<?php
/**
 * PSR-4 autoloader.
 *
 * @package HostKhata
 */

namespace HostKhata;

defined( 'ABSPATH' ) || exit;

/**
 * Maps a namespace prefix to a base directory following PSR-4.
 *
 * The plugin ships its own loader so it works from a plain zip upload,
 * without Composer or a vendor directory.
 *
 * @since 0.1.0
 */
final class Autoloader {

	/**
	 * Namespace prefix, including the trailing backslash.
	 *
	 * @var string
	 */
	private $prefix;

	/**
	 * Base directory for the prefix, including the trailing separator.
	 *
	 * @var string
	 */
	private $base_dir;

	/**
	 * Constructor.
	 *
	 * @since 0.1.0
	 *
	 * @param string $prefix   Namespace prefix, e.g. `HostKhata\`.
	 * @param string $base_dir Directory that holds the prefixed classes.
	 */
	public function __construct( string $prefix, string $base_dir ) {
		$this->prefix   = trim( $prefix, '\\' ) . '\\';
		$this->base_dir = rtrim( $base_dir, '/\\' ) . DIRECTORY_SEPARATOR;
	}

	/**
	 * Creates a loader and registers it on the SPL autoload stack.
	 *
	 * @since 0.1.0
	 *
	 * @param string $prefix   Namespace prefix.
	 * @param string $base_dir Base directory.
	 * @return self
	 */
	public static function register( string $prefix, string $base_dir ): self {
		$loader = new self( $prefix, $base_dir );

		spl_autoload_register( array( $loader, 'load_class' ) );

		return $loader;
	}

	/**
	 * Loads the file for a class, when it belongs to this loader's prefix.
	 *
	 * @since 0.1.0
	 *
	 * @param string $class_name Fully qualified class name.
	 * @return void
	 */
	public function load_class( string $class_name ): void {
		$file = $this->get_file_path( $class_name );

		if ( null !== $file && is_readable( $file ) ) {
			require_once $file;
		}
	}

	/**
	 * Resolves the expected file path for a class.
	 *
	 * @since 0.1.0
	 *
	 * @param string $class_name Fully qualified class name.
	 * @return string|null Absolute path, or null when the class is outside the prefix.
	 */
	public function get_file_path( string $class_name ): ?string {
		$class_name = ltrim( $class_name, '\\' );

		if ( 0 !== strncmp( $this->prefix, $class_name, strlen( $this->prefix ) ) ) {
			return null;
		}

		$relative = substr( $class_name, strlen( $this->prefix ) );

		return $this->base_dir . str_replace( '\\', DIRECTORY_SEPARATOR, $relative ) . '.php';
	}
}