import type { JSX } from "react"
import { Suspense } from "react"
import { User } from "lucide-react"

import { requirePermission } from "@/shared/lib/auth-guard"
import { Permissions } from "@/shared/types/permissions"
import { getClassStudents, getTeacherClasses, getStudentsSubjectScores } from "@/modules/classes/data-access"
import { StudentsFilters } from "@/modules/classes/components/students-filters"
import { StudentsTable } from "@/modules/classes/components/students-table"
import { EmptyState } from "@/shared/components/ui/empty-state"
import { Skeleton } from "@/shared/components/ui/skeleton"
import { getParam, type SearchParams } from "@/shared/lib/search-params"

export const dynamic = "force-dynamic"

async function StudentsResults({ searchParams, defaultClassId }: { searchParams: Promise<SearchParams>, defaultClassId?: string }): Promise<JSX.Element> {
  const params = await searchParams

  const q = getParam(params, "q") || undefined
  const classId = getParam(params, "classId")
  const status = getParam(params, "status")

  // If classId is explicit in URL, use it (unless "all"). If not, use defaultClassId.
  // If user explicitly selects "all", classId will be "all".
  // However, the requirement is "Default to showing the first class".
  // If classId param is missing, we use defaultClassId.
  const targetClassId = classId ? (classId !== "all" ? classId : undefined) : defaultClassId
  
  const filteredStudents = await getClassStudents({
    q,
    classId: targetClassId,
    status: status && status !== "all" ? status : undefined,
  })

  // Fetch subject scores for all filtered students
  if (filteredStudents.length > 0) {
    const studentIds = filteredStudents.map(s => s.id)
    const scores = await getStudentsSubjectScores(studentIds)
    for (const student of filteredStudents) {
      student.subjectScores = scores.get(student.id)
    }
  }

  const hasFilters = Boolean(q || (classId && classId !== "all") || (status && status !== "all"))

  if (filteredStudents.length === 0) {
    return (
      <EmptyState
        icon={User}
        title={hasFilters ? "No students match your filters" : "No students found"}
        description={hasFilters ? "Try clearing filters or adjusting keywords." : "There are no students in your classes yet."}
        action={hasFilters ? { label: "Clear filters", href: "/teacher/classes/students" } : undefined}
        className="h-[360px] bg-card"
      />
    )
  }

  return (
    <div className="rounded-md border bg-card">
      <StudentsTable students={filteredStudents} />
    </div>
  )
}

function StudentsResultsFallback() {
  return (
    <div className="rounded-md border bg-card">
      <div className="p-4">
        <Skeleton className="h-8 w-full" />
      </div>
      <div className="space-y-2 p-4 pt-0">
        {Array.from({ length: 8 }).map((_, idx) => (
          <Skeleton key={idx} className="h-10 w-full" />
        ))}
      </div>
    </div>
  )
}

export default async function StudentsPage({ searchParams }: { searchParams: Promise<SearchParams> }): Promise<JSX.Element> {
  await requirePermission(Permissions.CLASS_READ)
  const classes = await getTeacherClasses()
  
  // Logic to determine default class (first one available)
  const defaultClassId = classes.length > 0 ? classes[0].id : undefined

  return (
    <div className="flex h-full flex-col space-y-4 p-8">
      <div className="space-y-4">
        <Suspense fallback={<div className="h-10 w-full animate-pulse rounded-md bg-muted" />}>
          <StudentsFilters classes={classes} defaultClassId={defaultClassId} />
        </Suspense>

        <Suspense fallback={<StudentsResultsFallback />}>
          <StudentsResults searchParams={searchParams} defaultClassId={defaultClassId} />
        </Suspense>
      </div>
    </div>
  )
}