OfferExchange::CrossOfferResult
OfferExchange::crossOffer(OfferFrame& sellingWheatOffer,
int64_t maxWheatReceived, int64_t& numWheatReceived,
int64_t maxSheepSend, int64_t& numSheepSend)
{
Asset& sheep = sellingWheatOffer.getOffer().buying;
Asset& wheat = sellingWheatOffer.getOffer().selling;
AccountID& accountBID = sellingWheatOffer.getOffer().sellerID;
Database& db = mLedgerManager.getDatabase();
AccountFrame::pointer accountB;
accountB = AccountFrame::loadAccount(accountBID, db);
if (!accountB)
{
throw std::runtime_error(
"invalid database state: offer must have matching account");
}
TrustFrame::pointer wheatLineAccountB;
if (wheat.type() != ASSET_TYPE_NATIVE)
{
wheatLineAccountB = TrustFrame::loadTrustLine(accountBID, wheat, db);
if (!wheatLineAccountB)
{
throw std::runtime_error(
"invalid database state: offer must have matching trust line");
}
}
TrustFrame::pointer sheepLineAccountB;
if (sheep.type() == ASSET_TYPE_NATIVE)
{
numWheatReceived = INT64_MAX;
}
else
{
sheepLineAccountB = TrustFrame::loadTrustLine(accountBID, sheep, db);
if (!sheepLineAccountB)
{
throw std::runtime_error(
"invalid database state: offer must have matching trust line");
}
// compute numWheatReceived based on what the account can receive
int64_t sellerMaxSheep = sheepLineAccountB->getMaxAmountReceive();
if (!bigDivide(numWheatReceived, sellerMaxSheep,
sellingWheatOffer.getOffer().price.d,
sellingWheatOffer.getOffer().price.n))
{
numWheatReceived = INT64_MAX;
}
}
// adjust numWheatReceived with what the seller has
{
int64_t wheatCanSell;
if (wheat.type() == ASSET_TYPE_NATIVE)
{
// can only send above the minimum balance
wheatCanSell = accountB->getBalanceAboveReserve(mLedgerManager);
}
else
{
if (wheatLineAccountB->isAuthorized())
{
wheatCanSell = wheatLineAccountB->getBalance();
}
else
{
wheatCanSell = 0;
}
}
if (numWheatReceived > wheatCanSell)
{
numWheatReceived = wheatCanSell;
}
}
// you can receive the lesser of the amount of wheat offered or
// the amount the guy has
if (numWheatReceived >= sellingWheatOffer.getOffer().amount)
{
numWheatReceived = sellingWheatOffer.getOffer().amount;
}
else
{
// update the offer based on the balance (to determine if it should be
// deleted or not)
// note that we don't need to write into the db at this point as the
// actual update
// is done further down
sellingWheatOffer.getOffer().amount = numWheatReceived;
}
bool reducedOffer = false;
if (numWheatReceived > maxWheatReceived)
{
numWheatReceived = maxWheatReceived;
reducedOffer = true;
}
// this guy can get X wheat to you. How many sheep does that get him?
if (!bigDivide(numSheepSend, numWheatReceived,
sellingWheatOffer.getOffer().price.n,
sellingWheatOffer.getOffer().price.d))
{
numSheepSend = INT64_MAX;
}
if (numSheepSend > maxSheepSend)
{
// reduce the number even more if there is a limit on Sheep
numSheepSend = maxSheepSend;
reducedOffer = true;
}
// bias towards seller (this cannot overflow at this point)
numWheatReceived =
bigDivide(numSheepSend, sellingWheatOffer.getOffer().price.d,
sellingWheatOffer.getOffer().price.n);
bool offerTaken = false;
if (numWheatReceived == 0 || numSheepSend == 0)
{
if (reducedOffer)
{
return eOfferCantConvert;
}
else
{
// force delete the offer as it represents a bogus offer
numWheatReceived = 0;
numSheepSend = 0;
offerTaken = true;
}
}
offerTaken =
offerTaken || sellingWheatOffer.getOffer().amount <= numWheatReceived;
if (offerTaken)
{ // entire offer is taken
sellingWheatOffer.storeDelete(mDelta, db);
accountB->addNumEntries(-1, mLedgerManager);
accountB->storeChange(mDelta, db);
}
else
{
sellingWheatOffer.getOffer().amount -= numWheatReceived;
sellingWheatOffer.storeChange(mDelta, db);
}
// Adjust balances
if (sheep.type() == ASSET_TYPE_NATIVE)
{
accountB->getAccount().balance += numSheepSend;
accountB->storeChange(mDelta, db);
}
else
{
if (!sheepLineAccountB->addBalance(numSheepSend))
{
return eOfferCantConvert;
}
sheepLineAccountB->storeChange(mDelta, db);
}
if (wheat.type() == ASSET_TYPE_NATIVE)
{
accountB->getAccount().balance -= numWheatReceived;
accountB->storeChange(mDelta, db);
}
else
{
if (!wheatLineAccountB->addBalance(-numWheatReceived))
{
return eOfferCantConvert;
}
wheatLineAccountB->storeChange(mDelta, db);
}
mOfferTrail.push_back(
ClaimOfferAtom(accountB->getID(), sellingWheatOffer.getOfferID(), wheat,
numWheatReceived, sheep, numSheepSend));
return offerTaken ? eOfferTaken : eOfferPartial;
}
