#34

frontend/src/lib/useUnsavedChangesGuard.tsx

@@ -0,0 +1,69 @@
+import { createContext, useCallback, useContext, useMemo, useState } from 'react'
+
+import { useDialogue } from '@/components/dialogues/DialogueProvider'
+
+import type { FC, PropsWithChildren } from 'react'
+
+type UnsavedChangesSource = {
+    dirty:    boolean
+    discard:  () => void | Promise<void> }
+
+type UnsavedChangesGuardContextValue = {
+    hasUnsavedChanges:             boolean
+    registerUnsavedChangesSource:  (
+	source: UnsavedChangesSource | null,
+    ) => void
+    confirmDiscardNavigation:      () => Promise<boolean> }
+
+const UnsavedChangesGuardContext =
+    createContext<UnsavedChangesGuardContextValue | null> (null)
+
+
+export const UnsavedChangesGuardProvider: FC<PropsWithChildren> = ({ children }) => {
+  const dialogue = useDialogue ()
+  const [source, setSource] = useState<UnsavedChangesSource | null> (null)
+
+  const registerUnsavedChangesSource = useCallback ((
+      nextSource: UnsavedChangesSource | null,
+  ) => {
+    setSource (nextSource)
+  }, [])
+
+  const confirmDiscardNavigation = useCallback (async (): Promise<boolean> => {
+    if (!(source?.dirty))
+      return true
+
+    const confirmed = await dialogue.confirm ({
+	title: '未保存の変更があります',
+	description: 'このまま移動すると、保存していない変更は失われます。',
+	cancelText: 'このページに残る',
+	confirmText: '変更を破棄して移動',
+	variant: 'danger' })
+    if (!(confirmed))
+      return false
+
+    await source.discard ()
+    return true
+  }, [dialogue, source])
+
+  const value = useMemo<UnsavedChangesGuardContextValue> (() => ({
+      hasUnsavedChanges: source?.dirty === true,
+      registerUnsavedChangesSource,
+      confirmDiscardNavigation,
+  }), [confirmDiscardNavigation, registerUnsavedChangesSource, source?.dirty])
+
+  return (
+      <UnsavedChangesGuardContext.Provider value={value}>
+	{children}
+      </UnsavedChangesGuardContext.Provider>)
+}
+
+
+export const useUnsavedChangesGuard = (): UnsavedChangesGuardContextValue => {
+  const context = useContext (UnsavedChangesGuardContext)
+
+  if (context == null)
+    throw new Error ('UnsavedChangesGuardProvider が必要です．')
+
+  return context
+}