package keeper import ( "fmt" sdk "github.com/cosmos/cosmos-sdk/types" sdkerrors "github.com/cosmos/cosmos-sdk/types/errors" "github.com/kava-labs/kava/x/swap/types" ) // Deposit creates a new pool or adds liquidity to an existing pool. For a pool to be created, a pool // for the coin denominations must not exist yet, and it must be allowed by the swap module parameters. // // When adding liquidity to an existing pool, the provided coins are considered to be the desired deposit // amount, and the actual deposited coins may be less than or equal to the provided coins. A deposit // will never be exceed the coinA and coinB amounts. // // The slippage is calculated using both the price and inverse price of the provided coinA and coinB. // Since adding liquidity is not directional, like a swap would be, using both the price (coinB/coinA), // and the inverse price (coinA/coinB), protects the depositor from a large deviation in their deposit. // // The amount deposited may only change by B' < B or A' < A -- either B depreciates, or A depreciates. // Therefore, slippage can be written as a function of this depreciation d. Where the new price is // B*(1-d)/A or A*(1-d)/B, and the inverse of each, and is A/(B*(1-d)) and B/(A*(1-d)) // respectively. // // Since 1/(1-d) >= (1-d) for d <= 1, the maximum slippage is always in the appreciating price // A/(B*(1-d)) and B/(A*(1-d)). In other words, when the price of an asset depreciates, the // inverse price -- or the price of the other pool asset, appreciates by a larger amount. // It's this percent change we calculate and compare to the slippage limit provided. // // For example, if we have a pool with 100e6 ukava and 400e6 usdx. The ukava price is 4 usdx and the // usdx price is 0.25 ukava. If a depositor adds liquidity of 4e6 ukava and 14e6 usdx, a kava price of // 3.50 usdx and a usdx price of 0.29 ukava. This is a -12.5% slippage is the ukava price, and a 14.3% // slippage in the usdx price. // // These slippages can be calculated by S_B = ((A/B')/(A/B) - 1) and S_A ((B/A')/(B/A) - 1), simplifying to // S_B = (A/A' - 1), and S_B = (B/B' - 1). An error is returned when max(S_A, S_B) > slippageLimit. func (k Keeper) Deposit(ctx sdk.Context, depositor sdk.AccAddress, coinA sdk.Coin, coinB sdk.Coin, slippageLimit sdk.Dec) error { desiredAmount := sdk.NewCoins(coinA, coinB) poolID := types.PoolIDFromCoins(desiredAmount) poolRecord, found := k.GetPool(ctx, poolID) var ( pool *types.DenominatedPool depositAmount sdk.Coins shares sdk.Int err error ) if found { pool, depositAmount, shares, err = k.addLiquidityToPool(ctx, poolRecord, depositor, desiredAmount) } else { pool, depositAmount, shares, err = k.initializePool(ctx, poolID, depositor, desiredAmount) } if err != nil { return err } if depositAmount.AmountOf(coinA.Denom).IsZero() || depositAmount.AmountOf(coinB.Denom).IsZero() { return sdkerrors.Wrap(types.ErrInsufficientLiquidity, "deposit must be increased") } if shares.IsZero() { return sdkerrors.Wrap(types.ErrInsufficientLiquidity, "deposit must be increased") } maxPercentPriceChange := sdk.MaxDec( desiredAmount.AmountOf(coinA.Denom).ToDec().Quo(depositAmount.AmountOf(coinA.Denom).ToDec()), desiredAmount.AmountOf(coinB.Denom).ToDec().Quo(depositAmount.AmountOf(coinB.Denom).ToDec()), ) slippage := maxPercentPriceChange.Sub(sdk.OneDec()) if slippage.GT(slippageLimit) { return sdkerrors.Wrapf(types.ErrSlippageExceeded, "slippage %s > limit %s", slippage, slippageLimit) } k.updatePool(ctx, poolID, pool) if shareRecord, hasExistingShares := k.GetDepositorShares(ctx, depositor, poolID); hasExistingShares { k.BeforePoolDepositModified(ctx, poolID, depositor, shareRecord.SharesOwned) k.updateDepositorShares(ctx, depositor, poolID, shareRecord.SharesOwned.Add(shares)) } else { k.updateDepositorShares(ctx, depositor, poolID, shares) k.AfterPoolDepositCreated(ctx, poolID, depositor, shares) } err = k.bankKeeper.SendCoinsFromAccountToModule(ctx, depositor, types.ModuleAccountName, depositAmount) if err != nil { return err } ctx.EventManager().EmitEvent( sdk.NewEvent( types.EventTypeSwapDeposit, sdk.NewAttribute(types.AttributeKeyPoolID, poolID), sdk.NewAttribute(types.AttributeKeyDepositor, depositor.String()), sdk.NewAttribute(sdk.AttributeKeyAmount, depositAmount.String()), sdk.NewAttribute(types.AttributeKeyShares, shares.String()), ), ) return nil } func (k Keeper) depositAllowed(ctx sdk.Context, poolID string) bool { params := k.GetParams(ctx) for _, p := range params.AllowedPools { if poolID == types.PoolID(p.TokenA, p.TokenB) { return true } } return false } func (k Keeper) initializePool(ctx sdk.Context, poolID string, depositor sdk.AccAddress, reserves sdk.Coins) (*types.DenominatedPool, sdk.Coins, sdk.Int, error) { if allowed := k.depositAllowed(ctx, poolID); !allowed { return nil, sdk.Coins{}, sdk.ZeroInt(), sdkerrors.Wrap(types.ErrNotAllowed, fmt.Sprintf("can not create pool '%s'", poolID)) } pool, err := types.NewDenominatedPool(reserves) if err != nil { return nil, sdk.Coins{}, sdk.ZeroInt(), err } return pool, pool.Reserves(), pool.TotalShares(), nil } func (k Keeper) addLiquidityToPool(ctx sdk.Context, record types.PoolRecord, depositor sdk.AccAddress, desiredAmount sdk.Coins) (*types.DenominatedPool, sdk.Coins, sdk.Int, error) { pool, err := types.NewDenominatedPoolWithExistingShares(record.Reserves(), record.TotalShares) if err != nil { return nil, sdk.Coins{}, sdk.ZeroInt(), err } depositAmount, shares := pool.AddLiquidity(desiredAmount) return pool, depositAmount, shares, nil }