engineering-repr 1.1.1

//! String conversions

use std::{
    cmp::{min, Ordering},
    fmt::Display,
    str::FromStr,
};

use crate::{EQSupported, EngineeringQuantity, Error};

static POSITIVE_MULTIPLIERS: &str = " kMGTPEZYRQ";
static NEGATIVE_MULTIPLIERS: &str = " munpfazyrq"; // μ is not ASCII, which confounds things a little

fn exponent_to_multiplier(exp: i8) -> &'static str {
    let abs = exp.unsigned_abs() as usize;
    match (exp.cmp(&0), abs) {
        (Ordering::Equal, _) => "",
        (Ordering::Greater, _) => &POSITIVE_MULTIPLIERS[abs..=abs],
        (Ordering::Less, 2) => "μ", // special case as non-ASCII
        (Ordering::Less, _) => &NEGATIVE_MULTIPLIERS[abs..=abs],
    }
}

const fn multiplier_to_exponent(prefix: char) -> Option<i8> {
    Some(match prefix {
        //' ' => 0,
        'k' => 1,
        'M' => 2,
        'G' => 3,
        'T' => 4,
        'P' => 5,
        'E' => 6,
        'Z' => 7,
        'Y' => 8,
        'R' => 9,
        'Q' => 10,
        'm' => -1,
        'μ' | 'u' => -2,
        'n' => -3,
        'p' => -4,
        'f' => -5,
        'a' => -6,
        'z' => -7,
        'y' => -8,
        'r' => -9,
        'q' => -10,
        _ => return None,
    })
}

fn find_multiplier(s: &str) -> Option<(usize /* index */, i8 /* exponent */)> {
    for (i, c) in s.chars().enumerate() {
        if let Some(p) = multiplier_to_exponent(c) {
            return Some((i, p));
        }
    }
    None
}

/////////////////////////////////////////////////////////////////////////
// STRING TO NUMBER

impl<T: EQSupported<T> + FromStr> FromStr for EngineeringQuantity<T> {
    type Err = Error;

    /// # Example
    /// ```
    /// use engineering_repr::EngineeringQuantity as EQ;
    /// use std::str::FromStr as _;
    /// let eq = EQ::<i64>::from_str("1.5k").unwrap();
    /// assert_eq!(i64::try_from(eq).unwrap(), 1500);
    /// // RKM style strings
    /// let eq2 = EQ::<i64>::from_str("1k5").unwrap();
    /// assert_eq!(eq, eq2);
    /// ```
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let prefix = find_multiplier(s);
        // Is there a decimal? If so it's standard (non RKM) mode.
        let decimal = s.find('.');
        let (prefix_index, exponent) = match (prefix, decimal) {
            // Easy case: direct integer conversion
            (None, None) => {
                return T::from_str(s)
                    .map_err(|_| Error::ParseError)
                    .and_then(|i| EngineeringQuantity::from_raw(i, 0));
            }
            // 1.23 (no multiplier suffix)
            (None, Some(idx)) => (idx, 0),
            // General case
            (Some((id, exp)), _) => (id, exp),
        };

        let split_index = if let Some(d) = decimal {
            // Non-RKM mode (1.5k)
            d
        } else {
            // RKM mode (1k5)
            prefix_index
        };

        let mut to_convert = s.chars().take(split_index).collect::<String>();
        let mut trailing = s.chars().skip(split_index + 1).collect::<String>();

        // In non-RKM mode, don't convert the prefix (err, the suffix)
        if decimal.is_some() && prefix.is_some() {
            let _ = trailing.pop();
        }

        // Each 3 digits (or part thereof) represents another exponent.
        to_convert.push_str(&trailing);
        // If it's not a round multiple of 3, we need to pad !
        #[allow(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
        let whole_groups = (trailing.len() / 3) as i8;
        // convert to signed so we can trap a panic
        #[allow(clippy::cast_possible_wrap)]
        let mut exponent = exponent;
        match trailing.len() % 3 {
            0 => exponent -= whole_groups,
            n => {
                // n must be 1 or 2
                exponent -= whole_groups + 1;
                to_convert.push_str("0".repeat(3 - n).as_str());
            }
        }

        let significand = T::from_str(&to_convert).map_err(|_| Error::ParseError)?;
        #[allow(
            clippy::cast_possible_truncation,
            clippy::cast_possible_wrap,
            clippy::cast_sign_loss
        )]
        Self::from_raw(significand, exponent)
    }
}

/////////////////////////////////////////////////////////////////////////
// NUMBER TO STRING

impl<T: EQSupported<T>> Display for EngineeringQuantity<T> {
    /// Default behaviour is to output to 3 significant figures, skip unnecessary trailing zeros,
    /// standard (not RKM) mode.
    /// See [`EngineeringQuantity::default()`].
    /// # Examples
    /// ```
    /// use engineering_repr::EngineeringQuantity as EQ;
    /// let ee1 = EQ::<i32>::from(1200);
    /// assert_eq!(ee1.to_string(), "1.2k");
    /// let ee2 = EQ::<i32>::from(123456);
    /// assert_eq!(ee2.to_string(), "123k");
    /// ```
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        DisplayAdapter {
            value: *self,
            ..Default::default()
        }
        .fmt(f)
    }
}

/// A wrapper type which allows you to specify the desired output format.
/// It implements [`Display`].
///
/// This type may be conveniently created by [`EngineeringQuantity::with_precision()`]
/// and [`EngineeringQuantity::rkm_with_precision()`].
#[derive(Copy, Clone, Debug)]
pub struct DisplayAdapter<T: EQSupported<T>>
where
    T: ToString,
{
    /// The value to be displayed
    pub value: EngineeringQuantity<T>,
    /// The precision at which to display, or 0 to work it out losslessly
    pub max_significant_figures: usize,
    /// Specifies [RKM code](https://en.wikipedia.org/wiki/RKM_code) mode
    pub rkm: bool,
    /// Always emit the precision requested, even any unnecessary untrailing zeroes after the decimal point.
    pub strict: bool,
}

impl<T: EQSupported<T>> Default for DisplayAdapter<T> {
    fn default() -> Self {
        Self {
            value: EngineeringQuantity {
                significand: T::ZERO,
                exponent: 0,
            },
            max_significant_figures: 3,
            rkm: false,
            strict: false,
        }
    }
}

impl<T: EQSupported<T>> PartialEq<DisplayAdapter<T>> for &str {
    /// This is intended for use in tests.
    #[allow(clippy::cmp_owned)]
    fn eq(&self, other: &DisplayAdapter<T>) -> bool {
        *self == other.to_string()
    }
}

impl<T: EQSupported<T>> EngineeringQuantity<T> {
    /// Creates a standard [`DisplayAdapter`] for this object, with the given precision.
    /// ```
    /// use engineering_repr::EngineeringQuantity as EQ;
    /// let ee = EQ::<i32>::from(1234567);
    /// assert_eq!(ee.with_precision(2).to_string(), "1.2M");
    /// ```
    #[must_use]
    pub fn with_precision(&self, max_significant_figures: usize) -> DisplayAdapter<T> {
        DisplayAdapter {
            value: *self,
            max_significant_figures,
            rkm: false,
            strict: false,
        }
    }
    /// Creates an RKM [`DisplayAdapter`] for this object in RKM mode, with the given precision.
    /// ```
    /// use engineering_repr::EngineeringQuantity as EQ;
    /// let ee = EQ::<i32>::from(1234567);
    /// assert_eq!(ee.rkm_with_precision(2).to_string(), "1M2");
    /// ```
    #[must_use]
    pub fn rkm_with_precision(&self, max_significant_figures: usize) -> DisplayAdapter<T> {
        DisplayAdapter {
            value: *self,
            max_significant_figures,
            rkm: true,
            strict: false,
        }
    }
    /// Creates a [`DisplayAdapter`] for this object, with strict precision.
    /// The requested digits will always be output, even trailing zeroes.
    /// ```
    /// use engineering_repr::EngineeringQuantity as EQ;
    /// let ee = EQ::<i32>::from(1_200);
    /// assert_eq!(ee.with_strict_precision(3).to_string(), "1.20k");
    /// ```
    #[must_use]
    pub fn with_strict_precision(&self, max_significant_figures: usize) -> DisplayAdapter<T> {
        DisplayAdapter {
            value: *self,
            max_significant_figures,
            rkm: false,
            strict: true,
        }
    }
}

impl<T: EQSupported<T>> Display for DisplayAdapter<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        /*
         * We prepare the output string in five parts:
         * - Prefix   := "-" (negative) or "" (positive)
         * - Leaders  := Digits before output decimal point
         * - Point    := Output decimal point. This is "." (normal mode), or multiplier (rkm mode), or "" (normal mode and there are no trailers)
         * - Trailers := Digits after output decimal point
         * - Suffix   := multiplier (normal mode) or "" (rkm mode)
         *
         * Algorithm:
         * 1. Convert significand to digits
         * 2. Compute the output exponent such that the quantity to the left of the output decimal point is from 1 to 999
         *    (Positive exponents) Append zeroes in groups of 3 until we reach the true decimal point
         *    (Negative exponents) Append nothing
         * 3. Split into leading/trailing (this is a function of the exponent)
         * 4. Implement precision:
         *    If precision is arbitrary, trim all trailing zeroes.
         *    Otherwise, trim trailing digits as necessary to meet the request.
         */
        let detail = self.value.significand.abs_and_sign();
        let mut digits = detail.abs.to_string();
        // at first glance the output might reasonably be this value of `digits`, followed by `exponent` times "000"...
        // but we need to (re)compute the correct exponent for display.
        let prefix = if detail.negative { "-" } else { "" };
        #[allow(clippy::cast_possible_truncation)]
        let output_exponent = if self.value.exponent > 0 {
            // Append zeroes until we reach the decimal point (we may trim some later)
            digits.reserve((3 * self.value.exponent + 1).unsigned_abs() as usize);
            for _ in 0..self.value.exponent {
                digits.push_str("000");
            }
            ((digits.len() - 1) / 3) as i8
        } else {
            // Negative or zero exponent: Append nothing, but we need a different formula for the output exponent
            self.value.exponent + ((digits.len() - 1) / 3) as i8
        };
        let si = exponent_to_multiplier(output_exponent);

        let n_leading = if output_exponent > 0 {
            digits.len() - output_exponent.unsigned_abs() as usize * 3
        } else {
            match digits.len() % 3 {
                0 => 3,
                i => i,
            }
        };
        let precision = match self.max_significant_figures {
            0 => usize::MAX, // automatic mode: take the digits we've got from a full conversion, we'll trim trailing 0s in a moment
            i => i,
        };
        if self.strict {
            let pad = self.max_significant_figures.saturating_sub(digits.len());
            for _ in 0..pad {
                digits.push('0');
            }
        }
        let n_trailing = min(
            // number of digits remaining
            digits.len() - n_leading,
            // number of digits we'd take to reach the requested precision
            precision - min(precision, n_leading),
        );
        let leaders = &digits[0..n_leading];
        let mut trailers = &digits[n_leading..n_leading + min(n_trailing, precision)];
        if !self.strict {
            while trailers.ends_with('0') {
                trailers = &trailers[0..trailers.len() - 1];
            }
        }
        // Point and suffix strings resolve to a 3-boolean truth table...
        let (point, suffix) = match (output_exponent == 0, self.rkm, trailers.is_empty()) {
            // Output exponent is 0: mode is irrelevant, no suffix, suppress point if there are no digits after it
            (true, _, true) => ("", ""),
            (true, _, false) => (".", ""),

            // Exponent non zero, RKM mode: point is always SI, no suffix
            (false, true, _) => (si, ""),
            // Exponent non zero, Standard mode:
            (false, false, true) => ("", si), // No trailer, suppress point
            (false, false, false) => (".", si), // With trailer, output point
        };
        write!(f, "{prefix}{leaders}{point}{trailers}{suffix}")
    }
}

/////////////////////////////////////////////////////////////////////////
// CONVENIENCE TRAITS

/// A convenience trait for outputting integers directly in engineering notation.
///
/// [`DisplayAdapter`] implements [`Display`], so you can use the returned adapter
/// directly in a formatting macro.
pub trait EngineeringRepr<T: EQSupported<T>> {
    /// Outputs a number in engineering notation
    ///
    /// A request for 0 significant figures outputs exactly as many digits are necessary to maintain precision.
    /// ```
    /// use engineering_repr::EngineeringRepr as _;
    /// assert_eq!("123k", 123456.to_eng(3));
    /// assert_eq!("123.4k", 123456.to_eng(4));
    /// assert_eq!("123.456k", 123456.to_eng(0));
    /// ```
    /// # Panics
    /// If the value could not be rendered
    fn to_eng(self, sig_figures: usize) -> DisplayAdapter<T>;

    /// Outputs a number in RKM notation
    ///
    /// A request for 0 significant figures outputs exactly as many digits are necessary to maintain precision.
    /// ```
    /// use engineering_repr::EngineeringRepr as _;
    /// assert_eq!("123k", 123456.to_rkm(3));
    /// assert_eq!("123k4", 123456.to_rkm(4));
    /// assert_eq!("123k456", 123456.to_rkm(0));
    /// ```
    /// # Panics
    /// If the value could not be rendered
    fn to_rkm(self, sig_figures: usize) -> DisplayAdapter<T>;
}

macro_rules! impl_to_eng {
    {$($t:ty),+} => {$(
        impl<> EngineeringRepr<$t> for $t {
            fn to_eng(self, sig_figures: usize) -> DisplayAdapter<$t>
            {
                EngineeringQuantity::<$t>::try_from(self).unwrap().with_precision(sig_figures)
            }
            fn to_rkm(self, sig_figures: usize) -> DisplayAdapter<$t>
            {
                EngineeringQuantity::<$t>::try_from(self).unwrap().rkm_with_precision(sig_figures)
            }
        }
    )+}
}

impl_to_eng!(u16, u32, u64, u128, usize, i16, i32, i64, i128, isize);

/////////////////////////////////////////////////////////////////////////

#[cfg(test)]
mod test {
    use super::EngineeringQuantity as EQ;
    use std::str::FromStr as _;

    #[test]
    fn from_string() {
        for (i, s) in &[
            (1i128, "1"),
            (42, "42"),
            (999, "999"),
            (1000, "1k"),
            (1500, "1.5k"),
            (2345, "2.345k"),
            (9999, "9.999k"),
            (12_345, "12.345k"),
            (13_000, "13k"),
            (13_000, "13.k"),
            (13_000, "13.0k"),
            (999_999, "999.999k"),
            (1_000_000, "1.00M"),
            (2_345_678, "2.345678M"),
            (999_999_999, "999.999999M"),
            (12_345_000_000_000_000_000_000_000_000, "12.345R"),
            (12_345_000_000_000_000_000_000_000_000_000, "12.345Q"),
            (1000, "1k0"),
            (1500, "1k5"),
            (2345, "2k345"),
            (9999, "9k999"),
            (12_345, "12k345"),
            (13_000, "13k0"),
            (999_999, "999k999"),
            (1_000_000, "1M0"),
            (2_345_678, "2M345678"),
            (999_999_999, "999M999999"),
            (1_000_000_000, "1G0"),
            (1_000_000_000_000, "1T0"),
            (1_000_000_000_000_000, "1P0"),
            (1_000_000_000_000_000_000, "1E0"),
            (1_000_000_000_000_000_000_000, "1Z0"),
            (1_000_000_000_000_000_000_000_000, "1Y0"),
            (12_345_000_000_000_000_000_000_000_000, "12R345"), // I wonder if 1R means 1 ohm or 1 ronnaohm? :-)
            (12_345_000_000_000_000_000_000_000_000_000, "12Q345"),
        ] {
            let eq = EQ::<i128>::from_str(s).unwrap();
            let result = i128::from(eq);
            assert_eq!(result, *i, "input {s} expected {i}");
            let mut str2 = String::with_capacity(1 + s.len());
            str2.push('-');
            str2.push_str(s);
            let ee2 = EQ::<i128>::from_str(&str2).unwrap();
            assert_eq!(i128::from(ee2), -*i);
        }
    }

    #[test]
    fn parse_failures() {
        for s in &["foo", "1.2.3k", "--1"] {
            let _ = EQ::<i128>::from_str(s).expect_err(&format!("this should have failed: {s}"));
        }
    }

    #[test]
    fn to_string() {
        for (i, s) in &[
            (1i128, "1"),
            (42, "42"),
            (999, "999"),
            (1000, "1k"),
            (1500, "1.5k"),
            (2345, "2.34k"),
            (9999, "9.99k"),
            (12_345, "12.3k"),
            (13_000, "13k"),
            (999_999, "999k"),
            (1_000_000, "1M"),
            (2_345_678, "2.34M"),
            (999_999_999, "999M"),
            (12_345_000_000_000_000_000_000_000_000, "12.3R"),
            (12_345_000_000_000_000_000_000_000_000_000, "12.3Q"),
        ] {
            let ee = EQ::<i128>::from(*i);
            assert_eq!(ee.to_string(), *s);
            let ee2 = EQ::<i128>::from(-*i);
            let ss2 = ee2.to_string();
            assert_eq!(ss2.chars().next().unwrap(), '-');
            assert_eq!(&ss2[1..], *s);
        }
    }
    #[test]
    fn to_string_small() {
        for (i, e, s) in &[
            (1, -1, "1m"),
            (999, -1, "999m"),
            (1, -2, "1μ"),
            (1001, -2, "1m"),
            (1001, -1, "1"),
            (1_000_001, -2, "1"),
            (1_111, -1, "1.11"),
            (1010, -3, "1.01μ"),
            (1010, -4, "1.01n"),
            (1010, -5, "1.01p"),
            (1010, -6, "1.01f"),
            (1010, -7, "1.01a"),
            (1010, -8, "1.01z"),
            (1010, -9, "1.01y"),
            (1010, -10, "1.01r"),
            (1010, -11, "1.01q"),
        ] {
            let ee = EQ::<i128>::from_raw(*i, *e).unwrap();
            assert_eq!(ee.to_string(), *s, "inputs {i}, {e}");
            let ee2 = EQ::<i128>::from_raw(-*i, *e).unwrap();
            let mut expected = (*s).to_string();
            expected.insert(0, '-');
            assert_eq!(ee2.to_string(), expected, "inputs -{i}, {e}");
        }
        for (i, e, s) in &[
            (1, -1, "1m"),
            (999, -1, "999m"),
            (1, -2, "1μ"),
            (1001, -2, "1m001"),
            (1001, -1, "1.001"),
            (1_000_001, -2, "1"),
        ] {
            let ee = EQ::<i128>::from_raw(*i, *e).unwrap();
            assert_eq!(ee.rkm_with_precision(4).to_string(), *s, "inputs {i}, {e}");
        }
    }
    #[test]
    fn from_string_small() {
        for (i, e, s) in &[
            (1, -1, "1m"),
            (999, -1, "999m"),
            (1, -2, "1μ"),
            (1001, -2, "1.001m"),
            (1001, -1, "1.001"),
            (1, 0, "1"),
            (1_000_001, -2, "1.000001"),
            (1_111, -1, "1.111"),
            (1010, -3, "1.01μ"),
            (1010, -4, "1.01n"),
            (1010, -5, "1.01p"),
            (1010, -6, "1.01f"),
            (1010, -7, "1.01a"),
            (1010, -8, "1.01z"),
            (1010, -9, "1.01y"),
            (1010, -10, "1.01r"),
            (1010, -11, "1.01q"),
        ] {
            let ee3 = EQ::<i128>::from_str(s).unwrap();
            let expected_raw = (*i, *e);
            assert_eq!(ee3.to_raw(), expected_raw);
        }
        for (i, e, s) in &[
            (1, -1, "1m"),
            (999, -1, "999m"),
            (1, -2, "1μ"),
            (1001, -2, "1m001"),
            (1001, -1, "1.001"),
            (1_000_001, -2, "1.000001"),
        ] {
            let ee2 = EQ::<i64>::from_str(s).unwrap();
            let expected_raw = (*i, *e);
            assert_eq!(ee2.to_raw(), expected_raw);
        }
    }
    #[test]
    fn to_string_rkm() {
        for (i, s) in &[
            (1i128, "1"),
            (42, "42"),
            (999, "999"),
            (1000, "1k"),
            (1500, "1k5"),
            (2345, "2k3"),
            (9999, "9k9"),
            (12_345, "12k"),
            (13_000, "13k"),
            (999_999, "999k"),
            (1_000_000, "1M"),
            (2_345_678, "2M3"),
            (999_999_999, "999M"),
            (12_345_000_000_000_000_000_000_000_000, "12R"),
            (12_345_000_000_000_000_000_000_000_000_000, "12Q"),
        ] {
            let ee = EQ::<i128>::from(*i);
            assert_eq!(ee.rkm_with_precision(2).to_string(), *s);
            let ee2 = EQ::<i128>::from(-*i);
            let ss2 = ee2.rkm_with_precision(2).to_string();
            assert_eq!(ss2.chars().next().unwrap(), '-');
            assert_eq!(&ss2[1..], *s);
        }
    }

    #[test]
    fn traits() {
        use super::EngineeringRepr as _;
        assert_eq!("123k", 123_456.to_eng(3));
        assert_eq!("123.4k", 123_456.to_eng(4));
        assert_eq!("123k4", 123_456.to_rkm(4));
    }

    #[test]
    fn raw_to_string() {
        for (sig, exp, str) in &[
            (1, 0i8, "1"),
            (1, 1, "1k"),
            (1000, 0, "1k"),
            (1000, 1, "1M"),
        ] {
            let e = EQ::<i128>::from_raw(*sig, *exp).unwrap();
            assert_eq!(e.to_string(), *str, "test case: {sig},{exp} -> {str}");
        }
    }

    #[test]
    fn overflow() {
        let e = EQ::from_raw(1u16, 0).unwrap();
        let e2 = EQ::from_raw(1u16, 1).unwrap();
        assert_ne!(e, e2);
        println!("{e:?} -> {e}");
        println!("{e2:?} -> {e2}");
        let _ = e.to_string();
    }

    #[test]
    fn auto_precision() {
        for (i, s) in &[
            (1i128, "1"),
            (42, "42"),
            (100, "100"),
            (999, "999"),
            (1000, "1k"),
            (1500, "1.5k"),
            (2345, "2.345k"),
            (9999, "9.999k"),
            (12_345, "12.345k"),
            (13_000, "13k"),
            (999_999, "999.999k"),
            (1_000_000, "1M"),
            (2_345_678, "2.345678M"),
            (999_999_999, "999.999999M"),
            (12_345_600_000_000_000_000_000_000_000, "12.3456R"),
            (12_345_600_000_000_000_000_000_000_000_000, "12.3456Q"),
        ] {
            let ee = EQ::<i128>::from(*i);
            assert_eq!(ee.with_precision(0).to_string(), *s, "input={}", *i);
            let ee2 = EQ::<i128>::from(-*i);
            let ss2 = ee2.with_precision(0).to_string();
            assert_eq!(ss2.chars().next().unwrap(), '-');
            assert_eq!(&ss2[1..], *s, "input={}", -*i);
        }
    }
    #[test]
    fn strict_precision() {
        let ee = EQ::<i64>::from_raw(1234, -3).unwrap();
        assert_eq!(ee.with_strict_precision(6).to_string(), "1.23400μ");
    }
}