refactor: ExitSwapExternAmountOut (#1244)

* refactor: ExitSwapExternAmountOut * better name for interface extension * implement types.PoolExitSwapExternAmountOutExtension * update changelog * interface assertion for PoolI in balancer pool * err check on extendedPool.ExitSwapExternAmountOut * ZeroDec() * comma in calcPoolInGivenSingleOut call * redundnet type in calcPoolInGivenSingleOut * comment for feeRatio * fix comment for calcPoolInGivenSingleOut and the converse * whitespace in ExitSwapExternAmountOut * fix changelog entry * godoc for PoolExitSwapExternAmountOutExtension * fmt * gofumpt * deduct shares on exit, make exit pool logic shared, improve names * rename to ExitSwapExactAmountOutExtension * comment out TestNewExitSwapShareAmountInCmd * fix ExitSwapExactAmountOut by truncating int on return from calcPoolSharesInGivenSingleAssetOut * revert x/gamm/cli_test.go to original state with TestNewExitSwapExternAmountOutCmd uncommented * uncomment ExitSwapExactAmountOut in TestActiveBalancerPool * change variable name to exitingCoins * fmt * Update x/gamm/keeper/pool_service.go * Update x/gamm/pool-models/balancer/amm.go * Update x/gamm/keeper/pool_service.go Co-authored-by: Aleksandr Bezobchuk <[email protected]>
osmosis-labs · Apr 18, 2022 · 298ad00 · 298ad00
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -43,6 +43,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Features
 
+* [#1244](https://github.com/osmosis-labs/osmosis/pull/1244) Refactor `x/gamm`'s `ExitSwapExternAmountOut`.
 * [#1107](https://github.com/osmosis-labs/osmosis/pull/1107) Update to wasmvm v0.24.0, re-enabling building on M1 macs!
 
 ### Minor improvements & Bug Fixes

diff --git a/x/gamm/client/cli/cli_test.go b/x/gamm/client/cli/cli_test.go
@@ -608,52 +608,51 @@ func (s IntegrationTestSuite) TestNewJoinSwapExternAmountInCmd() {
 	}
 }
 
-// Todo: Re-add once implemented
-// func (s IntegrationTestSuite) TestNewExitSwapExternAmountOutCmd() {
-// 	val := s.network.Validators[0]
+func (s IntegrationTestSuite) TestNewExitSwapExternAmountOutCmd() {
+	val := s.network.Validators[0]
 
-// 	testCases := []struct {
-// 		name         string
-// 		args         []string
-// 		expectErr    bool
-// 		respType     proto.Message
-// 		expectedCode uint32
-// 	}{
-// 		{
-// 			"exit swap extern amount out", // osmosisd tx gamm exit-swap-extern-amount-out --pool-id=1 10stake 1 --from=validator --keyring-backend=test --chain-id=testing --yes
-// 			[]string{
-// 				"10stake", "10000000000000000000",
-// 				fmt.Sprintf("--%s=%d", cli.FlagPoolId, 1),
-// 				fmt.Sprintf("--%s=%s", flags.FlagFrom, val.Address.String()),
-// 				// common args
-// 				fmt.Sprintf("--%s=true", flags.FlagSkipConfirmation),
-// 				fmt.Sprintf("--%s=%s", flags.FlagBroadcastMode, flags.BroadcastBlock),
-// 				fmt.Sprintf("--%s=%s", flags.FlagFees, sdk.NewCoins(sdk.NewCoin(sdk.DefaultBondDenom, sdk.NewInt(10))).String()),
-// 			},
-// 			false, &sdk.TxResponse{}, 0,
-// 		},
-// 	}
+	testCases := []struct {
+		name         string
+		args         []string
+		expectErr    bool
+		respType     proto.Message
+		expectedCode uint32
+	}{
+		{
+			"exit swap extern amount out", // osmosisd tx gamm exit-swap-extern-amount-out --pool-id=1 10stake 1 --from=validator --keyring-backend=test --chain-id=testing --yes
+			[]string{
+				"10stake", "10000000000000000000",
+				fmt.Sprintf("--%s=%d", cli.FlagPoolId, 1),
+				fmt.Sprintf("--%s=%s", flags.FlagFrom, val.Address.String()),
+				// common args
+				fmt.Sprintf("--%s=true", flags.FlagSkipConfirmation),
+				fmt.Sprintf("--%s=%s", flags.FlagBroadcastMode, flags.BroadcastBlock),
+				fmt.Sprintf("--%s=%s", flags.FlagFees, sdk.NewCoins(sdk.NewCoin(sdk.DefaultBondDenom, sdk.NewInt(10))).String()),
+			},
+			false, &sdk.TxResponse{}, 0,
+		},
+	}
 
-// 	for _, tc := range testCases {
-// 		tc := tc
+	for _, tc := range testCases {
+		tc := tc
 
-// 		s.Run(tc.name, func() {
-// 			cmd := cli.NewExitSwapExternAmountOut()
-// 			clientCtx := val.ClientCtx
+		s.Run(tc.name, func() {
+			cmd := cli.NewExitSwapExternAmountOut()
+			clientCtx := val.ClientCtx
 
-// 			out, err := clitestutil.ExecTestCLICmd(clientCtx, cmd, tc.args)
-// 			if tc.expectErr {
-// 				s.Require().Error(err)
-// 			} else {
-// 				s.Require().NoError(err, out.String())
-// 				s.Require().NoError(clientCtx.Codec.UnmarshalJSON(out.Bytes(), tc.respType), out.String())
+			out, err := clitestutil.ExecTestCLICmd(clientCtx, cmd, tc.args)
+			if tc.expectErr {
+				s.Require().Error(err)
+			} else {
+				s.Require().NoError(err, out.String())
+				s.Require().NoError(clientCtx.Codec.UnmarshalJSON(out.Bytes(), tc.respType), out.String())
 
-// 				txResp := tc.respType.(*sdk.TxResponse)
-// 				s.Require().Equal(tc.expectedCode, txResp.Code, out.String())
-// 			}
-// 		})
-// 	}
-// }
+				txResp := tc.respType.(*sdk.TxResponse)
+				s.Require().Equal(tc.expectedCode, txResp.Code, out.String())
+			}
+		})
+	}
+}
 
 // TODO: Re-add once implemented
 // func (s IntegrationTestSuite) TestNewJoinSwapShareAmountOutCmd() {

diff --git a/x/gamm/keeper/msg_server.go b/x/gamm/keeper/msg_server.go
@@ -224,7 +224,7 @@ func (server msgServer) ExitSwapExternAmountOut(goCtx context.Context, msg *type
 		return nil, err
 	}
 
-	shareInAmount, err := server.keeper.ExitSwapExternAmountOut(ctx, sender, msg.PoolId, msg.TokenOut, msg.ShareInMaxAmount)
+	shareInAmount, err := server.keeper.ExitSwapExactAmountOut(ctx, sender, msg.PoolId, msg.TokenOut, msg.ShareInMaxAmount)
 	if err != nil {
 		return nil, err
 	}

diff --git a/x/gamm/keeper/pool_service.go b/x/gamm/keeper/pool_service.go
@@ -395,20 +395,31 @@ func (k Keeper) ExitSwapShareAmountIn(
 	return tokenOutAmount, nil
 }
 
-func (k Keeper) ExitSwapExternAmountOut(
+func (k Keeper) ExitSwapExactAmountOut(
 	ctx sdk.Context,
 	sender sdk.AccAddress,
 	poolId uint64,
 	tokenOut sdk.Coin,
 	shareInMaxAmount sdk.Int,
 ) (shareInAmount sdk.Int, err error) {
-	// Basically what we have to do is:
-	// estimate how many LP shares this would take to do.
-	// We do so by calculating how much a swap of half of tokenOut to TokenIn would be.
-	// Then we calculate how many LP shares that'd be worth.
-	// We should have code for that once we implement JoinPoolNoSwap.
-	// Then check if the number of shares is LTE to shareInMaxAmount.
-	// if so, use the needed number of shares, do exit pool, and the swap.
-
-	panic("To implement later")
+	pool, err := k.getPoolForSwap(ctx, poolId)
+	if err != nil {
+		return sdk.Int{}, err
+	}
+
+	extendedPool, ok := pool.(types.PoolExitSwapExactAmountOutExtension)
+	if !ok {
+		return sdk.Int{}, fmt.Errorf("pool with id %d does not support this kind of exit", poolId)
+	}
+
+	shareInAmount, err = extendedPool.ExitSwapExactAmountOut(ctx, tokenOut, shareInMaxAmount)
+	if err != nil {
+		return sdk.Int{}, err
+	}
+
+	if err := k.applyExitPoolStateChange(ctx, pool, sender, shareInAmount, sdk.Coins{tokenOut}); err != nil {
+		return sdk.Int{}, err
+	}
+
+	return shareInAmount, nil
 }
diff --git a/x/gamm/keeper/pool_service_test.go b/x/gamm/keeper/pool_service_test.go
@@ -482,15 +482,15 @@ func (suite *KeeperTestSuite) TestActiveBalancerPool() {
 				// suite.Require().NoError(err)
 				_, err = suite.app.GAMMKeeper.ExitSwapShareAmountIn(suite.ctx, acc1, poolId, "foo", types.OneShare.MulRaw(10), sdk.ZeroInt())
 				suite.Require().NoError(err)
-				// _, err = suite.app.GAMMKeeper.ExitSwapExternAmountOut(suite.ctx, acc1, poolId, foocoin, sdk.NewInt(1000000000000000000))
-				// suite.Require().NoError(err)
+				_, err = suite.app.GAMMKeeper.ExitSwapExactAmountOut(suite.ctx, acc1, poolId, foocoin, sdk.NewInt(1000000000000000000))
+				suite.Require().NoError(err)
 			} else {
 				suite.Require().Error(err)
 				_, err = suite.app.GAMMKeeper.JoinSwapShareAmountOut(suite.ctx, acc1, poolId, "foo", types.OneShare.MulRaw(10), sdk.NewInt(1000000000000000000))
 				suite.Require().Error(err)
 				_, err = suite.app.GAMMKeeper.ExitSwapShareAmountIn(suite.ctx, acc1, poolId, "foo", types.OneShare.MulRaw(10), sdk.ZeroInt())
 				suite.Require().Error(err)
-				_, err = suite.app.GAMMKeeper.ExitSwapExternAmountOut(suite.ctx, acc1, poolId, foocoin, sdk.NewInt(1000000000000000000))
+				_, err = suite.app.GAMMKeeper.ExitSwapExactAmountOut(suite.ctx, acc1, poolId, foocoin, sdk.NewInt(1000000000000000000))
 				suite.Require().Error(err)
 			}
 		}

diff --git a/x/gamm/pool-models/balancer/amm.go b/x/gamm/pool-models/balancer/amm.go
@@ -185,9 +185,9 @@ func (p Pool) SpotPrice(ctx sdk.Context, baseAsset, quoteAsset string) (sdk.Dec,
 	return ratio, nil
 }
 
-// balancer notation: pAo - poolshares amount out, given single asset in
+// balancer notation: pAo - pool shares amount out, given single asset in
 // the second argument requires the tokenWeightIn / total token weight.
-func calcPoolOutGivenSingleIn(
+func calcPoolSharesOutGivenSingleAssetIn(
 	tokenBalanceIn,
 	normalizedTokenWeightIn,
 	poolShares,
@@ -226,7 +226,7 @@ func (p *Pool) calcSingleAssetJoin(tokenIn sdk.Coin, swapFee sdk.Dec, tokenInPoo
 		return sdk.ZeroInt(), errors.New("pool misconfigured, total weight = 0")
 	}
 	normalizedWeight := tokenInPoolAsset.Weight.ToDec().Quo(totalWeight.ToDec())
-	return calcPoolOutGivenSingleIn(
+	return calcPoolSharesOutGivenSingleAssetIn(
 		tokenInPoolAsset.Token.Amount.ToDec(),
 		normalizedWeight,
 		totalShares.ToDec(),
@@ -330,22 +330,31 @@ func (p *Pool) CalcJoinPoolShares(_ctx sdk.Context, tokensIn sdk.Coins, swapFee
 	return numShares, newLiquidity, nil
 }
 
-func (p *Pool) ExitPool(ctx sdk.Context, exitingShares sdk.Int, exitFee sdk.Dec) (exitedCoins sdk.Coins, err error) {
-	exitedCoins, err = p.CalcExitPoolShares(ctx, exitingShares, exitFee)
+func (p *Pool) ExitPool(ctx sdk.Context, exitingShares sdk.Int, exitFee sdk.Dec) (exitingCoins sdk.Coins, err error) {
+	exitingCoins, err = p.CalcExitPoolShares(ctx, exitingShares, exitFee)
 	if err != nil {
 		return sdk.Coins{}, err
 	}
 
-	balances := p.GetTotalPoolLiquidity(ctx).Sub(exitedCoins)
-	err = p.UpdatePoolAssetBalances(balances)
-	if err != nil {
+	if err := p.exitPool(ctx, exitingCoins, exitingShares); err != nil {
 		return sdk.Coins{}, err
 	}
 
+	return exitingCoins, nil
+}
+
+// exitPool exits the pool given exitingCoins and exitingShares.
+// updates the pool's liquidity and totalShares.
+func (p *Pool) exitPool(ctx sdk.Context, exitingCoins sdk.Coins, exitingShares sdk.Int) error {
+	balances := p.GetTotalPoolLiquidity(ctx).Sub(exitingCoins)
+	if err := p.UpdatePoolAssetBalances(balances); err != nil {
+		return err
+	}
+
 	totalShares := p.GetTotalShares()
 	p.TotalShares = sdk.NewCoin(p.TotalShares.Denom, totalShares.Sub(exitingShares))
 
-	return exitedCoins, nil
+	return nil
 }
 
 func (p *Pool) CalcExitPoolShares(ctx sdk.Context, exitingShares sdk.Int, exitFee sdk.Dec) (exitedCoins sdk.Coins, err error) {
@@ -375,3 +384,64 @@ func (p *Pool) CalcExitPoolShares(ctx sdk.Context, exitingShares sdk.Int, exitFe
 	}
 	return exitedCoins, nil
 }
+
+// balancer notation: pAi - pool shares amount in, given single asset out.
+// the returned shares in have the fee included in them.
+// the second argument requires the tokenWeightOut / total token weight.
+func calcPoolSharesInGivenSingleAssetOut(
+	tokenBalanceOut,
+	normalizedTokenWeightOut,
+	poolSupply,
+	tokenAmountOut,
+	swapFee,
+	exitFee sdk.Dec,
+) sdk.Dec {
+	// feeRatio is defined as follows:
+	// 1 - ((1 - normalizedTokenWeightOut) * swapFee)
+	feeRatio := sdk.OneDec().Sub((sdk.OneDec().Sub(normalizedTokenWeightOut)).Mul(swapFee))
+
+	tokenAmountOutBeforeFee := tokenAmountOut.Quo(feeRatio)
+
+	// delta poolSupply is positive(total pool shares decreases)
+	// pool weight is always 1
+	sharesIn := solveConstantFunctionInvariant(tokenBalanceOut.Sub(tokenAmountOutBeforeFee), tokenBalanceOut, normalizedTokenWeightOut, poolSupply, sdk.OneDec())
+
+	// charge exit fee on the pool token side
+	// pAi = pAiAfterExitFee/(1-exitFee)
+	sharesInFeeIncluded := sharesIn.Quo(sdk.OneDec().Sub(exitFee))
+	return sharesInFeeIncluded
+}
+
+func (p *Pool) ExitSwapExactAmountOut(
+	ctx sdk.Context,
+	tokenOut sdk.Coin,
+	shareInMaxAmount sdk.Int,
+) (shareInAmount sdk.Int, err error) {
+	_, pAsset, err := p.getPoolAssetAndIndex(tokenOut.Denom)
+	if err != nil {
+		return sdk.Int{}, err
+	}
+
+	sharesIn := calcPoolSharesInGivenSingleAssetOut(
+		pAsset.Token.Amount.ToDec(),
+		pAsset.Weight.ToDec().Quo(p.TotalWeight.ToDec()),
+		p.GetTotalShares().ToDec(),
+		tokenOut.Amount.ToDec(),
+		p.GetSwapFee(ctx),
+		p.GetExitFee(ctx),
+	).TruncateInt()
+
+	if sharesIn.LTE(sdk.ZeroInt()) {
+		return sdk.Int{}, sdkerrors.Wrapf(types.ErrInvalidMathApprox, "token amount is zero or negative")
+	}
+
+	if sharesIn.GT(shareInMaxAmount) {
+		return sdk.Int{}, sdkerrors.Wrapf(types.ErrLimitMaxAmount, "%s token is larger than max amount", pAsset.Token.Denom)
+	}
+
+	if err := p.exitPool(ctx, sdk.NewCoins(tokenOut), sharesIn); err != nil {
+		return sdk.Int{}, err
+	}
+
+	return sharesIn, nil
+}
diff --git a/x/gamm/pool-models/balancer/balancer_pool.go b/x/gamm/pool-models/balancer/balancer_pool.go
@@ -13,7 +13,10 @@ import (
 	"github.com/osmosis-labs/osmosis/v7/x/gamm/types"
 )
 
-var _ types.PoolI = &Pool{}
+var (
+	_ types.PoolI                               = &Pool{}
+	_ types.PoolExitSwapExactAmountOutExtension = &Pool{}
+)
 
 // NewPool returns a weighted CPMM pool with the provided parameters, and initial assets.
 // Invariants that are assumed to be satisfied and not checked:

diff --git a/x/gamm/types/pool.go b/x/gamm/types/pool.go
@@ -75,6 +75,22 @@ type PoolI interface {
 	PokePool(blockTime time.Time)
 }
 
+// PoolExitSwapExactAmountOutExtension is an extension of the PoolI
+// interface definiting an abstraction for pools that hold tokens.
+// In addition, it supports ExitSwapExactAmountOut method.
+// See definition below.
+type PoolExitSwapExactAmountOutExtension interface {
+	PoolI
+
+	// ExitSwapExactAmountOut removes liquidity from a specified pool with a maximum amount of LP shares (shareInMaxAmount)
+	// and swaps to an exact amount of one of the token pairs (tokenOut)
+	ExitSwapExactAmountOut(
+		ctx sdk.Context,
+		tokenOut sdk.Coin,
+		shareInMaxAmount sdk.Int,
+	) (shareInAmount sdk.Int, err error)
+}
+
 func NewPoolAddress(poolId uint64) sdk.AccAddress {
 	key := append([]byte("pool"), sdk.Uint64ToBigEndian(poolId)...)
 	return address.Module(ModuleName, key)