public function install_package( $args = array() ) {
    global $wp_filesystem, $wp_theme_directories;

    $defaults = array(
      'source'                      => '', // Please always pass this.
      'destination'                 => '', // ...and this.
      'clear_destination'           => false,
      'clear_working'               => false,
      'abort_if_destination_exists' => true,
      'hook_extra'                  => array(),
    );

    $args = wp_parse_args( $args, $defaults );

    // These were previously extract()'d.
    $source            = $args['source'];
    $destination       = $args['destination'];
    $clear_destination = $args['clear_destination'];

    set_time_limit( 300 );

    if ( empty( $source ) || empty( $destination ) ) {
      return new WP_Error( 'bad_request', $this->strings['bad_request'] );
    }
    $this->skin->feedback( 'installing_package' );

    
/**
 * Filters the install response before the installation has started.
 *
 * Returning a truthy value, or one that could be evaluated as a WP_Error
 * will effectively short-circuit the installation, returning that value
 * instead.
 *
 * @since 2.8.0
 *
 * @param bool|WP_Error $response   Response.
 * @param array         $hook_extra Extra arguments passed to hooked filters.
 */
    $res = apply_filters( 'upgrader_pre_install', true, $args['hook_extra'] );

    if ( is_wp_error( $res ) ) {
      return $res;
    }

    // Retain the original source and destinations.
    $remote_source     = $args['source'];
    $local_destination = $destination;

    $source_files       = array_keys( $wp_filesystem->dirlist( $remote_source ) );
    $remote_destination = $wp_filesystem->find_folder( $local_destination );

    // Locate which directory to copy to the new folder. This is based on the actual folder holding the files.
    if ( 1 == count( $source_files ) && $wp_filesystem->is_dir( trailingslashit( $args['source'] ) . $source_files[0] . '/' ) ) {
      // Only one folder? Then we want its contents.
      $source = trailingslashit( $args['source'] ) . trailingslashit( $source_files[0] );
    } elseif ( count( $source_files ) == 0 ) {
      // There are no files?
      return new WP_Error( 'incompatible_archive_empty', $this->strings['incompatible_archive'], $this->strings['no_files'] );
    } else {
      // It's only a single file, the upgrader will use the folder name of this file as the destination folder.
      // Folder name is based on zip filename.
      $source = trailingslashit( $args['source'] );
    }

    
/**
 * Filters the source file location for the upgrade package.
 *
 * @since 2.8.0
 * @since 4.4.0 The $hook_extra parameter became available.
 *
 * @param string      $source        File source location.
 * @param string      $remote_source Remote file source location.
 * @param WP_Upgrader $this          WP_Upgrader instance.
 * @param array       $hook_extra    Extra arguments passed to hooked filters.
 */
    $source = apply_filters( 'upgrader_source_selection', $source, $remote_source, $this, $args['hook_extra'] );

    if ( is_wp_error( $source ) ) {
      return $source;
    }

    // Has the source location changed? If so, we need a new source_files list.
    if ( $source !== $remote_source ) {
      $source_files = array_keys( $wp_filesystem->dirlist( $source ) );
    }

    /*
		 * Protection against deleting files in any important base directories.
		 * Theme_Upgrader & Plugin_Upgrader also trigger this, as they pass the
		 * destination directory (WP_PLUGIN_DIR / wp-content/themes) intending
		 * to copy the directory into the directory, whilst they pass the source
		 * as the actual files to copy.
		 */
    $protected_directories = array( ABSPATH, WP_CONTENT_DIR, WP_PLUGIN_DIR, WP_CONTENT_DIR . '/themes' );

    if ( is_array( $wp_theme_directories ) ) {
      $protected_directories = array_merge( $protected_directories, $wp_theme_directories );
    }