/* global __app_id, __firebase_config, __initial_auth_token */
import React, { useState, useEffect, useRef } from 'react';
import { initializeApp } from 'firebase/app';
import { getAuth, signInAnonymously, signInWithCustomToken, onAuthStateChanged } from 'firebase/auth';
import { getFirestore, collection, addDoc, query, orderBy, onSnapshot, serverTimestamp } from 'firebase/firestore';

// Global variables provided by the Canvas environment for Firebase setup.
// These variables are populated automatically at runtime by the platform.


function App() {
    // State to store chat messages. Each message object will include text, sender, and timestamp.
    const [messages, setMessages] = useState([]);
    // State to hold the current message being typed by the user.
    const [newMessage, setNewMessage] = useState('');
    // State to indicate if the bot is currently processing a response.
    const [isLoading, setIsLoading] = useState(false);
    // State to store the current user's ID for chat history.
    const [userId, setUserId] = useState(null);
    // State to hold the Firebase Firestore database instance.
    const [db, setDb] = useState(null);
    // State to hold the Firebase Auth instance.
    const [auth, setAuth] = useState(null);
    // State to track if Firebase authentication has been initialized and ready.
    const [isAuthReady, setIsAuthReady] = useState(false);
    // State to store any error messages for display.
    const [error, setError] = useState(null);

    // Ref to automatically scroll to the latest message in the chat.
    const messagesEndRef = useRef(null);

    // useEffect hook for Firebase initialization and authentication.
    // This runs once when the component mounts.
    useEffect(() => {
        try {
            // Get the application ID from the global variable, or use a default.
            const appId = typeof __app_id !== 'undefined' ? __app_id : 'default-app-id';
            // Parse the Firebase configuration from the global variable.
            const firebaseConfig = JSON.parse(typeof __firebase_config !== 'undefined' ? __firebase_config : '{}');

            // Log Firebase config for debugging, but don't expose sensitive info directly.
            // console.log("Firebase Config:", firebaseConfig);

            // Check if firebase config is valid.
            if (Object.keys(firebaseConfig).length === 0) {
                console.error("Firebase config is empty. Cannot initialize Firebase.");
                setError("Firebase setup incomplete. Please ensure your Firebase project is configured correctly in the Canvas environment.");
                return;
            }

            // Initialize Firebase app with the provided configuration.
            const app = initializeApp(firebaseConfig);
            // Get Firestore and Auth instances.
            const firestoreDb = getFirestore(app);
            const firebaseAuth = getAuth(app);

            // Set the Firebase instances in state.
            setDb(firestoreDb);
            setAuth(firebaseAuth);

            // Set up an authentication state change listener.
            // This ensures that the user is signed in before attempting Firestore operations.
            const unsubscribeAuth = onAuthStateChanged(firebaseAuth, async (user) => {
                if (user) {
                    // If a user is already signed in, set their UID.
                    setUserId(user.uid);
                    setIsAuthReady(true);
                } else {
                    try {
                        // If no user is signed in, try to sign in with a custom token
                        // provided by the environment, or anonymously if no token exists.
                        if (typeof __initial_auth_token !== 'undefined') {
                            await signInWithCustomToken(firebaseAuth, __initial_auth_token);
                        } else {
                            await signInAnonymously(firebaseAuth);
                        }
                    } catch (authError) {
                        // Log and display authentication errors.
                        console.error("Firebase Auth Error:", authError);
                        setError(`Authentication failed: ${authError.message}. Please reload.`);
                    }
                    setIsAuthReady(true); // Mark auth as ready even if anonymous or error occurred
                }
            });

            // Cleanup function: unsubscribe from the auth listener when the component unmounts.
            return () => unsubscribeAuth();
        } catch (initError) {
            // Catch and display errors during Firebase initialization.
            console.error("Error initializing Firebase:", initError);
            setError(`Failed to initialize application: ${initError.message}. This might be due to incorrect Firebase configuration.`);
        }
    }, []); // Empty dependency array means this effect runs only once on mount.

    // useEffect hook for real-time message fetching from Firestore.
    // This runs whenever `db` or `isAuthReady` state changes, ensuring Firebase is ready.
    useEffect(() => {
        // Proceed only if Firestore database and authentication are ready.
        if (db && isAuthReady) {
            // Construct the Firestore collection path for public chat data.
            const appId = typeof __app_id !== 'undefined' ? __app_id : 'default-app-id'; // Re-declare appId for scope
            const chatCollectionRef = collection(db, `artifacts/${appId}/public/data/chats`);
            // Create a query to order messages by timestamp.
            // Note: For large datasets or complex queries, Firestore may require composite indexes.
            // For this simple chat, 'timestamp' ordering should work without explicit index creation.
            const q = query(chatCollectionRef, orderBy('timestamp'));

            // Set up a real-time listener (onSnapshot) to get updates whenever messages change.
            const unsubscribeSnapshot = onSnapshot(q, (snapshot) => {
                // Map the document snapshots to an array of message objects.
                const fetchedMessages = snapshot.docs.map(doc => ({
                    id: doc.id, // Document ID as key
                    ...doc.data() // All other fields from the document
                }));
                // Update the messages state with the fetched messages.
                setMessages(fetchedMessages);
            }, (snapshotError) => {
                // Handle errors during real-time fetching.
                console.error("Error fetching messages:", snapshotError);
                setError(`Failed to load messages from Firestore: ${snapshotError.message}. Check your database rules.`);
            });

            // Cleanup function: unsubscribe from the snapshot listener when the component unmounts
            // or when `db` or `isAuthReady` changes (causing re-run of this effect).
            return () => unsubscribeSnapshot();
        }
    }, [db, isAuthReady]); // Dependencies: runs when 'db' or 'isAuthReady' changes.

    // useEffect hook to scroll to the bottom of the chat window whenever messages change.
    useEffect(() => {
        messagesEndRef.current?.scrollIntoView({ behavior: "smooth" });
    }, [messages]); // Dependency: runs whenever 'messages' state updates.

    // Function to handle sending a new message and triggering bot response.
    const handleSendMessage = async () => {
        // Prevent sending empty messages or if Firebase is not ready.
        if (!newMessage.trim() || !db || !userId) return;

        setIsLoading(true); // Set loading state to true.
        setError(null); // Clear any previous errors.

        // --- Step 1: Add the user's message to Firestore ---
        try {
            const appId = typeof __app_id !== 'undefined' ? __app_id : 'default-app-id'; // Re-declare appId for scope
            await addDoc(collection(db, `artifacts/${appId}/public/data/chats`), {
                userId: userId, // User ID of the sender.
                text: newMessage, // The message text.
                timestamp: serverTimestamp(), // Firestore's server-side timestamp for accurate ordering.
                sender: 'user', // Mark the sender as 'user'.
            });
            setNewMessage(''); // Clear the input field after sending.
        } catch (e) {
            // Log and display any errors during adding the user message.
            console.error("Error adding user message:", e);
            setError(`Failed to send message to database: ${e.message}`);
            setIsLoading(false); // Stop loading.
            return; // Stop execution if user message failed to send.
        }

        // --- Step 2: Generate bot response using Gemini API ---
        try {
            // Prepare chat history for the Gemini API call.
            const chatHistory = [{ role: "user", parts: [{ text: newMessage }] }];
            const payload = { contents: chatHistory };
            const apiKey = ""; // API key is automatically provided by Canvas runtime if empty.
            const apiUrl = `https://generativelanguage.googleapis.com/v1beta/models/gemini-2.0-flash:generateContent?key=${apiKey}`;

            // Make a POST request to the Gemini API.
            const response = await fetch(apiUrl, {
                method: 'POST',
                headers: { 'Content-Type': 'application/json' },
                body: JSON.stringify(payload)
            });

            // Check for HTTP errors from the API.
            if (!response.ok) {
                const errorData = await response.json();
                throw new Error(`API Error: ${response.status} ${response.statusText} - ${errorData.error?.message || 'Unknown error'}`);
            }

            // Parse the JSON response from the API.
            const result = await response.json();

            let botResponseText = "Sorry, I couldn't generate a response. Please try again.";
            // Extract the bot's response text from the API result.
            if (result.candidates && result.candidates.length > 0 &&
                result.candidates[0].content && result.candidates[0].content.parts &&
                result.candidates[0].content.parts.length > 0) {
                botResponseText = result.candidates[0].content.parts[0].text;
            } else {
                console.warn("Unexpected API response structure:", result);
            }

            // --- Step 3: Add the bot's response message to Firestore ---
            const appId = typeof __app_id !== 'undefined' ? __app_id : 'default-app-id'; // Re-declare appId for scope
            await addDoc(collection(db, `artifacts/${appId}/public/data/chats`), {
                userId: 'bot', // Mark the sender as 'bot'.
                text: botResponseText, // The bot's generated response.
                timestamp: serverTimestamp(), // Server-side timestamp.
                sender: 'bot', // Mark the sender as 'bot'.
            });

        } catch (apiError) {
            // Catch and display any errors during API call or adding bot message.
            console.error("Error generating bot response:", apiError);
            setError(`Bot response failed: ${apiError.message}. Check your internet or API key.`);
        } finally {
            setIsLoading(false); // Always stop loading after the process completes or fails.
        }
    };

    return (
        // Main container for the chat application, styled with Tailwind CSS for responsiveness.
        // Changed background to a blue gradient reminiscent of the sea/sky.
        <div className="min-h-screen bg-gradient-to-br from-blue-200 via-blue-400 to-blue-600 flex flex-col items-center justify-center p-4 font-inter">
            {/* Tailwind CSS and Inter font import for consistent styling */}
            <link href="https://cdn.tailwindcss.com" rel="stylesheet" />
            <style>
                {`
                @import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;600;700&display=swap');
                body { font-family: 'Inter', sans-serif; }
                /* Ensure all elements have rounded corners for a modern look */
                * { border-radius: 0.5rem; }
                `}
            </style>
            {/* Main chat box container - changed shadow and added a subtle border */}
            <div className="w-full max-w-2xl bg-white rounded-xl shadow-2xl border-2 border-yellow-500 flex flex-col h-[550px] max-h-[85vh] min-h-[400px]">
                {/* Chat header - changed gradient to a warm orange/red/yellow theme like a sunset/straw hat */}
                <header className="bg-gradient-to-r from-orange-600 via-red-500 to-yellow-500 text-white p-4 rounded-t-xl shadow-md text-center">
                    <h1 className="text-3xl font-extrabold text-shadow-lg drop-shadow-xl">HuggingChat Grand Line</h1>
                    {/* SVG for a simple straw hat icon, inline for easy integration */}
                    <svg className="mx-auto mt-2 h-8 w-8" fill="currentColor" viewBox="0 0 20 20" xmlns="http://www.w3.org/2000/svg">
                        <path fillRule="evenodd" d="M10 2a8 8 0 00-8 8c0 3.866 2.015 7.234 5 9.071V19a1 1 0 001 1h4a1 1 0 001-1v-1.929c2.985-1.837 5-5.205 5-9.071a8 8 0 00-8-8zm4 7a4 4 0 10-8 0h8z" clipRule="evenodd"></path>
                    </svg>
                    {userId && (
                        <p className="text-sm mt-1 opacity-80">Your Pirate Crew ID: <span className="font-mono">{userId}</span></p>
                    )}
                </header>

                {/* Message display area */}
                <div className="flex-1 overflow-y-auto p-4 space-y-4 bg-gray-100"> {/* Changed background for contrast */}
                    {messages.length === 0 && !isLoading && !error ? (
                        // Display a welcome message if no messages and not loading/error.
                        <div className="text-center text-gray-600 mt-10 text-lg font-semibold">
                            Ahoy, matey! Start your adventure chat!
                        </div>
                    ) : (
                        // Map through messages and display them.
                        messages.map((msg) => (
                            <div
                                key={msg.id}
                                // Align messages based on sender (user on right, bot on left).
                                className={`flex ${msg.sender === 'user' ? 'justify-end' : 'justify-start'}`}
                            >
                                <div
                                    className={`max-w-[75%] px-4 py-2 rounded-xl shadow-md ${
                                        msg.sender === 'user'
                                            ? 'bg-yellow-400 text-amber-900 rounded-br-none' // User messages: Straw Hat yellow, darker text
                                            : 'bg-blue-600 text-white rounded-bl-none' // Bot messages: Ocean blue
                                    }`}
                                >
                                    <p className="text-sm break-words">{msg.text}</p>
                                    <span className={`block text-xs text-right mt-1 ${msg.sender === 'user' ? 'text-amber-800 opacity-90' : 'text-blue-200 opacity-90'}`}>
                                        {/* Display message timestamp, converting Firebase timestamp to Date if available. */}
                                        {msg.timestamp?.toDate ? msg.timestamp.toDate().toLocaleTimeString([], { hour: '2-digit', minute: '2-digit' }) : 'Setting Sail...'}
                                    </span>
                                </div>
                            </div>
                        ))
                    )}
                    {/* Loading indicator for bot typing */}
                    {isLoading && (
                        <div className="flex justify-start">
                            <div className="max-w-[75%] px-4 py-2 rounded-xl rounded-bl-none bg-blue-600 text-white shadow-sm">
                                <div className="flex items-center space-x-2">
                                    {/* Typing animation */}
                                    <span className="relative flex h-3 w-3">
                                        <span className="animate-ping absolute inline-flex h-full w-full rounded-full bg-yellow-300 opacity-75"></span>
                                        <span className="relative inline-flex rounded-full h-3 w-3 bg-yellow-400"></span>
                                    </span>
                                    <p>Bot is charting a course...</p>
                                </div>
                            </div>
                        </div>
                    )}
                    {/* Error message display */}
                    {error && (
                        <div className="text-red-700 bg-red-200 p-3 rounded-md border border-red-300 text-sm font-bold">
                            <p className="font-semibold">Bounty on your head!</p>
                            <p>{error}</p>
                            <p className="mt-1 text-xs">If this persists, please ensure your Firebase project details are correctly configured within the Hugging Face Spaces environment, and check your internet connection.</p>
                        </div>
                    )}
                    {/* Empty div to enable scrolling to the bottom */}
                    <div ref={messagesEndRef} />
                </div>

                {/* Message input area */}
                <div className="p-4 border-t border-yellow-500 flex items-center bg-gray-50 rounded-b-xl">
                    <input
                        type="text"
                        className="flex-1 p-3 border border-blue-400 rounded-full focus:outline-none focus:ring-2 focus:ring-yellow-500 placeholder-blue-600"
                        placeholder="Send a message to the Grand Line..."
                        value={newMessage}
                        onChange={(e) => setNewMessage(e.target.value)}
                        // Allow sending message with Enter key.
                        onKeyPress={(e) => {
                            if (e.key === 'Enter' && !isLoading) {
                                handleSendMessage();
                            }
                        }}
                        // Disable input while loading or if Firebase is not ready.
                        disabled={isLoading || !isAuthReady || !db}
                    />
                    <button
                        onClick={handleSendMessage}
                        // Styled with a vibrant yellow/orange gradient for a 'fruit' like feel
                        className="ml-3 px-5 py-3 bg-gradient-to-r from-yellow-500 to-orange-500 text-amber-900 font-bold rounded-full shadow-lg hover:from-yellow-600 hover:to-orange-600 focus:outline-none focus:ring-2 focus:ring-yellow-500 focus:ring-offset-2 transition-all duration-200 ease-in-out disabled:opacity-50 disabled:cursor-not-allowed"
                        // Disable button while loading or if Firebase is not ready.
                        disabled={isLoading || !isAuthReady || !db}
                    >
                        Sail!
                    </button>
                </div>
            </div>
        </div>
    );
}

export default App;