import scala.collection.mutable.ListBuffer

val openMobile = '['
val closeMobile = ']'
val sideDelimiter = '|'
val elementDelimiter = ','

trait Node

case class Mobile(children: List[Node]) extends Node

case class Leaf(weight: Double) extends Node

def parse(mobile: String): Mobile = {
  var i = 0

  def parseMobile(subj: String): Mobile = {
    var started = false
    var right = false
    val nodes = ListBuffer.empty[Node]

    while (i < subj.length) {
      val c = subj.charAt(i)

      c match {
        case `openMobile` =>
          if (!started)
            started = true
          else
            nodes += parseMobile(subj)
        case `closeMobile` =>
          if (!started)
            throw new Exception("Closing mobile without opening it")
          else {
            i += 1
            return Mobile(nodes.toList)
          }
        case `sideDelimiter` =>
          if (!right)
            right = true
          else
            throw new Exception("More than one side delimiter")
        case `elementDelimiter` =>
          if (i + 1 < subj.length) {
            if (subj.charAt(i + 1) == sideDelimiter || subj.charAt(i + 1) == closeMobile)
              throw new Exception("Comma at invalid position")
          }
          else
            throw new Exception("Comma at invalid position")
        case _ =>
          val number = parseNumber(subj)
          nodes += Leaf(if(right) number else -number)
      }

      i += 1
    }

    Mobile(nodes.toList)
  }

  def parseNumber(subj: String): Double = {
    val buffer = StringBuilder.newBuilder
    var reachedDot = false
    while (i < subj.length) {
      subj.charAt(i) match {
        case '.' =>
          if (!reachedDot)
            reachedDot = true
          else
            throw new Exception("More dots than allowed")
        case `elementDelimiter` | `openMobile` | `closeMobile` | `sideDelimiter` if buffer.length > 0 =>
          i -= 1
          return buffer.toDouble
        case c =>
          if (c.isDigit)
            buffer.append(c)
          else
            throw new Exception(s"Invalid character '$c'")
      }
      i += 1
    }

    buffer.toDouble
  }

  if (mobile.charAt(0) == openMobile)
    parseMobile(mobile.replaceAll("\\s", ""))
  else
    throw new Exception("blargh")
}

parse("[1,2|4,[1,2|4,5]]");