import React, { useState, useMemo, useRef, useEffect } from 'react';
import { View, ScrollView, TextInput, KeyboardAvoidingView, Platform, TouchableOpacity } from 'react-native';
import RNSSE from 'react-native-sse';
import { useTheme } from '@/hooks/useTheme';
import { Screen } from '@/components/Screen';
import { ThemedText } from '@/components/ThemedText';
import { ThemedView } from '@/components/ThemedView';
import { FontAwesome6 } from '@expo/vector-icons';
import { createStyles } from './styles';

interface Message {
  role: 'user' | 'assistant';
  content: string;
  timestamp: number;
}

export default function ChatScreen() {
  const { theme, isDark } = useTheme();
  const styles = useMemo(() => createStyles(theme), [theme]);

  const [messages, setMessages] = useState<Message[]>(() => [{
    role: 'assistant',
    content: '你好！我是你的健康饮食和减脂顾问助手。我可以帮助你：\n\n• 制定科学的饮食计划\n• 分析食物营养成分\n• 提供减脂建议\n• 解答健康问题\n\n请问有什么可以帮助你的吗？',
    timestamp: Date.now(),
  }]);
  const [inputText, setInputText] = useState('');
  const [loading, setLoading] = useState(false);
  const scrollViewRef = useRef<ScrollView>(null);
  const sseRef = useRef<RNSSE | null>(null);

  useEffect(() => {
    return () => {
      if (sseRef.current) {
        sseRef.current.close();
      }
    };
  }, []);

  const sendMessage = async () => {
    if (!inputText.trim() || loading) return;

    const userMessage: Message = {
      role: 'user',
      content: inputText.trim(),
      timestamp: Date.now(),
    };

    setMessages((prev) => [...prev, userMessage]);
    setInputText('');
    setLoading(true);

    // 构建对话历史
    const conversationHistory = messages
      .slice(1) // 跳过欢迎消息
      .map((msg) => ({ role: msg.role, content: msg.content }));

    try {
      /**
       * 服务端文件：server/src/routes/ai-chat.ts
       * 接口：POST /api/v1/ai-chat/chat
       * Body 参数：message: string, conversationHistory?: Array<{role: string, content: string}>
       */
      const url = `${process.env.EXPO_PUBLIC_BACKEND_BASE_URL}/api/v1/ai-chat/chat`;

      const sse = new RNSSE(url, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
          message: inputText.trim(),
          conversationHistory,
        }),
      });

      sseRef.current = sse;

      let assistantContent = '';
      const assistantMessage: Message = {
        role: 'assistant',
        content: '',
        timestamp: Date.now(),
      };

      // 添加空的助手消息
      setMessages((prev) => [...prev, assistantMessage]);

      sse.addEventListener('message', (event: any) => {
        if (event.data === '[DONE]') {
          sse.close();
          setLoading(false);
          return;
        }

        try {
          const data = JSON.parse(event.data);
          if (data.content) {
            assistantContent += data.content;
            setMessages((prev) => {
              const updated = [...prev];
              updated[updated.length - 1] = {
                ...updated[updated.length - 1],
                content: assistantContent,
              };
              return updated;
            });
          }
        } catch (e) {
          console.error('Parse error:', e);
        }
      });

      sse.addEventListener('error', (error: any) => {
        console.error('SSE error:', error);
        sse.close();
        setLoading(false);
        setMessages((prev) => {
          const updated = [...prev];
          updated[updated.length - 1] = {
            ...updated[updated.length - 1],
            content: assistantContent || '抱歉，我遇到了一些问题，请稍后再试。',
          };
          return updated;
        });
      });

    } catch (error) {
      console.error('Send message error:', error);
      setLoading(false);
      setMessages((prev) => [
        ...prev,
        {
          role: 'assistant',
          content: '抱歉，发送消息失败，请检查网络连接。',
          timestamp: Date.now(),
        },
      ]);
    }
  };

  return (
    <Screen backgroundColor={theme.backgroundRoot} statusBarStyle={isDark ? 'light' : 'dark'}>
      <ThemedView level="root" style={styles.header}>
        <ThemedText variant="h4" color={theme.textPrimary}>
          AI 健康助手
        </ThemedText>
        <View style={styles.headerStatus}>
          <View style={[styles.statusDot, { backgroundColor: loading ? '#10B981' : '#9CA3AF' }]} />
          <ThemedText variant="caption" color={theme.textMuted}>
            {loading ? '正在回复...' : '在线'}
          </ThemedText>
        </View>
      </ThemedView>

      <ScrollView
        ref={scrollViewRef}
        style={styles.messagesContainer}
        contentContainerStyle={styles.messagesContent}
        onContentSizeChange={() => {
          scrollViewRef.current?.scrollToEnd({ animated: true });
        }}
      >
        {messages.map((message, index) => (
          <View
            key={index}
            style={[
              styles.messageWrapper,
              message.role === 'user' ? styles.userMessage : styles.assistantMessage,
            ]}
          >
            <ThemedView
              level="default"
              style={[
                styles.messageBubble,
                message.role === 'user'
                  ? { backgroundColor: theme.primary }
                  : { backgroundColor: theme.backgroundTertiary },
              ]}
            >
              <ThemedText
                variant="body"
                color={message.role === 'user' ? theme.buttonPrimaryText : theme.textPrimary}
                style={styles.messageText}
              >
                {message.content}
              </ThemedText>
            </ThemedView>
            <ThemedText variant="tiny" color={theme.textMuted} style={styles.messageTime}>
              {new Date(message.timestamp).toLocaleTimeString('zh-CN', {
                hour: '2-digit',
                minute: '2-digit',
              })}
            </ThemedText>
          </View>
        ))}

        {loading && messages[messages.length - 1]?.role === 'assistant' && (
          <View style={[styles.messageWrapper, styles.assistantMessage]}>
            <ThemedView level="default" style={[styles.messageBubble, { backgroundColor: theme.backgroundTertiary }]}>
              <View style={styles.typingIndicator}>
                <View style={[styles.typingDot, { backgroundColor: theme.textMuted }]} />
                <View style={[styles.typingDot, { backgroundColor: theme.textMuted }]} />
                <View style={[styles.typingDot, { backgroundColor: theme.textMuted }]} />
              </View>
            </ThemedView>
          </View>
        )}
      </ScrollView>

      <KeyboardAvoidingView
        behavior={Platform.OS === 'ios' ? 'padding' : undefined}
        keyboardVerticalOffset={Platform.OS === 'ios' ? 90 : 0}
      >
        <ThemedView level="root" style={styles.inputContainer}>
          <TextInput
            style={styles.input}
            placeholder="输入你的问题..."
            placeholderTextColor={theme.textMuted}
            value={inputText}
            onChangeText={setInputText}
            multiline
            maxLength={500}
            editable={!loading}
          />

          <TouchableOpacity
            style={[styles.sendButton, { opacity: !inputText.trim() || loading ? 0.5 : 1 }]}
            onPress={sendMessage}
            disabled={!inputText.trim() || loading}
          >
            <FontAwesome6
              name="paper-plane"
              size={20}
              color={theme.buttonPrimaryText}
            />
          </TouchableOpacity>
        </ThemedView>
      </KeyboardAvoidingView>
    </Screen>
  );
}