Implement PSR-4 compliant class autoloader

includes/autoload.php

@@ -0,0 +1,41 @@
+<?php
+/**
+ * PSR-4 compliant class autoloader
+ *
+ * @see https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader.md
+ * @link https://www.php.net/manual/en/function.spl-autoload-register.php
+ * @param string $class fully-qualified class name
+ * @return void
+ */
+spl_autoload_register(function ($class) {
+
+    // project-specific namespace prefix
+    $prefix = '';
+
+    // base directory for the namespace prefix
+    $base_dir = 'src/';
+
+    // normalize the base directory with a trailing separator
+    $base_dir = rtrim($base_dir, DIRECTORY_SEPARATOR) . '/';
+
+    // does the class use the namespace prefix?
+    $len = strlen($prefix);
+    if (strncmp($prefix, $class, $len) !== 0) {
+        // no, move to the next registered autoloader
+        return;
+    }
+
+    // get the relative class name
+    $relative_class = substr($class, $len);
+
+    // replace the namespace prefix with the base directory, replace namespace
+    // separators with directory separators in the relative class name, append
+    // with .php
+    $file = $base_dir . str_replace('\\', '/', $relative_class) . '.php';
+
+    // if the file exists, require it
+    if (file_exists($file)) {
+        require $file;
+    }
+});
+