wp_ajax_send_link_to_editor

function wp_ajax_send_link_to_editor() {
	global $post, $wp_embed;

	check_ajax_referer( 'media-send-to-editor', 'nonce' );

	$src = wp_unslash( $_POST['src'] );
	if ( ! $src ) {
		wp_send_json_error();
	}

	if ( ! strpos( $src, '://' ) ) {
		$src = 'http://' . $src;
	}

	$src = esc_url_raw( $src );
	if ( ! $src ) {
		wp_send_json_error();
	}

	$link_text = trim( wp_unslash( $_POST['link_text'] ) );
	if ( ! $link_text ) {
		$link_text = wp_basename( $src );
	}

	$post = get_post( isset( $_POST['post_id'] ) ? $_POST['post_id'] : 0 );

	// Ping WordPress for an embed.
	$check_embed = $wp_embed->run_shortcode( '[embed]' . $src . '[/embed]' );

	// Fallback that WordPress creates when no oEmbed was found.
	$fallback = $wp_embed->maybe_make_link( $src );

	if ( $check_embed !== $fallback ) {
		// TinyMCE view for [embed] will parse this.
		$html = '[embed]' . $src . '[/embed]';
	} elseif ( $link_text ) {
		$html = '<a href="' . esc_url( $src ) . '">' . $link_text . '</a>';
	} else {
		$html = '';
	}

	// Figure out what filter to run:
	$type = 'file';
	$ext  = preg_replace( '/^.+?\.([^.]+)$/', '$1', $src );
	if ( $ext ) {
		$ext_type = wp_ext2type( $ext );
		if ( 'audio' === $ext_type || 'video' === $ext_type ) {
			$type = $ext_type;
		}
	}

	/** This filter is documented in wp-admin/includes/media.php */
	$html = apply_filters( "{$type}_send_to_editor_url", $html, $src, $link_text );

	wp_send_json_success( $html );
}