import { useState, useRef, useCallback } from 'react';
import {
  View,
  Text,
  TextInput,
  FlatList,
  TouchableOpacity,
  StyleSheet,
  KeyboardAvoidingView,
  Platform,
  ActivityIndicator,
  Alert,
} from 'react-native';
import { Ionicons } from '@expo/vector-icons';
import { useAuthContext } from '../../lib/AuthContext';
import * as api from '../../lib/api';

type Message = {
  id: string;
  role: 'user' | 'assistant';
  content: string;
  timestamp: Date;
};

export default function ChatScreen() {
  const { token } = useAuthContext();
  const [messages, setMessages] = useState<Message[]>([
    {
      id: '0',
      role: 'assistant',
      content: 'Ahoj! Jsem vas AI asistent pro Task Team. Mohu vam pomoci s ukoly, planovani a organizaci. Na co se chcete zeptat?',
      timestamp: new Date(),
    },
  ]);
  const [input, setInput] = useState('');
  const [sending, setSending] = useState(false);
  const flatListRef = useRef<FlatList>(null);

  const sendMessage = useCallback(async () => {
    if (!input.trim() || !token || sending) return;

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

    setMessages((prev) => [...prev, userMsg]);
    setInput('');
    setSending(true);

    try {
      const res = await api.sendChatMessage(token, userMsg.content);
      const aiMsg: Message = {
        id: (Date.now() + 1).toString(),
        role: 'assistant',
        content: res.data?.reply || 'Omlouvam se, nepodarilo se zpracovat odpoved.',
        timestamp: new Date(),
      };
      setMessages((prev) => [...prev, aiMsg]);
    } catch (err: any) {
      const errMsg: Message = {
        id: (Date.now() + 1).toString(),
        role: 'assistant',
        content: `Chyba: ${err.message}`,
        timestamp: new Date(),
      };
      setMessages((prev) => [...prev, errMsg]);
    } finally {
      setSending(false);
    }
  }, [input, token, sending]);

  const renderMessage = ({ item }: { item: Message }) => {
    const isUser = item.role === 'user';
    return (
      <View
        style={[
          styles.msgRow,
          isUser ? styles.msgRowUser : styles.msgRowAi,
        ]}
      >
        {!isUser && (
          <View style={styles.avatar}>
            <Ionicons name="sparkles" size={16} color="#3B82F6" />
          </View>
        )}
        <View
          style={[
            styles.bubble,
            isUser ? styles.bubbleUser : styles.bubbleAi,
          ]}
        >
          <Text
            style={[
              styles.bubbleText,
              isUser && { color: '#fff' },
            ]}
          >
            {item.content}
          </Text>
          <Text style={[styles.timestamp, isUser && { color: 'rgba(255,255,255,0.6)' }]}>
            {item.timestamp.toLocaleTimeString('cs-CZ', {
              hour: '2-digit',
              minute: '2-digit',
            })}
          </Text>
        </View>
      </View>
    );
  };

  return (
    <KeyboardAvoidingView
      style={styles.container}
      behavior={Platform.OS === 'ios' ? 'padding' : undefined}
      keyboardVerticalOffset={90}
    >
      <FlatList
        ref={flatListRef}
        data={messages}
        keyExtractor={(item) => item.id}
        renderItem={renderMessage}
        contentContainerStyle={styles.listContent}
        onContentSizeChange={() =>
          flatListRef.current?.scrollToEnd({ animated: true })
        }
      />

      <View style={styles.inputBar}>
        <TextInput
          style={styles.input}
          placeholder="Napiste zpravu..."
          value={input}
          onChangeText={setInput}
          multiline
          maxLength={2000}
          editable={!sending}
          onSubmitEditing={sendMessage}
          blurOnSubmit={false}
        />
        <TouchableOpacity
          style={[styles.sendBtn, (!input.trim() || sending) && styles.sendBtnDisabled]}
          onPress={sendMessage}
          disabled={!input.trim() || sending}
        >
          {sending ? (
            <ActivityIndicator size="small" color="#fff" />
          ) : (
            <Ionicons name="send" size={20} color="#fff" />
          )}
        </TouchableOpacity>
      </View>
    </KeyboardAvoidingView>
  );
}

const styles = StyleSheet.create({
  container: { flex: 1, backgroundColor: '#F8FAFC' },
  listContent: { padding: 12, paddingBottom: 4 },
  msgRow: { flexDirection: 'row', marginBottom: 12, maxWidth: '85%' },
  msgRowUser: { alignSelf: 'flex-end' },
  msgRowAi: { alignSelf: 'flex-start' },
  avatar: {
    width: 32,
    height: 32,
    borderRadius: 16,
    backgroundColor: '#EFF6FF',
    alignItems: 'center',
    justifyContent: 'center',
    marginRight: 8,
    marginTop: 4,
  },
  bubble: { borderRadius: 16, padding: 12, maxWidth: '100%' },
  bubbleUser: {
    backgroundColor: '#3B82F6',
    borderBottomRightRadius: 4,
  },
  bubbleAi: {
    backgroundColor: '#fff',
    borderBottomLeftRadius: 4,
    borderWidth: 1,
    borderColor: '#E2E8F0',
  },
  bubbleText: { fontSize: 15, lineHeight: 21, color: '#1E293B' },
  timestamp: { fontSize: 10, color: '#94A3B8', marginTop: 4, textAlign: 'right' },
  inputBar: {
    flexDirection: 'row',
    alignItems: 'flex-end',
    padding: 12,
    backgroundColor: '#fff',
    borderTopWidth: 1,
    borderTopColor: '#E2E8F0',
  },
  input: {
    flex: 1,
    borderWidth: 1,
    borderColor: '#E2E8F0',
    borderRadius: 20,
    paddingHorizontal: 16,
    paddingVertical: 10,
    fontSize: 15,
    maxHeight: 100,
    backgroundColor: '#F8FAFC',
  },
  sendBtn: {
    width: 42,
    height: 42,
    borderRadius: 21,
    backgroundColor: '#3B82F6',
    alignItems: 'center',
    justifyContent: 'center',
    marginLeft: 8,
  },
  sendBtnDisabled: { backgroundColor: '#94A3B8' },
});