refactor(common): extract frontmatter code into commons

Signed-off-by: Philip Molares <philip.molares@udo.edu>

commons/src/title-extraction/generate-note-title.spec.ts

@@ -0,0 +1,58 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { generateNoteTitle } from './generate-note-title.js'
+import { NoteFrontmatter, NoteTextDirection } from './types/frontmatter.js'
+import { NoteType } from './types/frontmatter.js'
+import { describe, expect, it } from '@jest/globals'
+
+const testFrontmatter: NoteFrontmatter = {
+  title: '',
+  description: '',
+  tags: [],
+  robots: '',
+  lang: 'en',
+  dir: NoteTextDirection.LTR,
+  newlinesAreBreaks: true,
+  GA: '',
+  disqus: '',
+  license: '',
+  type: NoteType.DOCUMENT,
+  opengraph: {},
+  slideOptions: {
+    transition: 'zoom',
+    autoSlide: 0,
+    autoSlideStoppable: true,
+    backgroundTransition: 'fade',
+    slideNumber: false
+  }
+}
+
+describe('generate note title', () => {
+  it('will choose the frontmatter title first', () => {
+    const actual = generateNoteTitle(
+      {
+        ...testFrontmatter,
+        title: 'frontmatter',
+        opengraph: { title: 'opengraph' }
+      },
+      'first-heading'
+    )
+    expect(actual).toEqual('frontmatter')
+  })
+
+  it('will choose the opengraph title second', () => {
+    const actual = generateNoteTitle(
+      { ...testFrontmatter, opengraph: { title: 'opengraph' } },
+      'first-heading'
+    )
+    expect(actual).toEqual('opengraph')
+  })
+
+  it('will choose the first heading third', () => {
+    const actual = generateNoteTitle({ ...testFrontmatter }, 'first-heading')
+    expect(actual).toEqual('first-heading')
+  })
+})