/// <summary>
/// Randomly selects from discrete options with unequal weights. The program state
/// shall be unchanged in the event of an exception.
/// </summary>
///
/// <typeparam name="T">The type of object to be selected.</typeparam>
/// <param name="weightedChoices">A list of (<typeparamref name="T"/>, double) tuples.
/// The first value of each tuple represents one of the choices, the second the weight
/// for that choice. The odds of selecting two choices equals the ratio of the weights
/// between them. All weights must be nonnegative, and at least one must be
/// positive.</param>
/// <returns>The selected object.</returns>
///
/// <exception cref="ArgumentException">Thrown if <c>weightedChoices</c> is
/// empty.</exception>
/// <exception cref="ArgumentOutOfRangeException">Thrown if any weight is
/// negative, or if no weight is positive.</exception>
internal static T weightedSample <T> (
System.Collections.Generic.IList <Tuple <T, double> > weightedChoices)
{
if (weightedChoices.Count == 0)
{
throw new ArgumentException(
Localizer.Format("#autoLOC_CustomAsteroids_ErrorNoSample"),
nameof(weightedChoices));
}
double norm = 0.0;
foreach (Tuple <T, double> choice in weightedChoices)
{
if (choice.Item2 < 0)
{
throw new ArgumentOutOfRangeException(
nameof(weightedChoices),
Localizer.Format("#autoLOC_CustomAsteroids_ErrorNegativeSample",
choice.Item2, choice.Item1));
}
norm += choice.Item2;
}
if (norm <= 0.0)
{
throw new ArgumentOutOfRangeException(
nameof(weightedChoices),
Localizer.Format("#autoLOC_CustomAsteroids_ErrorZeroSample"));
}
// important: no exceptions beyond this point
// assert: r is in [0, norm]
double threshold = norm * rng.NextDouble();
// If you stack up all the weights, at what level do you hit threshold?
double level = 0.0;
foreach (Tuple <T, double> choice in weightedChoices)
{
level += choice.Item2;
if (level >= threshold)
{
return(choice.Item1);
}
}
// Should only get here because of rounding error when threshold = norm
return(weightedChoices [weightedChoices.Count - 1].Item1);
}
/// <summary>
/// Uses criteria similar to ScenarioDiscoverableObjects to decide whether to create an
/// asteroid.
/// </summary>
protected override void checkSpawn()
{
if (areAsteroidsTrackable() &&
AsteroidManager.spawnRate() > 0.0 &&
countUntrackedAsteroids() < rng.Next(SPAWN_GROUP_MIN_LIMIT, SPAWN_GROUP_MAX_LIMIT))
{
if (rng.NextDouble() < 1.0 / (1.0 + SPAWN_ODDS_AGAINST))
{
spawnAsteroid();
}
else
{
Debug.Log("[StockalikeSpawner]: "
+ Localizer.Format("#autoLOC_CustomAsteroids_LogSpawnStock",
SPAWN_ODDS_AGAINST));
}
}
}