added a spoiler container (#947)

changed toolbar to insert the new spoiler container
changed tests accordingly

References:
https://github.com/markdown-it/markdown-it-container
Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/components/markdown-renderer/markdown-it-plugins/spoiler-container.ts

@@ -0,0 +1,36 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import MarkdownIt from 'markdown-it'
+import { escapeHtml } from 'markdown-it/lib/common/utils'
+import markdownItContainer from 'markdown-it-container'
+import Token from 'markdown-it/lib/token'
+import { MarkdownItPlugin } from '../replace-components/ComponentReplacer'
+import { RenderContainerReturn } from './alert-container'
+
+export const spoilerRegEx = /^spoiler\s+(.*)$/;
+
+const createSpoilerContainer = (): RenderContainerReturn => {
+  return (tokens: Token[], index: number) => {
+    const matches = spoilerRegEx.exec(tokens[index].info.trim())
+
+    if (tokens[index].nesting === 1 && matches && matches[1]) {
+      // opening tag
+      return `<details><summary>${escapeHtml(matches[1])}</summary>`
+
+    } else {
+      // closing tag
+      return '</details>\n'
+    }
+  }
+}
+
+export const spoilerContainer: MarkdownItPlugin = (markdownIt: MarkdownIt) => {
+  markdownItContainer(markdownIt, 'spoiler', {
+    validate: (params: string) => spoilerRegEx.test(params),
+    render: createSpoilerContainer()
+  })
+}