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Todoroff Events Co. - a decentralised marketplace application to create events and buy tickets.

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Table of Contents

• Description
• Technologies
• Installation
• How To Use

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Description

This repository consists of the contracts, their unit tests and Hardhat task for the decentralsied application that I created. The overall project represents an event management platform, where one factory contract Marketplace.sol is used by the user to create different events (equivalent to NFT collections) with set parameters like event name, ticket price, ticket quantity, ticket sale duration, etc. Once the event contract EventContract.sol is deployed, users can buy tickets (mint them) as long as the ticket sale period has not ended. When this happens, the Event organiser can call a function that would randomly select a ticket owner and would send one additional ticket to him/her.

Part of the assignment requires random number generation. The factory contract Marketplace.sol includes functionality from the Chainlink protocol, namely the VRF. It is used to generate a number off-chain that would represent a tokenId.The owner of the ticket with the corresponding tokenId is sent one additional ticket as a reward. The reason for this implementation lays in the fact that randomness, geenerated on-chain, by using private variables and their hashes or block timestamps, etc. is often regarded as pseudo-random and predictable. The only 'secure' way to do this happens via Chainlink and this is the sole reason for the entire project to deployed on Goerli (as this is the testnet, used the most for their testing services).

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Technologies

• HardHat
• Javascript
• Chainlink VRF (Verifiable Random Function)
• Openzeppelin libraries - contracts, utils (counters)
• Chai
• ethers.js

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Installation

First, make sure you have Goerli test ether. You can get some at: goerlifaucet.com

1. Clone the repository

2. Run npm install

3. Interacting with the contract - Although it can easily be done with Hardhat, it requires setting up a Goerli provider, etc. An easier alternative, in my opinion, would be:
   a/ Go to Remix
   b/ Create a new file called Marketplace.sol and paste the code of Marketplace.sol from this repository to the newly created file in Remix.
   c/ Do the same for EventContract.sol
   d/ In the SOLIDITY COMPILER tab, select compiler version 0.8.7 to match the one, required by the contracts and COMPILE Marketplace.sol
   e/ Go to the DEPLOY & RUN TRANSACTIONS tab. In the Environment dropdown, select Inejcted provider - Metamask (could be different if you use another wallet extension but look for injected provider). Then go to your wallet extension dashboard and connect it to the Goerli testnet
   f/ Back in Remix in DEPLOY & RUN TRANSACTIONS tab, in the At address window , paste the address 0x8e5c9A24053288CcC5ead816864c45403D9804d2.
   g/ An UI with the callable functions of the contract should pop up below.\

   CAUTION - attempting to deploy a new Marketplace.sol contract would require adding it to an already-funded subscription via the Chainlink subscription dashboard, otherwise the MintToRandomWinner will not execute. Additionally, two arguments must be passed to the constructor - the subscritionId and the VRFCoordinator address.

How To Use

This section will explain the specific functions for the two main contracts - Marketplace.sol and EventContract.sol and ommits the inherited functions. For any additional information, pelase take a look at the comments in the code of the contracts.

1. Marketplace.sol
   a/ eventContracts a public array with a getter function, which contains all the addresses of the deployed Event contracts from the factory contract.
   b/ createEventContract - deploys a new instance of the EventContract.sol with the parameters provided.
   c/ withdrawFundsFromEvent - accepts a uint as an argument, which is the index of the Event contract from the eventContracts array. Callable only by the event organiser for the selected event contract.

   -MintToRandomWinner- this function sends a request to a Chainlink oracle to generate a random number for the selected event contract. The oracle then returns the generated random number by calling the fulfillRandomWords function and stores it in the s_randomWords mapping. After fulfilrandomwords has stored the newly generated number in the mapping, it then uses it to generate a number between 0 and the amount of sold tickets for the event, which represents a tokenId, whose owner is being sent the winning ticket.

   • MarketplaceForTesting.sol contract is used for the unit testing and task and uses the requestId as a source of randomness to mimic one.

2. EventContract.sol
   a/mint - allows the user to buy tickets for the event. Require statements:
   -cannot mint after the totalSupply has been reached.
   -cannot mint if the ticket sale period has ended.
   -cannot mint if the transaction value is not the same as the ticket price.
   b/mintToWinner - sends the winner one additional ticket. Require statements:
   -can be called only by the event organiser via the factory contract's function MintToRandomWinner.

3. Tests The tests for both Marketplace.sol and EventContract.sol can be run by typing npx hardhat test. I used a mock VRF contract in order to conduct the tests properly.

4. Task I have also created a Hardhat task called Fullcycle that mimics the entire process of deploying the factory contract, creating an event, buying of tickets, lottery draw and withdrawal of funds. It can be run by typing npx hardhat fullcycle.

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Author Info

• LinkedIn - Petar Todorov
• Blog - 0xTodorov

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