package scalation.graphaltics.querylang

// FIX - waiting for 2.12 implementation of fastparse
// @see http://www.lihaoyi.com/fastparse/
import fastparse.all._

object Parser
{
    val White = WhitespaceApi.Wrapper
    {
        import fastparse.all._
        NoTrace (" ".rep)
    } // val

    import fastparse.noApi._
    import White._

    val number: P[Int] = P (CharIn('0'to'9').rep(1).!.map (_.toInt))
    val parens: P[Int] = P ("(" ~/ addSub ~ ")")
    val factor: P[Int] = P (number | parens)

    val divMul: P[Int] = P (factor ~ (CharIn("*/").! ~/ factor).rep).map (eval)
    val addSub: P[Int] = P (divMul ~ (CharIn("+-").! ~/ divMul).rep).map (eval)
    val expr: P[Int]   = P (" ".rep ~ addSub ~ " ".rep ~ End )

    def eval(tree: (Int, Seq [(String, Int)])) =
    {
        val (base, ops) = tree
        ops.foldLeft (base) { case (left, (op, right)) => op match {
            case "+" => left + right
            case "-" => left - right
            case "*" => left * right
            case "/" => left / right
        }} // foldLeft
    } // eval

    def check (str: String, num: Int) =
    {
        val Parsed.Success (value, _) = expr.parse (str)
        assert (value == num)
    } // check

} // Paerser

// run-main scalation.graphaltics.querylang.ParserTest

object ParserTest extends App
{
    import Parser._

    check ("1+1", 2)
    check ("1+   1*   2", 3)
    check ("(1+   1  *  2)+(   3*4*5)", 63)
    check ("15/3", 5)
    check ("63  /3", 21)
    check ("(1+    1*2)+(3      *4*5)/20", 6)
    check ("((1+      1*2)+(3*4*5))/3", 21)

} // ParserTest object