concordium_base 10.0.0

use crate::common::cbor::{
    CborDecoder, CborDeserialize, CborEncoder, CborSerializationResult, CborSerialize,
    UnsignedDecimalFraction,
};
use anyhow::Context;
use rust_decimal::Error;
use std::str::FromStr;

/// Protocol level token (PLT) amount representation. The numerical amount
/// represented is `value * 10^(-decimals)`.
/// The number of decimals in the token amount should always match the number of
/// decimals for the token it represents an amount for.
///
/// Since the number of decimals always matches the token, `TokenAmount`
/// can be considered a fixed point decimal and does not implement any floating
/// point behaviour. The type also does not implement any arithmetic operations.
/// This is intentional, any arithmetic operations and floating point operations
/// should be performed using e.g. `rust_decimal::Decimal` before converting to
/// `TokenAmount`. Notice also that the `decimal` part could be left out of the
/// `TokenAmount` representation without loss of information, but it is there to
/// make `TokenAmount` self-contained with regard to the numerical value
/// represented. This enables additional validation, both programmatic and at
/// user level.
#[derive(Debug, Clone, Copy, Eq, PartialEq, Hash, serde::Deserialize, serde::Serialize)]
#[serde(try_from = "TokenAmountJson", into = "TokenAmountJson")]
pub struct TokenAmount {
    /// The amount of tokens as an unscaled integer value.
    value: u64,
    /// The number of decimals in the token amount.
    decimals: u8,
}

impl CborSerialize for TokenAmount {
    fn serialize<C: CborEncoder>(&self, encoder: C) -> CborSerializationResult<()> {
        let decimal_fraction = UnsignedDecimalFraction::new(
            i64::from(self.decimals)
                .checked_neg()
                .context("convert decimals to exponent")?,
            self.value,
        );

        decimal_fraction.serialize(encoder)
    }
}

impl CborDeserialize for TokenAmount {
    fn deserialize<C: CborDecoder>(decoder: C) -> CborSerializationResult<Self>
    where
        Self: Sized,
    {
        let decimal_fraction = UnsignedDecimalFraction::deserialize(decoder)?;

        let decimals = decimal_fraction
            .exponent()
            .checked_neg()
            .and_then(|val| u8::try_from(val).ok())
            .context("convert exponent to decimals")?;
        let value = decimal_fraction.mantissa();

        Ok(Self { decimals, value })
    }
}

/// Rule for converting to `TokenAmount`
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub enum ConversionRule {
    /// Only allow conversions that preserve the exact same numerical value.
    Exact,
    /// Allow rounding when converting.
    AllowRounding,
}

impl TokenAmount {
    /// Construct a [`TokenAmount`] from a value without decimal places and the
    /// number of decimals, meaning the token amount is computed as `value *
    /// 10^(-decimals)`.
    pub fn from_raw(value: u64, decimals: u8) -> Self {
        Self { value, decimals }
    }

    /// The number of decimals in the token amount.
    ///
    /// The numerical amount represented by the `TokenAmount`
    /// is `value * 10^(-decimals)`
    pub fn decimals(&self) -> u8 {
        self.decimals
    }

    /// The amount of tokens as an unscaled integer value.
    ///
    /// The numerical amount represented by the `TokenAmount`
    /// is `value * 10^(-decimals)`
    pub fn value(&self) -> u64 {
        self.value
    }

    /// Converts [`rust_decimal::Decimal`] to a token amount of the same
    /// numerical value but represented with the given number of `decimals`.
    /// This may require rescaling but no rounding will be performed.
    /// If rounding is required to represent the numeric value with the given
    /// number of `decimals`, an error is returned.
    ///
    /// The given number of `decimals` should
    /// be equal to the number of decimals for the token it represents an amount
    /// for.
    pub fn try_from_rust_decimal(
        decimal: rust_decimal::Decimal,
        decimals: u8,
        conversion_rule: ConversionRule,
    ) -> TokenAmountConversionResult<Self> {
        let decimals_u32 = decimals as u32;
        let mut decimal_scaled = decimal;
        decimal_scaled.rescale(decimals_u32);
        if decimals_u32 > rust_decimal::Decimal::MAX_SCALE {
            return Err(TokenAmountConversionError::RustDecimal(
                rust_decimal::Error::ScaleExceedsMaximumPrecision(decimals_u32),
            ));
        }
        if decimal_scaled.scale() != decimals_u32 {
            // If scale was not changed to the requested scale, it means that
            // mantissa part would overflow at the requested scale
            return Err(TokenAmountConversionError::ValueOverflow);
        }
        let this = Self::from_raw(
            decimal_scaled
                .mantissa()
                .try_into()
                .map_err(|_| TokenAmountConversionError::ValueOverflow)?,
            decimals,
        );
        decimal_scaled.rescale(decimal.scale());
        if decimal_scaled.mantissa() != decimal.mantissa()
            && conversion_rule == ConversionRule::Exact
        {
            // If mantissa is not the same when scaling back, it means that we lost
            // precision (rounding) during the conversion
            return Err(TokenAmountConversionError::LossOfPrecision);
        }
        Ok(this)
    }

    /// Converts the token amount to a [`rust_decimal::Decimal`] of the same
    /// scale and same exact numerical value.
    pub fn try_to_rust_decimal(&self) -> TokenAmountConversionResult<rust_decimal::Decimal> {
        Ok(rust_decimal::Decimal::try_from_i128_with_scale(
            self.value as i128,
            self.decimals as u32,
        )?)
    }

    /// Interprets the given string as a decimal number (decimal separator must
    /// be "." if specified) and parses it into a token amount of the same
    /// numerical value represented with the given number of `decimals`.
    /// If rounding is required to represent the numeric value with the
    /// given number of `decimals`, an error is returned.
    ///
    /// The given number of `decimals` should
    /// be equal to the number of decimals for the token it represents an amount
    /// for.
    pub fn from_str(
        decimal_str: &str,
        decimals: u8,
        conversion_rule: ConversionRule,
    ) -> TokenAmountConversionResult<Self> {
        let decimal = match conversion_rule {
            ConversionRule::Exact => {
                rust_decimal::Decimal::from_str_exact(decimal_str).map_err(|err| match err {
                    Error::Underflow => TokenAmountConversionError::LossOfPrecision,
                    err => TokenAmountConversionError::RustDecimal(err),
                })?
            }
            ConversionRule::AllowRounding => rust_decimal::Decimal::from_str(decimal_str)?,
        };
        Self::try_from_rust_decimal(decimal, decimals, conversion_rule)
    }
}

/// Result of converting to or from [`TokenAmount`].
pub type TokenAmountConversionResult<T> = Result<T, TokenAmountConversionError>;

/// Error converting to or from [`TokenAmount`].
#[derive(Debug, thiserror::Error)]
pub enum TokenAmountConversionError {
    /// Error converting from [`TokenAmount`] or string to
    /// [`rust_decimal::Decimal`]
    #[error("error converting into rust_decimal::Decimal")]
    RustDecimal(#[from] rust_decimal::Error),
    #[error("precision lost due to rounding")]
    LossOfPrecision,
    #[error("value overflow")]
    ValueOverflow,
}

impl std::fmt::Display for TokenAmount {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        if self.decimals == 0 {
            self.value.fmt(f)
        } else {
            let mut value = format!(
                "{value:0width$}",
                width = self.decimals as usize + 1,
                value = self.value
            );
            value.insert(value.len() - self.decimals() as usize, '.');
            write!(f, "{}", value)
        }
    }
}

impl PartialOrd for TokenAmount {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        (self.decimals == other.decimals).then(|| self.value.cmp(&other.value))
    }
}

/// JSON representation of the token amount.
/// The purpose of this type is to derive the JSON representation matching other
/// SDKs.
#[derive(serde::Serialize, serde::Deserialize)]
struct TokenAmountJson {
    value: String,
    decimals: u8,
}

impl From<TokenAmount> for TokenAmountJson {
    fn from(amount: TokenAmount) -> Self {
        Self {
            value: amount.value.to_string(),
            decimals: amount.decimals,
        }
    }
}

impl TryFrom<TokenAmountJson> for TokenAmount {
    type Error = std::num::ParseIntError;

    fn try_from(json: TokenAmountJson) -> Result<Self, Self::Error> {
        Ok(Self {
            value: json.value.parse()?,
            decimals: json.decimals,
        })
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::common::cbor;
    use assert_matches::assert_matches;
    use std::cmp::Ordering;

    #[test]
    fn test_display() {
        let amount = TokenAmount {
            value: 123450,
            decimals: 3,
        };
        assert_eq!(amount.to_string().as_str(), "123.450");

        let amount = TokenAmount {
            value: 10,
            decimals: 5,
        };
        assert_eq!(amount.to_string().as_str(), "0.00010");
    }

    #[test]
    fn test_try_from_str_exact() {
        let str = "123.450";

        // Conversions that preserve the exact numerical value
        let token_amount = TokenAmount::from_str(str, 3, ConversionRule::Exact).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(123450, 3));
        let token_amount = TokenAmount::from_str(str, 2, ConversionRule::Exact).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(12345, 2));
        let token_amount = TokenAmount::from_str(str, 5, ConversionRule::Exact).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(12345000, 5));

        // Conversion that looses precision (requires rounding)
        let res = TokenAmount::from_str(str, 1, ConversionRule::Exact);
        assert_matches!(res, Err(TokenAmountConversionError::LossOfPrecision));
        let token_amount = TokenAmount::from_str(str, 1, ConversionRule::AllowRounding).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(1235, 1));

        // Conversion that looses precision while parsing the string
        let str = "1.000000000000000000000000000000000000001";
        let res = TokenAmount::from_str(str, 1, ConversionRule::Exact);
        assert_matches!(res, Err(TokenAmountConversionError::LossOfPrecision));
        let token_amount = TokenAmount::from_str(str, 1, ConversionRule::AllowRounding).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(10, 1));
    }

    #[test]
    fn test_try_from_rust_decimal() {
        let decimal = rust_decimal::Decimal::new(12600, 4);

        // Conversions that preserves the exact numerical value
        let token_amount =
            TokenAmount::try_from_rust_decimal(decimal, 4, ConversionRule::Exact).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(12600, 4));
        let token_amount =
            TokenAmount::try_from_rust_decimal(decimal, 2, ConversionRule::Exact).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(126, 2));
        let token_amount =
            TokenAmount::try_from_rust_decimal(decimal, 6, ConversionRule::Exact).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(1260000, 6));

        // Conversion that looses precision (requires rounding)
        let res = TokenAmount::try_from_rust_decimal(decimal, 1, ConversionRule::Exact);
        assert_matches!(res, Err(TokenAmountConversionError::LossOfPrecision));
        let token_amount =
            TokenAmount::try_from_rust_decimal(decimal, 1, ConversionRule::AllowRounding).unwrap();
        assert_eq!(token_amount, TokenAmount::from_raw(13, 1));

        // Conversion using out of range scale
        let res = TokenAmount::try_from_rust_decimal(decimal, 30, ConversionRule::Exact);
        assert_matches!(
            res,
            Err(TokenAmountConversionError::RustDecimal(
                rust_decimal::Error::ScaleExceedsMaximumPrecision(_)
            ))
        );

        // Conversion where value overflows at the requested scale
        let decimal = rust_decimal::Decimal::new(i64::MAX, 0);
        let res = TokenAmount::try_from_rust_decimal(decimal, 28, ConversionRule::Exact);
        assert_matches!(res, Err(TokenAmountConversionError::ValueOverflow));
    }

    #[test]
    fn test_try_to_rust_decimal() {
        let token_amount = TokenAmount::from_raw(12640, 4);

        let decimal = token_amount.try_to_rust_decimal().unwrap();
        assert_eq!(decimal.mantissa(), 12640);
        assert_eq!(decimal.scale(), 4);
    }

    #[test]
    fn test_partial_cmp() {
        // Check using same decimals.
        {
            let amount1 = TokenAmount::from_raw(123, 3);
            let amount2 = TokenAmount::from_raw(456, 3);
            assert_eq!(amount1.partial_cmp(&amount2), Some(Ordering::Less));
        }

        {
            // Check using different decimals.
            let amount1 = TokenAmount::from_raw(123, 3);
            let amount2 = TokenAmount::from_raw(456, 2);
            assert_eq!(amount1.partial_cmp(&amount2), None);
        }
    }

    #[test]
    fn test_token_amount_cbor() {
        let token_amount = TokenAmount::from_raw(12300, 3);
        let cbor = cbor::cbor_encode(&token_amount).unwrap();
        assert_eq!(hex::encode(&cbor), "c4822219300c");
        let token_amount_decoded: TokenAmount = cbor::cbor_decode(&cbor).unwrap();
        assert_eq!(token_amount_decoded, token_amount);

        let token_amount = TokenAmount {
            value: u64::MAX,
            decimals: 3,
        };
        let cbor = cbor::cbor_encode(&token_amount).unwrap();
        assert_eq!(hex::encode(&cbor), "c482221bffffffffffffffff");
        let token_amount_decoded: TokenAmount = cbor::cbor_decode(&cbor).unwrap();
        assert_eq!(token_amount_decoded, token_amount);
    }
}