"use client";

import { useEffect, useState } from "react";
import Link from "next/link";
import { Badge } from "@/components/ui/badge";
import { Card, CardHeader, CardTitle, CardContent } from "@/components/ui/card";
import { getDifficultyVariant, capitalize } from "@/lib/utils";
import { isQuestionCompleted } from "@/lib/progress";
import { CheckCircle, Star } from "lucide-react";
import type { LearningProgression as LearningProgressionType } from "@/types";

interface LearningProgressionProps {
  progression: LearningProgressionType;
}

export function LearningProgression({ progression }: LearningProgressionProps) {
  const [completedSlugs, setCompletedSlugs] = useState<Set<string>>(new Set());

  // Load completion status on mount (client-side only)
  useEffect(() => {
    const allQuestions = [
      ...progression.warmup,
      ...progression.core,
      ...progression.challenge,
    ];
    const completed = new Set<string>();
    for (const q of allQuestions) {
      if (isQuestionCompleted(q.slug)) {
        completed.add(q.slug);
      }
    }
    setCompletedSlugs(completed);
  }, [progression]);

  const hasQuestions =
    progression.warmup.length > 0 ||
    progression.core.length > 0 ||
    progression.challenge.length > 0;

  if (!hasQuestions) return null;

  // Calculate completion stats per tier
  const warmupCompleted = progression.warmup.filter(q => completedSlugs.has(q.slug)).length;
  const coreCompleted = progression.core.filter(q => completedSlugs.has(q.slug)).length;
  const challengeCompleted = progression.challenge.filter(q => completedSlugs.has(q.slug)).length;

  return (
    <Card>
      <CardHeader>
        <CardTitle>Learning Path</CardTitle>
      </CardHeader>
      <CardContent>
        <div className="space-y-6">
          {progression.warmup.length > 0 && (
            <div>
              <h4 className="font-semibold text-[var(--difficulty-easy)] mb-3 flex items-center gap-2">
                <span className="w-6 h-6 rounded-full bg-[var(--difficulty-easy-bg)] flex items-center justify-center text-sm">
                  1
                </span>
                Warmup
                {progression.warmup.length > 0 && (
                  <span className="ml-auto text-xs font-normal text-[var(--muted-foreground)]">
                    {warmupCompleted}/{progression.warmup.length}
                  </span>
                )}
              </h4>
              <p className="text-sm text-[var(--muted-foreground)] mb-3">
                Start here to build foundational understanding.
              </p>
              <div className="space-y-2">
                {progression.warmup.map((q) => (
                  <QuestionLink key={q.id} question={q} isCompleted={completedSlugs.has(q.slug)} />
                ))}
              </div>
            </div>
          )}

          {progression.core.length > 0 && (
            <div>
              <h4 className="font-semibold text-[var(--difficulty-medium)] mb-3 flex items-center gap-2">
                <span className="w-6 h-6 rounded-full bg-[var(--difficulty-medium-bg)] flex items-center justify-center text-sm">
                  2
                </span>
                Core Practice
                {progression.core.length > 0 && (
                  <span className="ml-auto text-xs font-normal text-[var(--muted-foreground)]">
                    {coreCompleted}/{progression.core.length}
                  </span>
                )}
              </h4>
              <p className="text-sm text-[var(--muted-foreground)] mb-3">
                Master the pattern with these representative problems.
              </p>
              <div className="space-y-2">
                {progression.core.map((q) => (
                  <QuestionLink key={q.id} question={q} isCompleted={completedSlugs.has(q.slug)} />
                ))}
              </div>
            </div>
          )}

          {progression.challenge.length > 0 && (
            <div>
              <h4 className="font-semibold text-[var(--difficulty-hard)] mb-3 flex items-center gap-2">
                <span className="w-6 h-6 rounded-full bg-[var(--difficulty-hard-bg)] flex items-center justify-center text-sm">
                  3
                </span>
                Challenge
                {progression.challenge.length > 0 && (
                  <span className="ml-auto text-xs font-normal text-[var(--muted-foreground)]">
                    {challengeCompleted}/{progression.challenge.length}
                  </span>
                )}
              </h4>
              <p className="text-sm text-[var(--muted-foreground)] mb-3">
                Test your mastery with complex variations.
              </p>
              <div className="space-y-2">
                {progression.challenge.map((q) => (
                  <QuestionLink key={q.id} question={q} isCompleted={completedSlugs.has(q.slug)} />
                ))}
              </div>
            </div>
          )}
        </div>
      </CardContent>
    </Card>
  );
}

interface QuestionLinkProps {
  question: LearningProgressionType["warmup"][number];
  isCompleted: boolean;
}

function QuestionLink({ question, isCompleted }: QuestionLinkProps) {
  return (
    <Link
      href={`/questions/${question.slug}`}
      className="flex items-center justify-between p-3 rounded-lg border border-[var(--border)] bg-[var(--card)] hover:border-[var(--primary)] transition-colors"
    >
      <div className="flex items-center gap-2">
        {isCompleted && (
          <CheckCircle className="h-4 w-4 text-green-500 flex-shrink-0" />
        )}
        <span className="font-medium">{question.title}</span>
        {question.is_optimal && (
          <span className="flex items-center gap-1 text-xs text-amber-500" title="This pattern is optimal for this problem">
            <Star className="h-3 w-3 fill-current" />
            Optimal
          </span>
        )}
      </div>
      <div className="flex items-center gap-2">
        {question.leetcode_id && (
          <span className="text-xs text-[var(--muted-foreground)]">
            #{question.leetcode_id}
          </span>
        )}
        <Badge variant={getDifficultyVariant(question.difficulty)}>
          {capitalize(question.difficulty)}
        </Badge>
      </div>
    </Link>
  );
}