catssyntax.scala

package syntax

import cats.data.NonEmptyList
import cats.syntax.reducible._

package object catssyntax {
  
  object InitLastNel {
    def unapply[T](nel: NonEmptyList[T]): Option[(List[T], T)] =
      (nel.init, nel.last).some
  }

  implicit class NonEmptyListOps[T](val nel: NonEmptyList[T]) extends AnyVal {

    /**
     * [[scala.collection.IterableLike#grouped]] for [[NonEmptyList]]
     */
    def grouped(groupSize: Int): NonEmptyList[NonEmptyList[T]] =
      nel.reduceLeftTo(elem => NonEmptyList.one(NonEmptyList.one(elem))) {
        case (InitLastNel(initGroups, lastGroup), elem)
            if lastGroup.size < groupSize =>
          NonEmptyList.ofInitLast(initGroups, lastGroup.append(elem))
        case (groups, elem) =>
          groups.append(NonEmptyList.one(elem))
      }

  }

}