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133 lines
5.1 KiB
133 lines
5.1 KiB
2 years ago
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# Non Fungible Cats
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Today's quest objective is to master Non Fungible Tokens, NFTs.
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To represent a simple token, we used a smart contract with with each blockchain address amount of tokens. We talk about fungible token because each token has the same value. A Non-Fungible Token is a token with a unique identifier, usually part of a collection. NFTs are used to represent playing cards, works of art, financial securities and even physical objects.
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Internally fungible token that we have seen in the prior quest are represented with a mapping from addresses to an amount:
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Address ---> Amount
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0x2FE34 20
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Non-Fungible Tokens are represented with a mapping of unique identifiers to an owner
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Identifier ---> Address
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123455 0x2FE34
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In addition, each token is linked to an Uniform Resource Identifier (URI) where additional information about the NFT can be found, such as metadata, an image...
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Identifier ---> Address
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123455 0x2FE34
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---> URI
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bafkreiajlq3
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### **Content**
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### Mandatory
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1. `Napping Cats `
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2. `Showcase`
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### Optional
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3. `Automated Reveal`
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---
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---
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# Exercise 1: Napping Cats
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In this exercise we will create a basic NFT smart contract, and use it to instantiate an NFT collection with some custom functions
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### Instructions
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#### Basic NFT
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- Create a smart contract `basicNFT`
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- Create a `constructor` function that takes a string that will be used as a name for the NFT.
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- Create a public function `ownerOf()` that associate a token to the address of its owner
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- Create a public function `TokenURI()` that associate a token to a resource
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- Create a function `transfer(uint, address)` that takes as parameters an identifier (a positive integer) and an address to allow the owner of a NFT to transfer it.
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_Optionally you can implement or reuse the full ERC721 standard_
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#### Napping cats
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- Create a smart contract `Napping Cats` that inherits from basicNFT
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- Its constructor function takes a new parameter, initial price, that fixes the initial sale price of the NFT collection
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- Instantiate the first three cats inside the smart contract with for each a json file (0.json, 1.json, 2.json) that contain a field name and a field image that points to a local or online image. NFTs initially don't have an owner
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#### Trading functions
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- Add to `Napping Cats` a function `listToken(uint256 id, uint256 price)` that lists the token for sale at the proposed price
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- Add to `Napping Cats` a function `buyToken(uint256 id)`, payable, that allows an user to buy a token
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- For the initial sale price defined by the constructor for new tokens
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- For the listed price by the function listToken
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_Optionally, the price for new tokens is an auction. It starts at 100x of the initial sale price or the last paid price for a new token and decreases over time to reach 0 after 24 hours._
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### Resources
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- [ERC721 standart](https://eips.ethereum.org/EIPS/eip-721)
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- [Uniform Ressource Identifier Definition](https://en.wikipedia.org/wiki/Uniform_Resource_Identifier)
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---
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---
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# Exercise 2: Showcase
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We will now be able to display our NFT collection on a website and allow user to use the interface to buy and sell tokens.
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### Instructions
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- Reuse the `Napping Cats` smart contract from the previous exercise
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- Create a webpage index.html that connects to the napping Cats smart contract and displays the corresponding URIs as a table
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- Add a button to connect a wallet.
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- Offer a buy button connected to the buyToken
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- _optionally : the buy button display the current price of this specific token_
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- Once the wallet is connected, offer a sell token under the tokens owned by the user
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- The button should open a modal or include an input field to give a listing price.
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- provide a script and a guide to deploy the smart contract and serve the webpage
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### Resources
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- [ERC721 Standard](https://ethereum.org/en/developers/docs/standards/tokens/erc-721/)
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- [solidity docs](https://docs.soliditylang.org/)
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- [learn X in Y](https://learnxinyminutes.com/docs/solidity/)
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- [Remix IDE](https://remix.ethereum.org)
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- [hardhat](https://hardhat.org)
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---
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---
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# Exercise 3: Automated Reveal (Optional)
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In some auctions, NFT images are only revealed once purchased.
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For this we will create a node server that will serve the images only once they are purchased.
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### Instructions
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- Create a node server file index.js
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- Listen on port 3030 and connect to a local node 8545
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- Add the nappingCats exercise, modifying tokenURI to match the local node server
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- The server is launched with a smart contract address as parameter
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- For each request for an image X.jpg, only return it if the token has an owner.
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- Optionnally, using IPFS
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- The Json file contain the futur hash of tokens on IPFS
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- The server periodically monitor the smart contract for new owners
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- Once a new owner is found, the image is published on a local or remote IPFS server
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### Resources
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- [Express documentation](https://expressjs.com/en/4x/api.html)
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- [IPFS documentation](https://docs.ipfs.tech/reference/)
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- [Pinata documentation (commercial pining serivce)](https://docs.pinata.cloud/pinata-api/pinning-services-api)
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---
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---
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