// 添加小工具
if ( function_exists('register_sidebar') ) {
	register_sidebar(array(
		'name'          => '正文小工具',
		'id'            => 'inline-content',
		'description'   => '用于在正文中添加小工具',
		'before_widget' => '<aside id="%1$s" class="widget inline-content %2$s">',
		'after_widget'  => '<div class="clear"></div></aside>',
		'before_title'  => '<h3 class="widget-title">',
		'after_title'   => '</h3>',
	));
}

// 添加到正文第二个段落下面，修改数字2可调整位置
add_filter( 'the_content', 'insert_content_filter' );
function insert_content_filter( $content ) {
	ob_start();
	$sidebar = dynamic_sidebar('inline-content');
	$new_content = ob_get_clean();
	if ( is_single() && ! is_admin() ) {
		return insert_content( $new_content, 2, $content );
	}
	return $content;
}

// 添加到正文段落中
function insert_content( $new_content, $paragraph_id, $content ) {
	$closing_p = '</p>';
	$paragraphs = explode( $closing_p, $content );
	foreach ($paragraphs as $index => $paragraph) {
		if ( trim( $paragraph ) ) {
			$paragraphs[$index] .= $closing_p;
		}
		if ( $paragraph_id == $index + 1 ) {
			$paragraphs[$index] .= $new_content;
		}
	}
	return implode( '', $paragraphs );
}