package main

import (
	"fmt"
	"math/rand"
	"os"
	"strconv"
	"strings"
	"time"
)

var r *rand.Rand

func main() {
	parm := "1d20"
	if len(os.Args) > 0 {
		if len(os.Args) == 2 {
			parm = os.Args[1]
		} else if len(os.Args) == 3 {
			parm = os.Args[1] + "d" + os.Args[2]
		}
	}
	if strings.HasPrefix(parm, "d") {
		parm = "1" + parm
	}

	r = rand.New(rand.NewSource(time.Now().UnixNano()))
	num, sides, times := parseParm(parm)
	for i := times; i > 0; i-- {
		if times > 1 {
			fmt.Printf("%d: ", times-i+1)
		}
		fmt.Println(roll(num, sides))
	}
}

func parseParm(p string) (int, int, int) {
	var pts []string
	if strings.Contains(p, "d") {
		pts = strings.Split(p, "d")
	}
	var num, sides int
	if len(pts) > 0 {
		num = atoi(pts[0])
	}
	times := 1
	if len(pts) > 1 {
		if strings.Contains(pts[1], "x") {
			thesepts := strings.Split(pts[1], "x")
			if len(thesepts) > 1 {
				sides = atoi(thesepts[0])
				times = atoi(thesepts[1])
			}
		} else {
			sides = atoi(pts[1])
		}
	}
	return num, sides, times
}

func roll(num, sides int) int {
	ret := 0
	for ; num > 0; num-- {
		ret += r.Intn(sides) + 1
	}
	return ret
}

func atoi(a string) int {
	ret, err := strconv.Atoi(a)
	if err != nil {
		fmt.Println("Error parsing value:", a)
		os.Exit(1)
	}
	return ret
}