'use client';

import { useEffect, useState } from 'react';
import Link from 'next/link';
import { apiFetch } from '@/lib/auth';
import { Skeleton } from '@/components/ui/skeleton';
import { useT } from '@/i18n';

interface Domain { id: string; name: string; sessionCount: number; mastery: number; lastActive: string | null; weak: boolean }
interface Recommendation { title: string; url: string }
interface Analytics { domains: Domain[]; totalSessions: number; weakDomains: string[]; recommendations: Recommendation[] }

export default function LearningAnalyticsPage() {
  const t = useT();
  const [data, setData] = useState<Analytics | null>(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState('');

  useEffect(() => { loadAnalytics(); }, []);

  async function loadAnalytics() {
    try {
      const res = await apiFetch('/learning/analytics');
      if (!res.ok) throw new Error('加载失败');
      setData(await res.json());
    } catch (e: any) { setError(e.message); }
    setLoading(false);
  }

  if (loading) return (
    <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-12">
      <Skeleton className="h-8 w-48 mb-2" /><Skeleton className="h-5 w-72 mb-8" />
      <div className="grid grid-cols-1 md:grid-cols-3 gap-4 mb-8">{[1,2,3].map(i => <Skeleton key={i} className="h-24 rounded-xl" />)}</div>
      <Skeleton className="h-64 rounded-xl" />
    </div>
  );

  if (error) return (
    <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-20 text-center">
      <p className="text-red-500 mb-4">{error}</p>
      <button onClick={loadAnalytics} className="px-4 py-2 bg-brand-600 text-white rounded-lg text-sm hover:bg-brand-700">{t.common.retry}</button>
    </div>
  );

  const coveredDomains = data?.domains.filter(d => d.sessionCount > 0) || [];
  const weakDomains = data?.domains.filter(d => d.weak) || [];
  const avgMastery = data?.domains.length ? Math.round(data.domains.reduce((sum, d) => sum + d.mastery, 0) / data.domains.length) : 0;

  return (
    <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8 py-12">
      <div className="mb-8">
        <Link href="/my" className="text-sm text-muted-foreground hover:text-brand-600 mb-2 inline-block">&larr; {t.path.back}</Link>
        <h1 className="text-3xl font-bold text-foreground">{t.learning.analytics}</h1>
        <p className="mt-2 text-muted-foreground">{t.learning.analyticsDesc}</p>
      </div>

      <div className="grid grid-cols-1 md:grid-cols-3 gap-4 mb-8">
        <div className="bg-card rounded-xl border border-border p-6">
          <div className="text-sm text-muted-foreground mb-1">{t.learning.totalSessions}</div>
          <div className="text-2xl font-bold text-foreground">{data?.totalSessions || 0}</div>
        </div>
        <div className="bg-card rounded-xl border border-border p-6">
          <div className="text-sm text-muted-foreground mb-1">{t.learning.domainsCovered}</div>
          <div className="text-2xl font-bold text-foreground">{coveredDomains.length}/{data?.domains.length || 0}</div>
        </div>
        <div className="bg-card rounded-xl border border-border p-6">
          <div className="text-sm text-muted-foreground mb-1">{t.learning.avgMastery}</div>
          <div className="text-2xl font-bold text-foreground">{avgMastery}%</div>
        </div>
      </div>

      {data && data.domains.length > 0 && (
        <div className="bg-card rounded-2xl border border-border p-6 mb-8">
          <h2 className="text-lg font-semibold text-foreground mb-4">{t.learning.knowledgeDomains}</h2>
          <div className="space-y-4">
            {data.domains.map(domain => (
              <div key={domain.id}>
                <div className="flex items-center justify-between mb-1.5">
                  <div className="flex items-center gap-2">
                    <span className="text-sm font-medium text-foreground truncate min-w-0">{domain.name}</span>
                    {domain.weak && <span className="text-xs px-1.5 py-0.5 bg-amber-100 text-amber-700 rounded">{t.learning.toStrengthen}</span>}
                  </div>
                  <div className="flex items-center gap-3">
                    <span className="text-xs text-muted-foreground">{t.learning.conversations.replace('{count}', String(domain.sessionCount))}</span>
                    <span className={`text-xs font-medium tabular-nums ${domain.mastery >= 60 ? 'text-green-600' : domain.mastery >= 30 ? 'text-amber-600' : 'text-red-500'}`}>{domain.mastery}%</span>
                  </div>
                </div>
                <div className="w-full bg-muted rounded-full h-2">
                  <div className={`h-2 rounded-full transition-all ${domain.mastery >= 60 ? 'bg-green-500' : domain.mastery >= 30 ? 'bg-amber-500' : 'bg-red-500'}`} style={{ width: `${domain.mastery}%` }} />
                </div>
              </div>
            ))}
          </div>
        </div>
      )}

      {weakDomains.length > 0 && (
        <div className="bg-card rounded-2xl border border-border p-6 mb-8">
          <h2 className="text-lg font-semibold text-foreground mb-2">{t.learning.weakAreas}</h2>
          <p className="text-sm text-muted-foreground mb-4">{t.learning.weakDesc}</p>
          <div className="flex flex-wrap gap-2">
            {weakDomains.map(d => (
              <span key={d.id} className="px-3 py-1.5 text-sm bg-amber-50 text-amber-700 rounded-lg border border-amber-200">{d.name}</span>
            ))}
          </div>
        </div>
      )}

      {data && data.recommendations.length > 0 && (
        <div className="bg-card rounded-2xl border border-border p-6">
          <h2 className="text-lg font-semibold text-foreground mb-2">{t.learning.recommendations}</h2>
          <p className="text-sm text-muted-foreground mb-4">{t.learning.recDesc}</p>
          <div className="grid grid-cols-1 md:grid-cols-2 gap-3">
            {data.recommendations.map((rec, i) => (
              <Link key={i} href={rec.url} className="flex items-center gap-3 p-4 rounded-xl border border-border hover:bg-accent transition-colors group">
                <div className="w-10 h-10 bg-brand-100 rounded-lg flex items-center justify-center text-brand-600 font-bold shrink-0">{rec.title[0]}</div>
                <div>
                  <div className="text-sm font-medium text-foreground group-hover:text-brand-600 transition-colors">{rec.title}</div>
                  <div className="text-xs text-muted-foreground mt-0.5">{t.learning.clickToGo}</div>
                </div>
              </Link>
            ))}
          </div>
        </div>
      )}
    </div>
  );
}
