Add word count in document info modal (#738)

Co-authored-by: Tilman Vatteroth <git@tilmanvatteroth.de>

src/components/editor-page/document-bar/document-info/document-info-line-word-count.tsx

@@ -0,0 +1,45 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import React, { useEffect, useState } from 'react'
+import { Trans, useTranslation } from 'react-i18next'
+import { ShowIf } from '../../../common/show-if/show-if'
+import { DocumentInfoLine } from './document-info-line'
+import { UnitalicBoldText } from './unitalic-bold-text'
+import { useIFrameEditorToRendererCommunicator } from '../../render-context/iframe-editor-to-renderer-communicator-context-provider'
+
+/**
+ * Creates a new info line for the document information dialog that holds the
+ * word count of the note, based on counting in the rendered output.
+ */
+export const DocumentInfoLineWordCount: React.FC = () => {
+  useTranslation()
+  const iframeEditorToRendererCommunicator = useIFrameEditorToRendererCommunicator()
+  const [wordCount, setWordCount] = useState<number | null>(null)
+
+  useEffect(() => {
+    iframeEditorToRendererCommunicator?.onWordCountCalculated((words) => {
+      setWordCount(words)
+    })
+    iframeEditorToRendererCommunicator?.sendGetWordCount()
+    return () => {
+      iframeEditorToRendererCommunicator?.onWordCountCalculated(undefined)
+    }
+  }, [iframeEditorToRendererCommunicator, setWordCount])
+
+  return (
+    <DocumentInfoLine icon={'align-left'} size={'2x'}>
+      <ShowIf condition={wordCount === null}>
+        <Trans i18nKey={'common.loading'} />
+      </ShowIf>
+      <ShowIf condition={wordCount !== null}>
+        <Trans i18nKey={'editor.modal.documentInfo.words'}>
+          <UnitalicBoldText text={wordCount ?? ''} dataCy={'document-info-word-count'} />
+        </Trans>
+      </ShowIf>
+    </DocumentInfoLine>
+  )
+}