"use client";

import { useEffect, useState } from "react";
import Link from "next/link";
import { Button } from "@/components/ui/button";
import { Card, CardContent } from "@/components/ui/card";
import { Badge } from "@/components/ui/badge";
import { Activity, Clock, PlayCircle, Search, Lock, CheckSquare } from "lucide-react";
import { useActiveUser } from "@/hooks/useActiveUser";

interface TestData {
  id: string;
  title: string;
  type: string;
  exam_pattern: string;
  total_time: number;
  difficulty: string;
  scheduled_date?: string;
  end_date?: string;
}

export default function CBTPage() {
  const [exams, setExams] = useState<TestData[]>([]);
  const [loading, setLoading] = useState(true);
  const [search, setSearch] = useState("");
  const [targetExam, setTargetExam] = useState("");
  const [attempts, setAttempts] = useState<any[]>([]);
  const [showUpgradeModal, setShowUpgradeModal] = useState(false);
  const [showAllExams, setShowAllExams] = useState(false);
  const [selectedPattern, setSelectedPattern] = useState<string>("");
  const [dateFilter, setDateFilter] = useState("");

  const { userId, user, hasAccessTo, loading: userLoading } = useActiveUser();

  useEffect(() => {
    if (userLoading || !userId) return;

    async function loadUser() {
      try {
        const userRes = await fetch(`/api/users/${userId}`);
        if (!userRes.ok) throw new Error("Failed to load user target exam");
        const userData = await userRes.json();
        const pattern = userData.target_exam;
        setTargetExam(pattern === "NEET" ? "NEET" : pattern === "JEE_Advanced" ? "JEE Advanced" : "JEE");
        
        // Only set the initial pattern if it hasn't been changed by the user
        if (!selectedPattern) {
          setSelectedPattern(pattern.startsWith("JEE") ? "JEE" : "NEET");
        }
      } catch (err) {
        console.error("Error loading user:", err);
      }
    }
    loadUser();
  }, [userId, userLoading]);

  useEffect(() => {
    if (!userId || !selectedPattern) return;

    async function loadTests() {
      setLoading(true);
      try {
        let url = `/api/tests?user_id=${userId}`;
        if (selectedPattern !== "JEE") {
          url += `&exam_pattern=${selectedPattern}`;
        }
        const testRes = await fetch(url);
        if (testRes.ok) {
          let testsData = await testRes.json();
          if (selectedPattern === "JEE") {
            testsData = testsData.filter((t: any) => t.exam_pattern?.includes("JEE"));
          } else if (selectedPattern === "NEET") {
            testsData = testsData.filter((t: any) => t.exam_pattern === "NEET");
          }
          setExams(testsData);
        }

        const attemptsRes = await fetch(`/api/users/${userId}/attempts`);
        if (attemptsRes.ok) {
          const attemptsData = await attemptsRes.json();
          setAttempts(attemptsData);
        }
      } catch (err) {
        console.error("Error loading exams:", err);
      } finally {
        setLoading(false);
      }
    }
    loadTests();
  }, [userId, selectedPattern]);

  const filteredExams = exams.filter(exam => {
    const matchesSearch = exam.title.toLowerCase().includes(search.toLowerCase());
    if (!matchesSearch) return false;
    
    if (dateFilter) {
      if (!exam.scheduled_date) return false;
      const scheduledDate = new Date(exam.scheduled_date).toISOString().split('T')[0];
      if (scheduledDate !== dateFilter) return false;
    }
    
    return true;
  });

  const formatDate = (dateStr: string) => {
    return new Date(dateStr).toLocaleDateString("en-US", { year: 'numeric', month: 'short', day: 'numeric' });
  }

  // Get the highest score for each test if attempted multiple times
  const attemptsByTest = attempts.reduce((acc, curr) => {
    // Isolate analytics to first attempt only - ignore retakes
    if (curr.is_retake) return acc;

    if (!acc[curr.source_id] || acc[curr.source_id].score < curr.score) {
      acc[curr.source_id] = curr;
    }
    return acc;
  }, {} as Record<string, any>);

  if (userLoading || loading) {
    return (
      <div className="h-[70vh] flex flex-col items-center justify-center p-8">
        <div className="h-8 w-8 border-4 border-[var(--cyan-ai)] border-t-transparent rounded-full animate-spin mb-4"></div>
        <p className="text-muted-foreground font-medium animate-pulse">Loading exams...</p>
      </div>
    )
  }

  return (
    <div className="p-8 space-y-8 animate-in fade-in slide-in-from-bottom-4 duration-500 max-w-7xl mx-auto">
      <div className="flex flex-col md:flex-row md:items-end justify-between gap-4">
        <div>
          <h1 className="text-3xl md:text-4xl font-black tracking-tight flex items-center gap-3 mb-1">
            <span className="p-2.5 rounded-xl bg-yellow-50 dark:bg-[var(--cyan-ai-10)] border border-yellow-300/60 dark:border-[var(--cyan-ai-20)]">
              <CheckSquare className="text-yellow-600 dark:text-[var(--cyan-ai)]" size={28} />
            </span>
            Computer Based Tests (CBT)
          </h1>
          <p className="text-muted-foreground text-base font-medium max-w-2xl pl-1">
            Real exam environment simulations to conquer {selectedPattern === "NEET" ? "NEET" : (targetExam || "JEE")}.
          </p>
        </div>
        <div className="flex flex-col sm:flex-row gap-3">
          <div className="relative w-full sm:w-48">
            <input
              type="date"
              value={dateFilter}
              onChange={(e) => setDateFilter(e.target.value)}
              className="w-full px-4 py-2 bg-background border border-border rounded-xl text-sm focus:ring-2 focus:ring-[var(--cyan-ai)] outline-none text-foreground dark:[color-scheme:dark] [color-scheme:light]"
            />
          </div>
          <div className="relative w-full sm:w-64">
            <Search className="absolute left-3 top-1/2 -translate-y-1/2 text-muted-foreground" size={16} />
            <input
              type="text"
              placeholder="Search exams..."
              value={search}
              onChange={(e) => setSearch(e.target.value)}
              className="w-full pl-10 pr-4 py-2 bg-background border border-border rounded-xl text-sm focus:ring-2 focus:ring-[var(--cyan-ai)] outline-none"
            />
          </div>
        </div>
      </div>

      <div className="flex gap-3 overflow-x-auto pb-2 scrollbar-hide">
        {["JEE", "NEET"].map(p => {
          return (
            <Button
              key={p}
              variant={selectedPattern === p ? "default" : "outline"}
              onClick={() => setSelectedPattern(p)}
              className="rounded-full shadow-sm px-6 font-bold"
            >
              {p}
            </Button>
          )
        })}
      </div>

      <div className="space-y-6">
        <h2 className="text-xl font-bold border-b border-border pb-2 flex items-center gap-2">
          <Clock size={20} className="text-[var(--cyan-ai)]" /> Upcoming & Active Exams
        </h2>

        {/* BUG-08 fix: Filter out already attempted exams from Upcoming & Active list */}
        {(() => {
          const unattemptedExams = filteredExams.filter(exam => !attemptsByTest[exam.id]);
          
          if (loading) {
            return <div className="py-12 text-center text-muted-foreground">Loading test catalog...</div>;
          }
          
          if (unattemptedExams.length === 0) {
            return (
              <div className="py-8 text-center text-muted-foreground bg-secondary/10 border border-dashed border-border rounded-2xl p-6">
                {filteredExams.length > 0 ? (
                  <>
                    <p className="font-bold text-foreground mb-1">All available exams in this section have been attempted!</p>
                    <p className="text-xs text-muted-foreground">Review your scores, solution explanations, and performance in the Past Attempts section below.</p>
                  </>
                ) : (
                  <p>No active exams found for {selectedPattern === "NEET" ? "NEET" : "JEE"}. Try adjusting your filters!</p>
                )}
              </div>
            );
          }

          return (
            <div className="space-y-8">
              <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">
                {(showAllExams ? unattemptedExams : unattemptedExams.slice(0, 3)).map((exam) => {
                  const isLocked = !hasAccessTo("weekly-test-series");
                  
                  // Date logic
                  const now = new Date();
                  const scheduledTime = exam.scheduled_date ? new Date(exam.scheduled_date) : now;
                  const endTime = exam.end_date ? new Date(exam.end_date) : null;
                  const isUpcoming = scheduledTime > now;
                  const isExpired = endTime ? now > endTime : false;
                  
                  return (
                  <Card key={exam.id} className={`hover:border-[var(--cyan-ai-10)] hover:shadow-[0_0_15px_-5px_var(--cyan-ai)] transition-all group ${isLocked || isExpired ? 'opacity-80' : ''}`}>
                    <CardContent className="p-6">
                      <div className="flex justify-between items-start mb-4">
                        <div className="flex gap-2 flex-wrap">
                          <Badge variant="outline" className="bg-[var(--cyan-ai-10)] text-[var(--cyan-ai)] border-[var(--cyan-ai-20)]">
                            {exam.type} Test
                          </Badge>
                          {exam.exam_pattern && (
                            <Badge variant="outline" className="bg-primary/20 text-primary border-primary/30 uppercase tracking-wider text-[10px]">
                              {exam.exam_pattern === 'JEE_Main' ? 'JEE Main' : exam.exam_pattern === 'JEE_Advanced' ? 'JEE Advanced' : exam.exam_pattern}
                            </Badge>
                          )}
                        </div>
                        {isUpcoming ? (
                          <Badge variant="secondary" className="bg-yellow-500/10 text-yellow-500 border-yellow-500/20">
                            Upcoming
                          </Badge>
                        ) : isLocked ? (
                          <Badge variant="outline" className="bg-red-500/10 text-red-500 border-red-500/20 flex items-center gap-1">
                            <Lock size={12} /> Premium
                          </Badge>
                        ) : isExpired ? (
                          <Badge variant="outline" className="bg-muted text-muted-foreground border-muted-foreground/30">
                            Expired
                          </Badge>
                        ) : null}
                      </div>
                      <h3 className="font-bold text-lg leading-tight mb-2 group-hover:text-[var(--cyan-ai)] transition-colors">
                        {exam.title}
                      </h3>
                      <div className="text-sm text-muted-foreground space-y-1 mb-6">
                        <div className="font-medium text-foreground">
                          {isUpcoming ? `Available on ${formatDate(exam.scheduled_date!)}` : isExpired ? `Expired on ${formatDate(exam.end_date!)}` : 'Available Now'}
                        </div>
                        <div>{exam.total_time} Min • {exam.difficulty} Difficulty</div>
                      </div>
                      
                      {isUpcoming ? (
                        <Button disabled className="w-full gap-2 rounded-xl bg-secondary text-muted-foreground font-bold">
                          <Clock size={16} /> Starts Soon
                        </Button>
                      ) : isLocked ? (
                        <Button 
                          onClick={() => setShowUpgradeModal(true)}
                          className="w-full gap-2 rounded-xl bg-secondary text-muted-foreground border border-dashed border-border hover:border-[var(--cyan-ai-10)] hover:text-foreground font-bold"
                        >
                          <Lock size={16} /> Unlock Test
                        </Button>
                      ) : isExpired ? (
                        <Button disabled className="w-full gap-2 rounded-xl bg-secondary/50 text-muted-foreground border border-border font-bold">
                          Expired
                        </Button>
                      ) : (
                        <Link href={`/cbt/${exam.id}`}>
                          <Button className="w-full gap-2 rounded-xl bg-secondary text-foreground hover:bg-[var(--cyan-ai)] hover:text-background font-bold transition-colors">
                            <PlayCircle size={16} /> Start Exam
                          </Button>
                        </Link>
                      )}
                    </CardContent>
                  </Card>
                )})}
              </div>

              {unattemptedExams.length > 3 && !showAllExams && (
                <div className="flex justify-center mt-6">
                  <Button variant="outline" onClick={() => setShowAllExams(true)} className="rounded-xl border-dashed">
                    Show More Available Exams ({unattemptedExams.length - 3})
                  </Button>
                </div>
              )}
            </div>
          );
        })()}
      </div>

      <div className="space-y-6 pt-8">
        <h2 className="text-xl font-bold border-b border-border pb-2 flex items-center gap-2">
          <Activity size={20} className="text-muted-foreground" /> Past Attempts
        </h2>
        <div className="space-y-4">
          {attempts.filter(a => a.source_type === "Test" && exams.some(e => e.id === a.source_id)).length === 0 ? (
            <div className="py-8 text-center text-muted-foreground bg-secondary/10 border border-dashed border-border rounded-2xl">
              You haven't attempted any CBT exams yet.
            </div>
          ) : attempts.filter(a => a.source_type === "Test" && exams.some(e => e.id === a.source_id)).map((attempt, i) => {
            const exam = exams.find(e => e.id === attempt.source_id);
            // BUG-07 fix: use actual final_score from backend if available, else derive correctly
            // backend stores final_score = (correct*4) - (incorrect*1)
            const correctCount = attempt.answers ? attempt.answers.filter((a: any) => a.is_correct).length : attempt.score;
            const incorrectCount = attempt.answers ? (attempt.answers.filter((a: any) => a.selected_answer !== null).length - correctCount) : 0;
            const scoreCalc = attempt.final_score ?? ((correctCount * 4) - (incorrectCount * 1));
            const maxScore = attempt.total_questions * 4;
            const scorePercent = maxScore > 0 ? (scoreCalc / maxScore) * 100 : 0;
            const scoreColor = scorePercent >= 60 ? 'text-green-500' : scorePercent >= 35 ? 'text-amber-500' : 'text-red-500';
            
            return (
            <Card key={i} className="bg-secondary/20">
              <CardContent className="p-4 flex flex-col md:flex-row items-center justify-between gap-4">
                <div className="w-full md:w-auto">
                  <h3 className="font-bold">{exam?.title || 'Unknown Test'}</h3>
                  <p className="text-sm text-muted-foreground font-medium">{formatDate(attempt.submitted_at)}</p>
                </div>
                <div className="flex items-center gap-4 md:gap-8 w-full md:w-auto justify-between md:justify-end">
                  <div className="text-right">
                    <div className="text-xs md:text-sm text-muted-foreground font-bold uppercase tracking-wider">Score</div>
                    <div className="font-bold text-base md:text-lg">
                      <span className={scoreColor}>{scoreCalc}</span>
                      <span className="text-muted-foreground">/{maxScore}</span>
                    </div>
                  </div>
                  <div className="text-right">
                    <div className="text-xs md:text-sm text-muted-foreground font-bold uppercase tracking-wider">Accuracy</div>
                    <div className="font-bold text-base md:text-lg text-[var(--cyan-ai)]">{Math.round(attempt.accuracy)}%</div>
                  </div>
                  <Link href={`/dashboard/cbt/history/${attempt.id}`}>
                    <Button variant="outline" className="rounded-xl border-border hover:bg-primary hover:text-primary-foreground">
                      View Solutions
                    </Button>
                  </Link>
                </div>
              </CardContent>
            </Card>
          )})}
        </div>
      </div>

      {showUpgradeModal && (
        <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/80 backdrop-blur-sm animate-in fade-in duration-200">
          <div className="bg-background border border-border shadow-2xl rounded-2xl w-[450px] p-8 text-center space-y-6 animate-in zoom-in-95 duration-200">
            <div className="size-16 rounded-full bg-red-500/10 flex items-center justify-center mx-auto text-red-500">
              <Lock size={32} />
            </div>
            <h3 className="text-2xl font-bold">Upgrade to Premium Plan</h3>
            <p className="text-muted-foreground text-sm leading-relaxed">
              This CBT Mock Test is a premium feature. Free users get access to 1 Daily Practice Sheet and 5 Topic-wise Micro-tests. Upgrade to Pro or AI Coach to unlock unlimited practice and full-length weekly test series!
            </p>
            <div className="flex gap-4 pt-2">
              <Button variant="outline" className="flex-1 rounded-xl" onClick={() => setShowUpgradeModal(false)}>
                Maybe Later
              </Button>
              <Link href="/upgrade" className="flex-1">
                <Button className="w-full rounded-xl bg-primary text-primary-foreground font-bold shadow-[0_0_15px_-3px_var(--color-primary)]">
                  View Plans
                </Button>
              </Link>
            </div>
          </div>
        </div>
      )}
    </div>
  );
}