Pie Smart Pools

Pie Smart Pools are asset management agnostic(currently Balancer only) Decentralised Traded Funds. They share a common interface to make them easy to integrate in other products.

All Smart Pools are fully upgradeable to make it easy to add features and optimise gas usage at later stages.

Development

Setup the dev enviroment

Clone this repo. And copy the contents of env.example to a new file called .env and edit the the relevant values inside. DO NOT share this file with anyone as it will contain sensitive data.

Install all dependencies:

yarn

Build the project:

yarn build

Run the tests:

yarn test

Create coverage report:

yarn coverage

Running mainnet/testnet test

To test a new implementation in testnet conditions. Set the implementation of a test pool to the new version and run the following script.

POOL=[POOL_ADDRESS] npx buidler test ./mainnet-test/test.ts --network [rinkeby|kovan|rinkeby]

Integration

Adding and removing liquidity

To add liquidity approve the smart pool to pull the underlying tokens. And call:

function joinPool(uint256 _amount) external;

To remove liquidity:

function exitPool(uint256 _amount) external;

Getting pool details

To get the underlying tokens call:

function getTokens() external view returns(address[] memory);

To get the underlying tokens and amounts needed to mint a certain amount of pool shares call:

function calcTokensForAmount(uint256 _amount) external view returns(address[] memory tokens, uint256[] memory amounts);

Balancer smart pool specific

Get the address of the underlying balancer pool:

function getBPool() external view returns(address);

Get the swap fee:

function getSwapFee() external view returns (uint256);

Get if trading is enabled on the underlying balancer pool:

function isPublicSwap() external view returns (bool);

Capped pool specific

Some pools have a cap which limits the totalSupply of the pool shares token. To get the cap you call:

function getCap() external view returns(uint256);

Managing pie smart pools

The pie smart pools have 4 roles which can manage the pie up to some extent: controller, tokenBinder, publicSwapSetter and the circuitBreaker

Setting public swap

Pie smart pools use an underlying balancer pool. If under some circumstances the swapping needs to be disabled/enabled this can be done by the publicSwapSetter by calling:

function setPublicSwap(bool _public) external

Setting the cap

Under some conditions it might be a good idea to limit the amount that can be minted to limit potential losses of new pools. You can set the cap by calling from the controller:

function setCap(uint256 _cap) external 

Setting the swap fee

Every time a trade happens or the pool is joined with a single asset a swap fee is charged. To change the swap fee call from the controller:

function setSwapFee(uint256 _swapFee) external

Enabling and disabling join and exit

During rebalances it is advised to disable joining and exiting the pool. This can be done by calling from the controller:

function setJoinExitEnabled(bool _newValue) external

Setting the circuitBreaker address

The circuitBreaker is able to trip the circuit breaker. To set this address, call from the controller:

function setCircuitBreaker(address _newCircuitBreaker) external

Setting the annual fee

On every join and exit the annual fee is charged. 10**17 == 10%. A 10% fee is the maximum. To set the fee call from the controller:

function setAnnualFee(uint256 _newFee) external

Setting fee recipient

To set the address which receives the annual fee call from the controller:

function setFeeRecipient(address _newRecipient) external

Adding, removal, and weight adjustment of tokens through binding.

Binding and unbinding tokens removes them directly from the smart pool without changing the amount of pieTokens. These functions can only be called by the tokenBinder. When using these functions the pool should be locked and ideally the per pool share value should remain the same. NOTE: adjusting weights should be done carefully and quickly to prevent value from the pool to be leaked out.

To unbind (remove) a token call from the tokenBinder:

function unbind(address _token) external

To bind (add) a token call from the tokenBinder:

function bind(address _token, uint256 _balance, uint256 _denorm) external

To rebind(change a tokens weight) call from the tokenBinder:

 function rebind(address _token, uint256 _balance, uint256 _denorm) external

Circuit breaker

Due to the nature of unrestricted AMMs a single token in the pool experiencing catostrophic will result in all value of a pool being drained. To prevent this from happening a circuit breaker can be tripped by the circuitBreaker to halt swaps, joins and exits this can only be reverted by the controller. This can be done by calling the following function from the circuitBreaker:

function tripCircuitBreaker() external

Updating a token's weight

A token's weight can be updated while still retaining the per pool share value of a pie smart pool. When a token's weight goes down the underlying difference will be send to the controller and some of it's pool shares burned. When a tokens weight goes up the underlying difference will be send to the pool from the controller and pool shares will be minted. NOTE: Be aware of possible sandwhich attacks which could drain value from the pool during adjustment. To update a token's weight call from the controller:

function updateWeight(address _token, uint256 _newWeight)

Updating token weights gradually

By slowly shifting weights over the course of many blocks to the new tarket weights IL from the rebalancing can be minimised. Additionally this mechanic allows for deployment of so called "Liquidity Bootstrapping Pools" pools. Any pending weight adjust will be cancelled if new tokens are added or weights are adjusted. pokeWeights should be called periodically to trigger weight changes.

function updateWeightsGradually(uint256[] calldata _newWeights, uint256 _startBlock, uint256 _endBlock) external

Adding a token

For the sake of balancer smart pool compatibility adding a token is a two step process. During this process the price per pool share should remain the same because new pool shares are minted based on the weight of the new token added. To limit potential losses the weight should correctly reflect the market price of the token and the pool should be locked during adding. NOTE: always be wary about potential sandwhich attacks which could drain value from the pool

To add the token call the following two functions from the controller:

function commitAddToken(address _token, uint256 _balance, uint256 _denormalizedWeight) external

function applyAddToken() external

Removing a token

When removing a token the tokens are send to the controller and in return pool tokens are burned from the controller. This ensures the per pool share price should remain the same. Ideally you lock the pool to prevent value to be partially drained from the pool.

To remove a token call from the controller:

function removeToken(address _token) external