<?php
session_start();

if (!isset($_SESSION['user_id'])) {
    http_response_code(401);
    echo json_encode(['error' => 'User not authenticated']);
    exit;
}

require_once 'db/config.php';

header('Content-Type: application/json');

$action = isset($_POST['action']) ? $_POST['action'] : ($_GET['action'] ?? '');
$current_user_id = $_SESSION['user_id'];

try {
    switch ($action) {
        case 'get_new_messages':
            getNewMessages();
            break;
        case 'send_message':
            sendMessage();
            break;
        case 'create_room':
            createRoom();
            break;
        case 'start_private_chat':
            startPrivateChat();
            break;
        default:
            throw new Exception("Invalid action.");
    }
} catch (Exception $e) {
    http_response_code(400);
    echo json_encode(['success' => false, 'error' => $e->getMessage()]);
}

function sendMessage() {
    global $current_user_id;
    
    $message = trim($_POST['message'] ?? '');
    $room_id = $_POST['room_id'] ?? null;

    if (empty($message) && empty($_FILES['attachment']['name'])) {
        throw new Exception("Message or attachment cannot be empty.");
    }
    if (!$room_id) {
        throw new Exception("Invalid room.");
    }

    $pdo = db();
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    $has_attachment = false;
    $file_data = null;

    // Handle file upload
    if (isset($_FILES['attachment']) && $_FILES['attachment']['error'] == UPLOAD_ERR_OK) {
        $file = $_FILES['attachment'];
        if ($file['size'] > 100 * 1024 * 1024) { // 100MB limit
            throw new Exception("File size exceeds the 100MB limit.");
        }

        $upload_dir = 'uploads/';
        if (!is_dir($upload_dir)) {
            mkdir($upload_dir, 0775, true);
        }
        $file_name = uniqid() . '-' . basename($file['name']);
        $file_path = $upload_dir . $file_name;

        if (move_uploaded_file($file['tmp_name'], $file_path)) {
            $has_attachment = true;
            $file_data = [
                'name' => $file['name'],
                'path' => $file_path,
                'size' => $file['size'],
                'type' => $file['type']
            ];
        } else {
            throw new Exception("Failed to upload file.");
        }
    }

    $pdo->beginTransaction();

    $stmt = $pdo->prepare("INSERT INTO messages (user_id, room_id, message) VALUES (?, ?, ?)");
    $stmt->execute([$current_user_id, $room_id, $message]);
    $message_id = $pdo->lastInsertId();

    if ($has_attachment && $file_data) {
        $stmt = $pdo->prepare("INSERT INTO files (message_id, original_name, file_path, file_size, mime_type) VALUES (?, ?, ?, ?, ?)");
        $stmt->execute([$message_id, $file_data['name'], $file_data['path'], $file_data['size'], $file_data['type']]);
    }

    $pdo->commit();
    echo json_encode(['success' => true]);
}


function getNewMessages() {
    global $current_user_id;
    $roomId = $_GET['room_id'] ?? 0;
    $lastMessageId = $_GET['last_message_id'] ?? 0;

    if (empty($roomId)) {
        echo json_encode([]);
        exit;
    }

    $pdo = db();
    
    // Check if user is a member of the room
    $stmt = $pdo->prepare("SELECT 1 FROM room_members WHERE room_id = ? AND user_id = ?");
    $stmt->execute([$roomId, $current_user_id]);
    if ($stmt->fetchColumn() === false) {
        // If not a member, check if it's a public room (no members defined)
        $stmt = $pdo->prepare("SELECT COUNT(*) FROM room_members WHERE room_id = ?");
        $stmt->execute([$roomId]);
        if ($stmt->fetchColumn() > 0) {
            http_response_code(403);
            throw new Exception("Access denied to room");
        }
    }

    // Poll for new messages
    $startTime = time();
    $timeout = 25; // 25 seconds timeout for long polling

    while (time() - $startTime < $timeout) {
        $stmt = $pdo->prepare("
            SELECT 
                m.id, m.message, m.created_at, u.username,
                f.original_name as file_name, f.file_path, f.file_size, f.mime_type as file_type
            FROM messages m
            JOIN users u ON m.user_id = u.id
            LEFT JOIN files f ON m.id = f.message_id
            WHERE m.room_id = ? AND m.id > ?
            ORDER BY m.id ASC
        ");
        $stmt->execute([$roomId, $lastMessageId]);
        $messages = $stmt->fetchAll(PDO::FETCH_ASSOC);

        if (!empty($messages)) {
            echo json_encode($messages);
            exit;
        }
        
        // Wait for a short period before polling again
        sleep(1);
    }

    // If no new messages after timeout, return empty array
    echo json_encode([]);
}

function createRoom() {
    global $current_user_id;
    $room_name = trim($_POST['room_name'] ?? '');
    if (empty($room_name)) {
        throw new Exception("Room name cannot be empty.");
    }
    $pdo = db();
    $stmt = $pdo->prepare("INSERT INTO rooms (name, created_by) VALUES (?, ?)");
    $stmt->execute([$room_name, $current_user_id]);
    $new_room_id = $pdo->lastInsertId();

    $stmt = $pdo->prepare("INSERT INTO room_members (room_id, user_id) VALUES (?, ?)");
    $stmt->execute([$new_room_id, $current_user_id]);

    echo json_encode(['success' => true, 'room_id' => $new_room_id]);
}

function startPrivateChat() {
    global $current_user_id;
    $other_user_id = $_POST['user_id'] ?? null;
    if (!$other_user_id || $other_user_id == $current_user_id) {
        throw new Exception("Invalid user ID.");
    }

    $pdo = db();
    // Check if a private room already exists between the two users
    $stmt = $pdo->prepare("
        SELECT r.id FROM rooms r
        JOIN room_members rm1 ON r.id = rm1.room_id
        JOIN room_members rm2 ON r.id = rm2.room_id
        WHERE r.is_private = 1
          AND rm1.user_id = ?
          AND rm2.user_id = ?
    ");
    $stmt->execute([$current_user_id, $other_user_id]);
    $room = $stmt->fetch();

    if ($room) {
        echo json_encode(['success' => true, 'room_id' => $room['id']]);
    } else {
        // Create a new private room
        $stmt = $pdo->prepare("INSERT INTO rooms (name, created_by, is_private) VALUES (?, ?, 1)");
        $stmt->execute(["Private Chat", $current_user_id]);
        $new_room_id = $pdo->lastInsertId();

        // Add both users to the new room
        $stmt = $pdo->prepare("INSERT INTO room_members (room_id, user_id) VALUES (?, ?), (?, ?)");
        $stmt->execute([$new_room_id, $current_user_id, $new_room_id, $other_user_id]);

        echo json_encode(['success' => true, 'room_id' => $new_room_id]);
    }
}