MIDTERM: Launching an ICO

Welcome to the Blockchain for Developers DeCal's midterm assignment. You'll be designing your own ICO.

Midterm Instructions

Your task is to complete both Token.sol and Crowdsale.sol such that they each function as described below. Queue.sol is also a necessary data structure contract. Notice that Token.sol inherits from contracts/interfaces/ERC20Interface.sol.

Implement all three contracts and test them in order to demonstrate your understanding of external calls, timestamping, testing, and everything else learned so far!

All work should be done in contracts/Crowdsale.sol, contracts/Queue.sol and contracts/Token.sol. Do not make changes to any other files. The exception to this is for testing: add as many test files as you need, of course

Rules

You will be building an ERC20-compliant token platform with a few caveats. Firstly, the token sale will be capped, so there can only be a limited number of tokens in circulation. Tokens can be minted and destroyed (burned), as well as refunded. The crux of the project is to set up a crowdsale where buyers must enter a Queue, waiting in line to place their order for tokens. Buyers waiting in line must make sure they are not the last person in line: you must have someone behind you to place a token order!

Details follow:

• Crowdsale.sol contract specifications:
  • Must deploy Token.sol
  • The contract must keep track of how many tokens have been sold
  • The contract must only sell to/refund buyers between start-time and end-time
  • The contract must forward all funds to the owner after sale is over
  • Owner:
    • Must be set on deployment
    • Must be able to time-cap the sale
      • Must keep track of start-time
      • Must keep track of end-time/time remaining since start-time
    • Must be able to specify an initial amount of tokens to create
    • Must be able to specify the amount of tokens 1 wei is worth
    • Must be able to mint new tokens
      • This amount would be added to totalSupply in Token.sol
    • Must be able to burn tokens not sold yet
      • This amount would be subtracted from totalSupply in Token.sol
    • Must be able to receive funds from contract after the sale is over
  • Buyers:
    • Must be able to buy tokens directly from the contract and as long as the sale has not ended, if they are first in the queue and there is someone waiting line behind them
      • This would change their balance in Token.sol
      • This would change the number of tokens sold
    • Must be able to refund their tokens as long as the sale has not ended. Their place in the queue does not matter
      • This would change their balance in Token.sol
      • This would change the number of tokens sold
  • Events:
    • Fired on token purchase
    • Fired on token refund
• Queue.sol (this is a first-in-first-out data structure, more info here):
  • Must have a finite size, please keep this set to 5
  • Must have a time limit someone can keep their spot in the front; this prevents griefing
  • Must have the following methods:
    • qsize(): Returns the number of people waiting in line
    • empty(): Returns whether the queue is empty or not
    • getFirst(): Returns the address of the person in the front of the queue
    • checkPlace(): Allows msg.sender to check their position in the queue
    • checkTime(): Allows anyone to expel the first person in line if their time limit is up
    • dequeue(): Removes the first person in line; either when their time is up or when they are done with their purchase
    • enqueue(address addr): Places addr in the first empty position in the queue
  • The queue should only permit buyers to place an order if they are not the only ones in line, i.e. if there is at least one person waiting behind them
  • Events:
    • Fired when someone's time limit is over and they are ejected from the front of the queue
• Token.sol contract specifications:
  • Must implement ERC20Interface.sol fully
  • Must work in conjunction with Crowdsale.sol
    • totalSupply would be set on deployment of Crowdsale.sol
  • Users:
    • All standard functionality from ERC20Interface.sol
    • Must be able to burn their tokens
      • This amount would be subtracted from totalSupply
  • Events:
    • All standard events from ERC20Interface.sol
    • Fired on buyers burning their tokens

Minimum Requirements

You have a lot freedom to carry out this assignment as you please. You will be graded on the following:

• At minimum, adhering to the requirements specified above
  • Any additional functionality is a welcome addition
  • If any mathematical operations are necessary, we expect overflow not to be an issue
    • To this end, contracts/utils/Math.sol and contracts/utils/SafeMath.sol have been provided
• Fully-fleshed out, specific tests
  • Reminder that Mocha tests run asynchronously
  • Make sure to group related tests together
  • Use descriptive strings for test cases and assertions

Extra Credit

• Have the token get more expensive with each purchase. In other words, implement an early-bird incentive
• Enforce a black/white-list of addresses that are/aren't able to participate in the crowdsale
• Provide a use-case contract for your token, something buyers would use it for
  • This could be a small game or another novel use; it doesn't have to be too sophisticated
• MetaMask or frontend integration

Testing

You can verify that your smart contract is implemented correctly with truffle test. Be sure to have a ganache server running in a separate terminal.

Refresher: in an empty terminal, run ganache-cli to initialize a default ganache server. If you get errors, read the ganache documentation.

Truffle Console

If you're having trouble passing the tests and would like to play around with the contracts manually:

1. Run truffle migrate
2. Run truffle console, This will open up a Node JavaScript console that is connected to your ganache server