Add Auction Simulations (#419)

* first pass

* fix bid amount calculation

* untested refactor of sim ops and genesis

* refactor operations and fix auction bug

* add param changes and genesis

* address minor TODO

* add first draft of invariants

* improve param generation

* complete invariants

* fix genesis tests

* log no-op better

* small fixes

* add missed comma

Co-authored-by: John Maheswaran <john@kava.io>

app/app.go

@@ -302,16 +302,15 @@ func NewApp(logger log.Logger, db dbm.DB, traceStore io.Writer, loadLatest bool,
 
 	app.mm.SetOrderEndBlockers(crisis.ModuleName, gov.ModuleName, staking.ModuleName, pricefeed.ModuleName)
 
-	// Note: genutils must occur after staking so that pools are properly
-	// initialized with tokens from genesis accounts.
-	//
-	// Note: Changing the order of the auth module and modules that use module accounts
-	// results in subtle changes to the way accounts are loaded from genesis.
 	app.mm.SetOrderInitGenesis(
-		auth.ModuleName, validatorvesting.ModuleName, distr.ModuleName,
+		auth.ModuleName, // loads all accounts - should run before any module with a module account
+		validatorvesting.ModuleName, distr.ModuleName,
 		staking.ModuleName, bank.ModuleName, slashing.ModuleName,
-		gov.ModuleName, mint.ModuleName, supply.ModuleName, crisis.ModuleName, genutil.ModuleName,
+		gov.ModuleName, mint.ModuleName,
 		pricefeed.ModuleName, cdp.ModuleName, auction.ModuleName, bep3.ModuleName, kavadist.ModuleName, // TODO is this order ok?
+		supply.ModuleName,  // calculates the total supply from account - should run after modules that modify accounts in genesis
+		crisis.ModuleName,  // runs the invariants at genesis - should run after other modules
+		genutil.ModuleName, // genutils must occur after staking so that pools are properly initialized with tokens from genesis accounts.
 	)
 
 	app.mm.RegisterInvariants(&app.crisisKeeper)

app/sim_test.go

@@ -35,6 +35,7 @@ import (
 	stakingsimops "github.com/cosmos/cosmos-sdk/x/staking/simulation/operations"
 	"github.com/cosmos/cosmos-sdk/x/supply"
 
+	auctionsimops "github.com/kava-labs/kava/x/auction/simulation/operations"
 	bep3simops "github.com/kava-labs/kava/x/bep3/simulation/operations"
 	pricefeedsimops "github.com/kava-labs/kava/x/pricefeed/simulation/operations"
 )
@@ -59,6 +60,7 @@ const (
 	OpWeightMsgUndelegate                              = "op_weight_msg_undelegate"
 	OpWeightMsgBeginRedelegate                         = "op_weight_msg_begin_redelegate"
 	OpWeightMsgUnjail                                  = "op_weight_msg_unjail"
+	OpWeightMsgPlaceBid                                = "op_weight_msg_place_bid"
 	OpWeightMsgPricefeed                               = "op_weight_msg_pricefeed"
 	OpWeightMsgCreateAtomicSwap                        = "op_weight_msg_create_atomic_Swap"
 )
@@ -269,6 +271,17 @@ func testAndRunTxs(app *App, config simulation.Config) []simulation.WeightedOper
 			}(nil),
 			slashingsimops.SimulateMsgUnjail(app.slashingKeeper),
 		},
+		{
+			func(_ *rand.Rand) int {
+				var v int
+				ap.GetOrGenerate(app.cdc, OpWeightMsgPlaceBid, &v, nil,
+					func(_ *rand.Rand) {
+						v = 100
+					})
+				return v
+			}(nil),
+			auctionsimops.SimulateMsgPlaceBid(app.accountKeeper, app.auctionKeeper),
+		},
 		{
 			func(_ *rand.Rand) int {
 				var v int
@@ -285,7 +298,7 @@ func testAndRunTxs(app *App, config simulation.Config) []simulation.WeightedOper
 				var v int
 				ap.GetOrGenerate(app.cdc, OpWeightMsgPricefeed, &v, nil,
 					func(_ *rand.Rand) {
-						v = 10000 // TODO
+						v = 100
 					})
 				return v
 			}(nil),

x/auction/alias.go

@@ -55,6 +55,7 @@ var (
 	// functions aliases
 	NewKeeper                            = keeper.NewKeeper
 	NewQuerier                           = keeper.NewQuerier
+	RegisterInvariants                   = keeper.RegisterInvariants
 	NewSurplusAuction                    = types.NewSurplusAuction
 	NewDebtAuction                       = types.NewDebtAuction
 	NewCollateralAuction                 = types.NewCollateralAuction

x/auction/genesis.go

@@ -22,7 +22,7 @@ func InitGenesis(ctx sdk.Context, keeper Keeper, supplyKeeper types.SupplyKeeper
 	for _, a := range gs.Auctions {
 		keeper.SetAuction(ctx, a)
 		// find the total coins that should be present in the module account
-		totalAuctionCoins.Add(a.GetModuleAccountCoins())
+		totalAuctionCoins = totalAuctionCoins.Add(a.GetModuleAccountCoins())
 	}
 
 	// check if the module account exists

x/auction/genesis_test.go

@@ -29,6 +29,12 @@ func TestInitGenesis(t *testing.T) {
 		tApp := app.NewTestApp()
 		keeper := tApp.GetAuctionKeeper()
 		ctx := tApp.NewContext(true, abci.Header{})
+		// setup module account
+		supplyKeeper := tApp.GetSupplyKeeper()
+		moduleAcc := supplyKeeper.GetModuleAccount(ctx, auction.ModuleName)
+		require.NoError(t, moduleAcc.SetCoins(testAuction.GetModuleAccountCoins()))
+		supplyKeeper.SetModuleAccount(ctx, moduleAcc)
+
 		// create genesis
 		gs := auction.NewGenesisState(
 			10,
@@ -38,7 +44,7 @@ func TestInitGenesis(t *testing.T) {
 
 		// run init
 		require.NotPanics(t, func() {
-			auction.InitGenesis(ctx, keeper, tApp.GetSupplyKeeper(), gs)
+			auction.InitGenesis(ctx, keeper, supplyKeeper, gs)
 		})
 
 		// check state is as expected
@@ -59,7 +65,7 @@ func TestInitGenesis(t *testing.T) {
 			return false
 		})
 	})
-	t.Run("invalid", func(t *testing.T) {
+	t.Run("invalid (invalid nextAuctionID)", func(t *testing.T) {
 		// setup keepers
 		tApp := app.NewTestApp()
 		ctx := tApp.NewContext(true, abci.Header{})
@@ -71,6 +77,24 @@ func TestInitGenesis(t *testing.T) {
 			auction.GenesisAuctions{testAuction},
 		)
 
+		// check init fails
+		require.Panics(t, func() {
+			auction.InitGenesis(ctx, tApp.GetAuctionKeeper(), tApp.GetSupplyKeeper(), gs)
+		})
+	})
+	t.Run("invalid (missing mod account coins)", func(t *testing.T) {
+		// setup keepers
+		tApp := app.NewTestApp()
+		ctx := tApp.NewContext(true, abci.Header{})
+
+		// create invalid genesis
+		gs := auction.NewGenesisState(
+			10,
+			auction.DefaultParams(),
+			auction.GenesisAuctions{testAuction},
+		)
+		// invalid as there is no module account setup
+
 		// check init fails
 		require.Panics(t, func() {
 			auction.InitGenesis(ctx, tApp.GetAuctionKeeper(), tApp.GetSupplyKeeper(), gs)

x/auction/keeper/auctions.go

@@ -175,7 +175,7 @@ func (k Keeper) PlaceBidSurplus(ctx sdk.Context, a types.SurplusAuction, bidder
 		),
 	)
 	if bid.Amount.LT(minNewBidAmt) {
-		return a, types.ErrBidTooSmall(k.codespace, bid, sdk.NewCoin(a.Bid.Denom, minNewBidAmt))
+		return a, types.ErrBidTooSmall(k.codespace, bid, sdk.Coin{Denom: a.Bid.Denom, Amount: minNewBidAmt}) // not using NewCoin as it can panic
 	}
 
 	// New bidder pays back old bidder
@@ -239,7 +239,7 @@ func (k Keeper) PlaceForwardBidCollateral(ctx sdk.Context, a types.CollateralAuc
 	)
 	minNewBidAmt = sdk.MinInt(minNewBidAmt, a.MaxBid.Amount) // allow new bids to hit MaxBid even though it may be less than the increment %
 	if bid.Amount.LT(minNewBidAmt) {
-		return a, types.ErrBidTooSmall(k.codespace, bid, sdk.NewCoin(a.Bid.Denom, minNewBidAmt))
+		return a, types.ErrBidTooSmall(k.codespace, bid, sdk.Coin{Denom: a.Bid.Denom, Amount: minNewBidAmt}) // not using NewCoin as it can panic
 	}
 	if a.MaxBid.IsLT(bid) {
 		return a, types.ErrBidTooLarge(k.codespace, bid, a.MaxBid)
@@ -314,10 +314,10 @@ func (k Keeper) PlaceReverseBidCollateral(ctx sdk.Context, a types.CollateralAuc
 		),
 	)
 	if lot.Amount.GT(maxNewLotAmt) {
-		return a, types.ErrLotTooLarge(k.codespace, lot, sdk.NewCoin(a.Lot.Denom, maxNewLotAmt))
+		return a, types.ErrLotTooLarge(k.codespace, lot, sdk.Coin{Denom: a.Lot.Denom, Amount: maxNewLotAmt}) // not using NewCoin as it can panic
 	}
 	if lot.IsNegative() {
-		return a, types.ErrLotTooSmall(k.codespace, lot, sdk.NewCoin(a.Lot.Denom, sdk.ZeroInt()))
+		return a, types.ErrLotTooSmall(k.codespace, lot, sdk.Coin{Denom: a.Lot.Denom, Amount: sdk.ZeroInt()})
 	}
 
 	// New bidder pays back old bidder
@@ -380,10 +380,10 @@ func (k Keeper) PlaceBidDebt(ctx sdk.Context, a types.DebtAuction, bidder sdk.Ac
 		),
 	)
 	if lot.Amount.GT(maxNewLotAmt) {
-		return a, types.ErrLotTooLarge(k.codespace, lot, sdk.NewCoin(a.Lot.Denom, maxNewLotAmt))
+		return a, types.ErrLotTooLarge(k.codespace, lot, sdk.Coin{Denom: a.Lot.Denom, Amount: maxNewLotAmt}) // not using NewCoin as it can panic
 	}
 	if lot.IsNegative() {
-		return a, types.ErrLotTooSmall(k.codespace, lot, sdk.NewCoin(a.Lot.Denom, sdk.ZeroInt()))
+		return a, types.ErrLotTooSmall(k.codespace, lot, sdk.Coin{Denom: a.Lot.Denom, Amount: sdk.ZeroInt()})
 	}
 
 	// New bidder pays back old bidder

x/auction/keeper/invariants.go

@@ -0,0 +1,143 @@
+package keeper
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/cosmos/cosmos-sdk/store/prefix"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+
+	"github.com/kava-labs/kava/x/auction/types"
+)
+
+// RegisterInvariants registers all staking invariants
+func RegisterInvariants(ir sdk.InvariantRegistry, k Keeper) {
+
+	ir.RegisterRoute(types.ModuleName, "module-account",
+		ModuleAccountInvariants(k))
+	ir.RegisterRoute(types.ModuleName, "valid-auctions",
+		ValidAuctionInvariant(k))
+	ir.RegisterRoute(types.ModuleName, "valid-index",
+		ValidIndexInvariant(k))
+}
+
+// ModuleAccountInvariant checks that the module account's coins matches those stored in auctions
+func ModuleAccountInvariants(k Keeper) sdk.Invariant {
+	return func(ctx sdk.Context) (string, bool) {
+
+		totalAuctionCoins := sdk.NewCoins()
+		k.IterateAuctions(ctx, func(auction types.Auction) bool {
+			a, ok := auction.(types.GenesisAuction)
+			if !ok {
+				panic("stored auction type does not fulfill GenesisAuction interface")
+			}
+			totalAuctionCoins = totalAuctionCoins.Add(a.GetModuleAccountCoins())
+			return false
+		})
+
+		moduleAccCoins := k.supplyKeeper.GetModuleAccount(ctx, types.ModuleName).GetCoins()
+		broken := !moduleAccCoins.IsEqual(totalAuctionCoins)
+
+		invariantMessage := sdk.FormatInvariant(
+			types.ModuleName,
+			"module account",
+			fmt.Sprintf(
+				"\texpected ModuleAccount coins: %s\n"+
+					"\tactual ModuleAccount coins:   %s\n",
+				totalAuctionCoins, moduleAccCoins),
+		)
+		return invariantMessage, broken
+	}
+}
+
+// ValidAuctionInvariant verifies that all auctions in the store are independently valid
+func ValidAuctionInvariant(k Keeper) sdk.Invariant {
+	return func(ctx sdk.Context) (string, bool) {
+		var validationErr error
+		var invalidAuction types.Auction
+		k.IterateAuctions(ctx, func(auction types.Auction) bool {
+			a, ok := auction.(types.GenesisAuction)
+			if !ok {
+				panic("stored auction type does not fulfill GenesisAuction interface")
+			}
+
+			currentTime := ctx.BlockTime()
+			if !currentTime.Equal(time.Time{}) { // this avoids a simulator bug where app.InitGenesis is called with blockTime=0 instead of the correct time
+				if a.GetEndTime().Before(currentTime) {
+					validationErr = fmt.Errorf("endTime after current block time (%s)", currentTime)
+					invalidAuction = a
+					return true
+				}
+			}
+
+			if err := a.Validate(); err != nil {
+				validationErr = err
+				invalidAuction = a
+				return true
+			}
+			return false
+		})
+
+		broken := validationErr != nil
+		invariantMessage := sdk.FormatInvariant(
+			types.ModuleName,
+			"valid auctions",
+			fmt.Sprintf(
+				"\tfound invalid auction, reason: %s\n"+
+					"\tauction:\n\t%s\n",
+				validationErr, invalidAuction),
+		)
+		return invariantMessage, broken
+	}
+}
+
+// ValidIndexInvariant checks that all auctions in the store are also in the index and vice versa.
+func ValidIndexInvariant(k Keeper) sdk.Invariant {
+	return func(ctx sdk.Context) (string, bool) {
+		/* Method:
+		- check all the auction IDs in the index have a corresponding auction in the store
+		- index is now valid but there could be extra auction in the store
+		- check for these extra auctions by checking num items in the store equals that of index (store keys are always unique)
+		- doesn't check the IDs in the auction structs match the IDs in the keys
+		*/
+
+		// Check all auction IDs in the index are in the auction store
+		store := prefix.NewStore(ctx.KVStore(k.storeKey), types.AuctionKeyPrefix)
+
+		indexIterator := sdk.KVStorePrefixIterator(ctx.KVStore(k.storeKey), types.AuctionByTimeKeyPrefix)
+		defer indexIterator.Close()
+
+		var indexLength int
+		for ; indexIterator.Valid(); indexIterator.Next() {
+			indexLength++
+
+			idBytes := indexIterator.Value()
+			auctionBytes := store.Get(idBytes)
+			if auctionBytes == nil {
+				invariantMessage := sdk.FormatInvariant(
+					types.ModuleName,
+					"valid index",
+					fmt.Sprintf("\tauction with ID '%d' found in index but not in store", types.Uint64FromBytes(idBytes)))
+				return invariantMessage, true
+			}
+		}
+
+		// Check length of auction store matches the length of the index
+		storeIterator := sdk.KVStorePrefixIterator(ctx.KVStore(k.storeKey), types.AuctionKeyPrefix)
+		defer storeIterator.Close()
+		var storeLength int
+		for ; storeIterator.Valid(); storeIterator.Next() {
+			storeLength++
+		}
+
+		if storeLength != indexLength {
+			invariantMessage := sdk.FormatInvariant(
+				types.ModuleName,
+				"valid index",
+				fmt.Sprintf("\tmismatched number of items in auction store (%d) and index (%d)", storeLength, indexLength))
+			return invariantMessage, true
+		}
+
+		return "", false
+	}
+}

x/auction/module.go

@@ -110,8 +110,10 @@ func NewAppModule(keeper Keeper, supplyKeeper types.SupplyKeeper) AppModule {
 	}
 }
 
-// RegisterInvariants performs a no-op.
+// RegisterInvariants registers the module invariants.
-func (AppModule) RegisterInvariants(_ sdk.InvariantRegistry) {}
+func (am AppModule) RegisterInvariants(ir sdk.InvariantRegistry) {
+	RegisterInvariants(ir, am.keeper)
+}
 
 // Route module message route name
 func (AppModule) Route() string {

x/auction/simulation/genesis.go

@@ -2,21 +2,170 @@ package simulation
 
 import (
 	"fmt"
+	"math/rand"
+	"time"
 
 	"github.com/cosmos/cosmos-sdk/codec"
+	sdk "github.com/cosmos/cosmos-sdk/types"
 	"github.com/cosmos/cosmos-sdk/types/module"
+	"github.com/cosmos/cosmos-sdk/x/auth"
+	authexported "github.com/cosmos/cosmos-sdk/x/auth/exported"
+	"github.com/cosmos/cosmos-sdk/x/simulation"
+	"github.com/cosmos/cosmos-sdk/x/supply"
 
 	"github.com/kava-labs/kava/x/auction/types"
+	cdptypes "github.com/kava-labs/kava/x/cdp/types"
 )
 
+const (
+	// Block time params are un-exported constants in cosmos-sdk/x/simulation.
+	// Copy them here in lieu of importing them.
+	minTimePerBlock time.Duration = (10000 / 2) * time.Second
+	maxTimePerBlock time.Duration = 10000 * time.Second
+
+	// Calculate the average block time
+	AverageBlockTime time.Duration = (maxTimePerBlock - minTimePerBlock) / 2
+	// MaxBidDuration is a crude way of ensuring that BidDuration ≤ MaxAuctionDuration for all generated params
+	MaxBidDuration time.Duration = AverageBlockTime * 50
+)
+
+func GenBidDuration(r *rand.Rand) time.Duration {
+	d, err := RandomPositiveDuration(r, 0, MaxBidDuration)
+	if err != nil {
+		panic(err)
+	}
+	return d
+}
+func GenMaxAuctionDuration(r *rand.Rand) time.Duration {
+	d, err := RandomPositiveDuration(r, MaxBidDuration, AverageBlockTime*200)
+	if err != nil {
+		panic(err)
+	}
+	return d
+}
+
+func GenIncrementCollateral(r *rand.Rand) sdk.Dec {
+	return simulation.RandomDecAmount(r, sdk.MustNewDecFromStr("1"))
+}
+
+var GenIncrementDebt = GenIncrementCollateral
+var GenIncrementSurplus = GenIncrementCollateral
+
 // RandomizedGenState generates a random GenesisState for auction
 func RandomizedGenState(simState *module.SimulationState) {
 
-	// TODO implement this fully
+	p := types.NewParams(
-	// - randomly generating the genesis params
+		GenMaxAuctionDuration(simState.Rand),
-	// - overwriting with genesis provided to simulation
+		GenBidDuration(simState.Rand),
-	auctionGenesis := types.DefaultGenesisState()
+		GenIncrementSurplus(simState.Rand),
+		GenIncrementDebt(simState.Rand),
+		GenIncrementCollateral(simState.Rand),
+	)
+	if err := p.Validate(); err != nil {
+		panic(err)
+	}
+	auctionGenesis := types.NewGenesisState(
+		types.DefaultNextAuctionID,
+		p,
+		nil,
+	)
 
+	// Add auctions
+	auctions := types.GenesisAuctions{
+		types.NewDebtAuction(
+			cdptypes.LiquidatorMacc, // using cdp account rather than generic test one to avoid having to set permissions on the supply keeper
+			sdk.NewInt64Coin("usdx", 100),
+			sdk.NewInt64Coin("ukava", 1000000000000),
+			simState.GenTimestamp.Add(time.Hour*5),
+			sdk.NewInt64Coin("debt", 100), // same as usdx
+		),
+	}
+	var startingID = auctionGenesis.NextAuctionID
+	var ok bool
+	var totalAuctionCoins sdk.Coins
+	for i, a := range auctions {
+		auctions[i], ok = a.WithID(uint64(i) + startingID).(types.GenesisAuction)
+		if !ok {
+			panic("can't convert Auction to GenesisAuction")
+		}
+		totalAuctionCoins = totalAuctionCoins.Add(a.GetModuleAccountCoins())
+	}
+	auctionGenesis.NextAuctionID = startingID + uint64(len(auctions))
+	auctionGenesis.Auctions = append(auctionGenesis.Auctions, auctions...)
+
+	// Also need to update the auction module account (to reflect the coins held in the auctions)
+	var authGenesis auth.GenesisState
+	simState.Cdc.MustUnmarshalJSON(simState.GenState[auth.ModuleName], &authGenesis)
+
+	auctionModAcc, found := getAccount(authGenesis.Accounts, supply.NewModuleAddress(types.ModuleName))
+	if !found {
+		auctionModAcc = supply.NewEmptyModuleAccount(types.ModuleName)
+	}
+	if err := auctionModAcc.SetCoins(totalAuctionCoins); err != nil {
+		panic(err)
+	}
+	authGenesis.Accounts = replaceOrAppendAccount(authGenesis.Accounts, auctionModAcc)
+
+	// TODO adding bidder coins as well - this should be moved elsewhere
+	bidder, found := getAccount(authGenesis.Accounts, simState.Accounts[0].Address) // 0 is the bidder // FIXME
+	if !found {
+		panic("bidder not found")
+	}
+	bidderCoins := sdk.NewCoins(sdk.NewInt64Coin("usdx", 10000000000))
+	if err := bidder.SetCoins(bidder.GetCoins().Add(bidderCoins)); err != nil {
+		panic(err)
+	}
+	authGenesis.Accounts = replaceOrAppendAccount(authGenesis.Accounts, bidder)
+
+	simState.GenState[auth.ModuleName] = simState.Cdc.MustMarshalJSON(authGenesis)
+
+	// Update the supply genesis state to reflect the new coins
+	// TODO find some way for this to happen automatically / move it elsewhere
+	var supplyGenesis supply.GenesisState
+	simState.Cdc.MustUnmarshalJSON(simState.GenState[supply.ModuleName], &supplyGenesis)
+	supplyGenesis.Supply = supplyGenesis.Supply.Add(totalAuctionCoins).Add(bidderCoins)
+	simState.GenState[supply.ModuleName] = simState.Cdc.MustMarshalJSON(supplyGenesis)
+
+	// TODO liquidator mod account doesn't need to be initialized for this example
+	// - it just mints kava, doesn't need a starting balance
+	// - and supply.GetModuleAccount creates one if it doesn't exist
+
+	// Note: this line prints out the auction genesis state, not just the auction parameters. Some sdk modules print out just the parameters.
 	fmt.Printf("Selected randomly generated %s parameters:\n%s\n", types.ModuleName, codec.MustMarshalJSONIndent(simState.Cdc, auctionGenesis))
 	simState.GenState[types.ModuleName] = simState.Cdc.MustMarshalJSON(auctionGenesis)
 }
+
+// Return an account from a list of accounts that matches an address.
+func getAccount(accounts []authexported.GenesisAccount, addr sdk.AccAddress) (authexported.GenesisAccount, bool) {
+	for _, a := range accounts {
+		if a.GetAddress().Equals(addr) {
+			return a, true
+		}
+	}
+	return nil, false
+}
+
+// In a list of accounts, replace the first account found with the same address. If not found, append the account.
+func replaceOrAppendAccount(accounts []authexported.GenesisAccount, acc authexported.GenesisAccount) []authexported.GenesisAccount {
+	newAccounts := accounts
+	for i, a := range accounts {
+		if a.GetAddress().Equals(acc.GetAddress()) {
+			newAccounts[i] = acc
+			return newAccounts
+		}
+	}
+	return append(newAccounts, acc)
+}
+
+func RandomPositiveDuration(r *rand.Rand, inclusiveMin, exclusiveMax time.Duration) (time.Duration, error) {
+	min := int64(inclusiveMin)
+	max := int64(exclusiveMax)
+	if min < 0 || max < 0 {
+		return 0, fmt.Errorf("min and max must be positive")
+	}
+	if min >= max {
+		return 0, fmt.Errorf("max must be < min")
+	}
+	randPositiveInt64 := r.Int63n(max-min) + min
+	return time.Duration(randPositiveInt64), nil
+}

x/auction/simulation/operations/msg.go

@@ -0,0 +1,177 @@
+package operations
+
+import (
+	"errors"
+	"fmt"
+	"math/big"
+	"math/rand"
+	"time"
+
+	"github.com/cosmos/cosmos-sdk/baseapp"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/x/auth"
+	authexported "github.com/cosmos/cosmos-sdk/x/auth/exported"
+	"github.com/cosmos/cosmos-sdk/x/simulation"
+
+	"github.com/kava-labs/kava/x/auction"
+)
+
+var (
+	noOpMsg             = simulation.NoOpMsg(auction.ModuleName)
+	ErrorNotEnoughCoins = errors.New("account doesn't have enough coins")
+)
+
+// Return a function that runs a random state change on the module keeper.
+// There's two error paths
+// - return a OpMessage, but nil error - this will log a message but keep running the simulation
+// - return an error - this will stop the simulation
+func SimulateMsgPlaceBid(authKeeper auth.AccountKeeper, keeper auction.Keeper) simulation.Operation {
+	handler := auction.NewHandler(keeper)
+
+	return func(r *rand.Rand, app *baseapp.BaseApp, ctx sdk.Context, accs []simulation.Account) (
+		simulation.OperationMsg, []simulation.FutureOperation, error) {
+
+		// get open auctions
+		openAuctions := auction.Auctions{}
+		keeper.IterateAuctions(ctx, func(a auction.Auction) bool {
+			openAuctions = append(openAuctions, a)
+			return false
+		})
+
+		// shuffle auctions slice so that bids are evenly distributed across auctions
+		rand.Shuffle(len(openAuctions), func(i, j int) {
+			openAuctions[i], openAuctions[j] = openAuctions[j], openAuctions[i]
+		})
+		// TODO do the same for accounts?
+		var accounts []authexported.Account
+		for _, acc := range accs {
+			accounts = append(accounts, authKeeper.GetAccount(ctx, acc.Address))
+		}
+
+		// search through auctions and an accounts to find a pair where a bid can be placed (ie account has enough coins to place bid on auction)
+		blockTime := ctx.BlockHeader().Time
+		bidder, openAuction, found := findValidAccountAuctionPair(accounts, openAuctions, func(acc authexported.Account, auc auction.Auction) bool {
+			_, err := generateBidAmount(r, auc, acc, blockTime)
+			if err == ErrorNotEnoughCoins {
+				return false // keep searching
+			} else if err != nil {
+				panic(err) // raise errors
+			}
+			return true // found valid pair
+		})
+		if !found {
+			return simulation.NewOperationMsgBasic(auction.ModuleName, "no-operation (no valid auction and bidder)", "", false, nil), nil, nil
+		}
+
+		// pick a bid amount for the chosen auction and bidder
+		amount, _ := generateBidAmount(r, openAuction, bidder, blockTime)
+
+		// create a msg
+		msg := auction.NewMsgPlaceBid(openAuction.GetID(), bidder.GetAddress(), amount)
+		if err := msg.ValidateBasic(); err != nil { // don't submit errors that fail ValidateBasic, use unit tests for testing ValidateBasic
+			return noOpMsg, nil, fmt.Errorf("expected msg to pass ValidateBasic: %s", msg.GetSignBytes())
+		}
+
+		// submit the msg
+		result := submitMsg(ctx, handler, msg)
+		// Return an operationMsg indicating whether the msg was submitted successfully
+		// Using result.Log as the comment field as it contains any error message emitted by the keeper
+		return simulation.NewOperationMsg(msg, result.IsOK(), result.Log), nil, nil
+	}
+}
+
+func submitMsg(ctx sdk.Context, handler sdk.Handler, msg sdk.Msg) sdk.Result {
+	ctx, write := ctx.CacheContext()
+	result := handler(ctx, msg)
+	if result.IsOK() {
+		write()
+	}
+	return result
+}
+
+func generateBidAmount(r *rand.Rand, auc auction.Auction, bidder authexported.Account, blockTime time.Time) (sdk.Coin, error) {
+	bidderBalance := bidder.SpendableCoins(blockTime)
+
+	switch a := auc.(type) {
+
+	case auction.DebtAuction:
+		if bidderBalance.AmountOf(a.Bid.Denom).LT(a.Bid.Amount) { // stable coin
+			return sdk.Coin{}, ErrorNotEnoughCoins
+		}
+		amt, err := RandIntInclusive(r, sdk.ZeroInt(), a.Lot.Amount) // pick amount less than current lot amount // TODO min bid increments
+		if err != nil {
+			panic(err)
+		}
+		return sdk.NewCoin(a.Lot.Denom, amt), nil // gov coin
+
+	case auction.SurplusAuction:
+		if bidderBalance.AmountOf(a.Bid.Denom).LT(a.Bid.Amount) { // gov coin // TODO account for bid increments
+			return sdk.Coin{}, ErrorNotEnoughCoins
+		}
+		amt, err := RandIntInclusive(r, a.Bid.Amount, bidderBalance.AmountOf(a.Bid.Denom))
+		if err != nil {
+			panic(err)
+		}
+		return sdk.NewCoin(a.Bid.Denom, amt), nil // gov coin
+
+	case auction.CollateralAuction:
+		if bidderBalance.AmountOf(a.Bid.Denom).LT(a.Bid.Amount) { // stable coin // TODO account for bid increments (in forward phase)
+			return sdk.Coin{}, ErrorNotEnoughCoins
+		}
+		if a.IsReversePhase() {
+			amt, err := RandIntInclusive(r, sdk.ZeroInt(), a.Lot.Amount) // pick amount less than current lot amount
+			if err != nil {
+				panic(err)
+			}
+			return sdk.NewCoin(a.Lot.Denom, amt), nil // collateral coin
+		} else {
+			amt, err := RandIntInclusive(r, a.Bid.Amount, sdk.MinInt(bidderBalance.AmountOf(a.Bid.Denom), a.MaxBid.Amount))
+			if err != nil {
+				panic(err)
+			}
+			// pick the MaxBid amount more frequently to increase chance auctions phase get into reverse phase
+			if r.Intn(10) == 0 { // 10%
+				amt = a.MaxBid.Amount
+			}
+			return sdk.NewCoin(a.Bid.Denom, amt), nil // stable coin
+		}
+
+	default:
+		return sdk.Coin{}, fmt.Errorf("unknown auction type")
+	}
+}
+
+// findValidAccountAuctionPair finds an auction and account for which the callback func returns true
+func findValidAccountAuctionPair(accounts []authexported.Account, auctions auction.Auctions, cb func(authexported.Account, auction.Auction) bool) (authexported.Account, auction.Auction, bool) {
+	for _, auc := range auctions {
+		for _, acc := range accounts {
+			if isValid := cb(acc, auc); isValid {
+				return acc, auc, true
+			}
+
+		}
+	}
+	return nil, nil, false
+}
+
+// RandInt randomly generates an sdk.Int in the range [inclusiveMin, inclusiveMax]. It works for negative and positive integers.
+func RandIntInclusive(r *rand.Rand, inclusiveMin, inclusiveMax sdk.Int) (sdk.Int, error) {
+	if inclusiveMin.GT(inclusiveMax) {
+		return sdk.Int{}, fmt.Errorf("min larger than max")
+	}
+	return RandInt(r, inclusiveMin, inclusiveMax.Add(sdk.OneInt()))
+}
+
+// RandInt randomly generates an sdk.Int in the range [inclusiveMin, exclusiveMax). It works for negative and positive integers.
+func RandInt(r *rand.Rand, inclusiveMin, exclusiveMax sdk.Int) (sdk.Int, error) {
+	// validate input
+	if inclusiveMin.GTE(exclusiveMax) {
+		return sdk.Int{}, fmt.Errorf("min larger or equal to max")
+	}
+	// shift the range to start at 0
+	shiftedRange := exclusiveMax.Sub(inclusiveMin) // should always be positive given the check above
+	// randomly pick from the shifted range
+	shiftedRandInt := sdk.NewIntFromBigInt(new(big.Int).Rand(r, shiftedRange.BigInt()))
+	// shift back to the original range
+	return shiftedRandInt.Add(inclusiveMin), nil
+}

x/auction/simulation/params.go

@@ -1,14 +1,46 @@
 package simulation
 
 import (
+	"fmt"
 	"math/rand"
 
 	"github.com/cosmos/cosmos-sdk/x/simulation"
+
+	"github.com/kava-labs/kava/x/auction/types"
 )
 
 // ParamChanges defines the parameters that can be modified by param change proposals
 // on the simulation
 func ParamChanges(r *rand.Rand) []simulation.ParamChange {
-	// TODO implement this
+	// Note: params are encoded to JSON before being stored in the param store. These param changes
-	return []simulation.ParamChange{}
+	// update the raw values in the store so values need to be JSON. This is why values that are represented
+	// as strings in JSON (such as time.Duration) have the escaped quotes.
+	// TODO should we encode the values properly with ModuleCdc.MustMarshalJSON()?
+	return []simulation.ParamChange{
+		simulation.NewSimParamChange(types.ModuleName, string(types.KeyBidDuration), "",
+			func(r *rand.Rand) string {
+				return fmt.Sprintf("\"%d\"", GenBidDuration(r))
+			},
+		),
+		simulation.NewSimParamChange(types.ModuleName, string(types.KeyMaxAuctionDuration), "",
+			func(r *rand.Rand) string {
+				return fmt.Sprintf("\"%d\"", GenMaxAuctionDuration(r))
+			},
+		),
+		simulation.NewSimParamChange(types.ModuleName, string(types.KeyIncrementCollateral), "",
+			func(r *rand.Rand) string {
+				return fmt.Sprintf("\"%d\"", GenIncrementCollateral(r))
+			},
+		),
+		simulation.NewSimParamChange(types.ModuleName, string(types.KeyIncrementDebt), "",
+			func(r *rand.Rand) string {
+				return fmt.Sprintf("\"%d\"", GenIncrementDebt(r))
+			},
+		),
+		simulation.NewSimParamChange(types.ModuleName, string(types.KeyIncrementSurplus), "",
+			func(r *rand.Rand) string {
+				return fmt.Sprintf("\"%d\"", GenIncrementSurplus(r))
+			},
+		),
+	}
 }

x/auction/types/auctions.go

@@ -69,6 +69,12 @@ func (a BaseAuction) Validate() error {
 	if a.EndTime.After(a.MaxEndTime) {
 		return fmt.Errorf("MaxEndTime < EndTime (%s < %s)", a.MaxEndTime, a.EndTime)
 	}
+	if !a.Lot.IsValid() {
+		return fmt.Errorf("invalid lot: %s", a.Lot)
+	}
+	if !a.Bid.IsValid() {
+		return fmt.Errorf("invalid bid: %s", a.Bid)
+	}
 	return nil
 }
 
@@ -148,6 +154,13 @@ func (a DebtAuction) GetModuleAccountCoins() sdk.Coins {
 // GetPhase returns the direction of a debt auction, which never changes.
 func (a DebtAuction) GetPhase() string { return "reverse" }
 
+func (a DebtAuction) Validate() error {
+	if !a.CorrespondingDebt.IsValid() {
+		return fmt.Errorf("invalid corresponding debt: %s", a.CorrespondingDebt)
+	}
+	return a.BaseAuction.Validate()
+}
+
 // NewDebtAuction returns a new debt auction.
 func NewDebtAuction(buyerModAccName string, bid sdk.Coin, initialLot sdk.Coin, endTime time.Time, debt sdk.Coin) DebtAuction {
 	// Note: Bidder is set to the initiator's module account address instead of module name. (when the first bid is placed, it is paid out to the initiator)
@@ -208,6 +221,19 @@ func (a CollateralAuction) GetPhase() string {
 	return "forward"
 }
 
+func (a CollateralAuction) Validate() error {
+	if !a.CorrespondingDebt.IsValid() {
+		return fmt.Errorf("invalid corresponding debt: %s", a.CorrespondingDebt)
+	}
+	if !a.MaxBid.IsValid() {
+		return fmt.Errorf("invalid max bid: %s", a.MaxBid)
+	}
+	if err := a.LotReturns.Validate(); err != nil {
+		return fmt.Errorf("invalid lot returns: %w", err)
+	}
+	return a.BaseAuction.Validate()
+}
+
 func (a CollateralAuction) String() string {
 	return fmt.Sprintf(`Auction %d:
   Initiator:              %s
@@ -251,16 +277,24 @@ type WeightedAddresses struct {
 
 // NewWeightedAddresses returns a new list addresses with weights.
 func NewWeightedAddresses(addrs []sdk.AccAddress, weights []sdk.Int) (WeightedAddresses, sdk.Error) {
-	if len(addrs) != len(weights) {
+	wa := WeightedAddresses{
-		return WeightedAddresses{}, sdk.ErrInternal("number of addresses doesn't match number of weights")
-	}
-	for _, w := range weights {
-		if w.IsNegative() {
-			return WeightedAddresses{}, sdk.ErrInternal("weights contain a negative amount")
-		}
-	}
-	return WeightedAddresses{
 		Addresses: addrs,
 		Weights:   weights,
-	}, nil
+	}
+	if err := wa.Validate(); err != nil {
+		return WeightedAddresses{}, sdk.ErrInternal(err.Error())
+	}
+	return wa, nil
+}
+
+func (wa WeightedAddresses) Validate() error {
+	if len(wa.Addresses) != len(wa.Weights) {
+		return fmt.Errorf("number of addresses doesn't match number of weights")
+	}
+	for _, w := range wa.Weights {
+		if w.IsNegative() {
+			return fmt.Errorf("weights contain a negative amount")
+		}
+	}
+	return nil
 }