Add Random Emoji on-chain NFT on OpenSea example (#3)

* Add Random Emoji on-chain NFT on OpenSea example

* Update README.md

* Migrate example to VRF v2

* Adjust Readme file

* Remove numWords constructor parameter because the contract needs exactly four random values from VRF

random-svg-nft/.env.example

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+ETHERSCAN_API_KEY=<YOUR ETHERSCAN API>
+RINKEBY_URL=https://eth-rinkeby.alchemyapi.io/v2/<YOUR ALCHEMY KEY>
+PRIVATE_KEY=<YOUR PRIVATE KEY>
+SUBSCRIPTION_ID=<ID>

random-svg-nft/.eslintignore

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+node_modules
+artifacts
+cache
+coverage

random-svg-nft/.eslintrc.js

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+module.exports = {
+  env: {
+    browser: false,
+    es2021: true,
+    mocha: true,
+    node: true,
+  },
+  plugins: ["@typescript-eslint"],
+  extends: [
+    "standard",
+    "plugin:prettier/recommended",
+    "plugin:node/recommended",
+  ],
+  parser: "@typescript-eslint/parser",
+  parserOptions: {
+    ecmaVersion: 12,
+  },
+  rules: {
+    "node/no-unsupported-features/es-syntax": [
+      "error",
+      { ignores: ["modules"] },
+    ],
+  },
+};

random-svg-nft/.gitignore

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+node_modules
+.env
+coverage
+coverage.json
+typechain
+
+#Hardhat files
+cache
+artifacts
+
+yarn.lock
+package-lock.json

random-svg-nft/.npmignore

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+hardhat.config.ts
+scripts
+test

random-svg-nft/.prettierignore

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+node_modules
+artifacts
+cache
+coverage*
+gasReporterOutput.json

random-svg-nft/.solhint.json

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+{
+  "extends": "solhint:recommended",
+  "rules": {
+    "compiler-version": ["error", "^0.8.0"],
+    "func-visibility": ["warn", { "ignoreConstructors": true }]
+  }
+}

random-svg-nft/.solhintignore

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+node_modules

random-svg-nft/README.md

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+# Random Emoji NFT collection on OpenSea
+
+This demo project demonstrates how to create randomly generated on-chain Emoji NFTs using Chainlink VRF and how to host that collection on OpenSea on Rinkeby Testnet.
+
+## What we are building
+
+![demo](demo.png)
+
+## Getting started
+
+### Prerequisites
+
+Be sure to have installed the following
+
+- [Git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
+- [Node.js](https://nodejs.org/en/download/)
+- [Yarn](https://yarnpkg.com/getting-started/install)
+
+### Installation
+
+1. Get a RPC API Key from a node provider such as [Alchemy](https://www.alchemy.com/), [Infura](https://infura.io/), [Moralis](https://moralis.io/), or [QuickNode](https://www.quicknode.com/). This example uses the RINKEBY Ethereum test network.
+2. Clone the repo
+
+```
+git clone https://github.com/smartcontractkit/smart-contract-examples.git
+```
+
+3. Enter the direcory
+
+```
+cd smart-contract-examples/random-svg-nft
+```
+
+### Build and Deploy
+
+1. Install packages
+
+```shell
+yarn
+```
+
+2. Compile contracts
+
+```shell
+yarn compile
+```
+
+3. Run tests
+
+```shell
+yarn test
+```
+
+or
+
+```shell
+REPORT_GAS=true yarn test
+```
+
+4. Run test coverage
+
+```shell
+yarn coverage
+```
+
+5. Deploy contract to Rinkeby
+
+Go to [Chainlink VRF Subscription Managment Page](https://vrf.chain.link/), connect your wallet, create new subscription and fund it. Make sure to have at least 1 Rinkeby LINK in your wallet, you can obtain it from the [Chainlink Faucet](https://faucets.chain.link/arbitrum-rinkeby)
+
+Copy the `.env.example` file to a file named `.env`, and put your Private Key, RPC API Key, [Etherscan API Key](https://etherscan.io/apis), and Subscription ID like this
+
+```shell
+ETHERSCAN_API_KEY=<YOUR ETHERSCAN API>
+RINKEBY_URL=https://eth-rinkeby.alchemyapi.io/v2/<YOUR ALCHEMY KEY>
+PRIVATE_KEY=<YOUR PRIVATE KEY>
+SUBSCRIPTION_ID=<ID>
+```
+
+After that run the deployment script which will
+
+- deploy your smart contract to the Rinkeby
+- verify it on Etherscan
+
+```shell
+yarn deploy
+```
+
+Lastly, navigate back to the Chainlink VRF Subscription Managment Page and add the address of deployed smart contract as subscription consumer.
+
+If the verification process fails because the new contract hasn't been indexed yet on Etherscan, run the next command from your terminal
+
+```shell
+npx hardhat verify --network rinkeby <CONTRACT_ADDRESS> 0xd89b2bf150e3b9e13446986e571fb9cab24b13cea0a43ea20a6049a85cc807cc <SUBSCRIPTION_ID> 1000000 4 3
+```
+
+### Minting
+
+Call `mint()` function of your contract. Soon after the successful transaction, your NFT will be available on [OpenSea](https://testnets.opensea.io/)

random-svg-nft/contracts/EmojiNFT.sol

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+//SPDX-License-Identifier: MIT
+pragma solidity ^0.8.7;
+
+import "@chainlink/contracts/src/v0.8/interfaces/VRFCoordinatorV2Interface.sol";
+import "@chainlink/contracts/src/v0.8/VRFConsumerBaseV2.sol";
+import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";
+import "@openzeppelin/contracts/utils/Counters.sol";
+import "@openzeppelin/contracts/utils/Strings.sol";
+import "@openzeppelin/contracts/utils/Base64.sol";
+
+contract EmojiNFT is ERC721URIStorage, VRFConsumerBaseV2 {
+  using Counters for Counters.Counter;
+  Counters.Counter private tokenIds;
+
+  string[] private emojis = [
+    unicode"😁",
+    unicode"😂",
+    unicode"😍",
+    unicode"😭",
+    unicode"😴",
+    unicode"😎",
+    unicode"🤑",
+    unicode"🥳",
+    unicode"😱",
+    unicode"🙄"
+  ];
+
+  VRFCoordinatorV2Interface internal immutable vrfCoordinator;
+  bytes32 internal immutable keyHash;
+  uint64 internal immutable subscriptionId;
+  uint32 internal immutable callbackGasLimit;
+  uint32 internal immutable numWords;
+  uint16 internal immutable requestConfirmations;
+
+  mapping(uint256 => address) requestToSender;
+
+  event RandomnessRequested(uint256 indexed requestId);
+
+  constructor(
+    address _vrfCoordinator,
+    bytes32 _keyHash,
+    uint64 _subscriptionId,
+    uint32 _callbackGasLimit,
+    uint16 _requestConfirmations
+  ) VRFConsumerBaseV2(_vrfCoordinator) ERC721("EmojiNFT", "EMOJI") {
+    vrfCoordinator = VRFCoordinatorV2Interface(_vrfCoordinator);
+    keyHash = _keyHash;
+    subscriptionId = _subscriptionId;
+    callbackGasLimit = _callbackGasLimit;
+    numWords = 4;
+    requestConfirmations = _requestConfirmations;
+  }
+
+  function mint() public returns (uint256 requestId) {
+    requestId = vrfCoordinator.requestRandomWords(
+      keyHash,
+      subscriptionId,
+      requestConfirmations,
+      callbackGasLimit,
+      numWords
+    );
+
+    requestToSender[requestId] = msg.sender;
+
+    emit RandomnessRequested(requestId);
+  }
+
+  function pickRandomColor(uint256 firstRandomNumber, uint256 secondRandomNumber, uint256 thirdRandomNumber)
+    internal
+    pure
+    returns (string memory)
+  {
+    uint256 r = firstRandomNumber % 256;
+    uint256 g = secondRandomNumber % 256;
+    uint256 b = thirdRandomNumber % 256;
+
+    return
+      string(
+        abi.encodePacked(
+          "rgb(",
+          Strings.toString(r),
+          ", ",
+          Strings.toString(g),
+          ", ",
+          Strings.toString(b),
+          ");"
+        )
+      );
+  }
+
+  function createOnChainSvg(string memory emoji, string memory color) internal pure returns(string memory svg) {
+    string memory baseSvg = "<svg xmlns='http://www.w3.org/2000/svg' preserveAspectRatio='xMinYMin meet' viewBox='0 0 350 350'><style>.base { font-size: 100px; }</style><rect width='100%' height='100%' style='fill:";
+    string memory afterColorSvg = "' /><text x='50%' y='50%' class='base' dominant-baseline='middle' text-anchor='middle'>";
+
+    svg = string(abi.encodePacked(baseSvg, color, afterColorSvg, emoji, "</text></svg>"));
+  }
+
+  function createTokenUri(string memory emoji, string memory svg) internal pure returns(string memory tokenUri) {
+    string memory json = Base64.encode(
+      bytes(
+        string(
+          abi.encodePacked(
+            '{"name": "',
+            emoji,
+            '", "description": "Random Emoji NFT Collection Powered by Chainlink VRF", "image": "data:image/svg+xml;base64,',
+            Base64.encode(bytes(svg)),
+            '"}'
+          )
+        )
+      )
+    );
+
+    tokenUri = string(
+      abi.encodePacked("data:application/json;base64,", json)
+    );
+  }
+
+  function fulfillRandomWords(uint256 requestId, uint256[] memory randomNumbers)
+    internal
+    override
+  {
+    uint256 tokenId = tokenIds.current();
+
+    uint256 emojiIndex = (randomNumbers[0] % emojis.length) + 1;
+    string memory emoji = emojis[emojiIndex];
+    string memory color = pickRandomColor(randomNumbers[1], randomNumbers[2], randomNumbers[3]);
+    string memory svg = createOnChainSvg(emoji, color);
+    string memory tokenUri = createTokenUri(emoji, svg);
+
+    _safeMint(requestToSender[requestId], tokenId);
+    _setTokenURI(tokenId, tokenUri);
+
+    tokenIds.increment();
+  }
+}

random-svg-nft/contracts/test/LinkToken.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.4.24;
+
+import "@chainlink/contracts/src/v0.4/LinkToken.sol";

random-svg-nft/contracts/test/VRFCoordinatorV2Mock.sol

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+//SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "@chainlink/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol";

random-svg-nft/hardhat.config.ts

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+import * as dotenv from "dotenv";
+
+import { HardhatUserConfig } from "hardhat/config";
+import "@nomiclabs/hardhat-etherscan";
+import "@nomiclabs/hardhat-waffle";
+import "@typechain/hardhat";
+import "hardhat-gas-reporter";
+import "solidity-coverage";
+
+dotenv.config();
+
+const config: HardhatUserConfig = {
+  solidity: {
+    compilers: [
+      {
+        version: "0.8.7",
+      },
+      {
+        version: "0.4.24",
+      },
+    ],
+  },
+  networks: {
+    rinkeby: {
+      url: process.env.RINKEBY_URL || "",
+      accounts:
+        process.env.PRIVATE_KEY !== undefined ? [process.env.PRIVATE_KEY] : [],
+    },
+  },
+  gasReporter: {
+    enabled: process.env.REPORT_GAS !== undefined,
+    currency: "USD",
+  },
+  etherscan: {
+    apiKey: {
+      rinkeby: process.env.ETHERSCAN_API_KEY,
+    },
+  },
+};
+
+export default config;