feat(布置作业): 课上老师改了作业，学生页面上弹出改了哪些题，点「刷新」就拿到新题单

看板「改 / 新的一节 / 清掉」和后台课堂作业的增改删，前后比较学生看到的那一节，
真变了才按班推 lesson_update（加了、去掉了、语言、顺序），走学生的 /ws/config，老师不收。
没点刷新又改会合并成一条。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/api/src/events.ts

@@ -1,4 +1,4 @@
-import type { FlowchartUpdate } from '@oj2/contract'
+import type { FlowchartUpdate, LessonUpdate } from '@oj2/contract'
 
 import { redis } from './redis'
 
@@ -50,6 +50,30 @@ export function parseSessionRevoked(raw: string): SessionRevoked | null {
   }
 }
 
+/**
+ * 按班广播：课上老师改了今天这节布置的题（见契约 lessonUpdateSchema）。学生的 /ws/config 连接
+ * 握手时按自己的班订阅 classEventTopic；换了班要等重连才跟上，课上不会发生。
+ */
+export const classEventChannel = 'class:events'
+
+export function classEventTopic(className: string) {
+  return `events:class:${className}`
+}
+
+export async function publishLessonUpdate(className: string, data: LessonUpdate) {
+  await redis.publish(classEventChannel, JSON.stringify({ className, data }))
+}
+
+export function parseClassEvent(raw: string): { className: string; data: LessonUpdate } | null {
+  try {
+    const value = JSON.parse(raw) as { className: string; data: LessonUpdate }
+    if (typeof value.className !== 'string' || !value.className || !value.data || typeof value.data !== 'object') return null
+    return value
+  } catch {
+    return null
+  }
+}
+
 interface UserEvent {
   userId: number
   data: FlowchartUpdate | Record<string, unknown>

apps/api/src/index.ts

@@ -141,6 +141,7 @@ const server = Bun.serve<SubmissionSocketData>({
             tokenVersion: session.tokenVersion,
             username: user.username,
             adminType: user.adminType,
+            className: user.className,
           },
         })
       ) {

apps/api/src/routes/admin/lesson.ts

@@ -5,7 +5,7 @@ import { Hono } from 'hono'
 import { requireTeacher, type AppEnv } from '../../auth/middleware'
 import { db, schema } from '../../db'
 import { failure, parseBody, success } from '../../http'
-import { lessonDoneCounts, resolveLessonProblems } from '../../services/lesson'
+import { announceLessonChange, lessonDoneCounts, resolveLessonProblems, todayLessonSnapshot } from '../../services/lesson'
 import { localDateTime } from '../../time'
 import { queryInteger } from '../helpers'
 
@@ -125,10 +125,13 @@ adminLessonRoutes.post('/lessons', requireTeacher, async (c) => {
   if (!parsed.success) return parsed.response
   const result = await lessonValues(parsed.data)
   if ('code' in result) return failure(c, 400, result.code, result.message)
+  const before = await todayLessonSnapshot(result.values.className)
   const [row] = await db
     .insert(schema.classLesson)
     .values({ ...result.values, createdBy: c.get('user')!.id, updatedAt: new Date().toISOString() })
     .returning({ id: schema.classLesson.id })
+  // 补登的是今天、而且是最后一节，学生那边看到的就变了
+  await announceLessonChange(result.values.className, before)
   return success(c, { id: row!.id })
 })
 
@@ -138,6 +141,9 @@ adminLessonRoutes.put('/lessons/:id', requireTeacher, async (c) => {
   if (!parsed.success) return parsed.response
   const result = await lessonValues(parsed.data)
   if ('code' in result) return failure(c, 400, result.code, result.message)
+  // 班级能改：原来那个班和新的班学生看到的都可能变，两边各比一次
+  const classes = await affectedClasses(id, result.values.className)
+  const before = await Promise.all(classes.map((className) => todayLessonSnapshot(className)))
   // 布置的老师不换，和看板上「改」一样认第一次
   const [row] = await db
     .update(schema.classLesson)
@@ -145,11 +151,21 @@ adminLessonRoutes.put('/lessons/:id', requireTeacher, async (c) => {
     .where(eq(schema.classLesson.id, id))
     .returning({ id: schema.classLesson.id })
   if (!row) return failure(c, 404, 'lesson-not-found', '这一节已经被删掉了')
+  await Promise.all(classes.map((className, index) => announceLessonChange(className, before[index]!)))
   return success(c, null)
 })
 
 adminLessonRoutes.delete('/lessons/:id', requireTeacher, async (c) => {
   const id = queryInteger(c.req.param('id'), 0, { min: 1 })
+  const [className] = await affectedClasses(id)
+  const before = className ? await todayLessonSnapshot(className) : null
   await db.delete(schema.classLesson).where(eq(schema.classLesson.id, id))
+  if (className) await announceLessonChange(className, before)
   return success(c, null)
 })
+
+/** 这一节原来属于哪个班（已经没了就没有），再加上要改成的班，去重 */
+async function affectedClasses(id: number, nextClass?: string) {
+  const [row] = await db.select({ className: schema.classLesson.className }).from(schema.classLesson).where(eq(schema.classLesson.id, id))
+  return [...new Set([row?.className, nextClass].filter((name): name is string => !!name))]
+}

apps/api/src/routes/classroom.ts

@@ -24,7 +24,7 @@ import { failure, parseBody, success } from '../http'
 import { isAccepted } from '../judge/status'
 import { activityRows, classMemberIds, FLOWCHART_PASSED, lessonLanguageFilter, SOLVED_RESULTS, suggestActiveClass } from '../services/class-activity'
 import { accepted } from '../services/learning-stats'
-import { resolveLessonProblems } from '../services/lesson'
+import { announceLessonChange, resolveLessonProblems, todayLessonSnapshot } from '../services/lesson'
 import { calendarDay, dayStart, localTime } from '../time'
 
 export const classroomRoutes = new Hono<AppEnv>()
@@ -744,6 +744,8 @@ classroomRoutes.put('/classroom/lesson', requireTeacher, async (c) => {
 
   const [exists] = await db.select({ id: schema.user.id }).from(schema.user).where(eq(schema.user.className, className)).limit(1)
   if (!exists) return failure(c, 400, 'class-not-found', `没有 ${className} 这个班`)
+  // 改之前学生看到的那一节，改完比一比、告诉全班改了哪些
+  const before = await todayLessonSnapshot(className)
 
   // 要改的是哪一行：点名的那一节（只认这个班今天的），新开一节就没有，老写法是今天最后布置的那一节
   const [target] = newLesson
@@ -762,6 +764,7 @@ classroomRoutes.put('/classroom/lesson', requireTeacher, async (c) => {
         .limit(1)
   if (!problemDisplayIds.length) {
     if (target) await db.delete(schema.classLesson).where(eq(schema.classLesson.id, target.id))
+    await announceLessonChange(className, before)
     return success(c, null)
   }
 
@@ -785,5 +788,6 @@ classroomRoutes.put('/classroom/lesson', requireTeacher, async (c) => {
       updatedAt: now,
     })
   }
+  await announceLessonChange(className, before)
   return success(c, null)
 })

apps/api/src/services/lesson.ts

@@ -1,8 +1,9 @@
-import { isSqlProblem, STUDENT_ROLES, type LessonLanguage } from '@oj2/contract'
-import { and, eq, inArray, isNull, sql } from 'drizzle-orm'
+import { isSqlProblem, STUDENT_ROLES, type LessonLanguage, type LessonUpdate } from '@oj2/contract'
+import { and, desc, eq, inArray, isNull, sql } from 'drizzle-orm'
 
 import { db, schema } from '../db'
-import { dayNumber, dayStart } from '../time'
+import { publishLessonUpdate } from '../events'
+import { calendarDay, dayNumber, dayStart } from '../time'
 import { FLOWCHART_PASSED, SOLVED_RESULTS } from './class-activity'
 
 /**
@@ -97,3 +98,65 @@ export async function lessonDoneCounts(lessons: { id: number; className: string;
   `)
   return new Map([...result].map((row) => [row.k, row.done]))
 }
+
+interface LessonSnapshot {
+  id: number
+  problemIds: number[]
+  language: LessonLanguage | null
+}
+
+/**
+ * 学生此刻看到的那一节：这个班今天最后布置的（和 routes/classroom.ts 的 lessonPlan 同一个取法），
+ * 没布置为 null。改之前、改之后各拍一张，交给 announceLessonChange 比
+ */
+export async function todayLessonSnapshot(className: string): Promise<LessonSnapshot | null> {
+  const [row] = await db
+    .select({ id: schema.classLesson.id, problemIds: schema.classLesson.problemIds, language: schema.classLesson.language })
+    .from(schema.classLesson)
+    .where(and(eq(schema.classLesson.className, className), eq(schema.classLesson.day, calendarDay())))
+    .orderBy(desc(schema.classLesson.createdAt), desc(schema.classLesson.id))
+    .limit(1)
+  return row?.problemIds.length ? { ...row, language: row.language ?? null } : null
+}
+
+/**
+ * 改完之后再拍一张，和改之前那张比；学生看到的那一节变了，就告诉这个班改了哪些（见契约 lessonUpdateSchema）。
+ * 推送失败只记日志：布置已经存下了，不能因为 Redis 抖一下让老师看到报错
+ */
+export async function announceLessonChange(className: string, before: LessonSnapshot | null) {
+  try {
+    const after = await todayLessonSnapshot(className)
+    if (!before && !after) return
+    const sameLesson = !!before && !!after && before.id === after.id
+    if (sameLesson && before.language === after.language && before.problemIds.join() === after.problemIds.join()) return
+
+    const ids = [...new Set([...(before?.problemIds ?? []), ...(after?.problemIds ?? [])])]
+    const rows = ids.length
+      ? await db
+          .select({ id: schema.problem.id, displayId: schema.problem.displayId, title: schema.problem.title })
+          .from(schema.problem)
+          .where(and(inArray(schema.problem.id, ids), eq(schema.problem.visible, true), isNull(schema.problem.contestId)))
+      : []
+    const byId = new Map(rows.map((row) => [row.id, { problemDisplayId: row.displayId, title: row.title }]))
+    const pick = (list: number[]) => list.flatMap((id) => byId.get(id) ?? [])
+
+    const afterIds = after?.problemIds ?? []
+    const beforeIds = sameLesson ? before.problemIds : []
+    const added = afterIds.filter((id) => !beforeIds.includes(id))
+    const removed = beforeIds.filter((id) => !afterIds.includes(id))
+    const kept = afterIds.filter((id) => beforeIds.includes(id))
+    const keptBefore = beforeIds.filter((id) => afterIds.includes(id))
+    await publishLessonUpdate(className, {
+      type: 'lesson_update',
+      kind: !after ? 'cleared' : sameLesson ? 'changed' : 'assigned',
+      language: after?.language ?? null,
+      problems: pick(afterIds),
+      added: sameLesson ? pick(added) : [],
+      removed: pick(removed),
+      languageChanged: sameLesson && before.language !== after.language,
+      reordered: sameLesson && kept.join() !== keptBefore.join(),
+    } satisfies LessonUpdate)
+  } catch (error) {
+    console.error('Failed to announce lesson change', error)
+  }
+}

apps/api/src/websocket.ts

@@ -1,4 +1,4 @@
-import { submissionUpdateSchema, type FlowchartUpdate } from '@oj2/contract'
+import { STUDENT_ROLES, submissionUpdateSchema, type FlowchartUpdate } from '@oj2/contract'
 import { and, eq, inArray } from 'drizzle-orm'
 
 import { touchSession } from './auth/session'
@@ -9,7 +9,18 @@ import { parseSubmissionEvent, submissionUpdateChannel, userSubmissionTopic } fr
 import { JudgeStatus } from './judge/status'
 import { createSubscriberRedis } from './redis'
 import { asRecord } from './routes/helpers'
-import { configTopic, configUpdateChannel, parseSessionRevoked, parseUserEvent, sessionRevokedChannel, userEventChannel, userEventTopic } from './events'
+import {
+  classEventChannel,
+  classEventTopic,
+  configTopic,
+  configUpdateChannel,
+  parseClassEvent,
+  parseSessionRevoked,
+  parseUserEvent,
+  sessionRevokedChannel,
+  userEventChannel,
+  userEventTopic,
+} from './events'
 
 /** 本机的几种写法。开发时 Vite 代理会让 Origin（5173）和 Host（3000）对不上 */
 const LOCAL_HOSTNAMES = new Set(['localhost', '127.0.0.1', '::1', '[::1]'])
@@ -63,6 +74,8 @@ export interface SubmissionSocketData {
   /** 握手时从会话里读，三种 kind 都会填；collab 通道用它判断老师身份、拼 room_open 里的姓名 */
   username?: string
   adminType?: string
+  /** 握手时的班级。学生的 config 通道按它订阅班级广播（老师改了这节课的题），见 classTopicOf */
+  className?: string | null
   /** 当前所在协作房间的房主（学生）id，见 collab/handler.ts */
   roomOwnerId?: number
 }
@@ -204,6 +217,12 @@ export function startSessionSweep() {
   return timer
 }
 
+/** 学生的 config 通道额外挂的班级 topic；老师、没分班的没有 */
+function classTopicOf(ws: Bun.ServerWebSocket<SubmissionSocketData>) {
+  const { className, adminType } = ws.data
+  return className && adminType && STUDENT_ROLES.includes(adminType as (typeof STUDENT_ROLES)[number]) ? classEventTopic(className) : null
+}
+
 export function submissionWebSocketHandler(): Bun.WebSocketHandler<SubmissionSocketData> {
   return {
     open(ws) {
@@ -219,6 +238,8 @@ export function submissionWebSocketHandler(): Bun.WebSocketHandler<SubmissionSoc
       }
       if (ws.data.kind === 'config') {
         ws.subscribe(configTopic)
+        const classTopic = classTopicOf(ws)
+        if (classTopic) ws.subscribe(classTopic)
         return
       }
       ws.subscribe(userSubmissionTopic(ws.data.userId))
@@ -264,6 +285,8 @@ export function submissionWebSocketHandler(): Bun.WebSocketHandler<SubmissionSoc
       }
       if (ws.data.kind === 'config') {
         ws.unsubscribe(configTopic)
+        const classTopic = classTopicOf(ws)
+        if (classTopic) ws.unsubscribe(classTopic)
         return
       }
       ws.unsubscribe(userSubmissionTopic(ws.data.userId))
@@ -384,6 +407,12 @@ export async function bridgeSubmissionEvents(server: Bun.Server<SubmissionSocket
       server.publish(configTopic, raw)
       return
     }
+    if (channel === classEventChannel) {
+      // 禁用的学生不用查：sweepSessions / publishSessionRevoked 会把那条连接断掉
+      const event = parseClassEvent(raw)
+      if (event) server.publish(classEventTopic(event.className), JSON.stringify(event.data))
+      return
+    }
     if (channel === sessionRevokedChannel) {
       const revoked = parseSessionRevoked(raw)
       if (!revoked) return
@@ -439,6 +468,6 @@ export async function bridgeSubmissionEvents(server: Bun.Server<SubmissionSocket
   })
   // 连接层的 error 已经由 createSubscriberRedis 里的 withErrorLogging 打了
   // （带连接名），这里再挂一个只会把同一条错误打两遍
-  await subscriber.subscribe(submissionUpdateChannel, userEventChannel, configUpdateChannel, sessionRevokedChannel)
+  await subscriber.subscribe(submissionUpdateChannel, userEventChannel, configUpdateChannel, sessionRevokedChannel, classEventChannel)
   return subscriber
 }