extract scroll code from renderer into hook

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

src/components/editor/scroll/hooks/use-scroll-to-line-mark.ts

@@ -0,0 +1,43 @@
+import { RefObject, useCallback, useEffect, useRef } from 'react'
+import { LineMarkerPosition } from '../../../markdown-renderer/types'
+import { ScrollState } from '../scroll-props'
+import { findLineMarks } from '../utils'
+
+export const useScrollToLineMark = (scrollState: ScrollState | undefined, lineMarks: LineMarkerPosition[] | undefined, contentLineCount: number, renderer: RefObject<HTMLElement>): void => {
+  const lastScrollPosition = useRef<number>()
+
+  const scrollTo = useCallback((targetPosition: number): void => {
+    if (!renderer.current || targetPosition === lastScrollPosition.current) {
+      return
+    }
+    lastScrollPosition.current = targetPosition
+    renderer.current.scrollTo({
+      top: targetPosition
+    })
+  }, [renderer])
+
+  useEffect(() => {
+    if (!renderer.current || !lineMarks || lineMarks.length === 0 || !scrollState) {
+      return
+    }
+    if (scrollState.firstLineInView < lineMarks[0].line) {
+      scrollTo(0)
+      return
+    }
+    if (scrollState.firstLineInView > lineMarks[lineMarks.length - 1].line) {
+      scrollTo(renderer.current.offsetHeight)
+      return
+    }
+    const { lastMarkBefore, firstMarkAfter } = findLineMarks(lineMarks, scrollState.firstLineInView)
+    const positionBefore = lastMarkBefore ? lastMarkBefore.position : lineMarks[0].position
+    const positionAfter = firstMarkAfter ? firstMarkAfter.position : renderer.current.offsetHeight
+    const lastMarkBeforeLine = lastMarkBefore ? lastMarkBefore.line : 1
+    const firstMarkAfterLine = firstMarkAfter ? firstMarkAfter.line : contentLineCount
+    const linesBetweenMarkers = firstMarkAfterLine - lastMarkBeforeLine
+    const blockHeight = positionAfter - positionBefore
+    const lineHeight = blockHeight / linesBetweenMarkers
+    const position = positionBefore + (scrollState.firstLineInView - lastMarkBeforeLine) * lineHeight + scrollState.scrolledPercentage / 100 * lineHeight
+    const correctedPosition = Math.floor(position)
+    scrollTo(correctedPosition)
+  }, [contentLineCount, lineMarks, renderer, scrollState, scrollTo])
+}