import { useEffect, useState } from "react";
import { useNavigate, useParams } from "react-router-dom";
import {
  ArrowLeft, ClipboardList, NotebookPen,
  CheckCircle2, Circle, Users, Activity,
  ChevronDown, ChevronUp,
} from "lucide-react";

import { useCourses } from "@/contexts/AdminCoursesContext";
import { PageMeta } from "@/contexts/MetadataContext";
import { Button } from "@/components/ui/button";
import { Badge } from "@/components/ui/badge";
import { Separator } from "@/components/ui/separator";
import { Skeleton } from "@/components/ui/skeleton";

// ─── Helpers ──────────────────────────────────────────────────────────────────

function InfoRow({ label, children }) {
  return (
    <div className="flex flex-col gap-0.5">
      <span className="text-xs text-muted-foreground uppercase tracking-wide">{label}</span>
      <span className="text-sm font-medium">{children ?? <span className="italic text-muted-foreground">—</span>}</span>
    </div>
  );
}

function SectionCard({ title, children }) {
  return (
    <div className="rounded-lg border bg-card p-5 space-y-4">
      {title && (<><h2 className="text-sm font-semibold">{title}</h2><Separator /></>)}
      {children}
    </div>
  );
}

function StatCard({ label, value, color = "default" }) {
  const colors = {
    default: "bg-card border",
    green:   "bg-green-500/5  border-green-500/20",
    red:     "bg-red-500/5    border-red-500/20",
    blue:    "bg-blue-500/5   border-blue-500/20",
    amber:   "bg-amber-500/5  border-amber-500/20",
  };
  return (
    <div className={`rounded-lg border p-4 text-center ${colors[color]}`}>
      <p className="text-2xl font-bold">{value ?? 0}</p>
      <p className="text-xs text-muted-foreground mt-0.5">{label}</p>
    </div>
  );
}

const TYPE_LABELS = {
  multiple_choice: "Multiple Choice",
  multi_select:    "Multi Select",
  true_false:      "True / False",
};

function QuestionView({ question, index }) {
  return (
    <div className="rounded-lg border bg-card p-5 space-y-3">
      <div className="flex items-start justify-between gap-3">
        <div className="flex items-start gap-2 min-w-0">
          <span className="flex h-6 w-6 shrink-0 items-center justify-center rounded bg-muted text-xs font-semibold text-muted-foreground mt-0.5">
            {index + 1}
          </span>
          <p className="text-sm font-medium leading-snug">
            {question.question?.trim() || <span className="italic text-muted-foreground">Untitled</span>}
          </p>
        </div>
        <div className="flex items-center gap-2 shrink-0">
          <Badge variant="outline" className="text-xs">{TYPE_LABELS[question.type] ?? question.type}</Badge>
          <span className="text-xs text-muted-foreground whitespace-nowrap">
            {question.points ?? 1} pt{(question.points ?? 1) !== 1 ? "s" : ""}
          </span>
        </div>
      </div>
      {question.type === "multi_select" && (() => {
        const cnt = (question.options ?? []).filter((o) => o.is_correct).length;
        return cnt > 0 ? (
          <p className="text-xs font-medium text-blue-600 dark:text-blue-400 pl-8">
            Students select {cnt} answer{cnt !== 1 ? "s" : ""}
          </p>
        ) : null;
      })()}
      <ul className="space-y-1.5 pl-8">
        {(question.options ?? []).map((opt, oi) => (
          <li key={opt.option_id ?? oi} className="flex items-center gap-2 text-sm">
            {opt.is_correct ? (
              <CheckCircle2 className="h-4 w-4 text-green-500 shrink-0" />
            ) : (
              <Circle className="h-4 w-4 text-muted-foreground/40 shrink-0" />
            )}
            <span className={opt.is_correct ? "font-medium text-green-700 dark:text-green-400" : "text-muted-foreground"}>
              {opt.text}
            </span>
          </li>
        ))}
      </ul>
    </div>
  );
}

// ─── Completions tab ──────────────────────────────────────────────────────────

function CompletionRow({ row }) {
  const [open, setOpen] = useState(false);
  return (
    <>
      <tr
        className="border-b transition-colors hover:bg-muted/40 cursor-pointer"
        onClick={() => setOpen((v) => !v)}
      >
        <td className="px-4 py-3">
          <div>
            <p className="text-sm font-medium">{row.full_name}</p>
            <p className="text-xs text-muted-foreground">{row.email}</p>
          </div>
        </td>
        <td className="px-4 py-3 text-center text-sm">{row.attempt_count}</td>
        <td className="px-4 py-3 text-center">
          <span className="text-sm font-semibold">{row.best_score}%</span>
        </td>
        <td className="px-4 py-3 text-center">
          {row.passed ? (
            <Badge className="bg-green-500/10 text-green-700 dark:text-green-400 border-green-500/20">Passed</Badge>
          ) : (
            <Badge variant="outline" className="text-red-600 dark:text-red-400 border-red-500/20">Not yet</Badge>
          )}
        </td>
        <td className="px-4 py-3 text-xs text-muted-foreground whitespace-nowrap">
          {row.latest_at ? new Date(row.latest_at).toLocaleDateString() : "—"}
        </td>
        <td className="px-4 py-3 text-center">
          {open ? <ChevronUp className="h-4 w-4 mx-auto text-muted-foreground" /> : <ChevronDown className="h-4 w-4 mx-auto text-muted-foreground" />}
        </td>
      </tr>
      {open && (
        <tr className="bg-muted/30">
          <td colSpan={6} className="px-6 py-3">
            <table className="w-full text-xs">
              <thead>
                <tr className="text-muted-foreground border-b">
                  <th className="text-left py-1 font-medium">Attempt</th>
                  <th className="text-center py-1 font-medium">Score</th>
                  <th className="text-center py-1 font-medium">Points</th>
                  <th className="text-center py-1 font-medium">Result</th>
                  <th className="text-left py-1 font-medium">Date</th>
                </tr>
              </thead>
              <tbody>
                {(row.attempts ?? []).map((a) => (
                  <tr key={a.attempt_id} className="border-b border-border/50 last:border-0">
                    <td className="py-1.5 text-muted-foreground">#{a.attempt_number}</td>
                    <td className="py-1.5 text-center font-semibold">{a.score}%</td>
                    <td className="py-1.5 text-center text-muted-foreground">{a.earned_points}/{a.total_points}</td>
                    <td className="py-1.5 text-center">
                      {a.passed
                        ? <span className="text-green-600 dark:text-green-400 font-medium">Pass</span>
                        : <span className="text-red-500 font-medium">Fail</span>}
                    </td>
                    <td className="py-1.5 text-muted-foreground">{new Date(a.createdAt).toLocaleString()}</td>
                  </tr>
                ))}
              </tbody>
            </table>
          </td>
        </tr>
      )}
    </>
  );
}

function CompletionsTab({ completions, loading }) {
  if (loading) return <div className="space-y-3">{[...Array(3)].map((_, i) => <Skeleton key={i} className="h-12 w-full rounded-lg" />)}</div>;

  if (!completions) return (
    <div className="rounded-lg border border-dashed bg-card p-12 text-center">
      <p className="text-sm text-muted-foreground">No data yet.</p>
    </div>
  );

  const { summary, completions: rows } = completions;

  return (
    <div className="space-y-5">
      <div className="grid grid-cols-2 sm:grid-cols-5 gap-3">
        <StatCard label="Total Takers"    value={summary.total_takers}   />
        <StatCard label="Passed"          value={summary.passed_count}   color="green" />
        <StatCard label="Failed"          value={summary.failed_count}   color="red"   />
        <StatCard label="Pass Rate"       value={`${summary.pass_rate}%`} color="blue" />
        <StatCard label="Avg Score"       value={`${summary.avg_score}%`} />
      </div>

      {rows.length === 0 ? (
        <div className="rounded-lg border border-dashed bg-card p-10 text-center">
          <p className="text-sm text-muted-foreground">No one has attempted this assessment yet.</p>
        </div>
      ) : (
        <div className="rounded-lg border bg-card overflow-hidden">
          <table className="w-full">
            <thead className="bg-muted/50 border-b">
              <tr>
                <th className="text-left px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Student</th>
                <th className="text-center px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Attempts</th>
                <th className="text-center px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Best Score</th>
                <th className="text-center px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Status</th>
                <th className="text-left px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Last Attempt</th>
                <th className="w-8" />
              </tr>
            </thead>
            <tbody>
              {rows.map((row) => <CompletionRow key={row.user_id} row={row} />)}
            </tbody>
          </table>
        </div>
      )}
    </div>
  );
}

// ─── Sessions tab ─────────────────────────────────────────────────────────────

const SESSION_BADGE = {
  completed:   "bg-green-500/10 text-green-700 dark:text-green-400 border-green-500/20",
  expired:     "bg-red-500/10   text-red-600   dark:text-red-400   border-red-500/20",
  in_progress: "bg-amber-500/10 text-amber-700 dark:text-amber-400 border-amber-500/20",
};

function fmtDuration(secs) {
  if (secs == null) return "—";
  if (secs < 60) return `${secs}s`;
  const m = Math.floor(secs / 60);
  const s = secs % 60;
  return s > 0 ? `${m}m ${s}s` : `${m}m`;
}

function SessionsTab({ sessions, loading }) {
  if (loading) return <div className="space-y-3">{[...Array(4)].map((_, i) => <Skeleton key={i} className="h-10 w-full rounded-lg" />)}</div>;

  if (!sessions) return (
    <div className="rounded-lg border border-dashed bg-card p-12 text-center">
      <p className="text-sm text-muted-foreground">No data yet.</p>
    </div>
  );

  const { summary, sessions: rows } = sessions;

  return (
    <div className="space-y-5">
      <div className="grid grid-cols-2 sm:grid-cols-4 gap-3">
        <StatCard label="Total Sessions"  value={summary.total}       />
        <StatCard label="Completed"       value={summary.completed}   color="green" />
        <StatCard label="Expired"         value={summary.expired}     color="red"   />
        <StatCard label="In Progress"     value={summary.in_progress} color="amber" />
      </div>

      {rows.length === 0 ? (
        <div className="rounded-lg border border-dashed bg-card p-10 text-center">
          <p className="text-sm text-muted-foreground">No sessions recorded yet.</p>
        </div>
      ) : (
        <div className="rounded-lg border bg-card overflow-hidden">
          <table className="w-full">
            <thead className="bg-muted/50 border-b">
              <tr>
                <th className="text-left px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Student</th>
                <th className="text-center px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Status</th>
                <th className="text-left px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Started</th>
                <th className="text-left px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Expires At</th>
                <th className="text-center px-4 py-2.5 text-xs font-semibold text-muted-foreground uppercase tracking-wide">Time Spent</th>
              </tr>
            </thead>
            <tbody>
              {rows.map((s) => (
                <tr key={s.session_id} className="border-b last:border-0 hover:bg-muted/30 transition-colors">
                  <td className="px-4 py-3">
                    <p className="text-sm font-medium">{s.full_name}</p>
                    <p className="text-xs text-muted-foreground">{s.email}</p>
                  </td>
                  <td className="px-4 py-3 text-center">
                    <Badge className={SESSION_BADGE[s.status] ?? ""}>
                      {s.status === 'in_progress' ? 'In Progress' : s.status.charAt(0).toUpperCase() + s.status.slice(1)}
                    </Badge>
                  </td>
                  <td className="px-4 py-3 text-xs text-muted-foreground whitespace-nowrap">
                    {new Date(s.started_at).toLocaleString()}
                  </td>
                  <td className="px-4 py-3 text-xs text-muted-foreground whitespace-nowrap">
                    {s.expires_at ? new Date(s.expires_at).toLocaleString() : "—"}
                  </td>
                  <td className="px-4 py-3 text-center text-sm">{fmtDuration(s.time_spent_seconds)}</td>
                </tr>
              ))}
            </tbody>
          </table>
        </div>
      )}
    </div>
  );
}

function LoadingSkeleton() {
  return (
    <div className="space-y-4">
      <Skeleton className="h-32 w-full rounded-lg" />
      {[...Array(3)].map((_, i) => <Skeleton key={i} className="h-24 w-full rounded-lg" />)}
    </div>
  );
}

// ─── Page ─────────────────────────────────────────────────────────────────────

const TABS = [
  { key: "questions",    label: "Questions",    icon: ClipboardList },
  { key: "completions",  label: "Completions",  icon: Users         },
  { key: "sessions",     label: "Sessions",     icon: Activity      },
];

export default function ViewAssessment() {
  const navigate = useNavigate();
  const { courseId } = useParams();

  const {
    fetchAssessment, assessment,
    fetchAssessmentCompletions, fetchAssessmentSessions,
    completions, sessions,
    loading,
  } = useCourses();

  const [activeTab, setActiveTab] = useState("questions");

  useEffect(() => {
    fetchAssessment(courseId);
  }, [courseId]);

  // Lazy-load completions/sessions the first time each tab is opened
  const loadedRef = { completions: false, sessions: false };
  useEffect(() => {
    if (!assessment?.assessment_id) return;
    if (activeTab === "completions") fetchAssessmentCompletions(courseId, assessment.assessment_id);
    if (activeTab === "sessions")    fetchAssessmentSessions(courseId, assessment.assessment_id);
  }, [activeTab, assessment?.assessment_id]);

  const questions  = assessment?.questions ?? [];
  const totalPoints = questions.reduce((sum, q) => sum + (q.points ?? 1), 0);

  return (
    <div className="flex flex-col min-h-screen bg-muted/60">
      <PageMeta title="View Assessment - STARR" />

      {/* ── Header ── */}
      <div
        className="sticky z-20 shrink-0 border-b bg-white/70 dark:bg-zinc-900/70 backdrop-blur-md"
        style={{ top: "var(--navbar-h)" }}
      >
        <div className="lg:container lg:mx-auto lg:px-6 px-4">
          <div className="flex items-center gap-3 py-3">
            <Button type="button" variant="ghost" size="icon" onClick={() => navigate(-1)}>
              <ArrowLeft className="h-4 w-4" />
            </Button>
            <div className="flex-1 min-w-0">
              <h1 className="text-xl font-semibold leading-tight flex items-center gap-2">
                <ClipboardList className="h-5 w-5 text-muted-foreground" />
                View Assessment
              </h1>
              {assessment && (
                <p className="text-sm text-muted-foreground">
                  {questions.length} question{questions.length !== 1 ? "s" : ""} · {totalPoints} total point{totalPoints !== 1 ? "s" : ""}
                </p>
              )}
            </div>
            <Button variant="outline" size="sm" onClick={() => navigate(`/admin/courses/${courseId}/assessment`)}>
              <NotebookPen className="h-4 w-4 mr-2" />
              Modify Assessment
            </Button>
          </div>

          {/* Tabs */}
          {assessment && (
            <div className="flex gap-1 pb-0 -mb-px">
              {TABS.map(({ key, label, icon: Icon }) => (
                <button
                  key={key}
                  onClick={() => setActiveTab(key)}
                  className={`flex items-center gap-1.5 px-4 py-2.5 text-sm font-medium border-b-2 transition-colors
                    ${activeTab === key
                      ? "border-primary text-primary"
                      : "border-transparent text-muted-foreground hover:text-foreground"}`}
                >
                  <Icon className="h-3.5 w-3.5" />
                  {label}
                </button>
              ))}
            </div>
          )}
        </div>
      </div>

      {/* ── Content ── */}
      <div className="lg:container lg:mx-auto lg:px-6 px-4 py-6">
        <div className="max-w-3xl mx-auto space-y-5 pb-16">
          {loading && !assessment ? (
            <LoadingSkeleton />
          ) : !assessment ? (
            <div className="rounded-lg border border-dashed bg-card p-12 flex flex-col items-center gap-3 text-center">
              <ClipboardList className="h-8 w-8 text-muted-foreground/40" />
              <p className="text-sm text-muted-foreground">No assessment has been created for this course yet.</p>
              <Button size="sm" variant="outline" onClick={() => navigate(`/admin/courses/${courseId}/assessment`)}>
                <NotebookPen className="h-4 w-4 mr-2" />
                Create Assessment
              </Button>
            </div>
          ) : activeTab === "questions" ? (
            <>
              <SectionCard title="Settings">
                <div className="grid grid-cols-2 gap-4">
                  <InfoRow label="Title">{assessment.title || "Course Assessment"}</InfoRow>
                  <InfoRow label="Required">
                    <Badge variant={assessment.is_required ? "default" : "secondary"} className="mt-0.5">
                      {assessment.is_required ? "Required" : "Optional"}
                    </Badge>
                  </InfoRow>
                  <InfoRow label="Passing Score">{assessment.passing_score ?? 70}%</InfoRow>
                  <InfoRow label="Time Limit">
                    {assessment.time_limit_minutes ? `${assessment.time_limit_minutes} mins` : "No limit"}
                  </InfoRow>
                  <InfoRow label="Questions in Pool">{questions.length}</InfoRow>
                  <InfoRow label="Max Shown per Attempt">
                    {assessment.max_questions ? `${assessment.max_questions} (random)` : `All (${questions.length})`}
                  </InfoRow>
                  <InfoRow label="Total Points">{totalPoints}</InfoRow>
                  <InfoRow label="Max Failed Attempts">{assessment.max_attempts ?? 3}</InfoRow>
                  <InfoRow label="Cooldown After Fails">{assessment.cooldown_hours ?? 24}h</InfoRow>
                </div>
              </SectionCard>

              <div className="space-y-3">
                <p className="text-xs font-semibold uppercase tracking-widest text-muted-foreground px-1">Questions</p>
                {questions.length === 0 ? (
                  <div className="rounded-lg border border-dashed bg-card p-10 flex flex-col items-center gap-2 text-center">
                    <p className="text-sm text-muted-foreground">No questions added yet.</p>
                  </div>
                ) : (
                  questions.map((q, i) => <QuestionView key={q.question_id ?? i} question={q} index={i} />)
                )}
              </div>
            </>
          ) : activeTab === "completions" ? (
            <CompletionsTab completions={completions} loading={loading} />
          ) : (
            <SessionsTab sessions={sessions} loading={loading} />
          )}
        </div>
      </div>
    </div>
  );
}