Top 30 Songs using Custom Post Type

If I understood correctly, that Peak Postion is based on longest period the song was in same position (which I found odd), here’s what you could do:

• Have three meta fields
  :: song_meta_peak
  :: song_meta_weeks_now
  :: song_meta_weeks_peak

• First time song enters the list, you set peak meta to whatever the position is and both weeks_now and weeks_peak metas to 1

• Every week, if position is not changed, you add 1 to weeks_now meta

• Whenever the position changes you first check the weeks_now meta to find out how long the song has been in the previous position, and if it exceeds the weeks_peak you set peak meta to that previous position and override weeks_peak to match the weeks_now. After that you set weeks_now back to 1.

Hope that helps

Code Example

$oldWeeks = get_post_meta( $post_id, 'song_meta_weeks_now', true );
$oldWeeksPeak = get_post_meta( $post_id, 'song_meta_weeks_peak', true );

if ( POS. NOT CHANGED ) {
    update_post_meta( $post_id, 'song_meta_weeks_now', $oldWeeks + 1 );
} else {
    update_post_meta( $post_id, 'song_meta_weeks_now', 1 );
    if ( $oldWeeks > $oldWeeksPeak ) {
        update_post_meta( $post_id, 'song_meta_weeks_peak', $oldWeeks );
        update_post_meta( $post_id, 'song_meta_peak', PREVIOUS POS. );
    }
}