Reddit DailyProgrammer Challenge #130 - Roll the Dies

diceroll.go

package main

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

func rollDice(min int, max int) int {
	return rand.Intn(max) + min
}

func main() {
	rand.Seed(time.Now().UnixNano())
	value := os.Args[1]
	pattern := regexp.MustCompile("^[0-9]+d[0-9]+$")
	if !pattern.MatchString(value) {
		log.Fatalf("%s does not match the general expected pattern: ###d###", value)
	}

	dPos := strings.Index(value, "d")
	if dPos > 3 {
		log.Fatal("Cannot roll that many times...")
	}

	numPattern := regexp.MustCompile("[0-9]+")
	num := numPattern.FindString(value)

	mPattern := regexp.MustCompile("d[0-9]+")
	m := mPattern.FindString(value)[1:]

	numRolls, err := strconv.Atoi(num)
	if err != nil {
		log.Fatal("Error parsing number of rolls!")
	}

	numFaces, err := strconv.Atoi(m)
	if err != nil {
		log.Fatal("Error parsing number of faces!")
	}

	if numRolls < 1 || numRolls > 100 {
		log.Fatal("Number of rolls must be between 1 and 100")
	}

	if numFaces < 2 || numFaces > 100 {
		log.Fatal("Number of faces must be between 2 and 100")
	}

	for i := 0; i < numRolls; i++ {
		fmt.Printf("%d ", rollDice(1, numFaces))
	}
}