<?php

$arr = ['Массив' =>
  [
    'purchases' => 'Покупки',
    'food' 	=> 'Еда',
    'vegetables' => 'Овощи',
    'carrot' 	=> 'Морковка',
  ]
];


$newArr = [];
$prevUri = "";
foreach ( $arr['Массив'] as $key => $name ) {
	$uri = $prevUri ? "{$prevUri}/{$key}" : $key;
	$newArr['Массив'][$key] = [
		'name' => $name,
		'uri' => $uri,
	];
	$prevUri = $uri;
}

print_r($newArr);

Array
(
    [Массив] => Array
        (
            [purchases] => Array
                (
                    [name] => Покупки
                    [uri] => purchases
                )

            [food] => Array
                (
                    [name] => Еда
                    [uri] => purchases/food
                )

            [vegetables] => Array
                (
                    [name] => Овощи
                    [uri] => purchases/food/vegetables
                )

            [carrot] => Array
                (
                    [name] => Морковка
                    [uri] => purchases/food/vegetables/carrot
                )

        )

)

$data = "данные";
$path = __DIR__ . "/pathname/1/index.php";

$dirPath = pathinfo($path, PATHINFO_DIRNAME);
if ( !file_exists($dirPath) && !mkdir($dirPath, 0777, true) ) {
	// @TODO добавьте exception или выброс ошибки
}

if ( file_put_contents($path, $data) === false ) {
	// @TODO добавьте exception или выброс ошибки
}

<?php

$poster = null;
$list = [
	"https://i.ytimg.com/vi/".$video_id."/hqdefault.jpg",
	"https://i.ytimg.com/vi/".$video_id."/maxresdefault.jpg"
];

foreach ( $list as $url ) {
	$headers = get_headers($url, true);
	if ( !empty($headers[0]) && preg_match('#200|302#', $headers[0]) ) {
		$poster = $url;
		break;
	}
}

var_dump($poster);