cmd_parse.scala

import scala.io.Source._
import java.lang.Character.{isWhitespace => isSpace}
import scala.annotation.tailrec

def parseLine(s: String): (String, Seq[String]) = {
	parseCommand(s.iterator)
}

def parseCommand(s: Iterator[Char]): (String, Seq[String]) = {
	val elements = parseElements(s)
	(elements(0), elements.drop(1))
}

@tailrec
def parseElements(s: Iterator[Char], current: Seq[String] = Nil): Seq[String] = {
	if (s.hasNext) parseElements(s, current :+ parseElement(s))
	else current
}

@tailrec
def parseElement(s: Iterator[Char], current: String = "", quoted: Boolean = false): String = {
	if (s.hasNext) {
		s.next match {
			case '"' if !quoted =>
				parseElement(s, current, quoted = true)
			case '"' if quoted =>
				current
			case c if isSpace(c) && current.isEmpty && !quoted =>
				parseElement(s, current, quoted)
			case c if isSpace(c) && !quoted =>
				current
			case c =>
				parseElement(s, current + c, quoted)
		}
	} else current
}

def run(name: String, args: Seq[String]): Unit = {
	println(s"$name '${args.mkString("' '")}'")
}

fromFile("input.txt")
	.getLines()
	.map(_.trim)
	.filter(_.nonEmpty)
	.map(parseLine)
	.foreach((run _).tupled)