document.addEventListener("DOMContentLoaded", () => {
    // --- DOM Elements ---
    const joinScreen = document.getElementById("join-screen");
    const roomScreen = document.getElementById("room-screen");
    const roomNameInput = document.getElementById("room-name-input");
    const userNameInput = document.getElementById("user-name-input");
    const joinBtn = document.getElementById("join-btn");
    const errorMessage = document.getElementById("error-message");
    
    const roomHeader = document.getElementById("room-header");
    const userList = document.getElementById("user-list");
    const nowPlaying = document.getElementById("now-playing");
    const audioPlayer = document.getElementById("audio-player");
    const playPauseBtn = document.getElementById("play-pause-btn");
    const seekBar = document.getElementById("seek-bar");
    const timeDisplay = document.getElementById("time-display");
    
    const playlistElement = document.getElementById("playlist");
    const adminControls = document.getElementById("admin-controls");
    const fileInput = document.getElementById("file-input");
    const uploadBtn = document.getElementById("upload-btn");
    const uploadStatus = document.getElementById("upload-status");

    // --- State ---
    let ws = null;
    let roomName = "";
    let userName = "";
    let userId = "";
    let isAdmin = false;
    let isSeeking = false;

    // --- Event Listeners ---
    joinBtn.addEventListener("click", joinRoom);
    playPauseBtn.addEventListener("click", togglePlayPause);
    uploadBtn.addEventListener("click", uploadFile);
    seekBar.addEventListener("input", () => { isSeeking = true; });
    seekBar.addEventListener("change", () => {
        isSeeking = false;
        if (isAdmin) {
            const newPosition = parseFloat(seekBar.value);
            audioPlayer.currentTime = newPosition;
            sendMessage({ action: "seek", position: newPosition });
        }
    });
    audioPlayer.addEventListener("timeupdate", updateSeekBar);
    audioPlayer.addEventListener("loadedmetadata", updateSeekBar);


    // --- Functions ---
    function joinRoom() {
        roomName = roomNameInput.value.trim();
        userName = userNameInput.value.trim();

        if (!roomName || !userName) {
            errorMessage.textContent = "Room and User name are required.";
            return;
        }
        errorMessage.textContent = "";

        const wsProtocol = window.location.protocol === "https:" ? "wss://" : "ws://";
        const wsURL = `${wsProtocol}${window.location.host}/ws/${encodeURIComponent(roomName)}/${encodeURIComponent(userName)}`;

        ws = new WebSocket(wsURL);

        ws.onopen = () => {
            console.log("WebSocket connection established.");
            joinScreen.classList.remove("active");
            roomScreen.classList.add("active");
            roomHeader.textContent = `Room: ${roomName}`;
        };

        ws.onmessage = (event) => {
            const message = JSON.parse(event.data);
            handleWebSocketMessage(message);
        };

        ws.onerror = (error) => {
            console.error("WebSocket error:", error);
            errorMessage.textContent = "Failed to connect to the room.";
        };

        ws.onclose = () => {
            console.log("WebSocket connection closed.");
            alert("Connection lost. Please refresh the page to reconnect.");
            roomScreen.classList.remove("active");
            joinScreen.classList.add("active");
        };
    }

    function handleWebSocketMessage(message) {
        console.log("Received message:", message);
        switch (message.type) {
            case "initial_state":
                userId = message.user_id;
                updateState(message.payload);
                break;
            case "state_update":
                updateState(message.payload);
                break;
            case "user_list_update": // Handles only user changes without interrupting playback
                updateUI(message.payload);
                break;
        }
    }

    function updateState(state) {
        // Determine admin status before updating the UI
        isAdmin = state.admin_user_id === userId;
        
        updateUI(state);

        // Sync audio player
        const currentTrackUrl = state.current_track ? `/tmp/${encodeURIComponent(state.current_track)}` : "";
        if (state.current_track && audioPlayer.src.endsWith(currentTrackUrl) === false) {
             audioPlayer.src = currentTrackUrl;
        }
       
        if (!state.current_track) {
            audioPlayer.src = "";
            nowPlaying.textContent = "Now Playing: Nothing";
            return;
        }

        // Avoid race conditions by only applying server state if not currently seeking
        if (!isSeeking) {
            // Correct for latency by gently nudging the time
            const timeDifference = Math.abs(audioPlayer.currentTime - state.position);
            if (timeDifference > 1.5) { // Resync if more than 1.5s out of sync
                 audioPlayer.currentTime = state.position;
            }
        }
        
        if (state.is_playing && audioPlayer.paused) {
            audioPlayer.play().catch(e => console.error("Autoplay failed:", e));
        } else if (!state.is_playing && !audioPlayer.paused) {
            audioPlayer.pause();
        }
    }

    function updateUI(state) {
        // Update User List
        userList.innerHTML = "Users: " + Object.values(state.users)
            .map(u => `<span class="${state.admin_user_id === Object.keys(state.users).find(key => state.users[key] === u) ? 'admin-badge' : ''}">${u.name}${state.admin_user_id === Object.keys(state.users).find(key => state.users[key] === u) ? ' (Admin)' : ''}</span>`)
            .join(", ");

        // Update Now Playing
        nowPlaying.textContent = state.current_track ? `Now Playing: ${state.current_track}` : "Now Playing: Nothing";
        
        // Update Playlist
        playlistElement.innerHTML = "";
        state.playlist.forEach(track => {
            const li = document.createElement("li");
            li.textContent = track;
            if (track === state.current_track) {
                li.classList.add("active");
            }
            if (isAdmin) {
                const playTrackBtn = document.createElement("button");
                playTrackBtn.textContent = "Play";
                playTrackBtn.className = "play-track-btn";
                playTrackBtn.onclick = () => {
                    sendMessage({ action: "change_track", track: track });
                };
                li.appendChild(playTrackBtn);
            }
            playlistElement.appendChild(li);
        });

        // Toggle Admin Controls
        const isCurrentlyAdmin = state.admin_user_id === userId;
        if (isCurrentlyAdmin) {
            adminControls.style.display = "block";
            playPauseBtn.disabled = false;
            seekBar.disabled = false;
        } else {
            adminControls.style.display = "none";
            playPauseBtn.disabled = true;
            seekBar.disabled = true;
        }
        
        // Update Play/Pause button text
        playPauseBtn.textContent = state.is_playing ? "Pause" : "Play";
    }

    function togglePlayPause() {
        if (!isAdmin) return;
        const isPlaying = !audioPlayer.paused;
        const action = isPlaying ? "pause" : "play";
        sendMessage({ action: action, position: audioPlayer.currentTime });
    }

    function updateSeekBar() {
        if (!isSeeking) {
            seekBar.max = audioPlayer.duration || 0;
            seekBar.value = audioPlayer.currentTime;
        }
        timeDisplay.textContent = `${formatTime(audioPlayer.currentTime)} / ${formatTime(audioPlayer.duration || 0)}`;
    }

    function formatTime(seconds) {
        const minutes = Math.floor(seconds / 60);
        const secs = Math.floor(seconds % 60);
        return `${minutes}:${secs.toString().padStart(2, '0')}`;
    }

    async function uploadFile() {
        if (!fileInput.files.length) {
            uploadStatus.textContent = "Please select a file.";
            return;
        }
        const file = fileInput.files[0];
        const formData = new FormData();
        formData.append("file", file);

        uploadStatus.textContent = "Uploading...";
        try {
            const response = await fetch(`/upload/${encodeURIComponent(roomName)}`, {
                method: "POST",
                body: formData,
            });
            if (!response.ok) {
                const errorData = await response.json();
                throw new Error(errorData.detail || "Upload failed");
            }
            const result = await response.json();
            uploadStatus.textContent = `Upload successful: ${result.filename}`;
            fileInput.value = ""; // Reset file input
        } catch (error) {
            uploadStatus.textContent = `Error: ${error.message}`;
            console.error("Upload error:", error);
        }
    }

    function sendMessage(message) {
        if (ws && ws.readyState === WebSocket.OPEN) {
            ws.send(JSON.stringify(message));
        }
    }
});