This library includes a stateless Typescript model of the Solidity DrawCalculator. It is intended to be uses as a tool to easily check if a User has won a prize for a particular draw. This could also be calculated on-chain through the DrawCalculator::calculate() view function but this library is much faster.

This project is available as an NPM package:

$ yarn add @pooltogether/draw-calculator-js

To create a claim or calculate winnings for an address:

1. Run yarn add @pooltogether/draw-calculator-js in your project to install the package.
2. Import the desired functions and types: import {drawCalculator, Draw, PrizeDistribution, DrawResults, filterResultsByValue, generatePicks, prepareClaims } from "@pooltogether/draw-calculator-js"

Starting with a particular drawId and userAddress, fetch the Draw information from the DrawBuffer contract:

const drawBuffer: Contract = new ethers.Contract(address, drawBufferAbi, signerOrProvider);
const drawId: number = await drawBuffer.getNewestDraw(); // can go back cardinality in time (8 draws)
const draw: Draw = await drawBuffer.functions.getDraw(drawId); // read-only rpc call

Next fetch the PrizeDistribution for the drawId from the PrizeDistributionBuffer contract:

// get PrizeDistribution from the  DrawCalculatorHistory contract for a particular drawId
const PrizeDistributionBufferContract: Contract = new ethers.Contract(
    address,
    prizeDistributionAbi,
    signerOrProvider,
);
const prizeDistribution = await PrizeDistributionBufferContract.functions.getPrizeDistribution(
    drawId,
); // read-only rpc call

Next, get the users balance using the convenient getNormalizedBalancesForDrawIds(address _user, uint32[] calldata _drawIds) view method on the DrawCalculator contract which returns an array of balances for drawIds: W

const drawCalculator: Contract = new ethers.Contract(address, drawCalculatorAbi, signerOrProvider);
const balances = await drawCalculator.functions.getNormalizedBalancesForDrawIds(userAddress, [
    drawId,
]); // read-only rpc call

Run this draw-calculator-js library locally to see the user has any prizes to claim:

const exampleUser: User = {
    address: userAddress // user address we want to calculate for
    normalizedBalances: balances
}

let results: DrawResults = batchCalculateDrawResults([prizeDistribution], [draw], exampleUser)

The results.totalValue field should indicate the total amount of prize available for userAddress for the drawId.

These results may then need to be filtered by value, since the user can only claim prizeDistribution.maxPicksPerUser number of prizes per draw.

results = filterResultsByValue(results, prizeDistribution.maxPicksPerUser);

Finally, to claim a prize, forward these DrawResults to prepareClaims(user: User, drawResult: DrawResults[]) to generate the data for the on-chain PrizeDistributor claim() call:

const claim: Claim = prepareClaims(user, [results]);

The on-chain call to PrizeDistributor::claim(address _user, uint32[] calldata _drawIds, bytes calldata _data) can then be populated and called with this data:

const PrizeDistributorContract = new ethers.Contract(
    address,
    PrizeDistributorAbi,
    signerOrProvider,
);
await PrizeDistributorContract.functions.claim(
    claim.userAddress,
    claim.drawIds,
    claim.encodedWinningPickIndices,
); //write rpc call

Congratulations you have now claimed a prize!

todo.

A full breakdown of the types can be found here

Unit tests can be run using:

$ yarn test

Fork/clone this repo. Create a pull request with the changes you would like to make. Unit tests must be passing.