import { useState, useCallback, useRef } from 'react'
import {
  View, Text, StyleSheet, TouchableOpacity, ActivityIndicator,
  Animated, ScrollView,
} from 'react-native'
import { SafeAreaView } from 'react-native-safe-area-context'
import { useLocalSearchParams, useRouter } from 'expo-router'
import { ArrowLeft, GraduationCap } from 'lucide-react-native'
import { C } from '@/lib/theme'
import { apiFetch } from '@/lib/api'
import { ENDPOINTS } from '@/lib/config'
import { useFocusEffect } from 'expo-router'

interface Card {
  id: string
  front: string
  back: string
  interval: number
  type?: string
}

type SessionState = 'loading' | 'reviewing' | 'done' | 'error'

const GRADE_LABELS: { grade: 1 | 2 | 3 | 4; label: string; color: string; bg: string; border: string }[] = [
  { grade: 1, label: 'Oublié',   color: '#dc2626', bg: 'rgba(239,68,68,0.10)',  border: 'rgba(239,68,68,0.30)' },
  { grade: 2, label: 'Difficile',color: '#b45309', bg: 'rgba(245,158,11,0.10)', border: 'rgba(245,158,11,0.30)' },
  { grade: 3, label: 'Bien',     color: '#047857', bg: 'rgba(16,185,129,0.10)', border: 'rgba(16,185,129,0.30)' },
  { grade: 4, label: 'Parfait',  color: '#A47148', bg: 'rgba(164,113,72,0.10)', border: 'rgba(164,113,72,0.30)' },
]

export default function SessionScreen() {
  const router = useRouter()
  const params = useLocalSearchParams<{ deckId: string; deckName: string }>()
  const { deckId, deckName } = params

  const [state, setState] = useState<SessionState>('loading')
  const [cards, setCards] = useState<Card[]>([])
  const [index, setIndex] = useState(0)
  const [flipped, setFlipped] = useState(false)
  const [reviewed, setReviewed] = useState(0)
  const [errorMsg, setErrorMsg] = useState<string | null>(null)

  // Animation flip
  const flipAnim = useRef(new Animated.Value(0)).current
  const frontInterp = flipAnim.interpolate({ inputRange: [0, 1], outputRange: ['0deg', '180deg'] })
  const backInterp = flipAnim.interpolate({ inputRange: [0, 1], outputRange: ['180deg', '360deg'] })

  const loadSession = useCallback(async () => {
    if (!deckId) return
    setState('loading')
    setIndex(0)
    setFlipped(false)
    setReviewed(0)
    flipAnim.setValue(0)
    try {
      const res = await apiFetch(ENDPOINTS.flashcardSession(deckId))
      const data = await res.json()
      if (!res.ok) throw new Error(data.error ?? `Erreur ${res.status}`)
      setCards(data.cards ?? [])
      setState(data.cards?.length === 0 ? 'done' : 'reviewing')
    } catch (e: any) {
      setErrorMsg(e.message ?? 'Erreur')
      setState('error')
    }
  }, [deckId])

  useFocusEffect(useCallback(() => { loadSession() }, [loadSession]))

  const flip = () => {
    if (flipped) return
    setFlipped(true)
    Animated.spring(flipAnim, { toValue: 1, useNativeDriver: true, friction: 8 }).start()
  }

  const grade = async (g: 1 | 2 | 3 | 4) => {
    const card = cards[index]
    if (!card) return
    try {
      await apiFetch(ENDPOINTS.flashcardReview, {
        method: 'POST',
        body: JSON.stringify({ cardId: card.id, grade: g }),
      })
    } catch { /* silencieux — on avance quand même */ }

    const next = index + 1
    setReviewed((r) => r + 1)
    if (next >= cards.length) {
      setState('done')
    } else {
      setIndex(next)
      setFlipped(false)
      Animated.timing(flipAnim, { toValue: 0, duration: 0, useNativeDriver: true }).start()
    }
  }

  const current = cards[index]
  const progress = cards.length > 0 ? index / cards.length : 0

  return (
    <SafeAreaView style={s.safe}>
      {/* Header */}
      <View style={s.header}>
        <TouchableOpacity onPress={() => router.back()} hitSlop={{ top: 8, bottom: 8, left: 8, right: 8 }}>
          <ArrowLeft size={22} color={C.ink} />
        </TouchableOpacity>
        <Text style={s.headerTitle} numberOfLines={1}>{deckName ?? 'Révision'}</Text>
        {state === 'reviewing' && (
          <Text style={s.counter}>{index + 1}/{cards.length}</Text>
        )}
      </View>

      {/* Barre de progression */}
      {state === 'reviewing' && (
        <View style={s.progressBarWrap}>
          <View style={[s.progressBarFill, { width: `${Math.round(progress * 100)}%` }]} />
        </View>
      )}

      {/* Contenu */}
      {state === 'loading' && (
        <View style={s.center}>
          <ActivityIndicator color={C.brand} size="large" />
        </View>
      )}

      {state === 'error' && (
        <View style={s.center}>
          <Text style={s.errorTxt}>{errorMsg}</Text>
          <TouchableOpacity onPress={loadSession} style={s.retryBtn}>
            <Text style={s.retryTxt}>Réessayer</Text>
          </TouchableOpacity>
        </View>
      )}

      {state === 'done' && (
        <View style={s.center}>
          <GraduationCap size={56} color={C.brand} />
          <Text style={s.doneTitle}>Session terminée !</Text>
          <Text style={s.doneSub}>
            {reviewed > 0 ? `${reviewed} carte${reviewed > 1 ? 's' : ''} révisée${reviewed > 1 ? 's' : ''}` : 'Tout est à jour 🎉'}
          </Text>
          <TouchableOpacity onPress={() => router.back()} style={s.doneBtn}>
            <Text style={s.doneBtnTxt}>Retour aux paquets</Text>
          </TouchableOpacity>
        </View>
      )}

      {state === 'reviewing' && current && (
        <View style={s.sessionWrap}>
          {/* Carte flip */}
          <TouchableOpacity activeOpacity={0.95} onPress={flip} style={s.cardWrap}>
            {/* Face avant */}
            <Animated.View style={[s.card, s.cardFront, { transform: [{ rotateY: frontInterp }] }]}>
              <ScrollView contentContainerStyle={s.cardContent} showsVerticalScrollIndicator={false}>
                <Text style={s.cardLabel}>Question</Text>
                <Text style={s.cardText}>{current.front}</Text>
              </ScrollView>
              {!flipped && (
                <View style={s.tapHint}>
                  <Text style={s.tapTxt}>Appuyez pour révéler la réponse</Text>
                </View>
              )}
            </Animated.View>

            {/* Face arrière */}
            <Animated.View style={[s.card, s.cardBack, { transform: [{ rotateY: backInterp }] }]}>
              <ScrollView contentContainerStyle={s.cardContent} showsVerticalScrollIndicator={false}>
                <Text style={s.cardLabel}>Réponse</Text>
                <Text style={s.cardText}>{current.back}</Text>
              </ScrollView>
            </Animated.View>
          </TouchableOpacity>

          {/* Boutons de note (visibles seulement après flip) */}
          {flipped && (
            <View style={s.gradeRow}>
              {GRADE_LABELS.map(({ grade: g, label, color, bg, border }) => (
                <TouchableOpacity
                  key={g}
                  style={[s.gradeBtn, { backgroundColor: bg, borderColor: border }]}
                  onPress={() => grade(g)}
                  activeOpacity={0.8}
                >
                  <Text style={[s.gradeNum, { color }]}>{g}</Text>
                  <Text style={[s.gradeLbl, { color }]}>{label}</Text>
                </TouchableOpacity>
              ))}
            </View>
          )}
        </View>
      )}
    </SafeAreaView>
  )
}

const s = StyleSheet.create({
  safe: { flex: 1, backgroundColor: C.paper },
  header: {
    flexDirection: 'row', alignItems: 'center', gap: 12,
    paddingHorizontal: 20, paddingVertical: 14,
    borderBottomWidth: 1, borderBottomColor: C.border,
  },
  headerTitle: { flex: 1, fontSize: 17, fontWeight: '700', color: C.ink },
  counter: { fontSize: 13, color: C.concrete, fontWeight: '600' },
  progressBarWrap: { height: 3, backgroundColor: C.border },
  progressBarFill: { height: 3, backgroundColor: C.brand },
  center: { flex: 1, alignItems: 'center', justifyContent: 'center', padding: 24 },
  sessionWrap: { flex: 1, padding: 20, justifyContent: 'space-between' },
  cardWrap: { flex: 1, marginBottom: 16 },
  card: {
    position: 'absolute', inset: 0,
    borderRadius: 18, borderWidth: 1, borderColor: C.border,
    backgroundColor: C.surface,
    backfaceVisibility: 'hidden',
    padding: 24,
  },
  cardFront: { zIndex: 1 },
  cardBack: { backgroundColor: '#f0f7ff' },
  cardContent: { flexGrow: 1, justifyContent: 'center', alignItems: 'center', paddingBottom: 48 },
  cardLabel: { fontSize: 11, fontWeight: '700', color: C.brand, letterSpacing: 1, textTransform: 'uppercase', marginBottom: 16 },
  cardText: { fontSize: 20, color: C.ink, textAlign: 'center', lineHeight: 30, fontWeight: '500' },
  tapHint: { position: 'absolute', bottom: 20, left: 0, right: 0, alignItems: 'center' },
  tapTxt: { fontSize: 12, color: C.concrete, fontStyle: 'italic' },
  gradeRow: { flexDirection: 'row', gap: 8 },
  gradeBtn: {
    flex: 1, alignItems: 'center', paddingVertical: 12, borderRadius: 14, borderWidth: 1.5,
  },
  gradeNum: { fontSize: 18, fontWeight: '800' },
  gradeLbl: { fontSize: 10, fontWeight: '600', marginTop: 2 },
  doneTitle: { fontSize: 24, fontWeight: '800', color: C.ink, marginTop: 20, marginBottom: 8 },
  doneSub: { fontSize: 15, color: C.concrete, marginBottom: 32 },
  doneBtn: { backgroundColor: C.brand, paddingHorizontal: 28, paddingVertical: 14, borderRadius: 14 },
  doneBtnTxt: { color: '#fff', fontWeight: '700', fontSize: 16 },
  errorTxt: { fontSize: 15, color: '#e11d48', textAlign: 'center', marginBottom: 12 },
  retryBtn: { backgroundColor: C.brand, paddingHorizontal: 20, paddingVertical: 10, borderRadius: 10 },
  retryTxt: { color: '#fff', fontWeight: '600' },
})