import React, { useState, useCallback, useRef } from 'react';
import {
  View,
  Text,
  StyleSheet,
  FlatList,
  TextInput,
  TouchableOpacity,
  KeyboardAvoidingView,
  Platform,
  Alert,
} from 'react-native';
import { Ionicons } from '@expo/vector-icons';
import { SafeAreaView } from 'react-native-safe-area-context';
import { api } from '@/services/api';
import { useBeneficiary } from '@/contexts/BeneficiaryContext';
import { AppColors, BorderRadius, FontSizes, Spacing } from '@/constants/theme';
import type { Message } from '@/types';

export default function ChatScreen() {
  const { currentBeneficiary, getBeneficiaryContext } = useBeneficiary();
  const [messages, setMessages] = useState<Message[]>([
    {
      id: '1',
      role: 'assistant',
      content: 'Hello! I\'m Julia, your AI assistant. How can I help you today?',
      timestamp: new Date(),
    },
  ]);
  const [input, setInput] = useState('');
  const [isSending, setIsSending] = useState(false);
  const flatListRef = useRef<FlatList>(null);
  const lastSendTimeRef = useRef<number>(0);
  const SEND_COOLDOWN_MS = 1000; // 1 second cooldown between messages

  const handleSend = useCallback(async () => {
    const trimmedInput = input.trim();
    if (!trimmedInput || isSending) return;

    // Debounce: prevent rapid-fire messages
    const now = Date.now();
    if (now - lastSendTimeRef.current < SEND_COOLDOWN_MS) {
      return;
    }
    lastSendTimeRef.current = now;

    // Security: require beneficiary to be selected
    if (!currentBeneficiary?.id) {
      Alert.alert(
        'Select Patient',
        'Please select a patient from the Patients tab before starting a conversation.',
        [{ text: 'OK' }]
      );
      return;
    }

    const userMessage: Message = {
      id: Date.now().toString(),
      role: 'user',
      content: trimmedInput,
      timestamp: new Date(),
    };

    setMessages((prev) => [...prev, userMessage]);
    setInput('');
    setIsSending(true);

    try {
      // Prepend beneficiary context to the question if available
      const beneficiaryContext = getBeneficiaryContext();
      const questionWithContext = beneficiaryContext
        ? `${beneficiaryContext} ${trimmedInput}`
        : trimmedInput;

      // Pass deployment_id from selected beneficiary (required, no fallback)
      const deploymentId = currentBeneficiary.id.toString();
      const response = await api.sendMessage(questionWithContext, deploymentId);

      if (response.ok && response.data?.response) {
        const assistantMessage: Message = {
          id: (Date.now() + 1).toString(),
          role: 'assistant',
          content: response.data.response.body,
          timestamp: new Date(),
        };
        setMessages((prev) => [...prev, assistantMessage]);
      } else {
        const errorMessage: Message = {
          id: (Date.now() + 1).toString(),
          role: 'assistant',
          content: 'Sorry, I encountered an error. Please try again.',
          timestamp: new Date(),
        };
        setMessages((prev) => [...prev, errorMessage]);
      }
    } catch (error) {
      const errorMessage: Message = {
        id: (Date.now() + 1).toString(),
        role: 'assistant',
        content: 'Sorry, I couldn\'t connect to the server. Please check your internet connection.',
        timestamp: new Date(),
      };
      setMessages((prev) => [...prev, errorMessage]);
    } finally {
      setIsSending(false);
    }
  }, [input, isSending, currentBeneficiary, getBeneficiaryContext]);

  const renderMessage = ({ item }: { item: Message }) => {
    const isUser = item.role === 'user';

    return (
      <View
        style={[
          styles.messageContainer,
          isUser ? styles.userMessageContainer : styles.assistantMessageContainer,
        ]}
      >
        {!isUser && (
          <View style={styles.avatarContainer}>
            <Text style={styles.avatarText}>J</Text>
          </View>
        )}
        <View
          style={[
            styles.messageBubble,
            isUser ? styles.userBubble : styles.assistantBubble,
          ]}
        >
          <Text
            style={[
              styles.messageText,
              isUser ? styles.userMessageText : styles.assistantMessageText,
            ]}
          >
            {item.content}
          </Text>
          <Text style={[styles.timestamp, isUser && styles.userTimestamp]}>
            {item.timestamp.toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' })}
          </Text>
        </View>
      </View>
    );
  };

  return (
    <SafeAreaView style={styles.container} edges={['top']}>
      {/* Header */}
      <View style={styles.header}>
        <View style={styles.headerInfo}>
          <View style={styles.headerAvatar}>
            <Text style={styles.headerAvatarText}>J</Text>
          </View>
          <View>
            <Text style={styles.headerTitle}>Julia AI</Text>
            <Text style={styles.headerSubtitle}>
              {isSending
                ? 'Typing...'
                : currentBeneficiary
                  ? `About ${currentBeneficiary.name}`
                  : 'Online'}
            </Text>
          </View>
        </View>
        <TouchableOpacity
          style={styles.headerButton}
          onPress={() => Alert.alert('Coming Soon', 'Chat settings will be available in a future update.')}
        >
          <Ionicons name="ellipsis-vertical" size={24} color={AppColors.textPrimary} />
        </TouchableOpacity>
      </View>

      {/* Messages */}
      <KeyboardAvoidingView
        style={styles.chatContainer}
        behavior={Platform.OS === 'ios' ? 'padding' : undefined}
        keyboardVerticalOffset={Platform.OS === 'ios' ? 90 : 0}
      >
        <FlatList
          ref={flatListRef}
          data={messages}
          keyExtractor={(item) => item.id}
          renderItem={renderMessage}
          contentContainerStyle={styles.messagesList}
          showsVerticalScrollIndicator={false}
          onContentSizeChange={() => flatListRef.current?.scrollToEnd({ animated: true })}
        />

        {/* Input */}
        <View style={styles.inputContainer}>
          <TextInput
            style={styles.input}
            placeholder="Type a message..."
            placeholderTextColor={AppColors.textMuted}
            value={input}
            onChangeText={setInput}
            multiline
            maxLength={1000}
            editable={!isSending}
            onSubmitEditing={handleSend}
          />
          <TouchableOpacity
            style={[styles.sendButton, (!input.trim() || isSending) && styles.sendButtonDisabled]}
            onPress={handleSend}
            disabled={!input.trim() || isSending}
          >
            <Ionicons
              name={isSending ? 'hourglass' : 'send'}
              size={20}
              color={input.trim() && !isSending ? AppColors.white : AppColors.textMuted}
            />
          </TouchableOpacity>
        </View>
      </KeyboardAvoidingView>
    </SafeAreaView>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: AppColors.surface,
  },
  header: {
    flexDirection: 'row',
    alignItems: 'center',
    justifyContent: 'space-between',
    paddingHorizontal: Spacing.md,
    paddingVertical: Spacing.sm,
    backgroundColor: AppColors.background,
    borderBottomWidth: 1,
    borderBottomColor: AppColors.border,
  },
  headerInfo: {
    flexDirection: 'row',
    alignItems: 'center',
  },
  headerAvatar: {
    width: 40,
    height: 40,
    borderRadius: BorderRadius.full,
    backgroundColor: AppColors.success,
    justifyContent: 'center',
    alignItems: 'center',
    marginRight: Spacing.sm,
  },
  headerAvatarText: {
    fontSize: FontSizes.lg,
    fontWeight: '600',
    color: AppColors.white,
  },
  headerTitle: {
    fontSize: FontSizes.lg,
    fontWeight: '600',
    color: AppColors.textPrimary,
  },
  headerSubtitle: {
    fontSize: FontSizes.sm,
    color: AppColors.success,
  },
  headerButton: {
    padding: Spacing.xs,
  },
  chatContainer: {
    flex: 1,
  },
  messagesList: {
    padding: Spacing.md,
    paddingBottom: Spacing.lg,
  },
  messageContainer: {
    flexDirection: 'row',
    marginBottom: Spacing.md,
    alignItems: 'flex-end',
  },
  userMessageContainer: {
    justifyContent: 'flex-end',
  },
  assistantMessageContainer: {
    justifyContent: 'flex-start',
  },
  avatarContainer: {
    width: 32,
    height: 32,
    borderRadius: BorderRadius.full,
    backgroundColor: AppColors.success,
    justifyContent: 'center',
    alignItems: 'center',
    marginRight: Spacing.xs,
  },
  avatarText: {
    fontSize: FontSizes.sm,
    fontWeight: '600',
    color: AppColors.white,
  },
  messageBubble: {
    maxWidth: '75%',
    padding: Spacing.sm + 4,
    borderRadius: BorderRadius.lg,
  },
  userBubble: {
    backgroundColor: AppColors.primary,
    borderBottomRightRadius: BorderRadius.sm,
  },
  assistantBubble: {
    backgroundColor: AppColors.background,
    borderBottomLeftRadius: BorderRadius.sm,
  },
  messageText: {
    fontSize: FontSizes.base,
    lineHeight: 22,
  },
  userMessageText: {
    color: AppColors.white,
  },
  assistantMessageText: {
    color: AppColors.textPrimary,
  },
  timestamp: {
    fontSize: FontSizes.xs,
    color: AppColors.textMuted,
    marginTop: Spacing.xs,
    alignSelf: 'flex-end',
  },
  userTimestamp: {
    color: 'rgba(255,255,255,0.7)',
  },
  inputContainer: {
    flexDirection: 'row',
    alignItems: 'flex-end',
    padding: Spacing.md,
    backgroundColor: AppColors.background,
    borderTopWidth: 1,
    borderTopColor: AppColors.border,
  },
  input: {
    flex: 1,
    backgroundColor: AppColors.surface,
    borderRadius: BorderRadius.xl,
    paddingHorizontal: Spacing.md,
    paddingVertical: Spacing.sm,
    fontSize: FontSizes.base,
    color: AppColors.textPrimary,
    maxHeight: 100,
    marginRight: Spacing.sm,
  },
  sendButton: {
    width: 44,
    height: 44,
    borderRadius: BorderRadius.full,
    backgroundColor: AppColors.primary,
    justifyContent: 'center',
    alignItems: 'center',
  },
  sendButtonDisabled: {
    backgroundColor: AppColors.surface,
  },
});