updated inde.php file

index.php

<?php

use \Psr\Http\Message\ServerRequestInterface as Request;
use \Psr\Http\Message\ResponseInterface as Response;
require '../vendor/autoload.php';

$app = new \Slim\App();

function availableLibraryId($id) {
    return (int)$id && $id > 0 && $id <= 5;
}
$app->get('/', function (Request $request, Response $response) {
    $response->getBody()->write("Welcome to the Adroit Library Demo.");
    return $response;
});
$app->group('/library', function () {
   
    $this->map(['GET'], '', function (Request $request, Response $response) {
        return $response->withJson(['message' => 'Welcome, please pick a libray']);
    });
    $this->get('/{id}', function (Request $request, Response $response, $args) {
        if(availableLibraryId($args['id'])) {
            return $response->withJson(['message' => "library ".$args['id']]);
        }
        return $response->withJson(['message' => 'library Not Found'], 404);    
    });
    $this->map(['POST', 'PUT', 'PATCH'], '/{id}', function (Request $request, Response $response, $args) {
        if(availableLibraryId($args['id'])) {
            return $response->withJson(['message' => "library ".$args['id']." updated successfully"]);
        }
        return $response->withJson(['message' => 'library Not Found'], 404);  
    });
    $this->delete('/{id}', function (Request $request, Response $response, $args) {
        if(availableLibraryId($args['id'])) {
            return $response->withJson(['message' => "library ".$args['id']." deleted successfully"]);
        }
        return $response->withJson(['message' => 'library Not Found'], 404);  
    });
});
$app->run();