import { useEffect, useRef, useState } from 'react';
import {
  Animated,
  Dimensions,
  Modal,
  ScrollView,
  Text,
  View,
} from 'react-native';
import { useSafeAreaInsets } from 'react-native-safe-area-context';
import { Ionicons } from '@expo/vector-icons';
import { useTranslation } from 'react-i18next';
import { apiFetch } from '../../lib/api';
import { useColors } from '../../lib/theme';
import { Button } from '../Button';
import type { Plan } from '../../hooks/useMe';

export type ChangePreviewItem = {
  resource: string;
  current: number | string;
  newLimit: number | string;
  overBy: number;
  action: 'keep' | 'limited' | 'paused' | 'grace_then_off' | 'degraded' | 'unlocked';
  detail: string;
  graceUntilDays?: number;
};

export type ChangePreview = {
  from: Plan;
  to: Plan;
  direction: 'upgrade' | 'downgrade' | 'same';
  gains: string[];
  keeps: string[];
  changes: ChangePreviewItem[];
};

type Props = {
  visible: boolean;
  targetPlan: Plan;
  onConfirm: () => void;
  onClose: () => void;
};

const SCREEN_HEIGHT = Dimensions.get('window').height;
const PLAN_LABEL: Record<Plan, string> = {
  free: 'Free',
  pro: 'Pro',
  legend: 'Legend',
};

function ActionChip({ action }: { action: ChangePreviewItem['action'] }) {
  const { t } = useTranslation();
  const configs: Record<ChangePreviewItem['action'], { label: string; fg: string; bg: string }> = {
    keep:          { label: t('plan.change.action_keep'),          fg: '#16a34a', bg: 'rgba(22,163,74,0.1)' },
    limited:       { label: t('plan.change.action_limited'),       fg: '#d97706', bg: 'rgba(217,119,6,0.1)' },
    paused:        { label: t('plan.change.action_paused'),        fg: '#737373', bg: 'rgba(115,115,115,0.1)' },
    grace_then_off:{ label: t('plan.change.action_grace'),         fg: '#d97706', bg: 'rgba(217,119,6,0.1)' },
    degraded:      { label: t('plan.change.action_degraded'),      fg: '#dc2626', bg: 'rgba(220,38,38,0.1)' },
    unlocked:      { label: t('plan.change.action_unlocked'),      fg: '#16a34a', bg: 'rgba(22,163,74,0.1)' },
  };
  const c = configs[action];
  return (
    <View style={{ paddingHorizontal: 6, paddingVertical: 2, borderRadius: 5, backgroundColor: c.bg, alignSelf: 'flex-start' }}>
      <Text style={{ fontSize: 10, fontFamily: 'Nunito_600SemiBold', color: c.fg }}>{c.label}</Text>
    </View>
  );
}

export function PlanChangeSheet({ visible, targetPlan, onConfirm, onClose }: Props) {
  const { t } = useTranslation();
  const colors = useColors();
  const insets = useSafeAreaInsets();
  const translateY = useRef(new Animated.Value(SCREEN_HEIGHT)).current;
  const [preview, setPreview] = useState<ChangePreview | null>(null);
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);

  useEffect(() => {
    if (!visible) return;
    setPreview(null);
    setError(null);
    setLoading(true);
    apiFetch<ChangePreview>(`/api/plan/change-preview?to=${targetPlan}`)
      .then(setPreview)
      .catch((e: Error) => setError(e.message))
      .finally(() => setLoading(false));
  }, [visible, targetPlan]);

  useEffect(() => {
    Animated.timing(translateY, {
      toValue: visible ? 0 : SCREEN_HEIGHT,
      duration: 320,
      useNativeDriver: true,
    }).start();
  }, [visible, translateY]);

  const isDowngrade = preview?.direction === 'downgrade';

  return (
    <Modal transparent visible={visible} animationType="none" onRequestClose={onClose}>
      <View style={{ flex: 1, justifyContent: 'flex-end' }}>
        <Animated.View
          style={{
            backgroundColor: colors.bg,
            borderTopLeftRadius: 24,
            borderTopRightRadius: 24,
            maxHeight: SCREEN_HEIGHT * 0.88,
            transform: [{ translateY }],
            shadowColor: '#000',
            shadowOffset: { width: 0, height: -4 },
            shadowOpacity: 0.08,
            shadowRadius: 16,
            elevation: 12,
          }}
        >
          {/* Handle */}
          <View style={{ alignItems: 'center', paddingTop: 10, paddingBottom: 4 }}>
            <View style={{ width: 40, height: 4, borderRadius: 2, backgroundColor: colors.border }} />
          </View>

          <ScrollView
            contentContainerStyle={{
              paddingHorizontal: 20,
              paddingBottom: insets.bottom + 24,
              paddingTop: 8,
              gap: 20,
            }}
            showsVerticalScrollIndicator={false}
          >
            {loading ? (
              <View style={{ paddingVertical: 48, alignItems: 'center' }}>
                <Text style={{ fontSize: 14, color: colors.textMuted, fontFamily: 'Nunito_400Regular' }}>
                  {t('common.loading')}
                </Text>
              </View>
            ) : error ? (
              <View style={{ paddingVertical: 32, alignItems: 'center', gap: 12 }}>
                <Text style={{ fontSize: 14, color: colors.error, fontFamily: 'Nunito_400Regular', textAlign: 'center' }}>
                  {error}
                </Text>
                <Button
                  title={t('common.back')}
                  onPress={onClose}
                  variant="ghost"
                />
              </View>
            ) : preview ? (
              <SheetContent
                preview={preview}
                targetPlan={targetPlan}
                isDowngrade={isDowngrade}
                colors={colors}
                onConfirm={onConfirm}
                onClose={onClose}
                t={t}
              />
            ) : null}
          </ScrollView>
        </Animated.View>
      </View>
    </Modal>
  );
}

type ContentProps = {
  preview: ChangePreview;
  targetPlan: Plan;
  isDowngrade: boolean;
  colors: import('../../lib/theme').ColorScheme;
  onConfirm: () => void;
  onClose: () => void;
  t: (k: string, opts?: Record<string, string | number>) => string;
};

function SheetContent({ preview, targetPlan, isDowngrade, colors, onConfirm, onClose, t }: ContentProps) {
  const fromLabel = PLAN_LABEL[preview.from];
  const toLabel = PLAN_LABEL[targetPlan];

  return (
    <>
      {/* Header */}
      <Text style={{ fontSize: 22, fontFamily: 'Nunito_700Bold', color: colors.text, lineHeight: 28 }}>
        {isDowngrade
          ? t('plan.change.header_downgrade', { from: fromLabel, to: toLabel })
          : t('plan.change.header_upgrade', { to: toLabel })}
      </Text>

      {/* Downgrade: Beruhigung zuerst */}
      {isDowngrade && (
        <View style={{ gap: 10 }}>
          <Text style={{ fontSize: 14, color: colors.text, fontFamily: 'Nunito_600SemiBold' }}>
            {t('plan.change.downgrade_reassurance')}
          </Text>
          {preview.keeps.length > 0 && (
            <View style={{ gap: 6 }}>
              {preview.keeps.map((k, i) => (
                <View key={i} style={{ flexDirection: 'row', alignItems: 'flex-start', gap: 8 }}>
                  <Ionicons name="checkmark-circle-outline" size={16} color={colors.success} style={{ marginTop: 1 }} />
                  <Text style={{ flex: 1, fontSize: 14, color: colors.text, fontFamily: 'Nunito_400Regular', lineHeight: 20 }}>
                    {k}
                  </Text>
                </View>
              ))}
            </View>
          )}
        </View>
      )}

      {/* Upgrade: gains */}
      {!isDowngrade && preview.gains.length > 0 && (
        <View style={{ gap: 8 }}>
          <Text style={{ fontSize: 12, fontFamily: 'Nunito_700Bold', color: colors.textMuted, textTransform: 'uppercase', letterSpacing: 0.8 }}>
            {t('plan.change.section_gains')}
          </Text>
          <View style={{ gap: 6 }}>
            {preview.gains.map((g, i) => (
              <View key={i} style={{ flexDirection: 'row', alignItems: 'flex-start', gap: 8 }}>
                <Ionicons name="checkmark-circle" size={16} color={colors.success} style={{ marginTop: 1 }} />
                <Text style={{ flex: 1, fontSize: 14, color: colors.text, fontFamily: 'Nunito_400Regular', lineHeight: 20 }}>
                  {g}
                </Text>
              </View>
            ))}
          </View>
        </View>
      )}

      {/* Upgrade: keeps */}
      {!isDowngrade && preview.keeps.length > 0 && (
        <View style={{ gap: 8 }}>
          <Text style={{ fontSize: 12, fontFamily: 'Nunito_700Bold', color: colors.textMuted, textTransform: 'uppercase', letterSpacing: 0.8 }}>
            {t('plan.change.section_keeps')}
          </Text>
          <View style={{ gap: 6 }}>
            {preview.keeps.map((k, i) => (
              <View key={i} style={{ flexDirection: 'row', alignItems: 'flex-start', gap: 8 }}>
                <Ionicons name="checkmark-outline" size={16} color={colors.textMuted} style={{ marginTop: 1 }} />
                <Text style={{ flex: 1, fontSize: 14, color: colors.textMuted, fontFamily: 'Nunito_400Regular', lineHeight: 20 }}>
                  {k}
                </Text>
              </View>
            ))}
          </View>
        </View>
      )}

      {/* Downgrade: changes list */}
      {isDowngrade && preview.changes.length > 0 && (
        <View style={{ gap: 10 }}>
          <Text style={{ fontSize: 12, fontFamily: 'Nunito_700Bold', color: colors.textMuted, textTransform: 'uppercase', letterSpacing: 0.8 }}>
            {t('plan.change.section_changes')}
          </Text>
          <View style={{ gap: 8 }}>
            {preview.changes.map((c, i) => (
              <View
                key={i}
                style={{
                  backgroundColor: colors.surface,
                  borderRadius: 12,
                  padding: 12,
                  gap: 6,
                  borderWidth: 1,
                  borderColor: colors.border,
                }}
              >
                <View style={{ flexDirection: 'row', alignItems: 'center', justifyContent: 'space-between', gap: 8 }}>
                  <Text style={{ fontSize: 14, fontFamily: 'Nunito_600SemiBold', color: colors.text, flex: 1 }}>
                    {c.resource}
                  </Text>
                  <ActionChip action={c.action} />
                </View>
                <Text style={{ fontSize: 13, color: colors.textMuted, fontFamily: 'Nunito_400Regular', lineHeight: 18 }}>
                  {c.detail}
                </Text>
                {c.graceUntilDays != null && c.graceUntilDays > 0 && (
                  <View style={{ flexDirection: 'row', alignItems: 'center', gap: 4 }}>
                    <Ionicons name="time-outline" size={12} color={colors.warning} />
                    <Text style={{ fontSize: 12, color: colors.warning, fontFamily: 'Nunito_600SemiBold' }}>
                      {t('plan.change.grace_days', { count: c.graceUntilDays })}
                    </Text>
                  </View>
                )}
              </View>
            ))}
          </View>
        </View>
      )}

      {/* Downgrade: was nicht passiert */}
      {isDowngrade && (
        <View
          style={{
            backgroundColor: 'rgba(22,163,74,0.06)',
            borderRadius: 12,
            padding: 14,
            gap: 4,
            borderWidth: 1,
            borderColor: 'rgba(22,163,74,0.15)',
          }}
        >
          <Text style={{ fontSize: 13, fontFamily: 'Nunito_600SemiBold', color: colors.success }}>
            {t('plan.change.downgrade_no_delete_title')}
          </Text>
          <Text style={{ fontSize: 13, color: colors.text, fontFamily: 'Nunito_400Regular', lineHeight: 18 }}>
            {t('plan.change.downgrade_no_delete_body')}
          </Text>
        </View>
      )}

      {/* Upgrade: Abrechnungs-Hinweis statt Kauf-Button */}
      {!isDowngrade && (
        <View
          style={{
            backgroundColor: colors.surface,
            borderRadius: 12,
            padding: 14,
            borderWidth: 1,
            borderColor: colors.border,
          }}
        >
          <Text style={{ fontSize: 12, color: colors.textMuted, fontFamily: 'Nunito_400Regular', lineHeight: 17 }}>
            {t('plan.change.billing_hint')}
          </Text>
        </View>
      )}

      {/* Downgrade: Recovery-Sicherheitssatz */}
      {isDowngrade && (
        <Text style={{ fontSize: 13, color: colors.textMuted, fontFamily: 'Nunito_400Regular', lineHeight: 19, fontStyle: 'italic' }}>
          {t('plan.change.downgrade_recovery_note')}
        </Text>
      )}

      {/* CTAs */}
      <View style={{ gap: 10, marginTop: 4 }}>
        <Button
          title={isDowngrade ? t('plan.change.cta_confirm_downgrade') : t('plan.change.cta_confirm_upgrade')}
          onPress={onConfirm}
          size="lg"
        />

        {isDowngrade && (
          <Button
            title={t('plan.change.cta_stay', { plan: PLAN_LABEL[preview.from] })}
            onPress={onClose}
            variant="ghost"
          />
        )}

        {!isDowngrade && (
          <Button
            title={t('common.cancel')}
            onPress={onClose}
            variant="ghost"
          />
        )}
      </View>
    </>
  );
}