[WordPress]公開側からメディアを追加する

公開側で画像をアップロードして任意の投稿のアイキャッチに設定したい場合などに。

function insert_attachment($media, $post_id, $old_id, $title, $caption) {
    require_once(ABSPATH.'wp-admin/includes/image.php');
    require_once(ABSPATH.'wp-admin/includes/file.php');
    require_once(ABSPATH.'wp-admin/includes/media.php');
    $wp_upload_dir = wp_upload_dir();
    $post_data = [
            'post_title' => $title,
            'post_content' => $caption,
            'guid' => $wp_upload_dir['url'].'/'.basename($media)
    ];
    if ( $post_id && $thumbnail_id = media_handle_upload($media, $post_id, $post_data) ) {
        if ( $old_id ) {//旧アイキャッチを削除
            wp_delete_attachment($old_id, true);
        }
        //アイキャッチ設定
        set_post_thumbnail($post_id, $thumbnail_id);
        return true;
    }
    return false;
}

$media = 'file';
insert_attachment($media, $post_id, $old_id, $title, $caption);

$mediaはtype='file'のname

<form method="post" enctype="multipart/form-data">
    <input type="file" name="file">
</form>