fix(frontend): save pending code drafts before page exit

frontend/tests/useCodeDraft.test.ts

@@ -0,0 +1,164 @@
+import assert from 'node:assert/strict'
+import { test, type TestContext } from 'node:test'
+import { effectScope, nextTick } from 'vue'
+import { codeTemplates, useCodeDraft, type Language } from '../src/composables/useCodeDraft.ts'
+
+type SavedDraft = { version: number; language: Language; drafts: Record<Language, string> }
+
+function browser(t: TestContext) {
+  const page = new EventTarget()
+  const document = Object.assign(new EventTarget(), {
+    visibilityState: 'visible' as DocumentVisibilityState,
+  })
+  const storage = {
+    items: new Map<string, string>(),
+    writes: 0,
+    failWrites: false,
+    getItem(key: string) {
+      return this.items.get(key) ?? null
+    },
+    setItem(key: string, value: string) {
+      this.writes++
+      if (this.failWrites) throw new Error('Storage unavailable')
+      this.items.set(key, value)
+    },
+  }
+  const globals = { window: page, document, localStorage: storage }
+  const descriptors = Object.keys(globals).map(
+    (name) => [name, Object.getOwnPropertyDescriptor(globalThis, name)] as const,
+  )
+  for (const [name, value] of Object.entries(globals)) {
+    Object.defineProperty(globalThis, name, { configurable: true, writable: true, value })
+  }
+  t.mock.timers.enable({ apis: ['setTimeout'] })
+  const scopes: ReturnType<typeof effectScope>[] = []
+  t.after(() => {
+    for (const scope of scopes) scope.stop()
+    for (const [name, descriptor] of descriptors) {
+      if (descriptor) Object.defineProperty(globalThis, name, descriptor)
+      else Reflect.deleteProperty(globalThis, name)
+    }
+  })
+  return {
+    page,
+    document,
+    storage,
+    open(problemId = '1001') {
+      const scope = effectScope()
+      scopes.push(scope)
+      return { scope, ...scope.run(() => useCodeDraft(problemId))! }
+    },
+    read(problemId = '1001'): SavedDraft | null {
+      return JSON.parse(storage.getItem('kf-oj:code-draft:' + problemId) ?? 'null')
+    },
+  }
+}
+
+test('pagehide saves the latest edit before the debounce and restores it after reload', (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// latest edit before refresh'
+  env.page.dispatchEvent(new Event('pagehide'))
+  assert.equal(env.read()?.drafts.cpp, draft.code.value)
+  assert.equal(draft.state.value, 'saved')
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+  draft.scope.stop()
+  assert.equal(env.open().code.value, '// latest edit before refresh')
+})
+
+test('hiding the page flushes pending edits; remaining visible does not', async (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// edited while visible'
+  await nextTick()
+  env.document.dispatchEvent(new Event('visibilitychange'))
+  assert.equal(env.storage.writes, 0)
+  env.document.visibilityState = 'hidden'
+  env.document.dispatchEvent(new Event('visibilitychange'))
+  assert.equal(env.read()?.drafts.cpp, draft.code.value)
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+})
+
+test('normal typing still debounces writes and saves the most recent edit', async (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// first edit'
+  await nextTick()
+  t.mock.timers.tick(399)
+  assert.equal(env.storage.writes, 0)
+  draft.code.value = '// second edit'
+  await nextTick()
+  t.mock.timers.tick(399)
+  assert.equal(env.storage.writes, 0)
+  t.mock.timers.tick(1)
+  assert.equal(env.read()?.drafts.cpp, '// second edit')
+  assert.equal(env.storage.writes, 1)
+})
+
+test('leaving a Vue page saves even an edit made in the same tick', (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  draft.code.value = '// latest edit before navigation'
+  draft.scope.stop()
+  assert.equal(env.read()?.drafts.cpp, '// latest edit before navigation')
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+})
+
+test('disposing the scope removes page lifecycle listeners', (t) => {
+  const env = browser(t)
+  const removePage = t.mock.method(env.page, 'removeEventListener')
+  const removeDocument = t.mock.method(env.document, 'removeEventListener')
+  env.open().scope.stop()
+  assert.deepEqual(
+    removePage.mock.calls.map((call) => call.arguments[0]),
+    ['pagehide'],
+  )
+  assert.deepEqual(
+    removeDocument.mock.calls.map((call) => call.arguments[0]),
+    ['visibilitychange'],
+  )
+  env.page.dispatchEvent(new Event('pagehide'))
+  env.document.visibilityState = 'hidden'
+  env.document.dispatchEvent(new Event('visibilitychange'))
+  assert.equal(env.storage.writes, 0)
+})
+
+test('pagehide preserves the selected language and keeps problem drafts separate', (t) => {
+  const env = browser(t)
+  const first = env.open('1001')
+  first.code.value = '// C++ draft'
+  first.language.value = 'python'
+  first.code.value = '# Python draft'
+  const second = env.open('1002')
+  second.code.value = '// another problem'
+  env.page.dispatchEvent(new Event('pagehide'))
+  assert.deepEqual(env.read('1001'), {
+    version: 1,
+    language: 'python',
+    drafts: { cpp: '// C++ draft', python: '# Python draft', rust: codeTemplates.rust },
+  })
+  assert.equal(env.read('1002')?.drafts.cpp, '// another problem')
+  first.scope.stop()
+  const restored = env.open('1001')
+  assert.equal(restored.language.value, 'python')
+  assert.equal(restored.code.value, '# Python draft')
+})
+
+test('a failed lifecycle save reports unavailable storage without throwing', (t) => {
+  const env = browser(t)
+  const draft = env.open()
+  env.storage.failWrites = true
+  draft.code.value = '// cannot persist yet'
+  assert.doesNotThrow(() => env.page.dispatchEvent(new Event('pagehide')))
+  assert.equal(draft.state.value, 'unavailable')
+  t.mock.timers.tick(400)
+  assert.equal(env.storage.writes, 1)
+  env.storage.failWrites = false
+  draft.code.value = '// storage recovered'
+  env.page.dispatchEvent(new Event('pagehide'))
+  assert.equal(draft.state.value, 'saved')
+  assert.equal(env.read()?.drafts.cpp, '// storage recovered')
+})