document.addEventListener('DOMContentLoaded', () => {
    const leaderboardBody = document.getElementById('leaderboard-body');
    const loadingIndicator = document.getElementById('loading-indicator');
    const lastUpdatedElement = document.getElementById('last-updated');
    const modal = document.getElementById('code-modal');
    const modalUsername = document.getElementById('modal-username');
    const modalCode = document.getElementById('modal-code');
    const closeModalButton = document.querySelector('.close-button');

    // Fetch from the FastAPI backend endpoint
    const API_URL = '/api/leaderboard';
    const REFRESH_INTERVAL_MS = 60 * 1000; // 60 seconds

    async function fetchData() {
        try {
            // Fetch directly from our backend API
            const response = await fetch(API_URL);
            if (!response.ok) {
                // Try to get error message from backend if available
                let errorMsg = `HTTP error! status: ${response.status}`;
                try {
                    const errorData = await response.json();
                    errorMsg = errorData.detail || errorMsg;
                } catch (e) { /* Ignore if response is not JSON */ }
                throw new Error(errorMsg);
            }
            const data = await response.json();
            // The data is expected to be the already sorted list of objects
            return data;
        } catch (error) {
            console.error("Failed to fetch leaderboard data:", error);
            lastUpdatedElement.textContent = `Error: ${error.message}`; // Display error
            return null; // Return null to indicate failure
        }
    }

    // No sorting needed here - backend does it
    // function sortData(data) { ... } // REMOVED

    function formatTimestamp(isoString) {
        // Keep this helper function
        try {
            const date = new Date(isoString);
            return date.toISOString().slice(0, 19).replace('T', ' ');
        } catch (e) {
            return 'Invalid Date';
        }
    }

    function renderLeaderboard(leaderboardData) {
        // Clear previous content
        leaderboardBody.innerHTML = '';

        if (!leaderboardData || leaderboardData.length === 0) {
             // Check if the loading indicator is still displayed, means fetch failed on load
            if (loadingIndicator.style.display !== 'none') {
                leaderboardBody.innerHTML = '<div class="leaderboard-row" style="justify-content: center; color: #aaa;">No data available or failed to load. Check logs.</div>';
            } else {
                 // If fetch failed during refresh, keep old data and show error in footer? Or clear?
                 // Let's clear for now and rely on error message in footer.
                 leaderboardBody.innerHTML = '<div class="leaderboard-row" style="justify-content: center; color: #aaa;">Failed to refresh data.</div>';
            }
            return;
        }

        leaderboardData.forEach((entry, index) => {
            const rank = index + 1;
            const row = document.createElement('div');
            row.className = 'leaderboard-row';
            row.setAttribute('data-rank', rank);

            row.innerHTML = `
                <div class="rank">#${rank}</div>
                <div class="username" title="${entry.username}">${entry.username}</div>
                <div class="score">${entry.score} pts</div>
                <div class="timestamp">${formatTimestamp(entry.timestamp)}</div>
                <div class="code-action">
                    <button class="view-code-btn" data-username="${entry.username}">View</button>
                </div>
            `;

            const button = row.querySelector('.view-code-btn');
            button._codeData = entry.code; // Store code directly
            button.addEventListener('click', handleViewCodeClick);

            leaderboardBody.appendChild(row);
        });
    }

    function handleViewCodeClick(event) {
        const button = event.currentTarget;
        const username = button.getAttribute('data-username');
        const code = button._codeData;
        showCodeModal(username, code);
    }

     function showCodeModal(username, code) {
        modalUsername.textContent = `Code from ${username}`;
        modalCode.textContent = code || '// No code submitted or available';

        if (typeof hljs !== 'undefined') {
            modalCode.className = 'language-python';
            hljs.highlightElement(modalCode);
        }
        modal.style.display = 'block';
    }

    function hideCodeModal() {
        modal.style.display = 'none';
        modalCode.textContent = '';
        modalUsername.textContent = '';
    }

    async function updateLeaderboard() {
         if (!leaderboardBody.hasChildNodes()) {
             loadingIndicator.style.display = 'flex';
         } else {
             lastUpdatedElement.textContent = 'Updating...';
         }

        const leaderboardData = await fetchData(); // Fetches already sorted data

        loadingIndicator.style.display = 'none'; // Hide loading indicator regardless of success/fail

        if (leaderboardData) {
            renderLeaderboard(leaderboardData);
             // Only update timestamp on success
             lastUpdatedElement.textContent = `Last updated: ${new Date().toLocaleTimeString()}`;
        } else {
            // Error occurred, message already set in fetchData
            // Optionally render empty state if needed
             if (!leaderboardBody.hasChildNodes()) {
                  renderLeaderboard(null); // Show 'No data' message if initial load failed
             }
        }
    }

    // --- Event Listeners ---
    closeModalButton.addEventListener('click', hideCodeModal);
    window.addEventListener('click', (event) => {
        if (event.target === modal) {
            hideCodeModal();
        }
    });

    // --- Initial Load and Auto-Refresh ---
    updateLeaderboard(); // Initial load
    setInterval(updateLeaderboard, REFRESH_INTERVAL_MS); // Refresh every 60 seconds
});