Interval.scala

import scala.math.Ordering.Implicits.infixOrderingOps

/** simple interval [min, max) (or >= min if max is empty) */
final class Interval[A](val min: A, val max: Option[A])(implicit num: Numeric[A]) extends Serializable {
  /** if max nonEmpty, then max > min */
  require(testRightBound(max, min))

  def in(value: A): Boolean =
    value >= min && testRightBound(max, value)

  def +(value: A): Interval[A] =
    new Interval(num.plus(min, value), max.map(num.plus(_, value)))

  private def testRightBound(max: Option[A], value: A): Boolean =
    max.isEmpty || max.exists(_ > value)

  private def canEqual(a: Any): Boolean = a.isInstanceOf[Interval[_]]

  override def equals(that: Any): Boolean =
    that match {
      case that: Interval[_] =>
        that.canEqual(this) &&
          this.min == that.min &&
          this.max == that.max
      case _ => false
    }

  override def hashCode(): Int = 13 * min.## + max.map(_.##).getOrElse(0)

  override def toString: String = (List(min) ++ max.toList).mkString("Interval(", ",", ")")
}

object Interval {

  def apply[A](min: A, max: A)(implicit num: Numeric[A]) = new Interval(min, Some(max))

  def apply[A](min: A)(implicit num: Numeric[A]) = new Interval(min, None)
}