feat: Open prevent page leave modal on browser back button navigation

Implemented a workaround to show the "prevent leave" modal when users
click the browser back button with unsaved changes. This solution
addresses a limitation in Next.js App Router which doesn't provide
built-in hooks for intercepting browser history navigation events.

Technical details:
- Creates a duplicate history entry as a buffer to prevent immediate
  back navigation, allowing the prevent leave modal to be displayed.
- Uses history.go(-2) to properly navigate when user confirms leaving
- Re-establishes buffer state when user cancels navigation

Note: This implementation specifically targets the browser back button
use case, which covers the vast majority of user navigation patterns.
Forward button navigation is not supported by this workaround, but I
think this is an acceptable trade-off considering the complexity of
fully emulating the browser's history behavior within a Next.js
application.

Author: LimChorngUan

Diff for: packages/ui/src/elements/LeaveWithoutSaving/index.tsx

@@ -1,5 +1,5 @@
 'use client'
-import React, { useCallback } from 'react'
+import React, { useCallback, useEffect } from 'react'
 
 import type { OnCancel } from '../ConfirmationModal/index.js'
 
@@ -12,34 +12,116 @@ import { usePreventLeave } from './usePreventLeave.js'
 
 const modalSlug = 'leave-without-saving'
 
+// Workaround to show the prevent leave page modal
+// when clicking the browser navigation button.
+// Note that this hook assumes only back button being used
+// and not forward button. Which is the case for most of the time.
+const useOnBrowserHistoryChange = ({
+  hasAcceptedLeave,
+  hasCancelledLeave,
+  onLeave,
+  onPrevent,
+  onStay,
+  shouldPreventLeave,
+  skip,
+}: {
+  hasAcceptedLeave: boolean
+  hasCancelledLeave: boolean
+  onLeave: () => void
+  onPrevent: () => void
+  onStay: () => void
+  shouldPreventLeave: boolean
+  skip: boolean
+}) => {
+  // Push a duplicated history entry to the stack
+  // so that when the popstate event is triggered
+  // it doesn't immediately navigate away.
+  // This creates a fake visual and we can show the
+  // prevent leave page modal in the meantime
+  useEffect(() => {
+    window.history.pushState(null, '', window.location.href)
+  }, [])
+
+  const handlePopState = useCallback(() => {
+    if (!skip) {
+      if (shouldPreventLeave) {
+        onPrevent()
+      } else {
+        window.history.go(-2) // -2 because we pushed a duplicate entry
+      }
+    }
+  }, [onPrevent, shouldPreventLeave, skip])
+
+  useEffect(() => {
+    window.addEventListener('popstate', handlePopState)
+
+    return () => {
+      window.removeEventListener('popstate', handlePopState)
+    }
+  }, [handlePopState])
+
+  useEffect(() => {
+    if (!skip) {
+      if (hasAcceptedLeave) {
+        onLeave()
+        window.history.go(-2)
+      } else if (hasCancelledLeave) {
+        onStay()
+        window.history.pushState(null, '', window.location.href) // Push a duplicate entry to the stack
+      }
+    }
+  }, [hasAcceptedLeave, hasCancelledLeave, onLeave, onStay, skip])
+}
+
 export const LeaveWithoutSaving: React.FC = () => {
   const { closeModal, openModal } = useModal()
   const modified = useFormModified()
   const { isValid } = useForm()
   const { user } = useAuth()
   const [hasAccepted, setHasAccepted] = React.useState(false)
+  const [hasCancelled, setHasCancelled] = React.useState(false)
   const { t } = useTranslation()
 
   const prevent = Boolean((modified || !isValid) && user)
 
   const onPrevent = useCallback(() => {
     openModal(modalSlug)
+    // Reset the modal confirm and cancel state
+    setHasAccepted(false)
+    setHasCancelled(false)
   }, [openModal])
 
   const handleAccept = useCallback(() => {
     closeModal(modalSlug)
+    setHasAccepted(true)
   }, [closeModal])
 
-  usePreventLeave({ hasAccepted, onAccept: handleAccept, onPrevent, prevent })
-
   const onCancel: OnCancel = useCallback(() => {
     closeModal(modalSlug)
+    setHasCancelled(true)
   }, [closeModal])
 
   const onConfirm = useCallback(() => {
     setHasAccepted(true)
   }, [])
 
+  const { preventTriggered } = usePreventLeave({
+    hasAccepted,
+    onAccept: handleAccept,
+    onPrevent,
+    prevent,
+  })
+
+  useOnBrowserHistoryChange({
+    hasAcceptedLeave: hasAccepted,
+    hasCancelledLeave: hasCancelled,
+    onLeave: handleAccept,
+    onPrevent,
+    onStay: onCancel,
+    shouldPreventLeave: prevent,
+    skip: preventTriggered,
+  })
+
   return (
     <ConfirmationModal
       body={t('general:changesNotSaved')}

Diff for: packages/ui/src/elements/LeaveWithoutSaving/usePreventLeave.tsx

@@ -4,7 +4,7 @@
 // Credit: `react-use` maintainers
 //    -  Source: https://github.com/streamich/react-use/blob/ade8d3905f544305515d010737b4ae604cc51024/src/useBeforeUnload.ts#L2
 import { useRouter } from 'next/navigation.js'
-import { useCallback, useEffect, useRef } from 'react'
+import { useCallback, useEffect, useRef, useState } from 'react'
 
 import { useRouteTransition } from '../../providers/RouteTransition/index.js'
 
@@ -79,6 +79,11 @@ export const usePreventLeave = ({
   const router = useRouter()
   const cancelledURL = useRef<string>('')
 
+  // This state is added to accomodate the workaround for useOnBrowserHistoryChange.
+  // This is to prevent useOnBrowserHistoryChange fires the prevent modal too
+  // when there's an in app navigation.
+  const [preventTriggered, setPreventTriggered] = useState(false)
+
   // check when page is about to be changed
   useEffect(() => {
     function isAnchorOfCurrentUrl(currentUrl: string, newUrl: string) {
@@ -130,6 +135,7 @@ export const usePreventLeave = ({
             event.stopPropagation()
 
             if (typeof onPrevent === 'function') {
+              setPreventTriggered(true)
               onPrevent()
             }
           }
@@ -157,4 +163,8 @@ export const usePreventLeave = ({
       startRouteTransition(() => router.push(cancelledURL.current))
     }
   }, [hasAccepted, onAccept, router, startRouteTransition])
+
+  return {
+    preventTriggered,
+  }
 }