nichanank/ui-ethereum-challenge

UI Ethereum Developer Challenge

Core Deliverables

• Token contract inherits from OpenZeppelin’s ERC20 standard implementation
• Token can only be transferred after a particular _startTime and before a particular _endTime, provided in the constructor
• Unit tests to account for the _startTime and _endTime constraints
• Contribution contract that users can donate ETH to. For their ETH-based contributions, Contribution issues tokens from the Token contract in return
• Contribution contract stores addresses of users that donate as well as the amount of ETH they’ve donated
• Contribution contract has a function that accepts a wallet address, and returns the amount of ETH that a wallet address has contributed to the Contribution contract
• Unit tests for the Contribution contract
• Use OpenZeppelin’s SafeMath library in the Contribution contract

Bonus Deliverables

• Events that emit when functions in Token and Contribution contracts execute
• Unit tests for the events

Design Decisions

• Emergency stop pattern implemented via inheriting OpenZeppelin's Pausable contract. This allows the owner (address that deployed the contract) to pause and unpause certain functionalities. In this case, the contribution function in the Contribution contract reverts if the contract is paused.
• Access control is implemented via inheriting OpenZeppelin's Ownable contract. This identifies the deployer address as the owner and gives the address access to call pause/unpause and withdraw functions in the Contribution contract. Token also inherits from Ownable to allow the contract deployer to set the address of the Contribution contract that is permitted to mint and issue tokens
• Owner must call setContributionContract from the Token contract before the Contribution contract is "allowed" to mint and issue new tokens. This way, there is a separation of concerns between Token logic and Contribution logic. Should there be a bug in the Contribution contract, the owner can pause contributions so no more money comes in and set a new Contribution contract without having to redeploy the Token contract.
• To prevent integer underflow/overflow, both Contribution and Token utilizes the SafeMath library to perform arithmatics. Contribution uses the library to update the amountContributed by a user should they make additional contributions. Token uses the library to calculate the number of tokens to issue to a user relative to their contribution amount (this multipler is a hypothetical constant)
• Both transfer and transferFrom functions of the ERC20 are restricted by startTime and endTime. Token owners can approve tokens outside this window, but transferFrom will not work
• Time constraints are only implemented on the transfer and transferFrom functions. This means that users can still contribute ETH to the Contribution contract and be issued new tokens outside of the startTime and endTime window because the contribution function calls mint and not transfer

External tools/libraries used

• Truffle suite for contract migration setup and testing
• Ganache v4.2.0 as a development blockchain
• @openzeppelin/test-helpers was used along with truffle for testing utils
• @openzeppelin/contracts used for the ERC20 implementation, SafeMath, Pausable, and Ownable contracts

Development

Environment

• Truffle v5.1.9 (core: 5.1.9)
• Solidity - ^0.6.0 (solc-js)
• Node v11.1.0
• Web3.js v1.2.1

Installation

1. Clone the repository using git clone https://github.com/nichanank/ui-ethereum-challenge.git
2. Navigate to the project repo cd ui-ethereum-challenge
3. Install dependencies npm i

Testing

• Have a development blockchain running (e.g. Ganache) on port 7545 and run truffle test