A Kitty Party is an informal savings scheme in which participants pool money each month, and a rotating winner gets that aggregated sum. There are as many iterations as participants, and the primary benefit is to be able to access a lump sum amount. There are variations on how the claimant is decided each cycle.

• more information on kitty parties is in user stories

The primary goal of this project is to model this process, keeping best practices and Consensys final project requirements in mind.

• design patterns used
• avoiding common attachs

Aside from truffle, the only noteworthy item is that to test oraclize, we need the Ethereum Bridge to be installed. More details below in the testing section.

• SafeAraryLib.sol

A very basic library that checks array bounds, linked with ExternalUintArrayStorage.sol.

• CircuitBreaker.sol has modifiers

    modifier notInEmergency(){require(circuitBreakerState == CircuitBreakerState.NoEmergency,"no emergency"); _;}
    modifier inEmergency(){require(circuitBreakerState != CircuitBreakerState.NoEmergency, "not in emergency"); _;}
    modifier inRedAlert(){require(circuitBreakerState == CircuitBreakerState.RedAlert, "in red alert"); _;}

• KittyPartyBase.sol descends from CircuitBreaker, and uses the modifiers

The lottery for a kitty party needs some form of randomization, and the goal was to be able to upgrade the randomization part of a deployed contract. This then meant that the storage needed to be separated out, and passed to a new randomizer, whose requirement is to implement IRandomizeRangeToArray.sol. It also meant that there was need for a uniform interface to be able to call the randomization that was currently installed.

/// @dev abstract function implementation, that makes the randomizer fill out the results
function doInitialLottery() internal {
    IRandomizeRangeToArray randomizer = IRandomizeRangeToArray(upgradableRandomizerAddress);
    randomizer.randomize(numberOfParticipants, externalStorageAddress);
}

There are two implementations of IRandomizeRangeToArray.sol:

• BlockRandomizer.sol
• OraclizeRandomizer.sol

In determining a random order of winners, a Wolfram Alpha query is used through Oraclize. This is wrapped in the contract RandomIndicesOraclizeBase.sol, which will produce a list of n integers within the range of 0 to y.

sequential.kittyparty.test is registered on ropsten, please visit with Metamask in a ropsten account.

This currently points to the deployed KittyPartySequential.sol contract, and is utilized in the frontend code:

//when on ropsten, can use ENS for contract address
var myContractAddress = "";
var myContractAbi = [..];
web3.eth.ens.getAddress('sequential.kittyparty.test').then((address)=>{
  window.myContract = new window.web3.eth.Contract (myContractAbi,address);
  refreshContractInfo();
});

truffle test

The only noteworthy item is that to test oraclize, we need the Ethereum Bridge to be installed

• README.md for KittyPartyLotteryOraclize.sol

• ropsten: https://ropsten.etherscan.io/address/0xaab4a8e3a7091523d9a230033843715afb98b4ad

Deployed :

• https://adeelhasan.github.io/kitty_party/
• this is connected to a KittyPartySequential contract
• have a ropsten account with at least 1 gWei
• click "Contribute to this Cycle"
• the metamask confirmation should come up
• state will get updated to reflect that the participant has contriuted for current cycle

https://vimeo.com/340220008 PowerPoint used in the video