package main

import (
  "fmt"
  "strings"
  "unicode"
  "strconv"
  "math"
  "github.com/Ubiquest/lightstack"
)

const floatResolution int = 5

func rpncalc(input string) float64 {
  if input == "" {
    return 0.0
  }
  stack := new(lightstack.Stack)
  var varMap map[string]float64
  varMap = make(map[string]float64)
  args := strings.Split(input, " ")

  for _, element := range args {
    if(unicode.IsDigit(rune(element[0]))) {
      val, _ := strconv.ParseFloat(element, floatResolution)
      stack.Push(val)
    } else if element[0] == '$' {
      val := varMap[element]
      stack.Push(val)
    } else if element[0] == '@' {
      stack.Push(element[1:len(element)])
    } else {
      equ := 0.0
      if element == "set" {
        lval, _ := stack.Pop().(string)
        rval, _ := stack.Pop().(float64)
        varMap["$" + lval] = rval
      } else if element == "+" {
        equ = stack.Pop().(float64) + stack.Pop().(float64)
      } else if element == "-" {
        lval, _ := stack.Pop().(float64)
        rval, _ := stack.Pop().(float64)
        equ = rval - lval
      } else if element == "*" {
        equ = stack.Pop().(float64) * stack.Pop().(float64)
      } else if element == "/" {
        lval, _ := stack.Pop().(float64)
        rval, _ := stack.Pop().(float64)
        equ = rval / lval
      } else if element == "%" {
        lval, _ := stack.Pop().(float64)
        rval, _ := stack.Pop().(float64)
        equ = float64(int(rval) % int(lval))
      } else if element == "^" {
        lval, _ := stack.Pop().(float64)
        rval, _ := stack.Pop().(float64)
        equ = math.Pow(rval, lval)
      } else if element == "sqrt" {
        lval, _ := stack.Pop().(float64)
        equ = math.Sqrt(lval)
      } else if element == "neg" {
        equ = -(stack.Pop().(float64))
      }
      stack.Push(equ)
    }
  }
  return stack.Top().(float64)
}

func main() {
  fmt.Println(rpncalc("4 @var1 set $var1 sqrt 25 + 9 / 3 3 -"))
}