AMMHelpers.h

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2023 Ripple Labs Inc.
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#ifndef RIPPLE_APP_MISC_AMMHELPERS_H_INCLUDED
#define RIPPLE_APP_MISC_AMMHELPERS_H_INCLUDED
 
#include <ripple/basics/IOUAmount.h>
#include <ripple/basics/Number.h>
#include <ripple/protocol/AMMCore.h>
#include <ripple/protocol/AmountConversions.h>
#include <ripple/protocol/Issue.h>
#include <ripple/protocol/Quality.h>
#include <ripple/protocol/STAccount.h>
#include <ripple/protocol/STAmount.h>
 
#include <type_traits>
 
namespace ripple {
 
STAmount
ammLPTokens(
    STAmount const& asset1,
    STAmount const& asset2,
    Issue const& lptIssue);
 
STAmount
lpTokensIn(
    STAmount const& asset1Balance,
    STAmount const& asset1Deposit,
    STAmount const& lptAMMBalance,
    std::uint16_t tfee);
 
STAmount
ammAssetIn(
    STAmount const& asset1Balance,
    STAmount const& lptAMMBalance,
    STAmount const& lpTokens,
    std::uint16_t tfee);
 
STAmount
lpTokensOut(
    STAmount const& asset1Balance,
    STAmount const& asset1Withdraw,
    STAmount const& lptAMMBalance,
    std::uint16_t tfee);
 
STAmount
withdrawByTokens(
    STAmount const& assetBalance,
    STAmount const& lptAMMBalance,
    STAmount const& lpTokens,
    std::uint16_t tfee);
 
inline bool
withinRelativeDistance(
    Quality const& calcQuality,
    Quality const& reqQuality,
    Number const& dist)
{
    if (calcQuality == reqQuality)
        return true;
    auto const [min, max] = std::minmax(calcQuality, reqQuality);
    // Relative distance is (max - min)/max. Can't use basic operations
    // on Quality. Have to use Quality::rate() instead, which
    // is inverse of quality: (1/max.rate - 1/min.rate)/(1/max.rate)
    return ((min.rate() - max.rate()) / min.rate()) < dist;
}
 
// clang-format off
template <typename Amt>
    requires(
        std::is_same_v<Amt, STAmount> || std::is_same_v<Amt, IOUAmount> ||
        std::is_same_v<Amt, XRPAmount>)
bool
withinRelativeDistance(Amt const& calc, Amt const& req, Number const& dist)
{
    if (calc == req)
        return true;
    auto const [min, max] = std::minmax(calc, req);
    return ((max - min) / max) < dist;
}
// clang-format on
 
template <typename TIn, typename TOut>
std::optional<TAmounts<TIn, TOut>>
changeSpotPriceQuality(
    TAmounts<TIn, TOut> const& pool,
    Quality const& quality,
    std::uint16_t tfee)
{
    auto const f = feeMult(tfee);  // 1 - fee
    auto const& a = f;
    auto const b = pool.in * (1 + f);
    Number const c = pool.in * pool.in - pool.in * pool.out * quality.rate();
    if (auto const res = b * b - 4 * a * c; res < 0)
        return std::nullopt;
    else if (auto const nTakerPaysPropose = (-b + root2(res)) / (2 * a);
             nTakerPaysPropose > 0)
    {
        auto const nTakerPays = [&]() {
            // The fee might make the AMM offer quality less than CLOB quality.
            // Therefore, AMM offer has to satisfy this constraint: o / i >= q.
            // Substituting o with swapAssetIn() gives:
            // i <= O / q - I / (1 - fee).
            auto const nTakerPaysConstraint =
                pool.out * quality.rate() - pool.in / f;
            if (nTakerPaysPropose > nTakerPaysConstraint)
                return nTakerPaysConstraint;
            return nTakerPaysPropose;
        }();
        if (nTakerPays <= 0)
            return std::nullopt;
        auto const takerPays = toAmount<TIn>(
            getIssue(pool.in), nTakerPays, Number::rounding_mode::upward);
        // should not fail
        if (auto const amounts =
                TAmounts<TIn, TOut>{
                    takerPays, swapAssetIn(pool, takerPays, tfee)};
            Quality{amounts} < quality &&
            !withinRelativeDistance(Quality{amounts}, quality, Number(1, -7)))
            Throw<std::runtime_error>("changeSpotPriceQuality failed");
        else
            return amounts;
    }
    return std::nullopt;
}
 
template <typename TIn, typename TOut>
TOut
swapAssetIn(
    TAmounts<TIn, TOut> const& pool,
    TIn const& assetIn,
    std::uint16_t tfee)
{
    return toAmount<TOut>(
        getIssue(pool.out),
        pool.out - (pool.in * pool.out) / (pool.in + assetIn * feeMult(tfee)),
        Number::rounding_mode::downward);
}
 
template <typename TIn, typename TOut>
TIn
swapAssetOut(
    TAmounts<TIn, TOut> const& pool,
    TOut const& assetOut,
    std::uint16_t tfee)
{
    return toAmount<TIn>(
        getIssue(pool.in),
        ((pool.in * pool.out) / (pool.out - assetOut) - pool.in) /
            feeMult(tfee),
        Number::rounding_mode::upward);
}
 
Number
square(Number const& n);
 
STAmount
adjustLPTokens(
    STAmount const& lptAMMBalance,
    STAmount const& lpTokens,
    bool isDeposit);
 
std::tuple<STAmount, std::optional<STAmount>, STAmount>
adjustAmountsByLPTokens(
    STAmount const& amountBalance,
    STAmount const& amount,
    std::optional<STAmount> const& amount2,
    STAmount const& lptAMMBalance,
    STAmount const& lpTokens,
    std::uint16_t tfee,
    bool isDeposit);
 
Number
solveQuadraticEq(Number const& a, Number const& b, Number const& c);
 
}  // namespace ripple
 
#endif  // RIPPLE_APP_MISC_AMMHELPERS_H_INCLUDED