WordPress - insert image as Markdown Extra

I'm getting a bit angry on the Markdown plugins of WordPress¹: all of them will store the text as HTML, while the original goal for me would be to store in Markdown, for future readability. With Parsedown²

• a persistent WordPress Object cache³ parsing on the fly is really not an issue.

So as always, I need to come up with a solution - a hack if that sounds better - to store posts in Markdown Extra⁴. The nasty part is the editor, especially with media, so I decided chop it into pieces.

This is for images only, since video or audio is not supported by any of the Markdown flavours I know.

<?php

add_filter( 'post_thumbnail_html', 'rebuild_media_string', 10 );
add_filter( 'image_send_to_editor', 'rebuild_media_string', 10 );

function preg_value ( $string, $pattern, $index = 1 ) {
    preg_match( $pattern, $string, $results );
    if ( isset ( $results[ $index ] ) && !empty ( $results [ $index ] ) )
        return $results [ $index ];
    else
        return false;
}

function rebuild_media_string( $str ) {
    if ( strstr ( $str, '<img' ) )
        $src = preg_value ( $str, '/src="([^"]+)"/' );
        $title = preg_value ( $str, '/title="([^"]+)"/' );
        $alt = preg_value ( $str, '/alt="([^"]+)"/' );
        if ( empty ( $alt ) && !empty ( $title ) ) $alt = $title;
        $wpid = preg_value ( $str, '/wp-image-(\d*)/' );
        $src = preg_value ( $str, '/src="([^"]+)"/' );
        $cl = preg_value ( $str, '/class="([^"]+)?(align(left|right|center))([^"]+)?"/', 2 );

        $img = '!['.$alt.']('. $src .' '. $title .'){#img-'. $wpid .' .'.$cl.'}';
        return $img;
    }
    else {
        return $str;
    }
}

(Oh, by the way: this entry was written by Peter Molnar, and originally posted on petermolnar dot net.)