Collected minor changes from #837 (#962)

Signed-off-by: Tilman Vatteroth <tilman.vatteroth@tu-dortmund.de>

src/components/markdown-renderer/hooks/use-convert-markdown-to-react-dom.ts

@@ -0,0 +1,43 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import MarkdownIt from 'markdown-it/lib'
+import { ReactElement, useMemo, useRef } from 'react'
+import ReactHtmlParser from 'react-html-parser'
+import { ComponentReplacer } from '../replace-components/ComponentReplacer'
+import { LineKeys } from '../types'
+import { buildTransformer } from '../utils/html-react-transformer'
+import { calculateNewLineNumberMapping } from '../utils/line-number-mapping'
+
+export const useConvertMarkdownToReactDom = (
+  markdownCode: string,
+  markdownIt: MarkdownIt,
+  componentReplacers?: () => ComponentReplacer[],
+  onPreRendering?: () => void,
+  onPostRendering?: () => void): ReactElement[] => {
+  const oldMarkdownLineKeys = useRef<LineKeys[]>()
+  const lastUsedLineId = useRef<number>(0)
+
+  return useMemo(() => {
+    if (onPreRendering) {
+      onPreRendering()
+    }
+    const html = markdownIt.render(markdownCode)
+    const contentLines = markdownCode.split('\n')
+    const {
+      lines: newLines,
+      lastUsedLineId: newLastUsedLineId
+    } = calculateNewLineNumberMapping(contentLines, oldMarkdownLineKeys.current ?? [], lastUsedLineId.current)
+    oldMarkdownLineKeys.current = newLines
+    lastUsedLineId.current = newLastUsedLineId
+    const transformer = componentReplacers ? buildTransformer(newLines, componentReplacers()) : undefined
+    const rendering = ReactHtmlParser(html, { transform: transformer })
+    if (onPostRendering) {
+      onPostRendering()
+    }
+    return rendering
+  }, [onPreRendering, onPostRendering, markdownCode, markdownIt, componentReplacers])
+}