import { useMemo, useState } from "react";
import { useQuery } from "@tanstack/react-query";
import { Card, CardContent } from "@/components/ui/card";
import { Badge } from "@/components/ui/badge";
import {
  Select,
  SelectContent,
  SelectItem,
  SelectTrigger,
  SelectValue,
} from "@/components/ui/select";
import {
  Table,
  TableBody,
  TableCell,
  TableHead,
  TableHeader,
  TableRow,
} from "@/components/ui/table";
import { Input } from "@/components/ui/input";
import { Button } from "@/components/ui/button";
import { Loader2, Download } from "lucide-react";
import AiStudyCoach from "@/components/ai/AiStudyCoach";
import AiGradeExplainer from "@/components/ai/AiGradeExplainer";
import { reportsService } from "@/services/reports.service";

const LEVELS = ["all", "A1", "A2", "B1", "B2", "C1", "C2"] as const;

function ScoreBadge({ score }: { score: number | null }) {
  if (score === null || score === undefined) {
    return <span className="text-muted-foreground">—</span>;
  }
  const color =
    score >= 7.5
      ? "bg-success/10 text-success"
      : score >= 6.0
        ? "bg-warning/10 text-warning"
        : "bg-destructive/10 text-destructive";
  return (
    <span
      className={`inline-flex items-center rounded-md px-2 py-0.5 text-xs font-semibold ${color}`}
    >
      {score.toFixed(1)}
    </span>
  );
}

export default function StudentPerformancePage() {
  const [entityId, setEntityId] = useState<string>("all");
  const [level, setLevel] = useState<(typeof LEVELS)[number]>("all");
  const [search, setSearch] = useState("");

  const { data: filters } = useQuery({
    queryKey: ["reports-filters"],
    queryFn: () => reportsService.filters(),
  });

  const { data, isLoading } = useQuery({
    queryKey: ["student-performance", entityId, level, search],
    queryFn: () =>
      reportsService.studentPerformance({
        entity_id: entityId === "all" ? undefined : Number(entityId),
        level: level === "all" ? undefined : level,
        search: search || undefined,
      }),
  });

  const rows = data?.items ?? [];

  const summary = useMemo(() => {
    if (!rows.length) return null;
    const overall = rows
      .map((r) => r.overall)
      .filter((v): v is number => v !== null);
    const avg = overall.length
      ? overall.reduce((a, b) => a + b, 0) / overall.length
      : null;
    return {
      total: rows.length,
      avg: avg !== null ? avg.toFixed(1) : "—",
      topLevel: rows[0]?.level ?? "—",
    };
  }, [rows]);

  const exportCsv = () => {
    const header = [
      "Student",
      "Entity",
      "Level",
      "Reading",
      "Listening",
      "Writing",
      "Speaking",
      "Overall",
      "Attempts",
    ];
    const lines = rows.map((r) =>
      [
        r.student_name,
        r.entity_name,
        r.level ?? "",
        r.reading ?? "",
        r.listening ?? "",
        r.writing ?? "",
        r.speaking ?? "",
        r.overall ?? "",
        r.attempts_count,
      ]
        .map((v) => `"${String(v).replace(/"/g, '""')}"`)
        .join(","),
    );
    const blob = new Blob([[header.join(","), ...lines].join("\n")], {
      type: "text/csv",
    });
    const url = URL.createObjectURL(blob);
    const a = document.createElement("a");
    a.href = url;
    a.download = `student-performance-${new Date().toISOString().slice(0, 10)}.csv`;
    a.click();
    URL.revokeObjectURL(url);
  };

  return (
    <div className="space-y-6">
      <div className="flex items-start justify-between gap-4">
        <div>
          <h1 className="text-2xl font-bold tracking-tight">
            Student Performance
          </h1>
          <p className="text-muted-foreground">
            Track student scores across all IELTS modules.
          </p>
        </div>
        <Button variant="outline" size="sm" onClick={exportCsv} disabled={!rows.length}>
          <Download className="h-4 w-4 mr-1" /> Export CSV
        </Button>
      </div>

      {summary && (
        <div className="grid gap-3 md:grid-cols-3">
          <Card className="border-0 shadow-sm">
            <CardContent className="p-4">
              <p className="text-xs text-muted-foreground">Students tracked</p>
              <p className="text-2xl font-bold">{summary.total}</p>
            </CardContent>
          </Card>
          <Card className="border-0 shadow-sm">
            <CardContent className="p-4">
              <p className="text-xs text-muted-foreground">Average overall band</p>
              <p className="text-2xl font-bold">{summary.avg}</p>
            </CardContent>
          </Card>
          <Card className="border-0 shadow-sm">
            <CardContent className="p-4">
              <p className="text-xs text-muted-foreground">Top performer level</p>
              <p className="text-2xl font-bold">{summary.topLevel}</p>
            </CardContent>
          </Card>
        </div>
      )}

      <AiStudyCoach />

      <div className="flex flex-wrap gap-3 items-center">
        <Input
          placeholder="Search student..."
          value={search}
          onChange={(e) => setSearch(e.target.value)}
          className="w-[220px]"
        />
        <Select value={entityId} onValueChange={setEntityId}>
          <SelectTrigger className="w-[180px]">
            <SelectValue placeholder="All Entities" />
          </SelectTrigger>
          <SelectContent>
            <SelectItem value="all">All Entities</SelectItem>
            {filters?.entities.map((e) => (
              <SelectItem key={e.id} value={String(e.id)}>
                {e.name}
              </SelectItem>
            ))}
          </SelectContent>
        </Select>
        <Select
          value={level}
          onValueChange={(v) => setLevel(v as (typeof LEVELS)[number])}
        >
          <SelectTrigger className="w-[140px]">
            <SelectValue placeholder="Level" />
          </SelectTrigger>
          <SelectContent>
            {LEVELS.map((l) => (
              <SelectItem key={l} value={l}>
                {l === "all" ? "All Levels" : l}
              </SelectItem>
            ))}
          </SelectContent>
        </Select>
      </div>

      <Card className="border-0 shadow-sm">
        <CardContent className="p-0">
          {isLoading ? (
            <div className="flex items-center justify-center p-12 text-muted-foreground">
              <Loader2 className="h-5 w-5 animate-spin mr-2" /> Loading
              performance data...
            </div>
          ) : rows.length === 0 ? (
            <div className="p-8 text-center text-muted-foreground">
              No completed attempts match these filters yet.
            </div>
          ) : (
            <Table>
              <TableHeader>
                <TableRow>
                  <TableHead>Student</TableHead>
                  <TableHead>Entity</TableHead>
                  <TableHead>Level</TableHead>
                  <TableHead className="text-center">Reading</TableHead>
                  <TableHead className="text-center">Listening</TableHead>
                  <TableHead className="text-center">Writing</TableHead>
                  <TableHead className="text-center">Speaking</TableHead>
                  <TableHead className="text-center">Overall</TableHead>
                  <TableHead className="text-center">Attempts</TableHead>
                  <TableHead className="w-10">AI</TableHead>
                </TableRow>
              </TableHeader>
              <TableBody>
                {rows.map((r) => (
                  <TableRow key={r.student_id}>
                    <TableCell className="font-medium">
                      {r.student_name}
                    </TableCell>
                    <TableCell>{r.entity_name || "—"}</TableCell>
                    <TableCell>
                      {r.level ? (
                        <Badge variant="outline">{r.level}</Badge>
                      ) : (
                        "—"
                      )}
                    </TableCell>
                    <TableCell className="text-center">
                      <ScoreBadge score={r.reading} />
                    </TableCell>
                    <TableCell className="text-center">
                      <ScoreBadge score={r.listening} />
                    </TableCell>
                    <TableCell className="text-center">
                      <ScoreBadge score={r.writing} />
                    </TableCell>
                    <TableCell className="text-center">
                      <ScoreBadge score={r.speaking} />
                    </TableCell>
                    <TableCell className="text-center">
                      <ScoreBadge score={r.overall} />
                    </TableCell>
                    <TableCell className="text-center text-sm text-muted-foreground">
                      {r.attempts_count}
                    </TableCell>
                    <TableCell>
                      <AiGradeExplainer studentName={r.student_name} />
                    </TableCell>
                  </TableRow>
                ))}
              </TableBody>
            </Table>
          )}
        </CardContent>
      </Card>
    </div>
  );
}