watch$(this.store)))),
+  ).subscribe({
     next: (res) => {
       if ('result' in res) {
         this.store.update(res.result)
         this.cache$.next(this.store.cache)
-        }
-        else {
+      } else {
         this.rpcError$.next(res)
       }
     },
@@ -26,7 +26,6 @@ export class PatchDB<T> {
       this.connectionError$.next(e)
     },
   })
-  })
 
   constructor (
     private readonly sources$: Observable<Source<T>[]>,
@@ -35,7 +34,6 @@ export class PatchDB<T> {
   ) { }
 
   clean () {
-    this.sourcesSub.unsubscribe()
-    this.updatesSub?.unsubscribe()
+    this.sub.unsubscribe()
   }
 }