/// <summary>
/// Either retrieves from memory, generates, or a combination of both, all primes upto
/// a given value
/// </summary>
/// <param name="target">The maximum limit on the value of primes</param>
/// <returns>A list of all primes less than or equal to the provided target</returns>
public IList <int> GetPrimesTo(int target)
{
//If there's no stored primes, generate them all
if (!Primes.Any())
{
Primes = _generator.GeneratePrimesTo(target).ToList();
}
else
{
//Is the last generated prime greater than the target
var lastPrime = Primes.Last();
if (lastPrime > target)
{
//Just return the primes upto that point
return(Primes.Where(p => p <= target).ToList());
}
//Add the primes between the current maximum and the target
Primes.AddRange(_generator.GeneratePrimesBetween(lastPrime + 1, target));
}
return(Primes.ToList());
}
