import React, { useState, useEffect, useRef } from 'react';
import {
  View,
  Text,
  StyleSheet,
  SafeAreaView,
  Alert,
  TouchableOpacity,
  TouchableWithoutFeedback,
  Keyboard,
  BackHandler,
  Platform,
  KeyboardAvoidingView,
} from 'react-native';
import { StatusBar } from 'expo-status-bar';
import { useFocusEffect } from '@react-navigation/native';
import { useAuth } from '../../contexts/AuthContext';
import Button from '../../components/Button';
import {
  CodeField,
  Cursor,
  useBlurOnFulfill,
  useClearByFocusCell,
} from 'react-native-confirmation-code-field';
import { COLORS } from '../../constants/colors';

const CELL_COUNT = 6;

const VerificationScreen = ({ navigation }) => {
  const [code, setCode] = useState('');
  const [countdown, setCountdown] = useState(60);
  const [canResend, setCanResend] = useState(false);
  const { verify, isLoading, pendingVerification, clearPendingVerification } = useAuth();
  const countdownRef = useRef(null);
  const ref = useBlurOnFulfill({ value: code, cellCount: CELL_COUNT });
  const [props, getCellOnLayoutHandler] = useClearByFocusCell({
    value: code,
    setValue: setCode,
  });

  useEffect(() => {
    if (!pendingVerification) {
      // If no pending verification, go back to login
      navigation.replace('Login');
      return;
    }

    startCountdown();
    return () => {
      if (countdownRef.current) {
        clearInterval(countdownRef.current);
      }
    };
  }, []);

  // Handle Android hardware back button
  useFocusEffect(
    React.useCallback(() => {
      const onBackPress = () => {
        handleGoBack();
        return true; // Prevent default behavior
      };

      if (Platform.OS === 'android') {
        const sub = BackHandler.addEventListener('hardwareBackPress', onBackPress);
        return () => sub.remove();
      }
    }, [handleGoBack])
  );

  const startCountdown = () => {
    setCountdown(60);
    setCanResend(false);
    
    countdownRef.current = setInterval(() => {
      setCountdown((prev) => {
        if (prev <= 1) {
          setCanResend(true);
          if (countdownRef.current) {
            clearInterval(countdownRef.current);
          }
          return 0;
        }
        return prev - 1;
      });
    }, 1000);
  };

  const handleVerify = async (filledCode) => {
    if (!filledCode.trim()) {
      Alert.alert('Ýalňyşlyk', 'Tassyklama koduny giriziň');
      return;
    }

    if (!/^\d{6}$/.test(filledCode.trim())) {
      Alert.alert('Ýalňyşlyk', 'Tassyklama kody 6 sanly bolmaly');
      return;
    }

    const result = await verify(filledCode.trim());
    
    if (result.success) {
      // Navigation will be handled by AuthContext
    } else {
      Alert.alert('Ýalňyşlyk', result.error);
    }
  };

  const handleVerifyWrapper = () => handleVerify(code);

  const handleResendCode = async () => {
    if (!canResend) return;
    
    // Here you would call the API to resend the code
    // For now, just restart the countdown 
    Alert.alert('Üstünlik', 'Täze tassyklama kody iberildi');
    startCountdown();
  };

  const handleGoBack = React.useCallback(() => {
    clearPendingVerification();
    
    // Check if we can go back, if not navigate to Login
    if (navigation.canGoBack()) {
      navigation.goBack();
    } else {
      navigation.navigate('Login');
    }
  }, [clearPendingVerification, navigation]);

  const formatPhoneNumber = (phone) => {
    if (!phone) return '';
    const phoneStr = phone.toString();
    
    return `+993 ${phoneStr.slice(0, 2)} ${phoneStr.slice(2, 4)}-${phoneStr.slice(4, 6)}-${phoneStr.slice(6)}`;
  };

  if (!pendingVerification) {
    return null; // Will navigate away in useEffect
  }

  return (
    <SafeAreaView style={styles.container}>
      <StatusBar style="dark" />
      
      <View style={styles.header}>
        <TouchableOpacity onPress={handleGoBack} style={styles.backButton}>
          <Text style={styles.backButtonText}>← Yza</Text>
        </TouchableOpacity>
      </View>

      <KeyboardAvoidingView
        style={{ flex: 1 }}
        behavior={Platform.OS === 'ios' ? 'padding' : 'height'}
      >
        <TouchableWithoutFeedback onPress={Keyboard.dismiss}>
          <View style={styles.content}>
            <View style={styles.logoContainer}>
              <View style={styles.verificationIcon}>
                <Text style={styles.verificationIconText}>✓</Text>
              </View>
              <Text style={styles.title}>Tassyklama</Text>
              <Text style={styles.subtitle}>
                {formatPhoneNumber(pendingVerification.phone)} belgisine iberilen 
                6 sanly tassyklama koduny giriziň
              </Text>
            </View>

            <View style={styles.formContainer}>
              <CodeField
                ref={ref}
                {...props}
                value={code}
                onChangeText={setCode}
                cellCount={CELL_COUNT}
                rootStyle={styles.otpContainer}
                keyboardType="number-pad"
                textContentType="oneTimeCode"
                renderCell={({ index, symbol, isFocused }) => (
                  <Text
                    key={index}
                    style={[styles.otpInput, isFocused && styles.otpInputHighlight]}
                    onLayout={getCellOnLayoutHandler(index)}>
                    {symbol || (isFocused ? <Cursor/> : null)}
                  </Text>
                )}
                onSubmitEditing={handleVerifyWrapper}
              />

              <Button
                title="Tassykla"
                onPress={handleVerifyWrapper}
                loading={isLoading}
                style={styles.verifyButton}
              />

              <View style={styles.resendContainer}>
                {canResend ? (
                  <TouchableOpacity onPress={handleResendCode}>
                    <Text style={styles.resendText}>Kodu gaýtadan iber</Text>
                  </TouchableOpacity>
                ) : (
                  <Text style={styles.countdownText}>
                    Gaýtadan ibermek üçin {countdown} sekunt garaşyň
                  </Text>
                )}
              </View>
            </View>
          </View>
        </TouchableWithoutFeedback>
      </KeyboardAvoidingView>
    </SafeAreaView>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: COLORS.background,
  },
  header: {
    paddingHorizontal: 24,
    paddingTop: 16,
  },
  backButton: {
    alignSelf: 'flex-start',
  },
  backButtonText: {
    fontSize: 16,
    color: COLORS.primary,
    fontWeight: '600',
  },
  content: {
    flex: 1,
    paddingHorizontal: 24,
    justifyContent: 'center',
  },
  logoContainer: {
    alignItems: 'center',
    marginBottom: 48,
  },
  verificationIcon: {
    width: 80,
    height: 80,
    borderRadius: 40,
    backgroundColor: COLORS.success,
    alignItems: 'center',
    justifyContent: 'center',
    marginBottom: 24,
    shadowColor: COLORS.success,
    shadowOffset: {
      width: 0,
      height: 4,
    },
    shadowOpacity: 0.3,
    shadowRadius: 8,
    elevation: 8,
  },
  verificationIconText: {
    fontSize: 32,
    color: COLORS.white,
    fontWeight: 'bold',
  },
  title: {
    fontSize: 28,
    fontWeight: 'bold',
    color: COLORS.textPrimary,
    marginBottom: 16,
    textAlign: 'center',
  },
  subtitle: {
    fontSize: 16,
    color: COLORS.textSecondary,
    textAlign: 'center',
    lineHeight: 22,
    paddingHorizontal: 20,
  },
  formContainer: {
    alignItems: 'center',
  },
  otpContainer: {
    width: '90%',
    marginBottom: 32,
  },
  otpInput: {
    width: 45,
    height: 60,
    lineHeight: 58,
    borderWidth: 1,
    borderRadius: 12,
    borderColor: COLORS.gray[300],
    color: COLORS.textPrimary,
    fontSize: 24,
    fontWeight: 'bold',
    textAlign: 'center',
  },
  otpInputHighlight: {
    borderColor: COLORS.primary,
  },
  verifyButton: {
    width: '100%',
    marginBottom: 32,
  },
  resendContainer: {
    alignItems: 'center',
  },
  resendText: {
    fontSize: 16,
    color: COLORS.primary,
    fontWeight: '600',
  },
  countdownText: {
    fontSize: 14,
    color: COLORS.textSecondary,
    textAlign: 'center',
  },
});

export default VerificationScreen;