refactor: remove isomorphic-ws

The package caused some issues while working on other features.
Mostly because bundlers have been unable to determine the correct
websocket constructor.
So I replaced it with a more object-oriented approach.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

commons/src/message-transporters/mocked-backend-transport-adapter.ts

@@ -0,0 +1,87 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { RealtimeDoc } from '../y-doc-sync/index.js'
+import { ConnectionState } from './message-transporter.js'
+import { Message, MessageType } from './message.js'
+import { TransportAdapter } from './transport-adapter.js'
+
+/**
+ * Provides a transport adapter that simulates a connection with a real HedgeDoc realtime backend.
+ */
+export class MockedBackendTransportAdapter implements TransportAdapter {
+  private readonly doc: RealtimeDoc
+
+  private connected = true
+
+  private closeHandler: undefined | (() => void)
+
+  private messageHandler: undefined | ((value: Message<MessageType>) => void)
+
+  constructor(initialContent: string) {
+    this.doc = new RealtimeDoc(initialContent)
+  }
+
+  bindOnCloseEvent(handler: () => void): () => void {
+    this.closeHandler = handler
+    return () => {
+      this.connected = false
+      this.closeHandler = undefined
+    }
+  }
+
+  bindOnConnectedEvent(handler: () => void): () => void {
+    handler()
+    return () => {
+      //empty on purpose
+    }
+  }
+
+  bindOnErrorEvent(): () => void {
+    return () => {
+      //empty on purpose
+    }
+  }
+
+  bindOnMessageEvent(
+    handler: (value: Message<MessageType>) => void
+  ): () => void {
+    this.messageHandler = handler
+    return () => {
+      this.messageHandler = undefined
+    }
+  }
+
+  disconnect(): void {
+    if (!this.connected) {
+      return
+    }
+    this.connected = false
+    this.closeHandler?.()
+  }
+
+  getConnectionState(): ConnectionState {
+    return this.connected
+      ? ConnectionState.CONNECTED
+      : ConnectionState.DISCONNECTED
+  }
+
+  send(value: Message<MessageType>): void {
+    if (value.type === MessageType.NOTE_CONTENT_STATE_REQUEST) {
+      new Promise(() => {
+        this.messageHandler?.({
+          type: MessageType.NOTE_CONTENT_UPDATE,
+          payload: this.doc.encodeStateAsUpdate(value.payload)
+        })
+      }).catch((error: Error) => console.error(error))
+    } else if (value.type === MessageType.READY) {
+      new Promise(() => {
+        this.messageHandler?.({
+          type: MessageType.READY
+        })
+      }).catch((error: Error) => console.error(error))
+    }
+  }
+}