feat: add utils.numbers package

utils/numbers/numbers.go

@@ -0,0 +1,120 @@
+package numbers
+
+import (
+	"strings"
+)
+
+func ToWords(num int) string {
+	if num == 0 {
+		return "zero"
+	}
+
+	billions := num / 1000000000
+	millions := (num % 1000000000) / 1000000
+	thousands := (num % 1000000) / 1000
+	hundreds := (num % 1000) / 100
+	tens := (num % 100) / 10
+	ones := num % 10
+
+	var sb strings.Builder
+
+	if billions > 0 {
+		sb.WriteString(threeDigitNumberToWords(billions))
+		sb.WriteString(" billion")
+	}
+
+	if millions > 0 {
+		sb.WriteString(threeDigitNumberToWords(millions))
+		sb.WriteString(" million")
+	}
+
+	if thousands > 0 {
+		sb.WriteString(threeDigitNumberToWords(thousands))
+		sb.WriteString(" thousand")
+	}
+
+	if hundreds > 0 {
+		sb.WriteString(twoDigitNumberToWords(hundreds))
+		sb.WriteString(" hundred")
+	}
+
+	if tens > 0 || ones > 0 {
+		sb.WriteString(twoDigitNumberToWords(tens*10 + ones))
+	}
+
+	return sb.String()
+}
+
+func threeDigitNumberToWords(num int) string {
+	if num == 0 {
+		return ""
+	}
+
+	hundreds := num / 100
+	tens := (num % 100) / 10
+	ones := num % 10
+
+	var sb strings.Builder
+
+	sb.WriteString(twoDigitNumberToWords(hundreds*100 + tens*10 + ones))
+
+	return sb.String()
+}
+
+var tensInOne = []string{
+	"ten",
+	"eleven",
+	"twelve",
+	"thirteen",
+	"fourteen",
+	"fifteen",
+	"sixteen",
+	"seventeen",
+	"eighteen",
+	"nineteen",
+}
+
+var tensPrefixes = map[int]string{
+	1: "",
+	2: "twenty",
+	3: "thirty",
+	4: "forty",
+	5: "fifty",
+	6: "sixty",
+	7: "seventy",
+	8: "eighty",
+	9: "ninety",
+}
+
+var onesWords = map[int]string{
+	1: "one",
+	2: "two",
+	3: "three",
+	4: "four",
+	5: "five",
+	6: "six",
+	7: "seven",
+	8: "eight",
+	9: "nine",
+}
+
+func twoDigitNumberToWords(num int) string {
+	if num == 0 {
+		return ""
+	}
+
+	tens := num / 10
+	ones := num % 10
+
+	if tens == 1 {
+		return tensInOne[ones]
+	} else if prefix, ok := tensPrefixes[tens]; ok {
+		return prefix + " " + oneDigitNumberToWords(ones)
+	}
+
+	return oneDigitNumberToWords(ones)
+}
+
+func oneDigitNumberToWords(num int) string {
+	return onesWords[num]
+}