Simple concept for a LiteCart REST API

api.php

<?php

  ob_start();

  include('includes/app_header.inc.php');

  try {

    $json = [];

    switch(true) {

    //--------------------------------------------------------------------
    // Return A List Of Orders
    //--------------------------------------------------------------------

      case (preg_match('#/orders$#', parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH))):

        if ($_SERVER['REQUEST_METHOD'] != 'GET') {
          throw new Exception('This resource does only support HTTP GET requests', 400);
        }

        $orders_query = database::query(
          "SELECT o.*, oi.name as order_status_name FROM ". DB_TABLE_ORDERS ." o
          LEFT JOIN ". DB_TABLE_ORDER_STATUSES_INFO ." oi on (oi.order_status_id = o.order_status_id and oi.language_code = '". database::input(language::$selected['code']) ."')
          ORDER BY o.date_created DESC;"
        );

        while ($row = database::fetch($orders_query)) {

          $json[] = [
            'id'            => $row['id'],
            'order_status'  => ['id' => $row['order_status_id'], 'name' => $row['order_status_name']],
            'total_amount'  => (float)$row['payment_due'],
            'total_weight'  => weight::convert($row['weight_total'], $row['weight_class'], 'kg'),
            'updated_at'    => date('c', strtotime($row['date_updated'])),
            'created_at'    => date('c', strtotime($row['date_created'])),
          ];
        }

        break;

    //--------------------------------------------------------------------
    // Return An Order
    //--------------------------------------------------------------------

      case (preg_match('#/orders/([0-9]+)$#', parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH), $matches)):

        $order_query = database::query(
          "SELECT id FROM ". DB_TABLE_ORDERS ."
          WHERE id = '". database::input($matches[1]) ."'
          LIMIT 1;"
        );

        if (!$row = database::fetch($order_query)) {
          throw new Exception('Could not find order in database', 404);
        }

        $order = new ent_order($row['id']);
        $json = $order->data;

        if ($_SERVER['REQUEST_METHOD'] == 'POST') {

          if (!$data = file_get_contents('php://input')) {
            throw new Exception('Invalid request body data', 400);
          }

          if (!$data = json_decode($data, true)) {
            throw new Exception('Invalid regquest json data', 400);
          }

          $order->data = array_replace($order->data, array_intersect_key($delivery_status, $order->data));
          $order->save();

          $json = ['status' => 'ok'];
        }

        break;

    //--------------------------------------------------------------------

      default:
        throw new Exception('Unknown resource', 404);
    }

    if ($buffer = ob_get_clean()) {
      throw new Exception('Unexpected buffer output: '. $buffer);
    }

    http_response_code(200);

  } catch (Exception $e) {

    http_response_code($e->getCode());
    $json = ['error' => $e->getMessage()];
  }

  //if (isset($_GET['pretty_print'])) {
    $json = json_encode($json, JSON_UNESCAPED_SLASHES | JSON_PRETTY_PRINT);
  //} else {
  //  $json = json_encode($json, JSON_UNESCAPED_SLASHES);
  //}

  if ($json === false) {
    $json = '{"error":"Unknown error while encoding JSON"}';
  }

  header('Date: '. date('r'));
  header('Content-Type: application/json; charset=UTF-8');
  header('Content-Length: '. strlen($json));

  echo $json;
  exit;