<?php
session_start();
require_once __DIR__ . '/db/config.php';

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

$action = $_GET['action'] ?? '';

switch ($action) {
    case 'search_users':
        search_users();
        break;
    case 'start_conversation':
        start_conversation();
        break;
    case 'get_conversations':
        get_conversations();
        break;
    case 'get_messages':
        get_messages();
        break;
    case 'send_message':
        send_message();
        break;
    default:
        http_response_code(400);
        echo json_encode(['error' => 'Invalid action']);
        exit;
}

function search_users() {
    $term = $_GET['term'] ?? '';
    if (empty($term)) {
        echo json_encode([]);
        exit;
    }

    $pdo = db();
    $stmt = $pdo->prepare("SELECT id, username FROM users WHERE username LIKE ? AND id != ?");
    $stmt->execute(['%' . $term . '%', $_SESSION['user_id']]);
    $users = $stmt->fetchAll(PDO::FETCH_ASSOC);

    header('Content-Type: application/json');
    echo json_encode($users);
}

function start_conversation() {
    $recipient_id = $_POST['recipient_id'] ?? '';
    if (empty($recipient_id)) {
        http_response_code(400);
        echo json_encode(['error' => 'Recipient ID is required']);
        exit;
    }

    $user_id = $_SESSION['user_id'];

    $pdo = db();

    // Check if a conversation already exists between the two users
    $stmt = $pdo->prepare("
        SELECT c.id
        FROM conversations c
        JOIN conversation_participants cp1 ON c.id = cp1.conversation_id
        JOIN conversation_participants cp2 ON c.id = cp2.conversation_id
        WHERE cp1.user_id = ? AND cp2.user_id = ?
    ");
    $stmt->execute([$user_id, $recipient_id]);
    $conversation = $stmt->fetch(PDO::FETCH_ASSOC);

    if ($conversation) {
        // Conversation already exists
        header('Content-Type: application/json');
        echo json_encode(['conversation_id' => $conversation['id']]);
        exit;
    }

    // Create a new conversation
    $pdo->beginTransaction();
    try {
        $stmt = $pdo->prepare("INSERT INTO conversations () VALUES ()");
        $stmt->execute();
        $conversation_id = $pdo->lastInsertId();

        $stmt = $pdo->prepare("INSERT INTO conversation_participants (conversation_id, user_id) VALUES (?, ?), (?, ?)");
        $stmt->execute([$conversation_id, $user_id, $conversation_id, $recipient_id]);

        $pdo->commit();

        header('Content-Type: application/json');
        echo json_encode(['conversation_id' => $conversation_id]);
    } catch (Exception $e) {
        $pdo->rollBack();
        http_response_code(500);
        echo json_encode(['error' => 'Failed to create conversation']);
    }
}

function get_conversations() {
    $user_id = $_SESSION['user_id'];
    $pdo = db();

    $stmt = $pdo->prepare("
        SELECT c.id, u.username, u.id as user_id
        FROM conversations c
        JOIN conversation_participants cp ON c.id = cp.conversation_id
        JOIN users u ON u.id = cp.user_id
        WHERE c.id IN (
            SELECT conversation_id
            FROM conversation_participants
            WHERE user_id = ?
        ) AND cp.user_id != ?
    ");
    $stmt->execute([$user_id, $user_id]);
    $conversations = $stmt->fetchAll(PDO::FETCH_ASSOC);

    header('Content-Type: application/json');
    echo json_encode($conversations);
}

function get_messages() {
    $conversation_id = $_GET['conversation_id'] ?? '';
    if (empty($conversation_id)) {
        http_response_code(400);
        echo json_encode(['error' => 'Conversation ID is required']);
        exit;
    }

    $pdo = db();
    $stmt = $pdo->prepare("SELECT * FROM messages WHERE conversation_id = ? ORDER BY created_at ASC");
    $stmt->execute([$conversation_id]);
    $messages = $stmt->fetchAll(PDO::FETCH_ASSOC);

    header('Content-Type: application/json');
    echo json_encode($messages);
}

function send_message() {
    $conversation_id = $_POST['conversation_id'] ?? '';
    $message_text = $_POST['message_text'] ?? '';

    if (empty($conversation_id) || empty($message_text)) {
        http_response_code(400);
        echo json_encode(['error' => 'Conversation ID and message text are required']);
        exit;
    }

    $sender_id = $_SESSION['user_id'];

    $pdo = db();
    $stmt = $pdo->prepare("INSERT INTO messages (conversation_id, sender_id, message_text) VALUES (?, ?, ?)");
    $stmt->execute([$conversation_id, $sender_id, $message_text]);

    header('Content-Type: application/json');
    echo json_encode(['success' => true]);
}