NextEdu/src/modules/homework/data-access.ts

import "server-only"

import { cache } from "react"
import { and, count, desc, eq, inArray, isNull, lte, or, sql } from "drizzle-orm"

import { db } from "@/shared/db"
import {
  homeworkAnswers,
  homeworkAssignmentQuestions,
  homeworkAssignmentTargets,
  homeworkAssignments,
  homeworkSubmissions,
} from "@/shared/db/schema"
import { getStudentIdsByClassId, getStudentIdsByClassIds } from "@/modules/classes/data-access"
import { getExamIdsByGradeIds, getExamSubjectIdMap } from "@/modules/exams/data-access"
import { getSubjectOptions } from "@/modules/school/data-access"

import type {
  HomeworkAssignmentListItem,
  HomeworkAssignmentReviewListItem,
  HomeworkQuestionContent,
  HomeworkAssignmentStatus,
  HomeworkSubmissionDetails,
  HomeworkSubmissionListItem,
  HomeworkSubmissionStatus,
  StudentHomeworkAssignmentListItem,
  StudentHomeworkProgressStatus,
  StudentHomeworkTakeData,
} from "./types"
import type { DataScope } from "@/shared/types/permissions"

export const isRecord = (v: unknown): v is Record<string, unknown> => typeof v === "object" && v !== null

const isHomeworkAssignmentStatus = (v: unknown): v is HomeworkAssignmentStatus =>
  v === "draft" || v === "published" || v === "archived"

const toHomeworkAssignmentStatus = (v: string | null | undefined): HomeworkAssignmentStatus =>
  isHomeworkAssignmentStatus(v) ? v : "draft"

const isHomeworkSubmissionStatus = (v: unknown): v is HomeworkSubmissionStatus =>
  v === "started" || v === "submitted" || v === "graded"

const toHomeworkSubmissionStatus = (v: string | null | undefined): HomeworkSubmissionStatus =>
  isHomeworkSubmissionStatus(v) ? v : "started"

const isHomeworkQuestionContent = (v: unknown): v is HomeworkQuestionContent =>
  isRecord(v)

export const toQuestionContent = (v: unknown): HomeworkQuestionContent | null => {
  if (!isHomeworkQuestionContent(v)) return null
  return v
}

export const getAssignmentMaxScoreById = async (assignmentIds: string[]): Promise<Map<string, number>> => {
  const ids = assignmentIds.filter((v) => v.trim().length > 0)
  if (ids.length === 0) return new Map()

  const rows = await db
    .select({
      assignmentId: homeworkAssignmentQuestions.assignmentId,
      maxScore: sql<number>`COALESCE(SUM(${homeworkAssignmentQuestions.score}), 0)`,
    })
    .from(homeworkAssignmentQuestions)
    .where(inArray(homeworkAssignmentQuestions.assignmentId, ids))
    .groupBy(homeworkAssignmentQuestions.assignmentId)

  const map = new Map<string, number>()
  for (const r of rows) map.set(r.assignmentId, Number(r.maxScore ?? 0))
  return map
}

export const getHomeworkAssignments = cache(async (params?: { creatorId?: string; ids?: string[]; classId?: string; scope?: DataScope }) => {
  const conditions = []

  if (params?.creatorId) conditions.push(eq(homeworkAssignments.creatorId, params.creatorId))
  if (params?.ids && params.ids.length > 0) conditions.push(inArray(homeworkAssignments.id, params.ids))
  if (params?.classId) {
    const classStudentIds = await getStudentIdsByClassId(params.classId)

    const targetAssignmentIds = await db
      .selectDistinct({ assignmentId: homeworkAssignmentTargets.assignmentId })
      .from(homeworkAssignmentTargets)
      .where(inArray(homeworkAssignmentTargets.studentId, classStudentIds))

    conditions.push(inArray(homeworkAssignments.id, targetAssignmentIds.map((t) => t.assignmentId)))
  }

  // Data scope filtering
  if (params?.scope) {
    if (params.scope.type === "owned") {
      conditions.push(eq(homeworkAssignments.creatorId, params.scope.userId))
    }
    if (params.scope.type === "class_taught" && params.scope.classIds.length > 0) {
      // Filter homework by assignments targeting students in teacher's classes
      const classStudentIds = await getStudentIdsByClassIds(params.scope.classIds)

      const targetAssignmentIds = await db
        .selectDistinct({ assignmentId: homeworkAssignmentTargets.assignmentId })
        .from(homeworkAssignmentTargets)
        .where(inArray(homeworkAssignmentTargets.studentId, classStudentIds))

      conditions.push(inArray(homeworkAssignments.id, targetAssignmentIds.map((t) => t.assignmentId)))
    }
    if (params.scope.type === "grade_managed" && params.scope.gradeIds.length > 0) {
      // Homework links to exam via sourceExamId, exam has gradeId
      const gradeExamIds = await getExamIdsByGradeIds(params.scope.gradeIds)

      conditions.push(inArray(homeworkAssignments.sourceExamId, gradeExamIds))
    }
    // "all" type: no filtering
  }

  const data = await db.query.homeworkAssignments.findMany({
    where: conditions.length ? and(...conditions) : undefined,
    orderBy: [desc(homeworkAssignments.createdAt)],
    with: {
      sourceExam: true,
    },
  })

  return data.map((a) => {
    const item: HomeworkAssignmentListItem = {
      id: a.id,
      sourceExamId: a.sourceExamId,
      sourceExamTitle: a.sourceExam.title,
      title: a.title,
      status: toHomeworkAssignmentStatus(a.status),
      availableAt: a.availableAt ? a.availableAt.toISOString() : null,
      dueAt: a.dueAt ? a.dueAt.toISOString() : null,
      allowLate: a.allowLate,
      lateDueAt: a.lateDueAt ? a.lateDueAt.toISOString() : null,
      maxAttempts: a.maxAttempts,
      createdAt: a.createdAt.toISOString(),
      updatedAt: a.updatedAt.toISOString(),
    }
    return item
  })
})

export const getHomeworkAssignmentReviewList = cache(async (params: { creatorId: string; scope?: DataScope }) => {
  const creatorId = params.creatorId.trim()
  if (!creatorId) return []

  const conditions = [eq(homeworkAssignments.creatorId, creatorId)]

  // Data scope filtering
  if (params.scope) {
    if (params.scope.type === "owned") {
      // Already filtered by creatorId above
    }
    if (params.scope.type === "class_taught" && params.scope.classIds.length > 0) {
      const classStudentIds = await getStudentIdsByClassIds(params.scope.classIds)

      const targetAssignmentIds = await db
        .selectDistinct({ assignmentId: homeworkAssignmentTargets.assignmentId })
        .from(homeworkAssignmentTargets)
        .where(inArray(homeworkAssignmentTargets.studentId, classStudentIds))

      conditions.push(inArray(homeworkAssignments.id, targetAssignmentIds.map((t) => t.assignmentId)))
    }
    if (params.scope.type === "grade_managed" && params.scope.gradeIds.length > 0) {
      const gradeExamIds = await getExamIdsByGradeIds(params.scope.gradeIds)

      conditions.push(inArray(homeworkAssignments.sourceExamId, gradeExamIds))
    }
  }

  const assignments = await db.query.homeworkAssignments.findMany({
    where: and(...conditions),
    orderBy: [desc(homeworkAssignments.createdAt)],
    with: { sourceExam: true },
  })

  if (assignments.length === 0) return []

  const assignmentIds = assignments.map((a) => a.id)

  const targetCountRows = await db
    .select({
      assignmentId: homeworkAssignmentTargets.assignmentId,
      targetCount: sql<number>`COUNT(*)`,
    })
    .from(homeworkAssignmentTargets)
    .where(inArray(homeworkAssignmentTargets.assignmentId, assignmentIds))
    .groupBy(homeworkAssignmentTargets.assignmentId)

  const targetCountByAssignmentId = new Map<string, number>()
  for (const r of targetCountRows) targetCountByAssignmentId.set(r.assignmentId, Number(r.targetCount ?? 0))

  const submittedCountRows = await db
    .select({
      assignmentId: homeworkSubmissions.assignmentId,
      submittedCount: sql<number>`COUNT(DISTINCT ${homeworkSubmissions.studentId})`,
    })
    .from(homeworkSubmissions)
    .where(
      and(
        inArray(homeworkSubmissions.assignmentId, assignmentIds),
        inArray(homeworkSubmissions.status, ["submitted", "graded"])
      )
    )
    .groupBy(homeworkSubmissions.assignmentId)

  const submittedCountByAssignmentId = new Map<string, number>()
  for (const r of submittedCountRows) submittedCountByAssignmentId.set(r.assignmentId, Number(r.submittedCount ?? 0))

  const gradedCountRows = await db
    .select({
      assignmentId: homeworkSubmissions.assignmentId,
      gradedCount: sql<number>`COUNT(DISTINCT ${homeworkSubmissions.studentId})`,
    })
    .from(homeworkSubmissions)
    .where(and(inArray(homeworkSubmissions.assignmentId, assignmentIds), eq(homeworkSubmissions.status, "graded")))
    .groupBy(homeworkSubmissions.assignmentId)

  const gradedCountByAssignmentId = new Map<string, number>()
  for (const r of gradedCountRows) gradedCountByAssignmentId.set(r.assignmentId, Number(r.gradedCount ?? 0))

  return assignments.map((a) => {
    const item: HomeworkAssignmentReviewListItem = {
      id: a.id,
      title: a.title,
      status: toHomeworkAssignmentStatus(a.status),
      sourceExamTitle: a.sourceExam.title,
      dueAt: a.dueAt ? a.dueAt.toISOString() : null,
      targetCount: targetCountByAssignmentId.get(a.id) ?? 0,
      submittedCount: submittedCountByAssignmentId.get(a.id) ?? 0,
      gradedCount: gradedCountByAssignmentId.get(a.id) ?? 0,
      createdAt: a.createdAt.toISOString(),
    }
    return item
  })
})

export const getHomeworkSubmissions = cache(async (params?: { assignmentId?: string; classId?: string; creatorId?: string; scope?: DataScope }) => {
  const conditions = []
  if (params?.assignmentId) conditions.push(eq(homeworkSubmissions.assignmentId, params.assignmentId))
  if (params?.classId) {
    const classStudentIds = await getStudentIdsByClassId(params.classId)

    const targetAssignmentIds = await db
      .selectDistinct({ assignmentId: homeworkAssignmentTargets.assignmentId })
      .from(homeworkAssignmentTargets)
      .where(inArray(homeworkAssignmentTargets.studentId, classStudentIds))

    conditions.push(inArray(homeworkSubmissions.studentId, classStudentIds))
    conditions.push(inArray(homeworkSubmissions.assignmentId, targetAssignmentIds.map((t) => t.assignmentId)))
  }
  if (params?.creatorId) {
    const creatorAssignmentIds = db
      .select({ assignmentId: homeworkAssignments.id })
      .from(homeworkAssignments)
      .where(eq(homeworkAssignments.creatorId, params.creatorId))

    conditions.push(inArray(homeworkSubmissions.assignmentId, creatorAssignmentIds))
  }

  // Data scope filtering
  if (params?.scope) {
    if (params.scope.type === "owned") {
      const creatorAssignmentIds = db
        .select({ assignmentId: homeworkAssignments.id })
        .from(homeworkAssignments)
        .where(eq(homeworkAssignments.creatorId, params.scope.userId))

      conditions.push(inArray(homeworkSubmissions.assignmentId, creatorAssignmentIds))
    }
    if (params.scope.type === "class_taught" && params.scope.classIds.length > 0) {
      const classStudentIds = await getStudentIdsByClassIds(params.scope.classIds)

      conditions.push(inArray(homeworkSubmissions.studentId, classStudentIds))
    }
    if (params.scope.type === "grade_managed" && params.scope.gradeIds.length > 0) {
      const gradeExamIds = await getExamIdsByGradeIds(params.scope.gradeIds)

      const gradeAssignmentIds = db
        .select({ assignmentId: homeworkAssignments.id })
        .from(homeworkAssignments)
        .where(inArray(homeworkAssignments.sourceExamId, gradeExamIds))

      conditions.push(inArray(homeworkSubmissions.assignmentId, gradeAssignmentIds))
    }
  }

  const data = await db.query.homeworkSubmissions.findMany({
    where: conditions.length ? and(...conditions) : undefined,
    orderBy: [desc(homeworkSubmissions.updatedAt)],
    with: {
      assignment: true,
      student: true,
    },
  })

  return data.map((s) => {
    const item: HomeworkSubmissionListItem = {
      id: s.id,
      assignmentId: s.assignmentId,
      assignmentTitle: s.assignment.title,
      studentName: s.student.name || "Unknown",
      submittedAt: s.submittedAt ? s.submittedAt.toISOString() : null,
      score: s.score ?? null,
      status: toHomeworkSubmissionStatus(s.status),
      isLate: s.isLate,
    }
    return item
  })
})

export const getHomeworkAssignmentById = cache(async (id: string, scope?: DataScope) => {
  const assignment = await db.query.homeworkAssignments.findFirst({
    where: eq(homeworkAssignments.id, id),
    with: {
      sourceExam: true,
    },
  })

  if (!assignment) return null

  // Data scope verification for single-item fetch
  if (scope && scope.type !== "all") {
    if (scope.type === "owned" && assignment.creatorId !== scope.userId) {
      return null
    }
    if (scope.type === "grade_managed" && scope.gradeIds.length > 0) {
      const examIds = await getExamIdsByGradeIds(scope.gradeIds)
      if (!examIds.includes(assignment.sourceExamId)) {
        return null
      }
    }
    if (scope.type === "class_taught" && scope.classIds.length > 0) {
      const studentIds = await getStudentIdsByClassIds(scope.classIds)
      if (studentIds.length > 0) {
        const target = await db.query.homeworkAssignmentTargets.findFirst({
          where: and(
            eq(homeworkAssignmentTargets.assignmentId, id),
            inArray(homeworkAssignmentTargets.studentId, studentIds)
          ),
        })
        if (!target) return null
      } else {
        return null
      }
    }
  }

  const [targetsRow] = await db
    .select({ c: count() })
    .from(homeworkAssignmentTargets)
    .where(eq(homeworkAssignmentTargets.assignmentId, id))

  const [submissionsRow] = await db
    .select({ c: count() })
    .from(homeworkSubmissions)
    .where(eq(homeworkSubmissions.assignmentId, id))

  const [submittedRow] = await db
    .select({ c: sql<number>`COUNT(DISTINCT ${homeworkSubmissions.studentId})` })
    .from(homeworkSubmissions)
    .where(
      and(eq(homeworkSubmissions.assignmentId, id), inArray(homeworkSubmissions.status, ["submitted", "graded"]))
    )

  const [gradedRow] = await db
    .select({ c: sql<number>`COUNT(DISTINCT ${homeworkSubmissions.studentId})` })
    .from(homeworkSubmissions)
    .where(and(eq(homeworkSubmissions.assignmentId, id), eq(homeworkSubmissions.status, "graded")))

  return {
    id: assignment.id,
    title: assignment.title,
    description: assignment.description,
    status: toHomeworkAssignmentStatus(assignment.status),
    sourceExamId: assignment.sourceExamId,
    sourceExamTitle: assignment.sourceExam.title,
    structure: assignment.structure as unknown,
    availableAt: assignment.availableAt ? assignment.availableAt.toISOString() : null,
    dueAt: assignment.dueAt ? assignment.dueAt.toISOString() : null,
    allowLate: assignment.allowLate,
    lateDueAt: assignment.lateDueAt ? assignment.lateDueAt.toISOString() : null,
    maxAttempts: assignment.maxAttempts,
    targetCount: targetsRow?.c ?? 0,
    submissionCount: submissionsRow?.c ?? 0,
    submittedCount: submittedRow?.c ?? 0,
    gradedCount: gradedRow?.c ?? 0,
    createdAt: assignment.createdAt.toISOString(),
    updatedAt: assignment.updatedAt.toISOString(),
  }
})

export const getHomeworkSubmissionDetails = cache(async (submissionId: string): Promise<HomeworkSubmissionDetails | null> => {
  const submission = await db.query.homeworkSubmissions.findFirst({
    where: eq(homeworkSubmissions.id, submissionId),
    with: {
      student: true,
      assignment: true,
    },
  })

  if (!submission) return null

  const answers = await db.query.homeworkAnswers.findMany({
    where: eq(homeworkAnswers.submissionId, submissionId),
    with: {
      question: true,
    },
  })

  const assignmentQ = await db.query.homeworkAssignmentQuestions.findMany({
    where: eq(homeworkAssignmentQuestions.assignmentId, submission.assignmentId),
    orderBy: [desc(homeworkAssignmentQuestions.order)],
  })

  const answersWithDetails = answers
    .map((ans) => {
      const aqRel = assignmentQ.find((q) => q.questionId === ans.questionId)
      return {
        id: ans.id,
        questionId: ans.questionId,
        questionContent: toQuestionContent(ans.question.content),
        questionType: ans.question.type,
        maxScore: aqRel?.score || 0,
        studentAnswer: ans.answerContent,
        score: ans.score,
        feedback: ans.feedback,
        order: aqRel?.order || 0,
      }
    })
    .sort((a, b) => a.order - b.order)

  // Fetch adjacent submissions for navigation
  const allSubmissions = await db.query.homeworkSubmissions.findMany({
    where: eq(homeworkSubmissions.assignmentId, submission.assignmentId),
    orderBy: [desc(homeworkSubmissions.updatedAt)],
    columns: { id: true },
  })

  const currentIndex = allSubmissions.findIndex((s) => s.id === submissionId)
  const prevSubmissionId = currentIndex > 0 ? allSubmissions[currentIndex - 1].id : null
  const nextSubmissionId = currentIndex >= 0 && currentIndex < allSubmissions.length - 1 ? allSubmissions[currentIndex + 1].id : null

  return {
    id: submission.id,
    assignmentId: submission.assignmentId,
    assignmentTitle: submission.assignment.title,
    studentName: submission.student.name || "Unknown",
    submittedAt: submission.submittedAt ? submission.submittedAt.toISOString() : null,
    status: toHomeworkSubmissionStatus(submission.status),
    totalScore: submission.score,
    answers: answersWithDetails,
    prevSubmissionId,
    nextSubmissionId,
  }
})

const toStudentProgressStatus = (v: string | null | undefined): StudentHomeworkProgressStatus => {
  if (v === "started") return "in_progress"
  if (v === "submitted") return "submitted"
  if (v === "graded") return "graded"
  return "not_started"
}

export const getStudentHomeworkAssignments = cache(async (studentId: string): Promise<StudentHomeworkAssignmentListItem[]> => {
  const now = new Date()

  const targetAssignmentIds = db
    .select({ assignmentId: homeworkAssignmentTargets.assignmentId })
    .from(homeworkAssignmentTargets)
    .where(eq(homeworkAssignmentTargets.studentId, studentId))

  const assignments = await db
    .select({
      id: homeworkAssignments.id,
      title: homeworkAssignments.title,
      sourceExamId: homeworkAssignments.sourceExamId,
      dueAt: homeworkAssignments.dueAt,
      availableAt: homeworkAssignments.availableAt,
      maxAttempts: homeworkAssignments.maxAttempts,
      createdAt: homeworkAssignments.createdAt,
    })
    .from(homeworkAssignments)
    .where(
      and(
        eq(homeworkAssignments.status, "published"),
        inArray(homeworkAssignments.id, targetAssignmentIds),
        or(isNull(homeworkAssignments.availableAt), lte(homeworkAssignments.availableAt, now))
      )
    )
    .orderBy(desc(homeworkAssignments.dueAt), desc(homeworkAssignments.createdAt))

  if (assignments.length === 0) return []

  // Fetch subject names via cross-module interfaces
  const examIds = assignments.map((a) => a.sourceExamId)
  const [examSubjectIdMap, subjectOptions] = await Promise.all([
    getExamSubjectIdMap(examIds),
    getSubjectOptions(),
  ])
  const subjectNameById = new Map<string, string>()
  for (const s of subjectOptions) subjectNameById.set(s.id, s.name)

  const assignmentIds = assignments.map((a) => a.id)
  const submissions = await db.query.homeworkSubmissions.findMany({
    where: and(eq(homeworkSubmissions.studentId, studentId), inArray(homeworkSubmissions.assignmentId, assignmentIds)),
    orderBy: [desc(homeworkSubmissions.updatedAt)],
  })

  const attemptsByAssignmentId = new Map<string, number>()
  const latestByAssignmentId = new Map<string, (typeof submissions)[number]>()
  const latestSubmittedByAssignmentId = new Map<string, (typeof submissions)[number]>()

  for (const s of submissions) {
    attemptsByAssignmentId.set(s.assignmentId, (attemptsByAssignmentId.get(s.assignmentId) ?? 0) + 1)
    if (!latestByAssignmentId.has(s.assignmentId)) latestByAssignmentId.set(s.assignmentId, s)
    if (s.status === "submitted" || s.status === "graded") {
      if (!latestSubmittedByAssignmentId.has(s.assignmentId)) latestSubmittedByAssignmentId.set(s.assignmentId, s)
    }
  }

  return assignments.map((a) => {
    const latest = latestSubmittedByAssignmentId.get(a.id) ?? latestByAssignmentId.get(a.id) ?? null
    const attemptsUsed = attemptsByAssignmentId.get(a.id) ?? 0
    const subjectId = examSubjectIdMap.get(a.sourceExamId) ?? null
    const subjectName = subjectId ? subjectNameById.get(subjectId) ?? null : null

    const item: StudentHomeworkAssignmentListItem = {
      id: a.id,
      title: a.title,
      subjectName: subjectName ?? null,
      dueAt: a.dueAt ? a.dueAt.toISOString() : null,
      availableAt: a.availableAt ? a.availableAt.toISOString() : null,
      maxAttempts: a.maxAttempts,
      attemptsUsed,
      progressStatus: toStudentProgressStatus(latest?.status),
      latestSubmissionId: latest?.id ?? null,
      latestSubmittedAt: latest?.submittedAt ? latest.submittedAt.toISOString() : null,
      latestScore: latest?.score ?? null,
    }
    return item
  })
})

export const getStudentHomeworkTakeData = cache(async (assignmentId: string, studentId: string): Promise<StudentHomeworkTakeData | null> => {
  const target = await db.query.homeworkAssignmentTargets.findFirst({
    where: and(eq(homeworkAssignmentTargets.assignmentId, assignmentId), eq(homeworkAssignmentTargets.studentId, studentId)),
  })
  if (!target) return null

  const assignment = await db.query.homeworkAssignments.findFirst({
    where: eq(homeworkAssignments.id, assignmentId),
  })
  if (!assignment) return null
  if (assignment.status !== "published") return null

  const now = new Date()
  if (assignment.availableAt && assignment.availableAt > now) return null

  const startedSubmission = await db.query.homeworkSubmissions.findFirst({
    where: and(
      eq(homeworkSubmissions.assignmentId, assignmentId),
      eq(homeworkSubmissions.studentId, studentId),
      eq(homeworkSubmissions.status, "started")
    ),
    orderBy: (s, { desc }) => [desc(s.createdAt)],
  })

  const latestSubmission =
    startedSubmission ??
    (await db.query.homeworkSubmissions.findFirst({
      where: and(eq(homeworkSubmissions.assignmentId, assignmentId), eq(homeworkSubmissions.studentId, studentId)),
      orderBy: (s, { desc }) => [desc(s.createdAt)],
    }))

  const assignmentQuestions = await db.query.homeworkAssignmentQuestions.findMany({
    where: eq(homeworkAssignmentQuestions.assignmentId, assignmentId),
    with: { 
      question: {
        with: {
          knowledgePoints: {
            with: {
              knowledgePoint: true
            }
          }
        }
      } 
    },
    orderBy: (q, { asc }) => [asc(q.order)],
  })

  const answersByQuestionId = new Map<string, { answer: unknown; score: number | null; feedback: string | null }>()
  if (latestSubmission) {
    const answers = await db.query.homeworkAnswers.findMany({
      where: eq(homeworkAnswers.submissionId, latestSubmission.id),
    })
    for (const ans of answers) {
      answersByQuestionId.set(ans.questionId, {
        answer: ans.answerContent,
        score: ans.score,
        feedback: ans.feedback,
      })
    }
  }

  return {
    assignment: {
      id: assignment.id,
      title: assignment.title,
      description: assignment.description,
      availableAt: assignment.availableAt ? assignment.availableAt.toISOString() : null,
      dueAt: assignment.dueAt ? assignment.dueAt.toISOString() : null,
      allowLate: assignment.allowLate,
      lateDueAt: assignment.lateDueAt ? assignment.lateDueAt.toISOString() : null,
      maxAttempts: assignment.maxAttempts,
    },
    submission: latestSubmission
      ? {
          id: latestSubmission.id,
          status: toHomeworkSubmissionStatus(latestSubmission.status),
          attemptNo: latestSubmission.attemptNo,
          submittedAt: latestSubmission.submittedAt ? latestSubmission.submittedAt.toISOString() : null,
          score: latestSubmission.score ?? null,
        }
      : null,
    questions: assignmentQuestions.map((aq) => {
      const saved = answersByQuestionId.get(aq.questionId)
      // Use optional chaining or fallback to empty array if knowledgePoints is not loaded/undefined
      const kps = aq.question.knowledgePoints ?? []
      return {
        questionId: aq.questionId,
        questionType: aq.question.type,
        questionContent: toQuestionContent(aq.question.content),
        maxScore: aq.score ?? 0,
        order: aq.order ?? 0,
        savedAnswer: saved?.answer ?? null,
        score: saved?.score ?? null,
        feedback: saved?.feedback ?? null,
        knowledgePoints: kps.map((kp) => ({
          id: kp.knowledgePoint.id,
          name: kp.knowledgePoint.name,
        })),
      }
    }),
  }
})

// Re-export stats functions for backward compatibility
// New code should import directly from "./stats-service"
export {
  getTeacherGradeTrends,
  getHomeworkAssignmentAnalytics,
  getStudentDashboardGrades,
  getHomeworkDashboardStats,
} from "./stats-service"
export type { HomeworkDashboardStats } from "./stats-service"