Supports any 01 prefix (010, 011, 014, 015, etc.) for future adaptability

Reviewed-on: #2

phone/phone.go

@@ -11,7 +11,8 @@ const (
 	// TODO: This should rather use a phone package to determine whether valid phone number for any region.
 	// Kenyan phone numbers: must be exactly 10 digits (07XXXXXXXX or 01XXXXXXXX) when starting with 0
 	// Or start with 254 / +254 and still follow the same pattern
-	phoneRegex = `^(?:\+254|254|0)(7\d{8}|1[01]\d{7})$`
+	// Supports any 01 prefix (010, 011, 014, 015, etc.) for future adaptability
+	phoneRegex = `^(?:\+254|254|0)(7\d{8}|1\d{8})$`
 )
 
 // IsValidPhoneNumber checks if the given number is a valid phone number
@@ -41,3 +42,34 @@ func FormatPhoneNumber(phone string) (string, error) {
 
 	return "+" + phone, nil
 }
+
+// FormatToLocalPhoneNumber converts a phone number like "+2547XXXXXXXX"
+// or "2547XXXXXXXX" into the local format "07XXXXXXXX" / "01XXXXXXXX".
+func FormatToLocalPhoneNumber(phone string) (string, error) {
+	// Remove leading "+" and spaces
+	phone = strings.TrimPrefix(phone, "+")
+	phone = strings.ReplaceAll(phone, " ", "")
+
+	// Must start with 254
+	if !strings.HasPrefix(phone, "254") {
+		return "", errors.New("invalid international phone format")
+	}
+
+	// Remove "254" prefix → get 7XXXXXXXX or 1XXXXXXXX
+	rest := phone[3:]
+
+	// Validate: must be 9 digits
+	if len(rest) != 9 {
+		return "", errors.New("invalid phone number length")
+	}
+
+	// Kenyan mobile numbers start with 7 or 1 (Safaricom/Airtel/Telkom prefixes)
+	if !(strings.HasPrefix(rest, "7") || strings.HasPrefix(rest, "1")) {
+		return "", errors.New("invalid Kenyan mobile prefix")
+	}
+
+	// Convert to local: prepend "0"
+	local := "0" + rest
+
+	return local, nil
+}