rippled/include/xrpl/tx/paths/OfferStream.h

#pragma once

#include <xrpl/basics/Log.h>
#include <xrpl/basics/chrono.h>
#include <xrpl/beast/utility/Journal.h>
#include <xrpl/ledger/View.h>
#include <xrpl/tx/paths/BookTip.h>
#include <xrpl/tx/paths/Offer.h>

#include <boost/container/flat_set.hpp>

namespace xrpl {

template <class TIn, class TOut>
class TOfferStreamBase
{
public:
    class StepCounter
    {
    private:
        std::uint32_t const limit_;
        std::uint32_t count_;
        beast::Journal j_;

    public:
        StepCounter(std::uint32_t limit, beast::Journal j) : limit_(limit), count_(0), j_(j)
        {
        }

        bool
        step()
        {
            if (count_ >= limit_)
            {
                JLOG(j_.debug()) << "Exceeded " << limit_ << " step limit.";
                return false;
            }
            count_++;
            return true;
        }
        std::uint32_t
        count() const
        {
            return count_;
        }
    };

protected:
    beast::Journal const j_;
    ApplyView& view_;
    ApplyView& cancelView_;
    Book book_;
    bool validBook_;
    NetClock::time_point const expire_;
    BookTip tip_;
    TOffer<TIn, TOut> offer_;
    std::optional<TOut> ownerFunds_;
    StepCounter& counter_;

    void
    erase(ApplyView& view);

    virtual void
    permRmOffer(uint256 const& offerIndex) = 0;

    template <class TTakerPays, class TTakerGets>
    bool
    shouldRmSmallIncreasedQOffer() const;

public:
    TOfferStreamBase(
        ApplyView& view,
        ApplyView& cancelView,
        Book const& book,
        NetClock::time_point when,
        StepCounter& counter,
        beast::Journal journal);

    virtual ~TOfferStreamBase() = default;

    /** Returns the offer at the tip of the order book.
        Offers are always presented in decreasing quality.
        Only valid if step() returned `true`.
    */
    TOffer<TIn, TOut>&
    tip() const
    {
        return const_cast<TOfferStreamBase*>(this)->offer_;
    }

    /** Advance to the next valid offer.
        This automatically removes:
            - Offers with missing ledger entries
            - Offers found unfunded
            - expired offers
        @return `true` if there is a valid offer.
    */
    bool
    step();

    TOut
    ownerFunds() const
    {
        return *ownerFunds_;
    }
};

/** Presents and consumes the offers in an order book.

    Two `ApplyView` objects accumulate changes to the ledger. `view`
    is applied when the calling transaction succeeds. If the calling
    transaction fails, then `view_cancel` is applied.

    Certain invalid offers are automatically removed:
    - Offers with missing ledger entries
    - Offers that expired
    - Offers found unfunded:
    An offer is found unfunded when the corresponding balance is zero
    and the caller has not modified the balance. This is accomplished
    by also looking up the balance in the cancel view.

    When an offer is removed, it is removed from both views. This grooms the
    order book regardless of whether or not the transaction is successful.
*/
class OfferStream : public TOfferStreamBase<STAmount, STAmount>
{
protected:
    void
    permRmOffer(uint256 const& offerIndex) override;

public:
    using TOfferStreamBase<STAmount, STAmount>::TOfferStreamBase;
};

/** Presents and consumes the offers in an order book.

    The `view_' ` `ApplyView` accumulates changes to the ledger.
    The `cancelView_` is used to determine if an offer is found
    unfunded or became unfunded.
    The `permToRemove` collection identifies offers that should be
    removed even if the strand associated with this OfferStream
    is not applied.

    Certain invalid offers are added to the `permToRemove` collection:
    - Offers with missing ledger entries
    - Offers that expired
    - Offers found unfunded:
    An offer is found unfunded when the corresponding balance is zero
    and the caller has not modified the balance. This is accomplished
    by also looking up the balance in the cancel view.
*/
template <class TIn, class TOut>
class FlowOfferStream : public TOfferStreamBase<TIn, TOut>
{
private:
    boost::container::flat_set<uint256> permToRemove_;

public:
    using TOfferStreamBase<TIn, TOut>::TOfferStreamBase;

    // The following interface allows offer crossing to permanently
    // remove self crossed offers.  The motivation is somewhat
    // unintuitive.  See the discussion in the comments for
    // BookOfferCrossingStep::limitSelfCrossQuality().
    void
    permRmOffer(uint256 const& offerIndex) override;

    boost::container::flat_set<uint256> const&
    permToRemove() const
    {
        return permToRemove_;
    }
};
}  // namespace xrpl