fictional document management system - outline

Outline.scala

case class Heading(weight: Int, text: String)
case class Node(heading: Heading, children: List[Node])

/** Converts a list of input headings into nested nodes */
def toOutline(headings: List[Heading]): Node = {
  def buildNodes(input: List[Heading]): List[Node] = input match {
    case Nil => Nil
    case head :: Nil => Node(head, Nil) :: Nil
    case head +: tail =>
      tail.splitAt(tail.indexWhere(head.weight == _.weight)) match {
        case (Nil, rest) =>
          if (rest.head.weight == head.weight)
            Node(head, Nil) +: buildNodes(rest)
          else
            Node(head, buildNodes(rest)) :: Nil
        case (children, rest) => Node(head, buildNodes(children)) +: buildNodes(rest)
      }
  }

  Node(Heading(0, ""), buildNodes(headings))
}

def toOutline2(headings: List[Heading]): Node = {
  def addToNode(target:Node, node:Node): Node = {
    require(node.heading.weight > target.heading.weight)
    if (target.children.isEmpty || target.children.last.heading.weight == node.heading.weight)
      target.copy(children=target.children :+ node)
    else
      target.copy(children = target.children.init :+ addToNode(target.children.last, node))
  }

  val nodes = headings.map(Node(_, List.empty))
  nodes.tail.foldLeft(nodes.head)(addToNode)
}

def parse(record: String): Option[Heading] = {
  val H = "H(\\d+)".r
  record.split(" ", 2) match {
    case Array(H(level), text) =>
      scala.util.Try(Heading(level.toInt, text.trim)).toOption
    case _ => None
  }
}

val input = """H1 All About Birds
H2 Kinds of Birds
H3 The Finch
H3 The Swan
H2 Habitats
H3 Wetlands"""

toOutline(input.split("\n").flatMap(parse).toList)