import React, { useState, useRef, useEffect, useCallback } from 'react';
import {
  View,
  Text,
  StyleSheet,
  KeyboardAvoidingView,
  Platform,
  ScrollView,
  TouchableOpacity,
  TextInput,
  ActivityIndicator,
  Keyboard,
} from 'react-native';
import { router, useLocalSearchParams } from 'expo-router';
import { Ionicons } from '@expo/vector-icons';
import { useAuth } from '@/contexts/AuthContext';
import { Button } from '@/components/ui/Button';
import { ErrorMessage } from '@/components/ui/ErrorMessage';
import { AppColors, BorderRadius, FontSizes, Spacing } from '@/constants/theme';
import { useNavigationFlow } from '@/hooks/useNavigationFlow';
import { api } from '@/services/api';

const CODE_LENGTH = 6;

export default function VerifyOTPScreen() {
  // Params from previous screens
  const params = useLocalSearchParams<{
    email: string;
    skipOtp: string;
    inviteCode: string;
    isNewUser: string;
  }>();

  const email = params.email || '';
  const skipOtp = params.skipOtp === '1';
  const inviteCode = params.inviteCode || '';
  const isNewUser = params.isNewUser === '1';

  // Auth context
  const { verifyOtp, requestOtp, isLoading: authLoading, error: authError, clearError } = useAuth();
  const nav = useNavigationFlow();

  // Local state
  const [code, setCode] = useState('');
  const [verifying, setVerifying] = useState(false);
  const [resending, setResending] = useState(false);
  const [localError, setLocalError] = useState<string | null>(null);
  const [resendCooldown, setResendCooldown] = useState(0);

  // Refs
  const inputRef = useRef<TextInput>(null);
  const hasAutoLoggedIn = useRef(false);

  // Clear errors on mount
  useEffect(() => {
    clearError();
  }, []);

  // Navigate after successful verification
  const navigateAfterSuccess = useCallback(async () => {
    try {
      // SIMPLIFIED FLOW:
      // - Login (existing user) → go straight to beneficiaries
      // - Registration (new user) → follow onboarding flow
      if (!isNewUser) {
        router.replace('/(tabs)');
        return;
      }

      // New user registration flow
      const profileResponse = await api.getProfile();

      if (!profileResponse.ok || !profileResponse.data) {
        throw new Error(profileResponse.error?.message || 'Failed to load profile');
      }

      const beneficiariesResponse = await api.getAllBeneficiaries();
      if (!beneficiariesResponse.ok) {
        throw new Error(beneficiariesResponse.error?.message || 'Failed to load beneficiaries');
      }

      // /auth/me returns { user: {...}, beneficiaries: [...] }
      // We need to extract user data from the nested 'user' object
      const userData = profileResponse.data.user || profileResponse.data;

      const profile = {
        id: userData.id,
        email: userData.email,
        firstName: userData.firstName,
        lastName: userData.lastName,
        phone: userData.phone,
      };

      const result = nav.controller.getRouteAfterLogin(
        profile,
        beneficiariesResponse.data || []
      );

      if (
        result.path === nav.ROUTES.AUTH.ENTER_NAME ||
        result.path === nav.ROUTES.AUTH.ADD_LOVED_ONE
      ) {
        result.params = { ...result.params, email, inviteCode };
      }

      nav.navigate(result, true);
    } catch (error) {
      setLocalError(error instanceof Error ? error.message : 'Failed to load profile data');
      setVerifying(false);
    }
  }, [email, inviteCode, nav, isNewUser]);

  // Auto-login for skipOtp (dev mode)
  useEffect(() => {
    if (!skipOtp || !email || hasAutoLoggedIn.current) return;

    hasAutoLoggedIn.current = true;

    const autoLogin = async () => {
      setVerifying(true);
      const success = await verifyOtp(email, '000000');
      if (success) {
        await navigateAfterSuccess();
      } else {
        setLocalError('Auto-login failed');
        setVerifying(false);
      }
    };

    autoLogin();
  }, [skipOtp, email, verifyOtp, navigateAfterSuccess]);

  // Focus input on mount (if not skipping OTP)
  useEffect(() => {
    if (!skipOtp) {
      setTimeout(() => inputRef.current?.focus(), 100);
    }
  }, [skipOtp]);

  // Resend cooldown timer
  useEffect(() => {
    if (resendCooldown > 0) {
      const timer = setTimeout(() => setResendCooldown(resendCooldown - 1), 1000);
      return () => clearTimeout(timer);
    }
  }, [resendCooldown]);

  // Handle code input
  const handleCodeChange = (text: string) => {
    const digits = text.replace(/\D/g, '').slice(0, CODE_LENGTH);
    setCode(digits);
    setLocalError(null);

    // Auto-submit when complete
    if (digits.length === CODE_LENGTH) {
      handleVerify(digits);
    }
  };

  // Verify OTP
  const handleVerify = useCallback(async (verifyCode?: string) => {
    const codeToVerify = verifyCode || code;

    if (codeToVerify.length !== CODE_LENGTH) {
      setLocalError('Please enter the 6-digit code');
      return;
    }

    setVerifying(true);
    setLocalError(null);

    const success = await verifyOtp(email, codeToVerify);

    if (success) {
      // If user has invite code, try to accept it (silent - don't block flow)
      if (inviteCode) {
        await api.acceptInvitation(inviteCode);
        // Don't block - continue with registration flow regardless of result
      }
      await navigateAfterSuccess();
      return;
    }

    setVerifying(false);
    setLocalError('Invalid verification code. Please try again.');
    setCode('');
    setTimeout(() => inputRef.current?.focus(), 100);
  }, [code, email, verifyOtp, navigateAfterSuccess]);

  // Resend OTP
  const handleResend = useCallback(async () => {
    if (resendCooldown > 0) return;

    setResending(true);
    setLocalError(null);

    const result = await requestOtp(email);

    setResending(false);

    if (result.success) {
      setResendCooldown(60);
      setCode('');
    } else {
      setLocalError('Failed to resend code');
    }
  }, [email, resendCooldown, requestOtp]);

  // Go back
  const handleBack = () => {
    router.back();
  };

  // Render code boxes
  const renderCodeBoxes = () => {
    return Array.from({ length: CODE_LENGTH }).map((_, i) => {
      const isActive = i === code.length;
      const isFilled = i < code.length;

      return (
        <View
          key={i}
          style={[
            styles.codeBox,
            isActive && styles.codeBoxActive,
            isFilled && styles.codeBoxFilled,
          ]}
        >
          <Text style={styles.codeDigit}>{code[i] || ''}</Text>
        </View>
      );
    });
  };

  // Auto-login loading screen
  if (skipOtp) {
    return (
      <View style={styles.autoLoginContainer}>
        <ActivityIndicator size="large" color={AppColors.primary} />
        <Text style={styles.autoLoginText}>Signing in...</Text>
      </View>
    );
  }

  const displayError = localError || authError?.message;

  return (
    <KeyboardAvoidingView
      style={styles.container}
      behavior={Platform.OS === 'ios' ? 'padding' : 'padding'}
      keyboardVerticalOffset={Platform.OS === 'ios' ? 0 : 20}
    >
      <ScrollView
        contentContainerStyle={styles.scrollContent}
        keyboardShouldPersistTaps="handled"
        showsVerticalScrollIndicator={false}
        bounces={false}
      >
        <TouchableOpacity style={styles.backButton} onPress={handleBack}>
          <Ionicons name="arrow-back" size={24} color={AppColors.textPrimary} />
        </TouchableOpacity>

        <View style={styles.iconContainer}>
          <View style={styles.iconCircle}>
            <Ionicons name="mail-open" size={Platform.OS === 'android' ? 36 : 48} color={AppColors.primary} />
          </View>
        </View>

        <View style={styles.header}>
          <Text style={styles.title}>Check your email</Text>
          <Text style={styles.subtitle}>We sent a verification code to</Text>
          <Text style={styles.email}>{email}</Text>
        </View>

        {displayError && (
          <ErrorMessage
            message={displayError}
            onDismiss={() => {
              setLocalError(null);
              clearError();
            }}
          />
        )}

        {/* Code Input Boxes */}
        <TouchableOpacity
          style={styles.codeContainer}
          activeOpacity={1}
          onPress={() => inputRef.current?.focus()}
        >
          {renderCodeBoxes()}
        </TouchableOpacity>

        {/* Hidden Input */}
        <TextInput
          ref={inputRef}
          style={styles.hiddenInput}
          value={code}
          onChangeText={handleCodeChange}
          keyboardType="number-pad"
          maxLength={CODE_LENGTH}
          autoComplete="one-time-code"
          textContentType="oneTimeCode"
        />

        <View style={styles.buttonContainer}>
          <Button
            title="Verify"
            onPress={() => handleVerify()}
            loading={verifying || authLoading}
            disabled={code.length !== CODE_LENGTH}
            fullWidth
            size="lg"
          />
        </View>

        {/* Resend */}
        <View style={styles.resendContainer}>
          <Text style={styles.resendText}>Didn't receive the code? </Text>
          {resendCooldown > 0 ? (
            <Text style={styles.resendCooldownText}>Resend in {resendCooldown}s</Text>
          ) : (
            <TouchableOpacity onPress={handleResend} disabled={resending}>
              <Text style={[styles.resendLink, resending && styles.resendLinkDisabled]}>
                {resending ? 'Sending...' : 'Resend'}
              </Text>
            </TouchableOpacity>
          )}
        </View>

        {/* Use different email */}
        <TouchableOpacity style={styles.changeEmailLink} onPress={handleBack}>
          <Text style={styles.changeEmailText}>Use a different email</Text>
        </TouchableOpacity>
      </ScrollView>
    </KeyboardAvoidingView>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: AppColors.background,
  },
  scrollContent: {
    flexGrow: 1,
    paddingHorizontal: Spacing.lg,
    paddingTop: Platform.OS === 'android' ? Spacing.md : Spacing.xl,
    paddingBottom: Spacing.xl,
  },
  autoLoginContainer: {
    flex: 1,
    backgroundColor: AppColors.background,
    justifyContent: 'center',
    alignItems: 'center',
    gap: Spacing.md,
  },
  autoLoginText: {
    fontSize: FontSizes.lg,
    color: AppColors.textSecondary,
  },
  backButton: {
    width: 44,
    height: 44,
    justifyContent: 'center',
    alignItems: 'flex-start',
    marginBottom: Platform.OS === 'android' ? Spacing.sm : Spacing.xl,
  },
  iconContainer: {
    alignItems: 'center',
    marginBottom: Platform.OS === 'android' ? Spacing.md : Spacing.xl,
  },
  iconCircle: {
    width: Platform.OS === 'android' ? 72 : 100,
    height: Platform.OS === 'android' ? 72 : 100,
    borderRadius: Platform.OS === 'android' ? 36 : 50,
    backgroundColor: `${AppColors.primary}15`,
    justifyContent: 'center',
    alignItems: 'center',
  },
  header: {
    alignItems: 'center',
    marginBottom: Platform.OS === 'android' ? Spacing.sm : Spacing.lg,
  },
  title: {
    fontSize: FontSizes['2xl'],
    fontWeight: '700',
    color: AppColors.textPrimary,
    marginBottom: Platform.OS === 'android' ? Spacing.xs : Spacing.md,
    textAlign: 'center',
  },
  subtitle: {
    fontSize: FontSizes.base,
    color: AppColors.textSecondary,
    textAlign: 'center',
  },
  email: {
    fontSize: FontSizes.base,
    fontWeight: '600',
    color: AppColors.textPrimary,
    marginTop: Spacing.xs,
  },
  codeContainer: {
    flexDirection: 'row',
    justifyContent: 'center',
    gap: Spacing.sm,
    marginVertical: Platform.OS === 'android' ? Spacing.md : Spacing.xl,
  },
  codeBox: {
    width: 48,
    height: 56,
    borderRadius: BorderRadius.md,
    borderWidth: 2,
    borderColor: AppColors.border,
    backgroundColor: AppColors.surface,
    justifyContent: 'center',
    alignItems: 'center',
  },
  codeBoxActive: {
    borderColor: AppColors.primary,
  },
  codeBoxFilled: {
    borderColor: AppColors.primary,
    backgroundColor: `${AppColors.primary}10`,
  },
  codeDigit: {
    fontSize: FontSizes['2xl'],
    fontWeight: '700',
    color: AppColors.textPrimary,
  },
  hiddenInput: {
    position: 'absolute',
    opacity: 0,
    height: 0,
    width: 0,
  },
  buttonContainer: {
    marginBottom: Spacing.lg,
  },
  resendContainer: {
    flexDirection: 'row',
    justifyContent: 'center',
    alignItems: 'center',
    paddingVertical: Spacing.md,
  },
  resendText: {
    fontSize: FontSizes.base,
    color: AppColors.textSecondary,
  },
  resendLink: {
    fontSize: FontSizes.base,
    color: AppColors.primary,
    fontWeight: '600',
  },
  resendLinkDisabled: {
    opacity: 0.5,
  },
  resendCooldownText: {
    fontSize: FontSizes.base,
    color: AppColors.textMuted,
  },
  changeEmailLink: {
    alignItems: 'center',
    paddingVertical: Spacing.sm,
  },
  changeEmailText: {
    fontSize: FontSizes.sm,
    color: AppColors.primary,
    fontWeight: '500',
  },
});