/* If you want to trim down the number of highscores, then call
* KeepSomeHighscores() and pass in a filter that returns TRUE for
* the highscores you want to keep. If you pass in NULL, a default
* filter that keeps about half the highscores will be used. This
* algorithm automatically keeps all highscores that are younger
* than a week. It's appropriate to call this function after you've
* first loaded highscores in your game, for example.
*/
public void KeepSomeHighscores(HighscoreFilter toKeep)
{
Random r = new System.Random();
DateTime now = DateTime.Now;
List <Highscore> keepers = new List <Highscore>();
lock (highscores)
{
foreach (Highscore hs in highscores)
{
if (toKeep == null)
{
/* highscores from the last week are kept */
double threshold = 0;
/* highscores older than a week have a 2:3 chance */
if (hs.Date.Ticks < now.Ticks - 10000000L * 60L * 60L * 24L * 7L)
{
threshold = 0.333f;
}
/* highscores older than 13 weeks (approx 3 months) have a higher
* chance of going away.
*/
if (hs.Date.Ticks < now.Ticks - 10000000L * 60L * 60L * 24L * 7L * 13L)
{
threshold = 0.75f;
}
if (r.NextDouble() >= threshold)
{
keepers.Add(hs);
}
}
else
{
if (toKeep(hs))
{
keepers.Add(hs);
}
}
}
highscores.Clear();
highscores.AddRange(keepers);
}
if (HighscoresChanged != null)
{
HighscoresChanged(this, EventArgs.Empty);
}
}
/* Given all highscores, return the set of scores that fulfills the given
* query filter predicate.
*/
public IEnumerable <Highscore> QueryHighscores(HighscoreFilter filter)
{
// Painfully, I have to create a copy, because the array
// may be separately modified by the worker thread, and I
// can't hold the lock while yield returning
Highscore[] hslist;
lock (highscores)
{
hslist = highscores.ToArray();
}
foreach (Highscore hs in hslist)
{
if (filter(hs))
{
yield return(hs);
}
}
}
