core-decimal-calc/src/calc.rs

use core::{convert::Infallible, fmt::Display, marker::PhantomData};

use num_traits::{float::FloatCore, PrimInt, Unsigned};
#[cfg(feature = "ufmt")]
use ufmt::derive::uDebug;

use crate::{Decimal, DecimalError};

#[derive(Debug)]
#[cfg_attr(feature = "ufmt", derive(uDebug))]
pub enum StackCalcError {
    StackOverflow,
    StackUnderflow,
    DecimalError(DecimalError),
}

impl Display for StackCalcError {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        match self {
            StackCalcError::StackOverflow => f.write_str("stack overflow"),
            StackCalcError::StackUnderflow => f.write_str("stack underflow"),
            StackCalcError::DecimalError(de) => de.fmt(f),
        }
    }
}

#[derive(Debug, Clone)]
pub struct StackCalc<F: FloatCore, const STACK: usize = 2, const DSIZE: usize = 5, EXP = u16> {
    stack: [Decimal<DSIZE, EXP>; STACK],
    index: usize,
    phantom: PhantomData<F>,
}

#[cfg(feature = "ufmt")]
impl<F: FloatCore + ufmt::uDebug, const STACK: usize, const DSIZE: usize, EXP: ufmt::uDebug>
    ufmt::uDebug for StackCalc<F, STACK, DSIZE, EXP>
{
    fn fmt<W>(&self, f: &mut ufmt::Formatter<'_, W>) -> Result<(), W::Error>
    where
        W: ufmt::uWrite + ?Sized,
    {
        f.debug_struct("StackCalc")?
            .field("stack", &self.stack.as_slice())?
            .field("index", &self.index)?
            .finish()
    }
}

impl<F: FloatCore, const STACK: usize, const DSIZE: usize, EXP: PrimInt> Default
    for StackCalc<F, STACK, DSIZE, EXP>
{
    fn default() -> Self {
        StackCalc {
            stack: [Decimal::default(); STACK],
            index: 0,
            phantom: PhantomData,
        }
    }
}

impl From<DecimalError> for StackCalcError {
    fn from(val: DecimalError) -> Self {
        StackCalcError::DecimalError(val)
    }
}

impl From<Infallible> for StackCalcError {
    fn from(_: Infallible) -> Self {
        unreachable!()
    }
}

impl<F: FloatCore, const STACK: usize, const DSIZE: usize, EXP: PrimInt + Unsigned>
    StackCalc<F, STACK, DSIZE, EXP>
{
    pub fn is_full(&self) -> bool {
        self.index == STACK
    }

    pub fn is_empty(&self) -> bool {
        self.index == 0
    }

    pub fn len(&self) -> usize {
        self.index
    }

    pub fn reset(&mut self) {
        self.index = 0;
    }

    pub fn last(&self) -> Option<Decimal<DSIZE, EXP>> {
        if self.is_empty() {
            return None;
        }
        Some(self.stack[self.index - 1])
    }

    pub fn iter(&self) -> impl Iterator<Item = &Decimal<DSIZE, EXP>> {
        self.stack.iter().take(self.index)
    }

    pub fn push(
        &mut self,
        val: impl TryInto<Decimal<DSIZE, EXP>, Error: Into<StackCalcError>>,
    ) -> Result<(), StackCalcError> {
        if self.is_full() {
            return Err(StackCalcError::StackOverflow);
        }
        self.stack[self.index] = val.try_into().map_err(Into::into)?;
        self.index += 1;
        Ok(())
    }

    pub fn pop(&mut self) -> Result<Decimal<DSIZE, EXP>, StackCalcError> {
        if self.is_empty() {
            return Err(StackCalcError::StackUnderflow);
        }
        self.index -= 1;
        Ok(self.stack[self.index])
    }

    fn pop_pair_float(&mut self) -> Result<(F, F), StackCalcError> {
        let a = self.pop()?;
        let b = self.pop()?;
        let a = a.to_float::<F>()?;
        let b = b.to_float::<F>()?;
        Ok((a, b))
    }

    fn calc_pair_float(
        &mut self,
        f: impl FnOnce(F, F) -> Result<F, StackCalcError>,
    ) -> Result<Decimal<DSIZE, EXP>, StackCalcError> {
        let (a, b) = self.pop_pair_float()?;
        let res = Decimal::from_float(f(a, b)?)?;
        self.push(res)?;
        Ok(res)
    }

    pub fn add(&mut self) -> Result<Decimal<DSIZE, EXP>, StackCalcError> {
        self.calc_pair_float(|a, b| Ok(b + a))
    }

    pub fn sub(&mut self) -> Result<Decimal<DSIZE, EXP>, StackCalcError> {
        self.calc_pair_float(|a, b| Ok(b - a))
    }

    pub fn mul(&mut self) -> Result<Decimal<DSIZE, EXP>, StackCalcError> {
        self.calc_pair_float(|a, b| Ok(b * a))
    }

    pub fn div(&mut self) -> Result<Decimal<DSIZE, EXP>, StackCalcError> {
        self.calc_pair_float(|a, b| Ok(b / a))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_add() -> Result<(), StackCalcError> {
        let mut calc = StackCalc::<f64, 3, 7>::default();
        calc.push(Decimal::default())?;
        calc.push(1337.42)?;
        assert_eq!(calc.add()?, Decimal::try_from(1337.42)?);
        calc.push(1337.42)?;
        assert_eq!(calc.add()?, Decimal::try_from(1337.42 * 2.0)?);
        calc.push(2.0)?;
        calc.push(3.0)?;
        assert!(matches!(
            calc.push(3.0).unwrap_err(),
            StackCalcError::StackOverflow
        ));
        calc.add()?;
        assert_eq!(calc.last().unwrap(), Decimal::try_from(5.0)?);
        calc.add()?;
        assert_eq!(
            calc.last().unwrap(),
            Decimal::try_from(1337.42 * 2.0 + 5.0)?
        );
        assert!(matches!(
            calc.add().unwrap_err(),
            StackCalcError::StackUnderflow
        ));
        Ok(())
    }
}