I now keep track of the last 15 songs played. If a song with the same
(artist, title) as one of the songs in the list attempts to play, we
skip it.
Songs with a negative score have a (20 * score) + 100 per cent chance of
playing. When score is -5, the song should never play.
I used to try to find a song 5 times before giving up and playing the
song with the current id. I have upped the threshold to 15.
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