refactor: extract scroll hooks

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

frontend/src/components/editor-page/editor-page-content.tsx

@@ -3,10 +3,8 @@
  *
  * SPDX-License-Identifier: AGPL-3.0-only
  */
-import { useApplicationState } from '../../hooks/common/use-application-state'
 import { useApplyDarkModeStyle } from '../../hooks/dark-mode/use-apply-dark-mode-style'
 import { useSaveDarkModePreferenceToLocalStorage } from '../../hooks/dark-mode/use-save-dark-mode-preference-to-local-storage'
-import { Logger } from '../../utils/logger'
 import { MotdModal } from '../common/motd-modal/motd-modal'
 import { CommunicatorImageLightbox } from '../markdown-renderer/extensions/image/communicator-image-lightbox'
 import { ExtensionEventEmitterProvider } from '../markdown-renderer/hooks/use-extension-event-emitter'
@@ -15,14 +13,14 @@ import { ChangeEditorContentContextProvider } from './change-content-context/cod
 import { EditorPane } from './editor-pane/editor-pane'
 import { useComponentsFromAppExtensions } from './editor-pane/hooks/use-components-from-app-extensions'
 import { HeadMetaProperties } from './head-meta-properties/head-meta-properties'
+import { useScrollState } from './hooks/use-scroll-state'
+import { useSetScrollSource } from './hooks/use-set-scroll-source'
 import { useUpdateLocalHistoryEntry } from './hooks/use-update-local-history-entry'
 import { RealtimeConnectionAlert } from './realtime-connection-alert/realtime-connection-alert'
 import { RendererPane } from './renderer-pane/renderer-pane'
 import { Sidebar } from './sidebar/sidebar'
 import { Splitter } from './splitter/splitter'
-import type { DualScrollState, ScrollState } from './synced-scroll/scroll-props'
-import equal from 'fast-deep-equal'
-import React, { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import React, { useMemo, useRef } from 'react'
 import { useTranslation } from 'react-i18next'
 
 export enum ScrollSource {
@@ -30,82 +28,31 @@ export enum ScrollSource {
   RENDERER = 'renderer'
 }
 
-const log = new Logger('EditorPage')
-
 /**
  * This is the content of the actual editor page.
  */
 export const EditorPageContent: React.FC = () => {
   useTranslation()
-  const scrollSource = useRef<ScrollSource>(ScrollSource.EDITOR)
-  const editorSyncScroll: boolean = useApplicationState((state) => state.editorConfig.syncScroll)
-
-  const [scrollState, setScrollState] = useState<DualScrollState>(() => ({
-    editorScrollState: { firstLineInView: 1, scrolledPercentage: 0 },
-    rendererScrollState: { firstLineInView: 1, scrolledPercentage: 0 }
-  }))
-
-  const onMarkdownRendererScroll = useCallback(
-    (newScrollState: ScrollState) => {
-      if (scrollSource.current === ScrollSource.RENDERER && editorSyncScroll) {
-        setScrollState((old) => {
-          const newState: DualScrollState = {
-            editorScrollState: newScrollState,
-            rendererScrollState: old.rendererScrollState
-          }
-          return equal(newState, old) ? old : newState
-        })
-      }
-    },
-    [editorSyncScroll]
-  )
-
-  useEffect(() => {
-    log.debug('New scroll state', scrollState, scrollSource.current)
-  }, [scrollState])
-
-  const onEditorScroll = useCallback(
-    (newScrollState: ScrollState) => {
-      if (scrollSource.current === ScrollSource.EDITOR && editorSyncScroll) {
-        setScrollState((old) => {
-          const newState: DualScrollState = {
-            rendererScrollState: newScrollState,
-            editorScrollState: old.editorScrollState
-          }
-          return equal(newState, old) ? old : newState
-        })
-      }
-    },
-    [editorSyncScroll]
-  )
 
   useApplyDarkModeStyle()
   useSaveDarkModePreferenceToLocalStorage()
   useUpdateLocalHistoryEntry()
 
-  const setRendererToScrollSource = useCallback(() => {
-    if (scrollSource.current !== ScrollSource.RENDERER) {
-      scrollSource.current = ScrollSource.RENDERER
-      log.debug('Make renderer scroll source')
-    }
-  }, [])
-
-  const setEditorToScrollSource = useCallback(() => {
-    if (scrollSource.current !== ScrollSource.EDITOR) {
-      scrollSource.current = ScrollSource.EDITOR
-      log.debug('Make editor scroll source')
-    }
-  }, [])
+  const scrollSource = useRef<ScrollSource>(ScrollSource.EDITOR)
+  const [editorScrollState, onMarkdownRendererScroll] = useScrollState(scrollSource, ScrollSource.EDITOR)
+  const [rendererScrollState, onEditorScroll] = useScrollState(scrollSource, ScrollSource.RENDERER)
+  const setRendererToScrollSource = useSetScrollSource(scrollSource, ScrollSource.RENDERER)
+  const setEditorToScrollSource = useSetScrollSource(scrollSource, ScrollSource.EDITOR)
 
   const leftPane = useMemo(
     () => (
       <EditorPane
-        scrollState={scrollState.editorScrollState}
+        scrollState={editorScrollState}
         onScroll={onEditorScroll}
         onMakeScrollSource={setEditorToScrollSource}
       />
     ),
-    [onEditorScroll, scrollState.editorScrollState, setEditorToScrollSource]
+    [onEditorScroll, editorScrollState, setEditorToScrollSource]
   )
 
   const rightPane = useMemo(
@@ -114,10 +61,10 @@ export const EditorPageContent: React.FC = () => {
         frameClasses={'h-100 w-100'}
         onMakeScrollSource={setRendererToScrollSource}
         onScroll={onMarkdownRendererScroll}
-        scrollState={scrollState.rendererScrollState}
+        scrollState={rendererScrollState}
       />
     ),
-    [onMarkdownRendererScroll, scrollState.rendererScrollState, setRendererToScrollSource]
+    [onMarkdownRendererScroll, rendererScrollState, setRendererToScrollSource]
   )
 
   const editorExtensionComponents = useComponentsFromAppExtensions()

frontend/src/components/editor-page/hooks/use-scroll-state.ts

@@ -0,0 +1,47 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { useApplicationState } from '../../../hooks/common/use-application-state'
+import { Logger } from '../../../utils/logger'
+import type { ScrollSource } from '../editor-page-content'
+import type { ScrollState } from '../synced-scroll/scroll-props'
+import type { RefObject } from 'react'
+import { useCallback, useEffect, useState } from 'react'
+
+const log = new Logger('useScrollState')
+
+/**
+ * Provides a {@link ScrollState} state and a function that updates the scroll state to a new value.
+ *
+ * @param scrollSourceRef The reference that defines which scroll source is active
+ * @param scrollSource The source for which the state should be created
+ * @return the created scroll state and the update function. The update function accepts only new values if the given scroll source isn't active to prevent callback loops.
+ */
+export const useScrollState = (
+  scrollSourceRef: RefObject<ScrollSource>,
+  scrollSource: ScrollSource
+): [scrollState: ScrollState, onScroll: (newScrollState: ScrollState) => void] => {
+  const editorSyncScroll: boolean = useApplicationState((state) => state.editorConfig.syncScroll)
+
+  const [scrollState, setScrollState] = useState<ScrollState>(() => ({
+    firstLineInView: 1,
+    scrolledPercentage: 0
+  }))
+
+  const onScroll = useCallback(
+    (newScrollState: ScrollState) => {
+      if (scrollSourceRef.current !== scrollSource && editorSyncScroll) {
+        setScrollState(newScrollState)
+      }
+    },
+    [editorSyncScroll, scrollSource, scrollSourceRef]
+  )
+
+  useEffect(() => {
+    log.debug(`New scroll state for ${scrollSource}`, scrollState)
+  }, [scrollSource, scrollState])
+
+  return [scrollState, onScroll]
+}

frontend/src/components/editor-page/hooks/use-set-scroll-source.ts

@@ -0,0 +1,30 @@
+/*
+ * SPDX-FileCopyrightText: 2023 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { Logger } from '../../../utils/logger'
+import type { ScrollSource } from '../editor-page-content'
+import type { MutableRefObject } from 'react'
+import { useCallback } from 'react'
+
+const log = new Logger('useSetScrollSource')
+
+/**
+ * Provides a function that updates the given {@link ScrollSource} reference to a given value.
+ *
+ * @param scrollSourceReference The reference to update
+ * @param targetScrollSource The value that should be set in the reference
+ * @return The function that sets the reference
+ */
+export const useSetScrollSource = (
+  scrollSourceReference: MutableRefObject<ScrollSource>,
+  targetScrollSource: ScrollSource
+) => {
+  return useCallback(() => {
+    if (scrollSourceReference.current !== targetScrollSource) {
+      scrollSourceReference.current = targetScrollSource
+      log.debug(`Make ${targetScrollSource} scroll source`)
+    }
+  }, [scrollSourceReference, targetScrollSource])
+}

frontend/src/components/editor-page/synced-scroll/scroll-props.ts

@@ -16,8 +16,3 @@ export interface ScrollState {
   firstLineInView: number
   scrolledPercentage: number
 }
-
-export interface DualScrollState {
-  editorScrollState: ScrollState
-  rendererScrollState: ScrollState
-}