pay lowest-bid remainder to auction creator

x/cosmostest/keeper/auction_expiry.go

@@ -2,8 +2,10 @@ package keeper
 
 import (
 	"cosmos-test/x/cosmostest/memdb"
+	"math/big"
 
 	"github.com/cosmos/cosmos-sdk/types"
+	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/pkg/errors"
 )
 
@@ -36,7 +38,21 @@ func (k *Keeper) EndExpiredAuctions(ctx types.Context) {
 			// clear auction
 			memdb.BidDB.ClearAuction(auctionId)
 
-			// pay out user
+			// pay out remainder to auction creator
+			ceiling := new(big.Int)
+			ceiling.SetString(auction.Ceiling, 10)
+			lowestBidAmt := new(big.Int)
+			lowestBidAmt.SetString(auction.Best.Amount, 10)
+			// only pay out if there is a difference
+			if ceiling.Cmp(lowestBidAmt) == 1 {
+				amtRemaining := new(big.Int)
+				amtRemaining.Sub(ceiling, lowestBidAmt)
+				coins := sdk.NewCoins(sdk.Coin{
+					Amount: sdk.NewIntFromBigInt(amtRemaining),
+					Denom:  auction.Denom,
+				})
+				k.bank.SendCoinsFromModuleToAccount(ctx, "cosmostest", sdk.AccAddress(auction.Owner), coins)
+			}
 
 			// end auction
 			k.SetAuction(ctx, auction)