Store the scroll position of the PDF per root doc (#20376)

GitOrigin-RevId: 561c38b7258df40f0e738fdc2575e23d9d15102a

services/web/frontend/js/shared/hooks/use-pdf-scroll-position.ts

@@ -0,0 +1,56 @@
+import { Dispatch, SetStateAction, useEffect, useRef, useState } from 'react'
+import customLocalStorage from '@/infrastructure/local-storage'
+import { debugConsole } from '@/utils/debugging'
+
+export type PdfScrollPosition = Record<string, any> | undefined
+
+export const usePdfScrollPosition = (
+  lastCompileRootDocId: string | null | undefined
+): [PdfScrollPosition, Dispatch<SetStateAction<PdfScrollPosition>>] => {
+  // scroll position of the PDF
+  const [position, setPosition] = useState<PdfScrollPosition>()
+
+  const lastCompileRootDocIdRef = useRef<string | null | undefined>(
+    lastCompileRootDocId
+  )
+  useEffect(() => {
+    lastCompileRootDocIdRef.current = lastCompileRootDocId
+  }, [lastCompileRootDocId])
+
+  const initialScrollPositionRef = useRef<PdfScrollPosition | null>(null)
+
+  // load the stored PDF scroll position when the compiled root doc changes
+  useEffect(() => {
+    if (lastCompileRootDocId) {
+      const position = customLocalStorage.getItem(
+        `pdf.position.${lastCompileRootDocId}`
+      )
+      if (position) {
+        debugConsole.log('loaded position for', lastCompileRootDocId, position)
+        initialScrollPositionRef.current = position
+        setPosition(position)
+      }
+    }
+  }, [lastCompileRootDocId])
+
+  // store the current root doc's PDF scroll position when it changes
+  useEffect(() => {
+    if (
+      lastCompileRootDocIdRef.current &&
+      position &&
+      position !== initialScrollPositionRef.current
+    ) {
+      debugConsole.log(
+        'storing position for',
+        lastCompileRootDocIdRef.current,
+        position
+      )
+      customLocalStorage.setItem(
+        `pdf.position.${lastCompileRootDocIdRef.current}`,
+        position
+      )
+    }
+  }, [position])
+
+  return [position, setPosition]
+}