rippled/include/xrpl/ledger/PaymentSandbox.h

#ifndef XRPL_LEDGER_PAYMENTSANDBOX_H_INCLUDED
#define XRPL_LEDGER_PAYMENTSANDBOX_H_INCLUDED

#include <xrpl/ledger/RawView.h>
#include <xrpl/ledger/Sandbox.h>
#include <xrpl/ledger/detail/ApplyViewBase.h>
#include <xrpl/protocol/AccountID.h>

#include <map>

namespace ripple {

namespace detail {

// VFALCO TODO Inline this implementation
//        into the PaymentSandbox class itself
class DeferredCredits
{
public:
    struct Adjustment
    {
        Adjustment(STAmount const& d, STAmount const& c, STAmount const& b)
            : debits(d), credits(c), origBalance(b)
        {
        }
        STAmount debits;
        STAmount credits;
        STAmount origBalance;
    };

    // Get the adjustments for the balance between main and other.
    // Returns the debits, credits and the original balance
    std::optional<Adjustment>
    adjustments(
        AccountID const& main,
        AccountID const& other,
        Currency const& currency) const;

    void
    credit(
        AccountID const& sender,
        AccountID const& receiver,
        STAmount const& amount,
        STAmount const& preCreditSenderBalance);

    void
    ownerCount(AccountID const& id, std::uint32_t cur, std::uint32_t next);

    // Get the adjusted owner count. Since DeferredCredits is meant to be used
    // in payments, and payments only decrease owner counts, return the max
    // remembered owner count.
    std::optional<std::uint32_t>
    ownerCount(AccountID const& id) const;

    void
    apply(DeferredCredits& to);

private:
    // lowAccount, highAccount
    using Key = std::tuple<AccountID, AccountID, Currency>;
    struct Value
    {
        explicit Value() = default;

        STAmount lowAcctCredits;
        STAmount highAcctCredits;
        STAmount lowAcctOrigBalance;
    };

    static Key
    makeKey(AccountID const& a1, AccountID const& a2, Currency const& c);

    std::map<Key, Value> credits_;
    std::map<AccountID, std::uint32_t> ownerCounts_;
};

}  // namespace detail

//------------------------------------------------------------------------------

/** A wrapper which makes credits unavailable to balances.

    This is used for payments and pathfinding, so that consuming
    liquidity from a path never causes portions of that path or
    other paths to gain liquidity.

    The behavior of certain free functions in the ApplyView API
    will change via the balanceHook and creditHook overrides
    of PaymentSandbox.

    @note Presented as ApplyView to clients
*/
class PaymentSandbox final : public detail::ApplyViewBase
{
public:
    PaymentSandbox() = delete;
    PaymentSandbox(PaymentSandbox const&) = delete;
    PaymentSandbox&
    operator=(PaymentSandbox&&) = delete;
    PaymentSandbox&
    operator=(PaymentSandbox const&) = delete;

    PaymentSandbox(PaymentSandbox&&) = default;

    PaymentSandbox(ReadView const* base, ApplyFlags flags)
        : ApplyViewBase(base, flags)
    {
    }

    PaymentSandbox(ApplyView const* base) : ApplyViewBase(base, base->flags())
    {
    }

    /** Construct on top of existing PaymentSandbox.

        The changes are pushed to the parent when
        apply() is called.

        @param parent A non-null pointer to the parent.

        @note A pointer is used to prevent confusion
              with copy construction.
    */
    // VFALCO If we are constructing on top of a PaymentSandbox,
    //        or a PaymentSandbox-derived class, we MUST go through
    //        one of these constructors or invariants will be broken.
    /** @{ */
    explicit PaymentSandbox(PaymentSandbox const* base)
        : ApplyViewBase(base, base->flags()), ps_(base)
    {
    }

    explicit PaymentSandbox(PaymentSandbox* base)
        : ApplyViewBase(base, base->flags()), ps_(base)
    {
    }
    /** @} */

    STAmount
    balanceHook(
        AccountID const& account,
        AccountID const& issuer,
        STAmount const& amount) const override;

    void
    creditHook(
        AccountID const& from,
        AccountID const& to,
        STAmount const& amount,
        STAmount const& preCreditBalance) override;

    void
    adjustOwnerCountHook(
        AccountID const& account,
        std::uint32_t cur,
        std::uint32_t next) override;

    std::uint32_t
    ownerCountHook(AccountID const& account, std::uint32_t count)
        const override;

    /** Apply changes to base view.

        `to` must contain contents identical to the parent
        view passed upon construction, else undefined
        behavior will result.
    */
    /** @{ */
    void
    apply(RawView& to);

    void
    apply(PaymentSandbox& to);
    /** @} */

    // Return a map of balance changes on trust lines. The low account is the
    // first account in the key. If the two accounts are equal, the map contains
    // the total changes in currency regardless of issuer. This is useful to get
    // the total change in XRP balances.
    std::map<std::tuple<AccountID, AccountID, Currency>, STAmount>
    balanceChanges(ReadView const& view) const;

    XRPAmount
    xrpDestroyed() const;

private:
    detail::DeferredCredits tab_;
    PaymentSandbox const* ps_ = nullptr;
};

}  // namespace ripple

#endif