'use client'

import React, { useState, useEffect, useCallback, useMemo } from 'react'
import { useParams, useRouter } from 'next/navigation'
import { useTheme } from '@/lib/ThemeContext'
import { StarRating, accuracyToStars } from '@/components/gamification/StarRating'

interface QAItem { id: string; question: string; answer: string }

function getApiBase() { return '' }

export default function MatchPage() {
  const { unitId } = useParams<{ unitId: string }>()
  const router = useRouter()
  const { isDark } = useTheme()

  const [allItems, setAllItems] = useState<QAItem[]>([])
  const [isLoading, setIsLoading] = useState(true)
  const [round, setRound] = useState(0)
  const [selectedLeft, setSelectedLeft] = useState<string | null>(null)
  const [matched, setMatched] = useState<Set<string>>(new Set())
  const [wrongPair, setWrongPair] = useState<string | null>(null)
  const [errors, setErrors] = useState(0)
  const [isComplete, setIsComplete] = useState(false)

  const glassCard = isDark
    ? 'bg-white/10 backdrop-blur-xl border border-white/10'
    : 'bg-white/80 backdrop-blur-xl border border-black/5'

  useEffect(() => {
    (async () => {
      try {
        const resp = await fetch(`${getApiBase()}/api/learning-units/${unitId}/qa`)
        if (resp.ok) { const d = await resp.json(); setAllItems(d.qa_items || []) }
      } catch {} finally { setIsLoading(false) }
    })()
  }, [unitId])

  // Take 6 items per round
  const roundItems = useMemo(() => {
    const start = round * 6
    return allItems.slice(start, start + 6)
  }, [allItems, round])

  // Shuffled right column
  const shuffledRight = useMemo(() => {
    return [...roundItems].sort(() => Math.random() - 0.5)
  }, [roundItems])

  const handleLeftTap = useCallback((id: string) => {
    if (matched.has(id)) return
    setSelectedLeft(id === selectedLeft ? null : id)
    setWrongPair(null)
  }, [selectedLeft, matched])

  const handleRightTap = useCallback((id: string) => {
    if (!selectedLeft || matched.has(id)) return

    if (selectedLeft === id) {
      // Correct match
      setMatched(prev => new Set([...prev, id]))
      setSelectedLeft(null)

      // Check if round complete
      if (matched.size + 1 >= roundItems.length) {
        const nextStart = (round + 1) * 6
        if (nextStart >= allItems.length) {
          setTimeout(() => setIsComplete(true), 500)
        } else {
          setTimeout(() => {
            setRound(r => r + 1)
            setMatched(new Set())
            setSelectedLeft(null)
          }, 800)
        }
      }
    } else {
      // Wrong match
      setWrongPair(id)
      setErrors(e => e + 1)
      setTimeout(() => {
        setWrongPair(null)
        setSelectedLeft(null)
      }, 600)
    }
  }, [selectedLeft, matched, roundItems, round, allItems])

  if (isLoading) {
    return <div className={`min-h-screen flex items-center justify-center ${isDark ? 'bg-gradient-to-br from-indigo-900 via-purple-900 to-pink-800' : 'bg-gradient-to-br from-slate-100 via-indigo-50 to-violet-100'}`}>
      <div className="w-8 h-8 border-4 border-indigo-400 border-t-transparent rounded-full animate-spin" />
    </div>
  }

  const totalPairs = allItems.length
  const matchedTotal = round * 6 + matched.size

  return (
    <div className={`min-h-screen flex flex-col ${isDark ? 'bg-gradient-to-br from-indigo-900 via-purple-900 to-pink-800' : 'bg-gradient-to-br from-slate-100 via-indigo-50 to-violet-100'}`}>
      {/* Header */}
      <div className={`${glassCard} border-0 border-b`}>
        <div className="max-w-2xl mx-auto px-6 py-4 flex items-center justify-between">
          <button onClick={() => router.push('/learn')} className={`flex items-center gap-2 text-sm ${isDark ? 'text-white/60 hover:text-white' : 'text-slate-500 hover:text-slate-900'}`}>
            <svg className="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24"><path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M15 19l-7-7 7-7" /></svg>
            Zurueck
          </button>
          <h1 className={`text-lg font-bold ${isDark ? 'text-white' : 'text-slate-900'}`}>Zuordnen</h1>
          <span className={`text-sm ${isDark ? 'text-white/50' : 'text-slate-500'}`}>{matchedTotal}/{totalPairs}</span>
        </div>
      </div>

      <div className="flex-1 flex items-center justify-center px-6 py-8">
        {isComplete ? (
          <div className={`${glassCard} rounded-3xl p-10 text-center max-w-md w-full`}>
            <StarRating stars={accuracyToStars(totalPairs, totalPairs + errors)} size="lg" animated />
            <h2 className={`text-2xl font-bold mt-4 mb-2 ${isDark ? 'text-white' : 'text-slate-900'}`}>Alle zugeordnet!</h2>
            <p className={`mb-6 ${isDark ? 'text-white/60' : 'text-slate-500'}`}>{errors} Fehler</p>
            <div className="flex gap-3">
              <button onClick={() => { setRound(0); setMatched(new Set()); setErrors(0); setIsComplete(false) }} className="flex-1 py-3 rounded-xl bg-gradient-to-r from-indigo-500 to-violet-500 text-white font-medium">Nochmal</button>
              <button onClick={() => router.push('/learn')} className={`flex-1 py-3 rounded-xl border font-medium ${isDark ? 'border-white/20 text-white/80' : 'border-slate-300 text-slate-700'}`}>Zurueck</button>
            </div>
          </div>
        ) : (
          <div className="w-full max-w-2xl grid grid-cols-2 gap-6">
            {/* Left column: English */}
            <div className="space-y-2">
              <p className={`text-xs font-medium text-center mb-2 ${isDark ? 'text-white/40' : 'text-slate-400'}`}>English</p>
              {roundItems.map(item => (
                <button
                  key={`l-${item.id}`}
                  onClick={() => handleLeftTap(item.id)}
                  disabled={matched.has(item.id)}
                  className={`w-full p-3 rounded-xl border-2 text-sm font-medium transition-all ${
                    matched.has(item.id)
                      ? 'opacity-30 border-green-400 bg-green-500/10 cursor-default'
                      : selectedLeft === item.id
                        ? (isDark ? 'border-blue-400 bg-blue-500/20 text-white' : 'border-blue-500 bg-blue-50 text-blue-900')
                        : (isDark ? 'border-white/20 bg-white/5 text-white hover:bg-white/10' : 'border-slate-200 bg-white text-slate-900 hover:bg-slate-50')
                  }`}
                >
                  {item.question}
                </button>
              ))}
            </div>

            {/* Right column: German (shuffled) */}
            <div className="space-y-2">
              <p className={`text-xs font-medium text-center mb-2 ${isDark ? 'text-white/40' : 'text-slate-400'}`}>Deutsch</p>
              {shuffledRight.map(item => (
                <button
                  key={`r-${item.id}`}
                  onClick={() => handleRightTap(item.id)}
                  disabled={matched.has(item.id) || !selectedLeft}
                  className={`w-full p-3 rounded-xl border-2 text-sm font-medium transition-all ${
                    matched.has(item.id)
                      ? 'opacity-30 border-green-400 bg-green-500/10 cursor-default'
                      : wrongPair === item.id
                        ? (isDark ? 'border-red-400 bg-red-500/20 text-red-200 animate-pulse' : 'border-red-500 bg-red-50 text-red-800 animate-pulse')
                        : (isDark ? 'border-white/20 bg-white/5 text-white hover:bg-white/10' : 'border-slate-200 bg-white text-slate-900 hover:bg-slate-50')
                  }`}
                >
                  {item.answer}
                </button>
              ))}
            </div>
          </div>
        )}
      </div>
    </div>
  )
}
