package parfact

import java.util.concurrent._

object Factorial{
  val CORES = 8;
  val executor = Executors.newCachedThreadPool()
  def done = executor.shutdown
  def future(x: =>BigInt) = executor.submit(new Callable[BigInt]{def call = x})
  def starts(i: Int, offset:Int) = Stream.range(1, i, i/CORES).map(_+offset)
  def partialFactorial(start:Int, end:Int) = Stream.range(start, end+1).map(x=>BigInt(x)).foldLeft(BigInt(1))((x,y)=>x * y);
  def pairsList(i: Int) = starts(i,0).zip(starts(i,-1).tail).toList
  def pairsListWithLast(i: Int) = pairsList(i)++List((pairsList(i).last._2+1,i))
  def partialFactorials(i: Int) = pairsListWithLast(i).map(x=>future({partialFactorial(x._1,x._2)})).map(_.get)
  def apply(i: Int) = partialFactorials(i).foldLeft(BigInt(1))((x,y)=>x * y)
}
object Main {

  def main(args: Array[String]): Unit = {
    val m = System.currentTimeMillis
    val x = Factorial(1000000)
    println((System.currentTimeMillis-m)/1000.0)
    Factorial.done
  }
}