MetaSwap

This contract is responsible for custody of closely pegged assets (eg. group of stablecoins) and automatic market making system. Users become an LP (Liquidity Provider) by depositing their tokens in desired ratios for an exchange of the pool token that represents their share of the pool. Users can burn pool tokens and withdraw their share of token(s).

Each time a swap between the pooled tokens happens, a set fee incurs which effectively gets distributed to the LPs.

In case of emergencies, admin can pause additional deposits, swaps, or single-asset withdraws - which stops the ratio of the tokens in the pool from changing. Users can always withdraw their tokens via multi-asset withdraws.

MetaSwap is a modified version of Swap that allows Swap's LP token to be utilized in pooling with other tokens. As an example, if there is a Swap pool consisting of [DAI, USDC, USDT], then a MetaSwap pool can be created with [sUSD, BaseSwapLPToken] to allow trades between either the LP token or the underlying tokens and sUSD. Note that when interacting with MetaSwap, users cannot deposit or withdraw via underlying tokens. In that case, MetaSwapDeposit.sol can be additionally deployed to allow interacting with unwrapped representations of the tokens.

Most of the logic is stored as a library MetaSwapUtils for the sake of reducing contract's deployment size.

Functions:

• getVirtualPrice()

• calculateSwap(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx)

• calculateSwapUnderlying(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx)

• calculateTokenAmount(uint256[] amounts, bool deposit)

• calculateRemoveLiquidityOneToken(uint256 tokenAmount, uint8 tokenIndex)

• initialize(contract IERC20[] _pooledTokens, uint8[] decimals, string lpTokenName, string lpTokenSymbol, uint256 _a, uint256 _fee, uint256 _adminFee, address lpTokenTargetAddress)

• initializeMetaSwap(contract IERC20[] _pooledTokens, uint8[] decimals, string lpTokenName, string lpTokenSymbol, uint256 _a, uint256 _fee, uint256 _adminFee, address lpTokenTargetAddress, contract ISwap baseSwap)

• swap(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx, uint256 minDy, uint256 deadline)

• swapUnderlying(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx, uint256 minDy, uint256 deadline)

• addLiquidity(uint256[] amounts, uint256 minToMint, uint256 deadline)

• removeLiquidityOneToken(uint256 tokenAmount, uint8 tokenIndex, uint256 minAmount, uint256 deadline)

• removeLiquidityImbalance(uint256[] amounts, uint256 maxBurnAmount, uint256 deadline)

Events:

• TokenSwapUnderlying(address buyer, uint256 tokensSold, uint256 tokensBought, uint128 soldId, uint128 boughtId)

Function getVirtualPrice() → uint256

Get the virtual price, to help calculate profit

Return Values:

• the virtual price, scaled to the POOL_PRECISION_DECIMALS

Function calculateSwap(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx) → uint256

Calculate amount of tokens you receive on swap

Parameters:

• tokenIndexFrom: the token the user wants to sell

• tokenIndexTo: the token the user wants to buy

• dx: the amount of tokens the user wants to sell. If the token charges a fee on transfers, use the amount that gets transferred after the fee.

Return Values:

• amount of tokens the user will receive

Function calculateSwapUnderlying(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx) → uint256

Calculate amount of tokens you receive on swap. For this function, the token indices are flattened out so that underlying tokens are represented.

Parameters:

• tokenIndexFrom: the token the user wants to sell

• tokenIndexTo: the token the user wants to buy

• dx: the amount of tokens the user wants to sell. If the token charges a fee on transfers, use the amount that gets transferred after the fee.

Return Values:

• amount of tokens the user will receive

Function calculateTokenAmount(uint256[] amounts, bool deposit) → uint256

A simple method to calculate prices from deposits or withdrawals, excluding fees but including slippage. This is helpful as an input into the various "min" parameters on calls to fight front-running

This shouldn't be used outside frontends for user estimates.

Parameters:

• amounts: an array of token amounts to deposit or withdrawal, corresponding to pooledTokens. The amount should be in each pooled token's native precision. If a token charges a fee on transfers, use the amount that gets transferred after the fee.

• deposit: whether this is a deposit or a withdrawal

Return Values:

• token amount the user will receive

Function calculateRemoveLiquidityOneToken(uint256 tokenAmount, uint8 tokenIndex) → uint256

Calculate the amount of underlying token available to withdraw when withdrawing via only single token

Parameters:

• tokenAmount: the amount of LP token to burn

• tokenIndex: index of which token will be withdrawn

Return Values:

• availableTokenAmount calculated amount of underlying token available to withdraw

Function initialize(contract IERC20[] _pooledTokens, uint8[] decimals, string lpTokenName, string lpTokenSymbol, uint256 _a, uint256 _fee, uint256 _adminFee, address lpTokenTargetAddress)

This overrides Swap's initialize function to prevent initializing without the address of the base Swap contract.

Parameters:

• _pooledTokens: an array of ERC20s this pool will accept

• decimals: the decimals to use for each pooled token, eg 8 for WBTC. Cannot be larger than POOL_PRECISION_DECIMALS

• lpTokenName: the long-form name of the token to be deployed

• lpTokenSymbol: the short symbol for the token to be deployed

• _a: the amplification coefficient _ n _ (n - 1). See the StableSwap paper for details

• _fee: default swap fee to be initialized with

• _adminFee: default adminFee to be initialized with

Function initializeMetaSwap(contract IERC20[] _pooledTokens, uint8[] decimals, string lpTokenName, string lpTokenSymbol, uint256 _a, uint256 _fee, uint256 _adminFee, address lpTokenTargetAddress, contract ISwap baseSwap)

Initializes this MetaSwap contract with the given parameters. MetaSwap uses an existing Swap pool to expand the available liquidity. _pooledTokens array should contain the base Swap pool's LP token as the last element. For example, if there is a Swap pool consisting of [DAI, USDC, USDT]. Then a MetaSwap pool can be created with [sUSD, BaseSwapLPToken] as _pooledTokens.

This will also deploy the LPToken that represents users' LP position. The owner of LPToken will be this contract - which means only this contract is allowed to mint new tokens.

Parameters:

• _pooledTokens: an array of ERC20s this pool will accept. The last element must be an existing Swap pool's LP token's address.

• decimals: the decimals to use for each pooled token, eg 8 for WBTC. Cannot be larger than POOL_PRECISION_DECIMALS

• lpTokenName: the long-form name of the token to be deployed

• lpTokenSymbol: the short symbol for the token to be deployed

• _a: the amplification coefficient _ n _ (n - 1). See the StableSwap paper for details

• _fee: default swap fee to be initialized with

• _adminFee: default adminFee to be initialized with

Function swap(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx, uint256 minDy, uint256 deadline) → uint256

Swap two tokens using this pool

Parameters:

• tokenIndexFrom: the token the user wants to swap from

• tokenIndexTo: the token the user wants to swap to

• dx: the amount of tokens the user wants to swap from

• minDy: the min amount the user would like to receive, or revert.

• deadline: latest timestamp to accept this transaction

Function swapUnderlying(uint8 tokenIndexFrom, uint8 tokenIndexTo, uint256 dx, uint256 minDy, uint256 deadline) → uint256

Swap two tokens using this pool and the base pool.

Parameters:

• tokenIndexFrom: the token the user wants to swap from

• tokenIndexTo: the token the user wants to swap to

• dx: the amount of tokens the user wants to swap from

• minDy: the min amount the user would like to receive, or revert.

• deadline: latest timestamp to accept this transaction

Function addLiquidity(uint256[] amounts, uint256 minToMint, uint256 deadline) → uint256

Add liquidity to the pool with the given amounts of tokens

Parameters:

• amounts: the amounts of each token to add, in their native precision

• minToMint: the minimum LP tokens adding this amount of liquidity should mint, otherwise revert. Handy for front-running mitigation

• deadline: latest timestamp to accept this transaction

Return Values:

• amount of LP token user minted and received

Function removeLiquidityOneToken(uint256 tokenAmount, uint8 tokenIndex, uint256 minAmount, uint256 deadline) → uint256

Remove liquidity from the pool all in one token. Withdraw fee that decays linearly over period of 4 weeks since last deposit will apply.

Parameters:

• tokenAmount: the amount of the token you want to receive

• tokenIndex: the index of the token you want to receive

• minAmount: the minimum amount to withdraw, otherwise revert

• deadline: latest timestamp to accept this transaction

Return Values:

• amount of chosen token user received

Function removeLiquidityImbalance(uint256[] amounts, uint256 maxBurnAmount, uint256 deadline) → uint256

Remove liquidity from the pool, weighted differently than the pool's current balances. Withdraw fee that decays linearly over period of 4 weeks since last deposit will apply.

Parameters:

• amounts: how much of each token to withdraw

• maxBurnAmount: the max LP token provider is willing to pay to remove liquidity. Useful as a front-running mitigation.

• deadline: latest timestamp to accept this transaction

Return Values:

• amount of LP tokens burned

Event TokenSwapUnderlying(address buyer, uint256 tokensSold, uint256 tokensBought, uint128 soldId, uint128 boughtId)

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