safe-token-swap 3.0.0

//! All fee information, to be used for validation currently

use crate::error::SwapError;
use arrayref::{array_mut_ref, array_ref, array_refs, mut_array_refs};
use safecoin_program::{
    program_error::ProgramError,
    program_pack::{IsInitialized, Pack, Sealed},
};
use std::convert::TryFrom;

/// Encapsulates all fee information and calculations for swap operations
#[derive(Clone, Debug, Default, PartialEq)]
pub struct Fees {
    /// Trade fees are extra token amounts that are held inside the token
    /// accounts during a trade, making the value of liquidity tokens rise.
    /// Trade fee numerator
    pub trade_fee_numerator: u64,
    /// Trade fee denominator
    pub trade_fee_denominator: u64,

    /// Owner trading fees are extra token amounts that are held inside the token
    /// accounts during a trade, with the equivalent in pool tokens minted to
    /// the owner of the program.
    /// Owner trade fee numerator
    pub owner_trade_fee_numerator: u64,
    /// Owner trade fee denominator
    pub owner_trade_fee_denominator: u64,

    /// Owner withdraw fees are extra liquidity pool token amounts that are
    /// sent to the owner on every withdrawal.
    /// Owner withdraw fee numerator
    pub owner_withdraw_fee_numerator: u64,
    /// Owner withdraw fee denominator
    pub owner_withdraw_fee_denominator: u64,

    /// Host fees are a proportion of the owner trading fees, sent to an
    /// extra account provided during the trade.
    /// Host trading fee numerator
    pub host_fee_numerator: u64,
    /// Host trading fee denominator
    pub host_fee_denominator: u64,
}

/// Helper function for calculating swap fee
pub fn calculate_fee(
    token_amount: u128,
    fee_numerator: u128,
    fee_denominator: u128,
) -> Option<u128> {
    if fee_numerator == 0 || token_amount == 0 {
        Some(0)
    } else {
        let fee = token_amount
            .checked_mul(fee_numerator)?
            .checked_div(fee_denominator)?;
        if fee == 0 {
            Some(1) // minimum fee of one token
        } else {
            Some(fee)
        }
    }
}

fn validate_fraction(numerator: u64, denominator: u64) -> Result<(), SwapError> {
    if denominator == 0 && numerator == 0 {
        Ok(())
    } else if numerator >= denominator {
        Err(SwapError::InvalidFee)
    } else {
        Ok(())
    }
}

impl Fees {
    /// Calculate the withdraw fee in pool tokens
    pub fn owner_withdraw_fee(&self, pool_tokens: u128) -> Option<u128> {
        calculate_fee(
            pool_tokens,
            u128::try_from(self.owner_withdraw_fee_numerator).ok()?,
            u128::try_from(self.owner_withdraw_fee_denominator).ok()?,
        )
    }

    /// Calculate the trading fee in trading tokens
    pub fn trading_fee(&self, trading_tokens: u128) -> Option<u128> {
        calculate_fee(
            trading_tokens,
            u128::try_from(self.trade_fee_numerator).ok()?,
            u128::try_from(self.trade_fee_denominator).ok()?,
        )
    }

    /// Calculate the owner trading fee in trading tokens
    pub fn owner_trading_fee(&self, trading_tokens: u128) -> Option<u128> {
        calculate_fee(
            trading_tokens,
            u128::try_from(self.owner_trade_fee_numerator).ok()?,
            u128::try_from(self.owner_trade_fee_denominator).ok()?,
        )
    }

    /// Calculate the host fee based on the owner fee, only used in production
    /// situations where a program is hosted by multiple frontends
    pub fn host_fee(&self, owner_fee: u128) -> Option<u128> {
        calculate_fee(
            owner_fee,
            u128::try_from(self.host_fee_numerator).ok()?,
            u128::try_from(self.host_fee_denominator).ok()?,
        )
    }

    /// Validate that the fees are reasonable
    pub fn validate(&self) -> Result<(), SwapError> {
        validate_fraction(self.trade_fee_numerator, self.trade_fee_denominator)?;
        validate_fraction(
            self.owner_trade_fee_numerator,
            self.owner_trade_fee_denominator,
        )?;
        validate_fraction(
            self.owner_withdraw_fee_numerator,
            self.owner_withdraw_fee_denominator,
        )?;
        validate_fraction(self.host_fee_numerator, self.host_fee_denominator)?;
        Ok(())
    }
}

/// IsInitialized is required to use `Pack::pack` and `Pack::unpack`
impl IsInitialized for Fees {
    fn is_initialized(&self) -> bool {
        true
    }
}

impl Sealed for Fees {}
impl Pack for Fees {
    const LEN: usize = 64;
    fn pack_into_slice(&self, output: &mut [u8]) {
        let output = array_mut_ref![output, 0, 64];
        let (
            trade_fee_numerator,
            trade_fee_denominator,
            owner_trade_fee_numerator,
            owner_trade_fee_denominator,
            owner_withdraw_fee_numerator,
            owner_withdraw_fee_denominator,
            host_fee_numerator,
            host_fee_denominator,
        ) = mut_array_refs![output, 8, 8, 8, 8, 8, 8, 8, 8];
        *trade_fee_numerator = self.trade_fee_numerator.to_le_bytes();
        *trade_fee_denominator = self.trade_fee_denominator.to_le_bytes();
        *owner_trade_fee_numerator = self.owner_trade_fee_numerator.to_le_bytes();
        *owner_trade_fee_denominator = self.owner_trade_fee_denominator.to_le_bytes();
        *owner_withdraw_fee_numerator = self.owner_withdraw_fee_numerator.to_le_bytes();
        *owner_withdraw_fee_denominator = self.owner_withdraw_fee_denominator.to_le_bytes();
        *host_fee_numerator = self.host_fee_numerator.to_le_bytes();
        *host_fee_denominator = self.host_fee_denominator.to_le_bytes();
    }

    fn unpack_from_slice(input: &[u8]) -> Result<Fees, ProgramError> {
        let input = array_ref![input, 0, 64];
        #[allow(clippy::ptr_offset_with_cast)]
        let (
            trade_fee_numerator,
            trade_fee_denominator,
            owner_trade_fee_numerator,
            owner_trade_fee_denominator,
            owner_withdraw_fee_numerator,
            owner_withdraw_fee_denominator,
            host_fee_numerator,
            host_fee_denominator,
        ) = array_refs![input, 8, 8, 8, 8, 8, 8, 8, 8];
        Ok(Self {
            trade_fee_numerator: u64::from_le_bytes(*trade_fee_numerator),
            trade_fee_denominator: u64::from_le_bytes(*trade_fee_denominator),
            owner_trade_fee_numerator: u64::from_le_bytes(*owner_trade_fee_numerator),
            owner_trade_fee_denominator: u64::from_le_bytes(*owner_trade_fee_denominator),
            owner_withdraw_fee_numerator: u64::from_le_bytes(*owner_withdraw_fee_numerator),
            owner_withdraw_fee_denominator: u64::from_le_bytes(*owner_withdraw_fee_denominator),
            host_fee_numerator: u64::from_le_bytes(*host_fee_numerator),
            host_fee_denominator: u64::from_le_bytes(*host_fee_denominator),
        })
    }
}

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

    #[test]
    fn pack_fees() {
        let trade_fee_numerator = 1;
        let trade_fee_denominator = 4;
        let owner_trade_fee_numerator = 2;
        let owner_trade_fee_denominator = 5;
        let owner_withdraw_fee_numerator = 4;
        let owner_withdraw_fee_denominator = 10;
        let host_fee_numerator = 7;
        let host_fee_denominator = 100;
        let fees = Fees {
            trade_fee_numerator,
            trade_fee_denominator,
            owner_trade_fee_numerator,
            owner_trade_fee_denominator,
            owner_withdraw_fee_numerator,
            owner_withdraw_fee_denominator,
            host_fee_numerator,
            host_fee_denominator,
        };

        let mut packed = [0u8; Fees::LEN];
        Pack::pack_into_slice(&fees, &mut packed[..]);
        let unpacked = Fees::unpack_from_slice(&packed).unwrap();
        assert_eq!(fees, unpacked);

        let mut packed = vec![];
        packed.extend_from_slice(&trade_fee_numerator.to_le_bytes());
        packed.extend_from_slice(&trade_fee_denominator.to_le_bytes());
        packed.extend_from_slice(&owner_trade_fee_numerator.to_le_bytes());
        packed.extend_from_slice(&owner_trade_fee_denominator.to_le_bytes());
        packed.extend_from_slice(&owner_withdraw_fee_numerator.to_le_bytes());
        packed.extend_from_slice(&owner_withdraw_fee_denominator.to_le_bytes());
        packed.extend_from_slice(&host_fee_numerator.to_le_bytes());
        packed.extend_from_slice(&host_fee_denominator.to_le_bytes());
        let unpacked = Fees::unpack_from_slice(&packed).unwrap();
        assert_eq!(fees, unpacked);
    }
}