<?php

namespace WP_CLI;

/**
 * Class Autoloader.
 *
 * This is a custom autoloader to replace the functionality that we would
 * normally get through the autoloader generated by Composer.
 *
 * We need this separate autoloader for the bootstrapping process, which happens
 * before the Composer autoloader(s) could be loaded.
 *
 * @package WP_CLI
 */
class Autoloader {

    /**
     * Array containing the registered namespace structures
     *
     * @var array
     */
    protected $namespaces = [];

    /**
     * Destructor for the Autoloader class.
     *
     * The destructor automatically unregisters the autoload callback function
     * with the SPL autoload system.
     */
    public function __destruct() {
        $this->unregister();
    }

    /**
     * Registers the autoload callback with the SPL autoload system.
     */
    public function register() {
        spl_autoload_register( [ $this, 'autoload' ] );
    }

    /**
     * Unregisters the autoload callback with the SPL autoload system.
     */
    public function unregister() {
        spl_autoload_unregister( [ $this, 'autoload' ] );
    }

    /**
     * Add a specific namespace structure with our custom autoloader.
     *
     * @param string  $root        Root namespace name.
     * @param string  $base_dir    Directory containing the class files.
     * @param string  $prefix      Prefix to be added before the class.
     * @param string  $suffix      Suffix to be added after the class.
     * @param boolean $lowercase   Whether the class should be changed to
     *                             lowercase.
     * @param boolean $underscores Whether the underscores should be changed to
     *                             hyphens.
     *
     * @return self
     */
    public function add_namespace(
        $root,
        $base_dir,
        $prefix = '',
        $suffix = '.php',
        $lowercase = false,
        $underscores = false
    ) {
        $this->namespaces[] = [
            'root'        => $this->normalize_root( (string) $root ),
            'base_dir'    => $this->add_trailing_slash( (string) $base_dir ),
            'prefix'      => (string) $prefix,
            'suffix'      => (string) $suffix,
            'lowercase'   => (bool) $lowercase,
            'underscores' => (bool) $underscores,
        ];

        return $this;
    }

    /**
     * The autoload function that gets registered with the SPL Autoloader
     * system.
     *
     * @param string $class The class that got requested by the spl_autoloader.
     */
    public function autoload( $class ) {

        // Iterate over namespaces to find a match.
        foreach ( $this->namespaces as $namespace ) {

            // Move on if the object does not belong to the current namespace.
            if ( 0 !== strpos( $class, $namespace['root'] ) ) {
                continue;
            }

            // Remove namespace root level to correspond with root filesystem, and
            // replace the namespace separator "\" by the system-dependent directory separator.
            $filename = str_replace(
                [ $namespace['root'], '\\' ],
                [ '', DIRECTORY_SEPARATOR ],
                $class
            );

            // Remove a leading backslash from the class name.
            $filename = $this->remove_leading_backslash( $filename );

            // Change to lower case if requested.
            if ( $namespace['lowercase'] ) {
                $filename = strtolower( $filename );
            }

            // Change underscores into hyphens if requested.
            if ( $namespace['underscores'] ) {
                $filename = str_replace( '_', '-', $filename );
            }

            // Add base_dir, prefix and suffix.
            $filepath = $namespace['base_dir']
                . $namespace['prefix']
                . $filename
                . $namespace['suffix'];

            // Throw an exception if the file does not exist or is not readable.
            if ( is_readable( $filepath ) ) {
                require_once $filepath;
            }
        }
    }

    /**
     * Normalize a namespace root.
     *
     * @param string $root Namespace root that needs to be normalized.
     *
     * @return string Normalized namespace root.
     */
    protected function normalize_root( $root ) {
        $root = $this->remove_leading_backslash( $root );

        return $this->add_trailing_backslash( $root );
    }

    /**
     * Remove a leading backslash from a string.
     *
     * @param string $string String to remove the leading backslash from.
     *
     * @return string Modified string.
     */
    protected function remove_leading_backslash( $string ) {
        return ltrim( $string, '\\' );
    }

    /**
     * Make sure a string ends with a trailing backslash.
     *
     * @param string $string String to check the trailing backslash of.
     *
     * @return string Modified string.
     */
    protected function add_trailing_backslash( $string ) {
        return rtrim( $string, '\\' ) . '\\';
    }

    /**
     * Make sure a string ends with a trailing slash.
     *
     * @param string $string String to check the trailing slash of.
     *
     * @return string Modified string.
     */
    protected function add_trailing_slash( $string ) {
        return rtrim( $string, '/\\' ) . '/';
    }
}