padded-number-internal 0.5.0

Internal parse functions for the padded-number crate
Documentation 
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//! # `padded-number-internal` - Internal crate whose items are then re-exported in `padded-number`

/// Error originating from `PaddedNumber::try_new`
#[derive(Debug, PartialEq, displaydoc::Display, thiserror::Error)]
pub enum ParsePaddedNumberError {
    /// "too few digits provided, expected at least '{0}', received '{1}'"
    TooShort(u8, u8),
    /// "too many digits provided, expected at most '{0}', received '{1}'"
    TooLong(u8, u8),
    /// "integer parse error, encountered non-ascii digit"
    InvalidNumber(#[source] std::num::ParseIntError),
}

#[doc(hidden)]
pub const fn parse(min: u8, max: u8, str: &str) -> Result<(u8, u64), ParsePaddedNumberError> {
    {
        let str_len = str.len();

        if str_len == 0 && min == 0 {
            return Ok((0, 0));
        }

        if str_len < min as usize {
            return Err(ParsePaddedNumberError::TooShort(min, str_len as u8));
        }

        if str_len > max as usize {
            return Err(ParsePaddedNumberError::TooLong(max, str_len as u8));
        }
    }

    let leading_zeros = konst::iter::eval!(konst::string::chars(str), take_while(|char| *char == '0'), count()) as u8;

    let remaining_number = konst::try_!(konst::result::map_err!(
        u64::from_str_radix(str, 10),
        ParsePaddedNumberError::InvalidNumber
    ));

    Ok((leading_zeros, remaining_number))
}