QualityFunction.h

#pragma once
 
#include <xrpl/basics/Number.h>
#include <xrpl/basics/contract.h>
#include <xrpl/beast/utility/Zero.h>
#include <xrpl/protocol/AMMCore.h>
#include <xrpl/protocol/Quality.h>
 
#include <cstdint>
#include <optional>
#include <stdexcept>
 
namespace xrpl {

class QualityFunction
{
private:
    // slope
    Number m_;
    // intercept
    Number b_;
    // seated if QF is for CLOB offer.
    std::optional<Quality> quality_;
 
public:
    struct AMMTag
    {
    };
    // AMMOffer for multi-path is like CLOB, i.e. the offer size
    // changes proportionally to its quality.
    struct CLOBLikeTag
    {
    };
    QualityFunction(Quality const& quality, CLOBLikeTag);
    template <typename TIn, typename TOut>
    QualityFunction(TAmounts<TIn, TOut> const& amounts, std::uint32_t tfee, AMMTag);

    void
    combine(QualityFunction const& qf);

    std::optional<Number>
    outFromAvgQ(Quality const& quality);

    [[nodiscard]] bool
    satisfiesAvgQ(Quality const& quality, Number const& out) const;

    [[nodiscard]] bool
    isConst() const
    {
        return quality_.has_value();
    }
 
    [[nodiscard]] std::optional<Quality> const&
    quality() const
    {
        return quality_;
    }
};
 
template <typename TIn, typename TOut>
QualityFunction::QualityFunction(
    TAmounts<TIn, TOut> const& amounts,
    std::uint32_t tfee,
    QualityFunction::AMMTag)
{
    if (amounts.in <= beast::kZero || amounts.out <= beast::kZero)
        Throw<std::runtime_error>("QualityFunction amounts are 0.");
    Number const cfee = feeMult(tfee);
    m_ = -cfee / amounts.in;
    b_ = amounts.out * cfee / amounts.in;
}
 
}  // namespace xrpl