'use client'

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

interface QAItem {
  id: string; question: string; answer: string
  translations?: Record<string, any>
}

function getApiBase() { return '' }

export default function MatchPage() {
  const { unitId } = useParams<{ unitId: string }>()
  const router = useRouter()
  const { isDark } = useTheme()
  const { t, wordInNative, nativeLang, isThirdLanguage } = useNativeLanguage()

  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 [firstTryCorrect, setFirstTryCorrect] = useState(0)
  const [retryCorrect, setRetryCorrect] = useState(0)
  const [errors, setErrors] = useState(0)
  const [failedIds, setFailedIds] = useState<Set<string>>(new Set())
  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])

  const roundItems = useMemo(() => allItems.slice(round * 6, round * 6 + 6), [allItems, round])
  const shuffledRight = useMemo(() => [...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) {
      setMatched(prev => new Set([...prev, id]))
      if (failedIds.has(id)) setRetryCorrect(c => c + 1)
      else setFirstTryCorrect(c => c + 1)
      setSelectedLeft(null)
      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 {
      setWrongPair(id)
      setErrors(e => e + 1)
      setFailedIds(prev => new Set([...prev, selectedLeft]))
      setTimeout(() => { setWrongPair(null); setSelectedLeft(null) }, 600)
    }
  }, [selectedLeft, matched, roundItems, round, allItems, failedIds])

  const restart = () => {
    setRound(0); setMatched(new Set()); setFirstTryCorrect(0); setRetryCorrect(0)
    setErrors(0); setFailedIds(new Set()); setIsComplete(false); setSelectedLeft(null)
  }

  if (isLoading) {
    return <div className="flex items-center justify-center py-20">
      <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
  const isPerfect = isComplete && errors === 0

  // Native helper panel: list of words in native language
  const nativePanel = (
    <div className={`${glassCard} rounded-2xl p-4`}>
      <p className={`text-xs font-medium mb-3 ${isDark ? 'text-cyan-300/70' : 'text-cyan-600'}`}>
        {nativeLang.toUpperCase()} · {t('english')} · {t('german')}
      </p>
      <div className="space-y-1.5">
        {roundItems.map(item => {
          const native = wordInNative(item.translations)
          const isSelected = selectedLeft === item.id
          const isMatched = matched.has(item.id)
          return (
            <div key={`n-${item.id}`}
              className={`flex items-center gap-2 px-3 py-2.5 rounded-lg border text-sm transition-all ${
                isMatched
                  ? 'opacity-30 border-green-400/30 bg-green-500/5'
                  : isSelected
                    ? (isDark ? 'border-cyan-400/50 bg-cyan-500/10 text-cyan-200' : 'border-cyan-400 bg-cyan-50 text-cyan-800')
                    : (isDark ? 'border-white/10 text-white/50' : 'border-slate-200 text-slate-500')
              }`}>
              <span className="flex-1 truncate">{native || '—'}</span>
              {native && !isMatched && (
                <AudioButton text={native} lang={nativeLang as 'en' | 'de'} isDark={isDark} size="sm" />
              )}
            </div>
          )
        })}
      </div>
    </div>
  )

  return (
    <ExerciseLayout
      title={t('match')}
      exerciseType="match"
      onBack={() => router.push('/learn')}
      progress={{ current: matchedTotal, total: totalPairs }}
      nativeHelper={nativePanel}
      score={
        <div className={`text-xs ${isDark ? 'text-white/50' : 'text-slate-500'}`}>
          <span className="text-green-400">✓{firstTryCorrect}</span>{' '}
          <span className="text-yellow-400">↻{retryCorrect}</span>{' '}
          <span className="text-red-400">✗{errors}</span>
        </div>
      }
    >
      {isComplete ? (
        <div className={`${glassCard} rounded-3xl p-10 text-center max-w-md mx-auto`}>
          <StarRating stars={isPerfect ? 3 : accuracyToStars(firstTryCorrect, totalPairs)} size="lg" animated />
          <h2 className={`text-2xl font-bold mt-4 mb-2 ${isDark ? 'text-white' : 'text-slate-900'}`}>
            {isPerfect ? t('well_done') : t('all_matched')}
          </h2>
          <div className={`flex justify-center gap-6 mb-4 text-sm ${isDark ? 'text-white/70' : 'text-slate-600'}`}>
            <div><span className="text-green-400 font-bold text-lg">{firstTryCorrect}</span><br/>{t('correct')}</div>
            <div><span className="text-yellow-400 font-bold text-lg">{retryCorrect}</span><br/>2.</div>
            <div><span className="text-red-400 font-bold text-lg">{errors}</span><br/>{t('errors')}</div>
          </div>
          <div className="flex gap-3">
            <button onClick={restart} className="flex-1 py-3 rounded-xl bg-gradient-to-r from-indigo-500 to-violet-500 text-white font-medium">{t('again')}</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'}`}>{t('back')}</button>
          </div>
        </div>
      ) : (
        <div className="grid grid-cols-2 gap-4">
          {/* Left: English */}
          <div className="space-y-2">
            <p className={`text-xs font-medium text-center mb-2 ${isDark ? 'text-white/40' : 'text-slate-400'}`}>
              {t('english')} / English
            </p>
            {roundItems.map(item => (
              <div key={`l-${item.id}`}
                className={`flex items-center gap-2 p-3 min-h-[48px] rounded-xl border-2 text-sm font-medium transition-all ${
                  matched.has(item.id) ? 'opacity-30 border-green-400 bg-green-500/10'
                  : 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' : 'border-slate-200 bg-white text-slate-900')
                }`}>
                <button onClick={() => handleLeftTap(item.id)} disabled={matched.has(item.id)} className="flex-1 text-left">{item.question}</button>
                {!matched.has(item.id) && <AudioButton text={item.question} lang="en" isDark={isDark} size="sm" />}
              </div>
            ))}
          </div>

          {/* Right: German */}
          <div className="space-y-2">
            <p className={`text-xs font-medium text-center mb-2 ${isDark ? 'text-white/40' : 'text-slate-400'}`}>
              {t('german')} / Deutsch
            </p>
            {shuffledRight.map(item => (
              <div key={`r-${item.id}`}
                className={`flex items-center gap-2 p-3 min-h-[48px] rounded-xl border-2 text-sm font-medium transition-all ${
                  matched.has(item.id) ? 'opacity-30 border-green-400 bg-green-500/10'
                  : 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' : 'border-slate-200 bg-white text-slate-900')
                }`}>
                <button onClick={() => handleRightTap(item.id)} disabled={matched.has(item.id) || !selectedLeft} className="flex-1 text-left">{item.answer}</button>
                {!matched.has(item.id) && <AudioButton text={item.answer} lang="de" isDark={isDark} size="sm" />}
              </div>
            ))}
          </div>
        </div>
      )}
    </ExerciseLayout>
  )
}