From 8629b537b0a4c5b022e4511671f013b56299963b Mon Sep 17 00:00:00 2001
From: vinchent <vinchent@vinchent.xyz>
Date: Sun, 22 Sep 2024 22:00:50 +0200
Subject: [PATCH] roman: check number range

---
 roman/roman.go      | 15 ++++++++++++---
 roman/roman_test.go |  6 +++---
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/roman/roman.go b/roman/roman.go
index 63e8ec1..8a3b8e5 100644
--- a/roman/roman.go
+++ b/roman/roman.go
@@ -1,6 +1,9 @@
 package roman
 
-import "strings"
+import (
+	"errors"
+	"strings"
+)
 
 type RomanNumeral struct {
 	Value  uint16
@@ -24,7 +27,12 @@ var allRomanNumerals = []RomanNumeral{
 	{1, "I"},
 }
 
-func ConvertToRoman(arabic uint16) string {
+var ErrNumberOutOfRange = errors.New("numbers should not be bigger than 3999")
+
+func ConvertToRoman(arabic uint16) (string, error) {
+	if arabic > 3999 {
+		return "", ErrNumberOutOfRange
+	}
 	var converted strings.Builder
 	for _, numeral := range allRomanNumerals {
 		for arabic >= numeral.Value {
@@ -33,9 +41,10 @@ func ConvertToRoman(arabic uint16) string {
 		}
 	}
 
-	return converted.String()
+	return converted.String(), nil
 }
 
+// XXX: This convert function doesn't check the validity of the roman numerals string
 func ConvertToArabic(roman string) uint16 {
 	var converted uint16
 	for _, numeral := range allRomanNumerals {
diff --git a/roman/roman_test.go b/roman/roman_test.go
index d6609bb..1495bbf 100644
--- a/roman/roman_test.go
+++ b/roman/roman_test.go
@@ -44,7 +44,7 @@ var cases = []struct {
 func TestRomanNemerals(t *testing.T) {
 	for _, test := range cases {
 		t.Run(fmt.Sprintf("%d gets converted to %q", test.Arabic, test.Roman), func(t *testing.T) {
-			got := ConvertToRoman(test.Arabic)
+			got, _ := ConvertToRoman(test.Arabic)
 			want := test.Roman
 
 			if got != want {
@@ -69,10 +69,10 @@ func TestConvertingToArabic(t *testing.T) {
 
 func TestPropertiesOfConversion(t *testing.T) {
 	assertion := func(arabic uint16) bool {
+		roman, err := ConvertToRoman(arabic)
 		if arabic > 3999 {
-			return true
+			return err == ErrNumberOutOfRange
 		}
-		roman := ConvertToRoman(arabic)
 		fromRoman := ConvertToArabic(roman)
 		return fromRoman == arabic
 	}