feat(extensions): Introduce app extensions

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

src/components/markdown-renderer/extensions/debugger-markdown-extension.ts

@@ -0,0 +1,26 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { MarkdownRendererExtension } from './base/markdown-renderer-extension'
+import type MarkdownIt from 'markdown-it'
+import { Logger } from '../../../utils/logger'
+import { isDevMode } from '../../../utils/test-modes'
+
+const log = new Logger('DebuggerMarkdownExtension')
+
+/**
+ * Adds console debug logging to the markdown rendering.
+ */
+export class DebuggerMarkdownExtension extends MarkdownRendererExtension {
+  public configureMarkdownItPost(markdownIt: MarkdownIt): void {
+    if (isDevMode) {
+      markdownIt.core.ruler.push('printStateToConsole', (state) => {
+        log.debug('Current state', state)
+        return false
+      })
+    }
+  }
+}