import "server-only"

import { and, asc, eq, inArray, sql } from "drizzle-orm"

import { db } from "@/shared/db"
import {
  classes,
  gradeRecords,
  subjects,
} from "@/shared/db/schema"
import type { DataScope } from "@/shared/types/permissions"

import type {
  ClassComparisonItem,
  GradeDistributionBucket,
  GradeDistributionResult,
  GradeTrendPoint,
  GradeTrendResult,
  SubjectComparisonItem,
} from "./types"

const toNumber = (v: unknown): number => {
  const n = typeof v === "number" ? v : Number(v)
  return Number.isFinite(n) ? n : 0
}

const normalize = (score: number, fullScore: number): number => {
  if (fullScore <= 0) return 0
  return Math.round((score / fullScore) * 10000) / 100
}

const buildScopeClassFilter = (scope: DataScope) => {
  if (scope.type === "all") return null
  if (scope.type === "class_taught") {
    return scope.classIds.length > 0 ? inArray(gradeRecords.classId, scope.classIds) : sql`1=0`
  }
  if (scope.type === "grade_managed") return sql`1=0`
  if (scope.type === "class_members") return null
  if (scope.type === "children") {
    return scope.childrenIds.length > 0
      ? inArray(gradeRecords.studentId, scope.childrenIds)
      : sql`1=0`
  }
  if (scope.type === "owned") return eq(gradeRecords.studentId, scope.userId)
  return sql`1=0`
}

export interface GradeTrendParams {
  classId: string
  subjectId?: string
  studentId?: string
  semester?: "1" | "2"
  scope: DataScope
  currentUserId?: string
}

export async function getGradeTrend(
  params: GradeTrendParams
): Promise<GradeTrendResult | null> {
  const conditions = [eq(gradeRecords.classId, params.classId)]
  if (params.subjectId) conditions.push(eq(gradeRecords.subjectId, params.subjectId))
  if (params.studentId) conditions.push(eq(gradeRecords.studentId, params.studentId))
  if (params.semester) conditions.push(eq(gradeRecords.semester, params.semester))

  if (params.scope.type === "class_members" && params.currentUserId) {
    conditions.push(eq(gradeRecords.studentId, params.currentUserId))
  }

  const scopeFilter = buildScopeClassFilter(params.scope)
  if (scopeFilter) conditions.push(scopeFilter)

  const rows = await db
    .select({
      record: gradeRecords,
      className: classes.name,
      subjectName: subjects.name,
    })
    .from(gradeRecords)
    .leftJoin(classes, eq(classes.id, gradeRecords.classId))
    .leftJoin(subjects, eq(subjects.id, gradeRecords.subjectId))
    .where(and(...conditions))
    .orderBy(asc(gradeRecords.createdAt))

  if (rows.length === 0) return null

  const points: GradeTrendPoint[] = rows.map((r) => {
    const score = toNumber(r.record.score)
    const fullScore = toNumber(r.record.fullScore)
    return {
      date: r.record.createdAt.toISOString(),
      title: r.record.title,
      score,
      fullScore,
      normalizedScore: normalize(score, fullScore),
      type: r.record.type,
    }
  })

  const avg = points.reduce((acc, p) => acc + p.normalizedScore, 0) / points.length
  const className = rows[0].className ?? "Class"
  const subjectName = rows[0].subjectName ?? "All Subjects"
  const studentLabel = params.studentId
    ? `Student ${params.studentId.slice(-4)}`
    : "Class Average"

  return {
    label: params.subjectId
      ? `${className} · ${subjectName} · ${studentLabel}`
      : `${className} · ${studentLabel}`,
    points,
    averageScore: Math.round(avg * 100) / 100,
  }
}

export interface ClassComparisonParams {
  gradeId: string
  subjectId: string
  examId?: string
  scope: DataScope
}

export async function getClassComparison(
  params: ClassComparisonParams
): Promise<ClassComparisonItem[]> {
  const classRows = await db
    .select({ id: classes.id, name: classes.name })
    .from(classes)
    .where(eq(classes.gradeId, params.gradeId))

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

  const scope = params.scope
  const allowedClassIds =
    scope.type === "class_taught"
      ? classRows.filter((c) => scope.classIds.includes(c.id)).map((c) => c.id)
      : classRows.map((c) => c.id)

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

  const result: ClassComparisonItem[] = []

  for (const cls of classRows) {
    if (!allowedClassIds.includes(cls.id)) continue

    const conditions = [
      eq(gradeRecords.classId, cls.id),
      eq(gradeRecords.subjectId, params.subjectId),
    ]
    if (params.examId) conditions.push(eq(gradeRecords.examId, params.examId))

    const rows = await db
      .select({
        score: gradeRecords.score,
        fullScore: gradeRecords.fullScore,
        studentId: gradeRecords.studentId,
      })
      .from(gradeRecords)
      .where(and(...conditions))

    if (rows.length === 0) {
      result.push({
        classId: cls.id, className: cls.name, averageScore: 0, medianScore: 0,
        passRate: 0, excellentRate: 0, count: 0, studentCount: 0,
      })
      continue
    }

    const normalized = rows.map((r) => normalize(toNumber(r.score), toNumber(r.fullScore)))
    const sorted = [...normalized].sort((a, b) => a - b)
    const mid = Math.floor(sorted.length / 2)
    const median = sorted.length % 2 === 0 ? (sorted[mid - 1] + sorted[mid]) / 2 : sorted[mid]
    const avg = normalized.reduce((a, b) => a + b, 0) / normalized.length
    const uniqueStudents = new Set(rows.map((r) => r.studentId)).size

    result.push({
      classId: cls.id,
      className: cls.name,
      averageScore: Math.round(avg * 100) / 100,
      medianScore: Math.round(median * 100) / 100,
      passRate: Math.round((normalized.filter((s) => s >= 60).length / normalized.length) * 10000) / 100,
      excellentRate: Math.round((normalized.filter((s) => s >= 85).length / normalized.length) * 10000) / 100,
      count: normalized.length,
      studentCount: uniqueStudents,
    })
  }

  return result
}

export interface SubjectComparisonParams {
  classId: string
  examId?: string
  scope: DataScope
}

export async function getSubjectComparison(
  params: SubjectComparisonParams
): Promise<SubjectComparisonItem[]> {
  const scopeFilter = buildScopeClassFilter(params.scope)
  const conditions = [eq(gradeRecords.classId, params.classId)]
  if (params.examId) conditions.push(eq(gradeRecords.examId, params.examId))
  if (scopeFilter) conditions.push(scopeFilter)

  const rows = await db
    .select({
      subjectId: gradeRecords.subjectId,
      subjectName: subjects.name,
      score: gradeRecords.score,
      fullScore: gradeRecords.fullScore,
    })
    .from(gradeRecords)
    .leftJoin(subjects, eq(subjects.id, gradeRecords.subjectId))
    .where(and(...conditions))

  const bySubject = new Map<string, { name: string; scores: number[] }>()

  for (const r of rows) {
    const sid = r.subjectId
    if (!sid) continue
    const entry = bySubject.get(sid) ?? { name: r.subjectName ?? "Unknown", scores: [] }
    entry.scores.push(normalize(toNumber(r.score), toNumber(r.fullScore)))
    bySubject.set(sid, entry)
  }

  const result: SubjectComparisonItem[] = []
  for (const [subjectId, entry] of bySubject.entries()) {
    if (entry.scores.length === 0) continue
    const sorted = [...entry.scores].sort((a, b) => a - b)
    const mid = Math.floor(sorted.length / 2)
    const median = sorted.length % 2 === 0 ? (sorted[mid - 1] + sorted[mid]) / 2 : sorted[mid]
    const avg = entry.scores.reduce((a, b) => a + b, 0) / entry.scores.length

    result.push({
      subjectId,
      subjectName: entry.name,
      averageScore: Math.round(avg * 100) / 100,
      medianScore: Math.round(median * 100) / 100,
      passRate: Math.round((entry.scores.filter((s) => s >= 60).length / entry.scores.length) * 10000) / 100,
      excellentRate: Math.round((entry.scores.filter((s) => s >= 85).length / entry.scores.length) * 10000) / 100,
      count: entry.scores.length,
    })
  }

  return result.sort((a, b) => b.averageScore - a.averageScore)
}

export interface GradeDistributionParams {
  classId: string
  subjectId?: string
  examId?: string
  scope: DataScope
  currentUserId?: string
}

export async function getGradeDistribution(
  params: GradeDistributionParams
): Promise<GradeDistributionResult> {
  const conditions = [eq(gradeRecords.classId, params.classId)]
  if (params.subjectId) conditions.push(eq(gradeRecords.subjectId, params.subjectId))
  if (params.examId) conditions.push(eq(gradeRecords.examId, params.examId))

  if (params.scope.type === "class_members" && params.currentUserId) {
    conditions.push(eq(gradeRecords.studentId, params.currentUserId))
  }

  const scopeFilter = buildScopeClassFilter(params.scope)
  if (scopeFilter) conditions.push(scopeFilter)

  const rows = await db
    .select({ score: gradeRecords.score, fullScore: gradeRecords.fullScore })
    .from(gradeRecords)
    .where(and(...conditions))

  const buckets: GradeDistributionBucket[] = [
    { label: "90-100", min: 90, max: 100, count: 0 },
    { label: "80-89", min: 80, max: 89, count: 0 },
    { label: "70-79", min: 70, max: 79, count: 0 },
    { label: "60-69", min: 60, max: 69, count: 0 },
    { label: "<60", min: 0, max: 59, count: 0 },
  ]

  for (const r of rows) {
    const normalized = normalize(toNumber(r.score), toNumber(r.fullScore))
    const rounded = Math.round(normalized)
    if (rounded >= 90) buckets[0].count++
    else if (rounded >= 80) buckets[1].count++
    else if (rounded >= 70) buckets[2].count++
    else if (rounded >= 60) buckets[3].count++
    else buckets[4].count++
  }

  return { buckets, totalCount: rows.length }
}