import React, { useState, useRef, useEffect } from 'react';
import { Send, Bot, User, Loader2, AlertTriangle } from 'lucide-react';
import { createFitnessChat } from '../services/geminiService';
import { WorkoutSession, Language, UserProfile, WorkoutPlan } from '../types';
import { Chat, GenerateContentResponse } from '@google/genai';
import { t } from '../services/i18n';

interface AICoachProps {
  history: WorkoutSession[];
  userProfile?: UserProfile;
  plans?: WorkoutPlan[];
  lang: Language;
}

interface Message {
  id: string;
  role: 'user' | 'model';
  text: string;
}

const AICoach: React.FC<AICoachProps> = ({ history, userProfile, plans, lang }) => {
  const [messages, setMessages] = useState<Message[]>([
    { id: 'intro', role: 'model', text: t('ai_intro', lang) }
  ]);
  const [input, setInput] = useState('');
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);
  const chatSessionRef = useRef<Chat | null>(null);
  const messagesEndRef = useRef<HTMLDivElement>(null);

  useEffect(() => {
    try {
      const chat = createFitnessChat(history, lang, userProfile, plans);
      if (chat) {
        chatSessionRef.current = chat;
      } else {
        setError(t('ai_error', lang));
      }
    } catch (err) {
      setError("Failed to initialize AI");
    }
  }, [history, lang, userProfile, plans]);

  const scrollToBottom = () => {
    messagesEndRef.current?.scrollIntoView({ behavior: "smooth" });
  };

  useEffect(() => {
    scrollToBottom();
  }, [messages]);

  const handleSend = async () => {
    if (!input.trim() || !chatSessionRef.current || loading) return;

    const userMsg: Message = { id: crypto.randomUUID(), role: 'user', text: input };
    setMessages(prev => [...prev, userMsg]);
    setInput('');
    setLoading(true);

    try {
      const result: GenerateContentResponse = await chatSessionRef.current.sendMessage(userMsg.text);
      const text = result.text;

      const aiMsg: Message = {
        id: crypto.randomUUID(),
        role: 'model',
        text: text || "Error generating response."
      };
      setMessages(prev => [...prev, aiMsg]);
    } catch (err) {
      console.error(err);
      let errorText = 'Connection error.';
      if (err instanceof Error) {
        try {
          const json = JSON.parse(err.message);
          if (json.error) errorText = json.error;
          else errorText = err.message;
        } catch {
          errorText = err.message;
        }
      }
      setMessages(prev => [...prev, { id: crypto.randomUUID(), role: 'model', text: errorText }]);
    } finally {
      setLoading(false);
    }
  };

  if (error) {
    return (
      <div className="flex flex-col items-center justify-center h-full p-6 text-center text-on-surface-variant">
        <AlertTriangle size={48} className="text-error mb-4" />
        <p>{error}</p>
      </div>
    )
  }

  return (
    <div className="flex flex-col h-full bg-surface">
      {/* Header */}
      <div className="p-4 bg-surface-container shadow-elevation-1 flex items-center gap-3 z-10">
        <div className="w-10 h-10 rounded-full bg-secondary-container flex items-center justify-center">
          <Bot size={20} className="text-on-secondary-container" />
        </div>
        <h2 className="text-xl font-normal text-on-surface">{t('ai_expert', lang)}</h2>
      </div>

      {/* Messages */}
      <div className="flex-1 overflow-y-auto p-4 space-y-4 pb-4">
        {messages.map((msg) => (
          <div key={msg.id} className={`flex ${msg.role === 'user' ? 'justify-end' : 'justify-start'}`}>
            <div className={`max-w-[85%] p-4 rounded-[20px] text-sm leading-relaxed shadow-sm ${msg.role === 'user'
              ? 'bg-primary text-on-primary rounded-br-none'
              : 'bg-surface-container-high text-on-surface border border-outline-variant/20 rounded-bl-none'
              }`}>
              {msg.text}
            </div>
          </div>
        ))}
        {loading && (
          <div className="flex justify-start">
            <div className="bg-surface-container-high px-4 py-3 rounded-[20px] rounded-bl-none flex gap-2 items-center text-on-surface-variant text-sm">
              <Loader2 size={16} className="animate-spin" />
              {t('ai_typing', lang)}
            </div>
          </div>
        )}
        <div ref={messagesEndRef} />
      </div>

      {/* Input */}
      <div className="p-4 bg-surface-container mt-auto">
        <div className="flex gap-2 items-center bg-surface-container-high rounded-full border border-outline-variant px-2 py-1">
          <input
            type="text"
            className="flex-1 bg-transparent border-none px-4 py-3 text-on-surface focus:outline-none placeholder-on-surface-variant"
            placeholder={t('ai_placeholder', lang)}
            value={input}
            onChange={(e) => setInput(e.target.value)}
            onKeyDown={(e) => e.key === 'Enter' && handleSend()}
          />
          <button
            onClick={handleSend}
            disabled={loading || !input.trim()}
            className="w-10 h-10 bg-primary rounded-full flex items-center justify-center text-on-primary hover:opacity-90 disabled:opacity-50 transition-opacity shrink-0"
          >
            <Send size={18} />
          </button>
        </div>
      </div>
    </div>
  );
};

export default AICoach;