ledger-prototype/utxo/src/amount.rs

use crate::Asset;
use serde::{de, ser::SerializeStruct, Deserialize, Serialize, Serializer};

/// The raw storage for cents, the more the better
pub type AmountCents = i128;

#[derive(Clone, Debug, Eq, PartialEq, thiserror::Error, Serialize)]
pub enum Error {
    #[error("{0} is not a valid number")]
    NoANumber(String),

    #[error("Overflow")]
    Overflow,

    #[error("Invalid asset name: {0}")]
    InvalidAssetName(String),
}

#[derive(Debug, Serialize, Deserialize)]
/// Human amount
///
/// This amount is used to represent the amount in a human readable way.  It is not being used
/// internally but it is defined to be used by any external interface.
pub struct HumanAmount {
    asset: Asset,
    amount: String,
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(untagged)]
/// Any amount
///
/// This amount will parse/encode any amount, either in cents or in human readable format.
pub enum AnyAmount {
    /// Amount in cents
    Cent(Amount),
    /// Amount in human readable format
    Human(HumanAmount),
}

impl TryInto<Amount> for AnyAmount {
    type Error = Error;

    fn try_into(self) -> Result<Amount, Self::Error> {
        match self {
            Self::Cent(a) => Ok(a),
            Self::Human(h) => h.asset.from_human(&h.amount),
        }
    }
}

/// Amount
///
/// The cents are stored in their lowest denomination, or their "cents".  For
/// instance a Bitcoin would be represented with a `precision` of 8, or dollars
/// in a 2 or 3.
///
/// For instance, if the dollar Asset has a `precision` of `2`, an `cents` of
/// 1255 will represent `12.55 USD`.
///
/// Amount will abstract all the math operations that can be performed with the
/// amounts, guarding that the `Asset` are the same before performing any
/// operation.
///
///
/// The `cents` and `Asset` must be used to store amounts in the storage
/// layer. Float or string representations should be used to display
#[derive(
    Clone, Debug, Eq, PartialEq, Deserialize, borsh::BorshSerialize, borsh::BorshDeserialize,
)]
pub struct Amount {
    asset: Asset,
    #[serde(deserialize_with = "deserialize_string_to_amount")]
    cents: AmountCents,
}

impl Serialize for Amount {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let mut state = serializer.serialize_struct("amount", 3)?;
        state.serialize_field("asset", &self.asset)?;
        state.serialize_field("cents", &self.cents.to_string())?;
        state.serialize_field("human", &self.to_string())?;
        state.end()
    }
}

fn deserialize_string_to_amount<'de, D>(deserializer: D) -> Result<AmountCents, D::Error>
where
    D: de::Deserializer<'de>,
{
    let s = String::deserialize(deserializer)?;
    s.parse::<AmountCents>().map_err(serde::de::Error::custom)
}

impl Amount {
    /// Creates a new amount from an asset and cents
    pub(crate) fn new(asset: Asset, cents: AmountCents) -> Self {
        Self { asset, cents }
    }

    #[inline]
    /// Returns the asset for this amount
    pub fn asset(&self) -> &Asset {
        &self.asset
    }

    #[inline]
    /// Return the cents
    pub fn cents(&self) -> AmountCents {
        self.cents
    }

    /// Attempts to do a checked addition of two amounts
    /// This will fails if assets are not the same or it overflows or underflows
    pub fn checked_add(&self, other: &Self) -> Option<Self> {
        if self.asset != other.asset {
            return None;
        }

        self.cents.checked_add(other.cents).map(|cents| Self {
            asset: self.asset.clone(),
            cents,
        })
    }
}

impl ToString for Amount {
    fn to_string(&self) -> String {
        self.try_into().unwrap()
    }
}

impl TryInto<String> for &Amount {
    type Error = Error;

    fn try_into(self) -> Result<String, Error> {
        let str = self.cents.abs().to_string();
        let precision = self.asset.precision;
        let len = u8::try_from(str.len()).map_err(|_| Error::Overflow)?;

        let (str, len) = if len < precision.checked_add(1).ok_or(Error::Overflow)? {
            (
                format!(
                    "{}{}",
                    "0".repeat(
                        precision
                            .checked_sub(len)
                            .and_then(|x| x.checked_add(1))
                            .ok_or(Error::Overflow)?
                            .into()
                    ),
                    str
                ),
                precision.checked_add(1).ok_or(Error::Overflow)?,
            )
        } else {
            (str, len)
        };

        let (left, right) = str.split_at(len.checked_sub(precision).ok_or(Error::Overflow)?.into());
        Ok(format!(
            "{}{}.{}",
            if self.cents.is_negative() { "-" } else { "" },
            left,
            right
        )
        .trim_end_matches('0')
        .trim_end_matches('.')
        .to_owned())
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn dollar() {
        let usd: Asset = "USD/4".parse().expect("asset");
        let amount = usd.new_amount(1022100);
        assert_eq!(amount.to_string(), "102.21");
    }

    #[test]
    fn bitcoin() {
        let btc: Asset = "BTC/8".parse().expect("asset");
        assert_eq!(btc.new_amount(1022100).to_string(), "0.010221");
        assert_eq!(btc.new_amount(10).to_string(), "0.0000001");
        assert_eq!(btc.new_amount(10000000).to_string(), "0.1");
        assert_eq!(btc.new_amount(100000000).to_string(), "1");
        assert_eq!(
            btc.new_amount(100000000)
                .checked_add(&btc.new_amount(100000000))
                .unwrap()
                .to_string(),
            "2",
        );
        assert_eq!(btc.new_amount(1000000000).to_string(), "10");
    }

    #[test]
    fn from_human() {
        let btc: Asset = "BTC/8".parse().expect("asset");
        let parsed_amount = btc.from_human("0.1").expect("valid amount");
        assert_eq!(parsed_amount.to_string(), "0.1");
        let parsed_amount = btc.from_human("-0.1").expect("valid amount");
        assert_eq!(parsed_amount.to_string(), "-0.1");
        let parsed_amount = btc.from_human("-0.000001").expect("valid amount");
        assert_eq!(parsed_amount.to_string(), "-0.000001");
        let parsed_amount = btc.from_human("-0.000000001").expect("valid amount");
        assert_eq!(parsed_amount.to_string(), "0");
        let parsed_amount = btc.from_human("0.000001").expect("valid amount");
        assert_eq!(parsed_amount.to_string(), "0.000001");
        let parsed_amount = btc.from_human("-0.000000100001").expect("valid amount");
        assert_eq!(parsed_amount.to_string(), "-0.0000001");
        let parsed_amount = btc.from_human("100000").expect("valid amount");
        assert_eq!(parsed_amount.to_string(), "100000");
    }
}