EQ Fee Projection

The EQ fee can be calculate from onchain data. Below is the code we use to project the EQ Fee on the UI. If your curious about more details to swap math take a look here.

function getEquilibriumFee(
    _idealBalance: CurrencyAmount,
    _beforeBalance: CurrencyAmount,
    _amount: CurrencyAmount,
    _fee: FeeLibraryV02
): { eqFee: CurrencyAmount; protocolSubsidy: CurrencyAmount } {
    const afterBalance = _beforeBalance.subtract(_amount)

    let safeZoneMaxCurrency = _idealBalance.multiply(_fee.delta1Rate)
    const safeZoneMax = new Fraction(safeZoneMaxCurrency.numerator, safeZoneMaxCurrency.denominator)
    const safeZoneMinCurrency = _idealBalance.multiply(_fee.delta2Rate)
    const safeZoneMin = new Fraction(safeZoneMinCurrency.numerator, safeZoneMinCurrency.denominator)
    const proxyBeforeBalanceCurrency = _beforeBalance.lessThan(safeZoneMax) ? _beforeBalance : safeZoneMax
    const proxyBeforeBalance = new Fraction(proxyBeforeBalanceCurrency.numerator, proxyBeforeBalanceCurrency.denominator)

    let eqFee = CurrencyAmount.fromRawAmount(_amount.currency, JSBI.BigInt(0))
    let protocolSubsidy = CurrencyAmount.fromRawAmount(_amount.currency, JSBI.BigInt(0))

    if (afterBalance.greaterThan(safeZoneMax) || afterBalance.equalTo(safeZoneMax)) {
        // no fee zone, protocol subsidezes it
        eqFee = _amount.multiply(_fee.protocolSubsidyRate)
        protocolSubsidy = eqFee
    } else if (afterBalance.greaterThan(safeZoneMin) || afterBalance.equalTo(safeZoneMin)) {
        // safe zone
        eqFee = getTrapezoidArea(_amount.currency, _fee.lambda1Rate, ZERO, safeZoneMax, safeZoneMin, proxyBeforeBalance, afterBalance)
    } else {
        // danger zone
        if (_beforeBalance.greaterThan(safeZoneMin) || _beforeBalance.equalTo(safeZoneMin)) {
            // across 2 or 3 zones
            // part 1
            eqFee = eqFee.add(
                getTrapezoidArea(_amount.currency, _fee.lambda1Rate, ZERO, safeZoneMax, safeZoneMin, proxyBeforeBalance, safeZoneMin)
            )
            // part 2
            eqFee = eqFee.add(
                getTrapezoidArea(_amount.currency, _fee.lambda2Rate, _fee.lambda1Rate, safeZoneMin, ZERO, safeZoneMin, afterBalance)
            )
        } else {
            // only in danger zone
            // part2 only
            eqFee = eqFee.add(
                getTrapezoidArea(_amount.currency, _fee.lambda2Rate, _fee.lambda1Rate, safeZoneMin, ZERO, _beforeBalance, afterBalance)
            )
        }
    }

    return {
        eqFee,
        protocolSubsidy,
    }
}