Various fixes in OTP digits handling and code formatting

src/arguments/add.rs

@@ -40,7 +40,7 @@ pub struct AddArgs {
         long,
         default_value_t = 6,
         default_value_if("type", "STEAM", "5"),
-        value_parser=value_parser!(u64).range(0..=9)
+        value_parser=value_parser!(u64).range(1..=10)
     )]
     pub digits: u64,
 

src/arguments/edit.rs

@@ -24,7 +24,7 @@ pub struct EditArgs {
     pub algorithm: Option<OTPAlgorithm>,
 
     /// Code digits
-    #[arg(short, long, value_parser=value_parser!(u64).range(0..=9))]
+    #[arg(short, long, value_parser=value_parser!(u64).range(1..=10))]
     pub digits: Option<u64>,
 
     /// Code period

src/otp/otp_element.rs

@@ -154,6 +154,8 @@ pub struct OTPElement {
     pub pin: Option<String>,
 }
 
+static ALLOWED_DIGITS_RANGE: std::ops::RangeInclusive<u64> = 1..=10;
+
 impl OTPElement {
     pub fn get_otpauth_uri(&self) -> String {
         let otp_type = self.type_.to_string().to_lowercase();
@@ -183,6 +185,10 @@ impl OTPElement {
     }
 
     pub fn get_otp_code(&self) -> Result<String, OtpError> {
+        if !ALLOWED_DIGITS_RANGE.contains(&self.digits) {
+            return Err(OtpError::InvalidDigits);
+        }
+
         match self.type_ {
             OTPType::Totp => {
                 let code = totp(&self.secret, self.algorithm)?;
@@ -222,11 +228,11 @@ impl OTPElement {
 
     fn format_code(&self, value: u32) -> Result<String, OtpError> {
         // Get the formatted code
-        let exponential = 10_u32
+        let exponential = 10_u64
             .checked_pow(self.digits as u32)
             .ok_or(OtpError::InvalidDigits)?;
-        let s = (value % exponential).to_string();
-        Ok("0".repeat(self.digits as usize - s.chars().count()) + s.as_str())
+        let s = (value as u64 % exponential).to_string();
+        Ok("0".repeat((self.digits as usize).saturating_sub(s.chars().count())) + s.as_str())
     }
 }
 
@@ -357,7 +363,7 @@ mod test {
     #[test]
     fn test_invalid_digits_should_not_overflow() {
         // Arrange
-        let invalid_digits_value = 10;
+        let invalid_digits_value = 11;
 
         let element = OTPElement {
             secret: "xr5gh44x7bprcqgrdtulafeevt5rxqlbh5wvked22re43dh2d4mapv5g".to_uppercase(),
@@ -378,6 +384,30 @@ mod test {
         assert_eq!(Err(OtpError::InvalidDigits), result);
     }
 
+    #[test]
+    fn test_10_digits_should_be_allowed() {
+        // Arrange
+        let invalid_digits_value = 10;
+
+        let element = OTPElement {
+            secret: "xr5gh44x7bprcqgrdtulafeevt5rxqlbh5wvked22re43dh2d4mapv5g".to_uppercase(),
+            issuer: String::from("IssuerText"),
+            label: String::from("LabelText"),
+            digits: invalid_digits_value,
+            type_: Totp,
+            algorithm: Sha1,
+            period: 30,
+            counter: None,
+            pin: None,
+        };
+
+        // Act
+        let result = element.get_otp_code();
+
+        // Assert
+        assert!(result.is_ok());
+    }
+
     #[test]
     fn test_lowercase_secret() {
         // Arrange / Act