import React, { useState } from 'react';
import {
  StyleSheet, View, Text, TextInput, TouchableOpacity, Alert,
  ActivityIndicator, KeyboardAvoidingView, Platform, ScrollView, Image,
} from 'react-native';
import { useTheme } from '../services/ThemeContext';
import DatabaseService from '../services/DatabaseService';

const APP_ICON = require('../../assets/icon.png');
const isBlank = (value) => !value?.trim();
const isEmailValid = (value) => value.includes('@') && value.includes('.');

const RegisterScreen = ({ navigation }) => {
  const { theme } = useTheme();
  const [username, setUsername] = useState('');
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const [confirmPassword, setConfirmPassword] = useState('');
  const [loading, setLoading] = useState(false);

  const handleRegister = async () => {
    if (isBlank(username)) { Alert.alert('Error', 'Please enter a username'); return; }
    if (username.trim().length < 3) { Alert.alert('Error', 'Username must be at least 3 characters'); return; }
    if (isBlank(email)) { Alert.alert('Error', 'Please enter an email'); return; }
    if (!isEmailValid(email)) { Alert.alert('Error', 'Please enter a valid email address'); return; }
    if (isBlank(password)) { Alert.alert('Error', 'Please enter a password'); return; }
    if (password.length < 6) { Alert.alert('Error', 'Password must be at least 6 characters'); return; }
    if (password !== confirmPassword) { Alert.alert('Error', 'Passwords do not match'); return; }

    setLoading(true);
    try {
      const exists = await DatabaseService.userExists(username.trim(), email.trim().toLowerCase());
      if (exists) { Alert.alert('Error', 'Username or email already taken'); setLoading(false); return; }

      const userId = await DatabaseService.createUser(username.trim(), email.trim().toLowerCase(), password);

      Alert.alert('Success', 'Account created!', [
        { text: 'OK', onPress: () => navigation.replace('Onboarding', { userId }) },
      ]);
    } catch (error) {
      console.error('Registration error:', error);
      Alert.alert('Error', 'Failed to register: ' + error.message);
    } finally {
      setLoading(false);
    }
  };

  return (
    <KeyboardAvoidingView
      behavior={Platform.OS === 'ios' ? 'padding' : 'height'}
      style={[styles.container, { backgroundColor: theme.background }]}
    >
      <ScrollView contentContainerStyle={styles.scrollContent} showsVerticalScrollIndicator={false}>
        <View style={styles.content}>
          <View style={styles.headerContainer}>
            <Image source={APP_ICON} style={styles.appIcon} resizeMode="contain" />
            <Text style={[styles.title, { color: theme.text }]}>Create Account</Text>
            <Text style={[styles.subtitle, { color: theme.textSecondary }]}>Set up your local photo library account</Text>
          </View>

          <View style={styles.inputContainer}>
            <Text style={[styles.label, { color: theme.textSecondary }]}>Username</Text>
            <TextInput
              style={[styles.input, { backgroundColor: theme.inputBg, borderColor: theme.border, color: theme.text }]}
              placeholder="Choose a username" placeholderTextColor={theme.textTertiary}
              value={username} onChangeText={setUsername} editable={!loading}
              autoCapitalize="none" autoCorrect={false}
            />

            <Text style={[styles.label, { color: theme.textSecondary }]}>Email</Text>
            <TextInput
              style={[styles.input, { backgroundColor: theme.inputBg, borderColor: theme.border, color: theme.text }]}
              placeholder="Enter your email" placeholderTextColor={theme.textTertiary}
              value={email} onChangeText={setEmail} editable={!loading}
              autoCapitalize="none" autoCorrect={false} keyboardType="email-address"
            />

            <Text style={[styles.label, { color: theme.textSecondary }]}>Password</Text>
            <TextInput
              style={[styles.input, { backgroundColor: theme.inputBg, borderColor: theme.border, color: theme.text }]}
              placeholder="Create a password (min 6 characters)" placeholderTextColor={theme.textTertiary}
              value={password} onChangeText={setPassword} editable={!loading}
              secureTextEntry autoCapitalize="none"
            />

            <Text style={[styles.label, { color: theme.textSecondary }]}>Confirm Password</Text>
            <TextInput
              style={[styles.input, { backgroundColor: theme.inputBg, borderColor: theme.border, color: theme.text }]}
              placeholder="Confirm your password" placeholderTextColor={theme.textTertiary}
              value={confirmPassword} onChangeText={setConfirmPassword} editable={!loading}
              secureTextEntry autoCapitalize="none"
            />
          </View>

          <TouchableOpacity
            style={[styles.primaryButton, { backgroundColor: theme.primary, borderColor: theme.border }, loading && styles.buttonDisabled]}
            onPress={handleRegister}
            disabled={loading}
          >
            {loading ? <ActivityIndicator color="#fff" /> : (
              <Text style={styles.primaryButtonText}>Create Account</Text>
            )}
          </TouchableOpacity>

          <TouchableOpacity
            style={[styles.secondaryButton, { backgroundColor: theme.background, borderColor: theme.border }]}
            onPress={() => navigation.navigate('Login')}
            disabled={loading}
          >
            <Text style={[styles.secondaryButtonText, { color: theme.text }]}>Back to Login</Text>
          </TouchableOpacity>
        </View>
      </ScrollView>
    </KeyboardAvoidingView>
  );
};

const styles = StyleSheet.create({
  container: { flex: 1 },
  scrollContent: { flexGrow: 1, justifyContent: 'center' },
  content: { paddingHorizontal: 24, paddingVertical: 40 },
  headerContainer: { marginBottom: 36, alignItems: 'center' },
  appIcon: { width: 80, height: 80, marginBottom: 16, borderRadius: 16 },
  title: { fontSize: 28, fontWeight: '700', marginBottom: 8 },
  subtitle: { fontSize: 15, textAlign: 'center' },
  inputContainer: { marginBottom: 24 },
  label: { fontSize: 13, fontWeight: '600', marginBottom: 6, marginTop: 16 },
  input: {
    borderWidth: 1, borderRadius: 8, paddingHorizontal: 14, paddingVertical: 12, fontSize: 15,
  },
  primaryButton: {
    borderRadius: 8, paddingVertical: 14, alignItems: 'center', marginBottom: 10, borderWidth: 1,
  },
  primaryButtonText: { color: '#fff', fontSize: 15, fontWeight: '600' },
  secondaryButton: {
    borderRadius: 8, paddingVertical: 14, alignItems: 'center', borderWidth: 1,
  },
  secondaryButtonText: { fontSize: 15, fontWeight: '600' },
  buttonDisabled: { opacity: 0.6 },
});

export default RegisterScreen;