// Package romannumerals is for handling roman numbers
package romannumerals
import (
	"fmt"
	"math"
)
var romanNum = map[int]string{
	1000: "M", 500: "D", 100: "C", 50: "L", 10: "X", 5: "V", 1: "I",
}
// ToRomanNumeral converts arabic numbers to roman ones
func ToRomanNumeral(arabic int) (roman string, err error) {
	if arabic > 3000 {
		return "", fmt.Errorf("bigger than 3000")
	}
	if arabic <= 0 {
		return "", fmt.Errorf("the input have to be positive")
	}
	// place value starts at 10^3
	for pv := 3; pv >= 0; pv-- {
		pow := int(math.Pow10(pv))
		switch arabic / pow {
		case 1:
			roman += romanNum[pow]
		case 2:
			roman += romanNum[pow] + romanNum[pow]
		case 3:
			roman += romanNum[pow] + romanNum[pow] + romanNum[pow]
		case 4:
			roman += romanNum[pow] + romanNum[pow*5]
		case 5:
			roman += romanNum[pow*5]
		case 6:
			roman += romanNum[pow*5] + romanNum[pow]
		case 7:
			roman += romanNum[pow*5] + romanNum[pow] + romanNum[pow]
		case 8:
			roman += romanNum[pow*5] + romanNum[pow] + romanNum[pow] + romanNum[pow]
		case 9:
			roman += romanNum[pow] + romanNum[pow*10]
		}
		// this one only makes sense because the int truncate
		arabic -= arabic / pow * pow
	}
	return roman, nil
}