NBA Top Shot

Introduction

This repository contains the smart contracts and transactions that implement the core functionality of NBA Top Shot.

The smart contracts are written in Cadence, a new resource oriented smart contract programming language designed for the Flow Blockchain.

What is NBA Top Shot

NBA Top Shot is the official digital collecitibles game for the National Basketball Association. Players collect and trade digital collectibles that represent highlights from the best players in the world. See more at nbatopshot.com

What is Flow?

Flow is a new blockchain for open worlds. Read more about it here.

What is Cadence?

Cadence is a new Resource-oriented programming language for developing smart contracts for the Flow Blockchain. Read more about it here

We recommend that anyone who is reading this should have already completed the Cadence Tutorials so they can build a basic understanding of the programming language.

Resource-oriented programming, and by extension Cadence, is the perfect programming environment for Non-Fungible Tokens (NFTs), because users are able to store their NFT objects directly in their accounts and transact peer-to-peer. Please see the blog post about resources to understand why they are perfect for digital assets like NBA Top Shot Moments.

Contributing

If you see an issue with the code for the contracts, the transactions, scripts, documentation, or anything else, please do not hesitate to make an issue or a pull request with your desired changes. This is an open source project and we welcome all assistance from the community!

Top Shot Contract Addresses

TopShot.cdc: This is the main Top Shot smart contract that defines the core functionality of the NFT.

Network	Contract Address
Testnet	`0x877931736ee77cff`
Mainnet	`0x0b2a3299cc857e29`

MarketTopShot.cdc: This is the top shot marketplace contract that allows users to buy and sell their NFTs.

Network	Contract Address
Testnet	`0x547f177b243b4d80`
Mainnet	`0xc1e4f4f4c4257510`

Non Fungible Token Standard

The NBA Top Shot contracts utilize the Flow NFT standard which is equivalent to ERC-721 or ERC-1155 on Ethereum. If you want to build an NFT contract, please familiarize yourself with the Flow NFT standard before starting and make sure you utilize it in your project in order to be interoperable with other tokens and contracts that implement the standard.

Top Shot Marketplace contract

The top shot marketplace contract was designed in the very early days of Cadence, and therefore uses some language features that are NOT RECCOMENDED to use by newer projects. For example, the marketplace contract stores the moments that are for sale in the sale collection. The correct way to manage this in cadence is to give a collection capability to the market collection so that the nfts do not have to leave the main collection when going up for sale. The sale collection would use this capability to withdraw moments from the main collection when they are purchased.

This way, any other smart contracts that need to check a user's account for what they own only need to check the main collection and not all of the sale collections that could possibly be in their account.

See the kitty items marketplace contract for an example of the current best practices when it comes to marketplace contracts.

Directory Structure

The directories here are organized into contracts, scripts, and transactions.

Contracts contain the source code for the Top Shot contracts that are deployed to Flow.

Scripts contain read-only transactions to get information about the state of someones Collection or about the state of the TopShot contract.

Transactions contain the transactions that various admins and users can use to perform actions in the smart contract like creating plays and sets, minting Moments, and transfering Moments.

contracts/ : Where the Top Shot related smart contracts live.
transactions/ : This directory contains all the transactions and scripts that are associated with the Top Shot smart contracts.
transactions/scripts/ : This contains all the read-only Cadence scripts that are used to read information from the smart contract or from a resource in account storage.
lib/ : This directory contains packages for specific programming languages to be able to read copies of the Top Shot smart contracts, transaction templates, and scripts. Also contains automated tests written in those languages. Currently, Go is the only language that is supported, but we are hoping to add javascript and other languages soon.

Contract Overview

Each Top Shot Moment NFT represents a play from a game in the NBA season. Plays are grouped into sets which usually have some overarching theme, like rarity or the type of the play.

A set can have one or more plays in it and the same play can exist in multiple sets, but the combination of a play and a set, otherwise known as an edition, is unique and is what classifies an individual Moment.

Multiple Moments can be minted from the same edition and each receives a serial number that indicates where in the edition it was minted.

Each Moment is a resource object with roughly the following structure:

pub resource Moment {

    // global unique Moment ID
    pub let id: UInt64
    
    // the ID of the Set that the Moment comes from
    pub let setID: UInt32

    // the ID of the Play that the Moment references
    pub let playID: UInt32

    // the place in the edition that this Moment was minted
    // Otherwise know as the serial number
    pub let serialNumber: UInt32
}

The other types that are defined in TopShot are as follows:

Play: A struct type that holds most of the metadata for the Moments. All plays in Top Shot will be stored and modified in the main contract.
SetData: A struct that contains constant information about sets in Top Shot like the name, the series, the id, and such.
Set: A resource that contains variable data for sets and the functionality to modify sets, like adding and retiring plays, locking the set, and minting Moments from the set.
MomentData: A struct that contains the metadata associated with a Moment. instances of it will be stored in each Moment.
NFT: A resource type that is the NFT that represents the Moment highlight a user owns. It stores its unique ID and other metadata. This is the collectible object that the users store in their accounts.
Collection: Similar to the NFTCollection resource from the NFT example, this resource is a repository for a user's Moments. Users can withdraw and deposit from this collection and get information about the contained Moments.
Admin: This is a resource type that can be used by admins to perform various acitions in the smart contract like starting a new series, creating a new play or set, and getting a reference to an existing set.

Metadata structs associated with plays and sets are stored in the main smart contract and can be queried by anyone. For example, If a player wanted to find out the name of the team that the player represented in their Moment plays for, they would call a public function in the TopShot smart contract called getPlayMetaDataByField, providing, from their owned Moment, the play and field that they want to query. They can do the same with information about sets.

The power to create new plays, sets, and Moments rests with the owner of the Admin resource.

Admins create plays and sets which are stored in the main smart contract, Admins can add plays to sets to create editions, which Moments can be minted from.

Admins also can restrict the abilities of sets and editions to be further expanded. A set begins as being unlocked, which means plays can be added to it, but when an admin locks the set, plays can no longer be added to it. This cannot be reversed.

The same applies to editions. Editions start out open, and an admin can mint as many Moments they want from the edition. When an admin retires the edition, Moments can no longer be minted from that edition. This cannot be reversed.

These rules are in place to ensure the scarcity of sets and editions once they are closed.

Once a user owns a Moment object, that Moment is stored directly in their account storage via their Collection object. The collection object contains a dictionary that stores the Moments and gives utility functions to move them in and out and to read data about the collection and its Moments.

How to Deploy and Test the Top Shot Contract

The first step for using any smart contract is deploying it to the blockchain, or emulator in our case. Do these commands in vscode. See the vscode extension instructions to learn how to use it.

Start the emulator with the Run emulator vscode command.
Open the NonFungibleToken.cdc file from the flow-nft repo and the TopShot.cdc file. Feel free to read as much as you want to familiarize yourself with the contracts.
In NonFungibleToken.cdc, click the deploy contract to account to deploy it.
Switch to a different account.
In TopShot.cdc, make sure it imports NonFungibleToken from the account you deployed it to.
Click the deploy contract to account button that appears over the TopShot contract declaration to deploy it to a new account.

This deploys the contract code. It also runs the contract's init function, which initializes the contract storage variables, stores the Collection and Admin resources in account storage, and creates links to the Collection.

As you can see, whenever we want to call a function, read a field, or use a type that is defined in a smart contract, we simply import that contract from the address it is defined in and then use the imported contract to access those type definitions and fields.

After the contracts have been deployed, you can run the sample transactions to interact with the contracts. A common order of creating new Moments would be

Creating new plays with transactions/admin/create_play.cdc.
Creating new sets with transactions/admin/create_set.cdc.
Adding plays to the sets to create editions with transactions/admin/add_plays_to_set.cdc.
Minting Moments from those editions with transactions/admin/batch_mint_moment.cdc.

You can also see the scripts in transactions/scripts to see how information can be read from the real Top Shot smart contract deployed on the Flow Beta Mainnet.

Accessing the NBA Top Shot smart contract on Flow Beta Mainnet

The Flow Beta mainnet is still a work in progress and still has a limited number of accounts that can run nodes and submit transactions. Anyone can read data from the contract by running any of the scripts in the transactions directory using one of the public access nodes.

For example, this is how you would query the total supply via the Flow CLI.

flow scripts execute transactions/scripts/get_totalSupply.cdc --host access.mainnet.nodes.onflow.org:9000

Make sure that the import address in the script is correct for mainnet.

NBA Top Shot Events

The smart contract and its various resources will emit certain events that show when specific actions are taken, like transferring an NFT. This is a list of events that can be emitted, and what each event means. You can find definitions for interpreting these events in Go by seeing the lib/go/events package.

pub event ContractInitialized()

This event is emitted when the TopShot contract is created.

Events for plays

pub event PlayCreated(id: UInt32, metadata: {String:String})

Emitted when a new play has been created and added to the smart contract by an admin.
pub event NewSeriesStarted(newCurrentSeries: UInt32)

Emitted when a new series has been triggered by an admin.

Events for set-Related actions

pub event SetCreated(setID: UInt32, series: UInt32)

Emitted when a new set is created.
pub event PlayAddedToSet(setID: UInt32, playID: UInt32)

Emitted when a new play is added to a set.
pub event PlayRetiredFromSet(setID: UInt32, playID: UInt32, numMoments: UInt32)

Emitted when a play is retired from a set. Indicates that that play/set combination and cannot be used to mint moments any more.
pub event SetLocked(setID: UInt32)

Emitted when a set is locked, meaning plays cannot be added.
pub event MomentMinted(momentID: UInt64, playID: UInt32, setID: UInt32, serialNumber: UInt32)

Emitted when a Moment is minted from a set. The momentID is the global unique identifier that differentiates a Moment from all other Top Shot Moments in existence. The serialNumber is the identifier that differentiates the Moment within an Edition. It corresponds to the place in that edition where it was minted.

Events for Collection-related actions

pub event Withdraw(id: UInt64, from: Address?)

Emitted when a Moment is withdrawn from a collection. id refers to the global Moment ID. If the collection was in an account's storage when it was withdrawn, from will show the address of the account that it was withdrawn from. If the collection was not in storage when the Moment was withdrawn, from will be nil.
pub event Deposit(id: UInt64, to: Address?)

Emitted when a Moment is deposited into a collection. id refers to the global Moment ID. If the collection was in an account's storage when it was deposited, to will show the address of the account that it was deposited to. If the collection was not in storage when the Moment was deposited, to will be nil.

NBA Top Shot Marketplace

The contracts/MarketTopShot.cdc contract allows users to create a sale object in their account to sell their Moments.

When a user wants to sell their Moment, they create a sale collection in their account and specify a beneficiary of a cut of the sale if they wish.

A Top Shot Sale Collection functions similarly to a regular Moment collection, but instead of a regular deposit function, the user has function to set a price for their Moment when they deposit it.

When another user wants to buy the Moment that is for sale, they simply send their fungible tokens to the purchase function and if they sent the correct amount, they get the Moment back.

Events for Market-related actions

pub event MomentListed(id: UInt64, price: UFix64, seller: Address?)

Emitted when a user lists a Moment for sale in their SaleCollection.
pub event MomentPriceChanged(id: UInt64, newPrice: UFix64, seller: Address?)

Emitted when a user changes the price of their Moment.
pub event MomentPurchased(id: UInt64, price: UFix64, seller: Address?)

Emitted when a user purchases a Moment that is for sale.
pub event MomentWithdrawn(id: UInt64, owner: Address?)

Emitted when a seller withdraws their Moment from their SaleCollection.
pub event CutPercentageChanged(newPercent: UFix64, seller: Address?)

Emitted when a seller changes the percentage cut that is taken from their sales and sent to a beneficiary.

License

The works in these folders /dapperlabs/nba-smart-contracts/blob/master/contracts/TopShot.cdc /dapperlabs/nba-smart-contracts/blob/master/contracts/MarketTopShot.cdc /dapperlabs/nba-smart-contracts/blob/master/contracts/TopShotAdminReceiver.cdc /dapperlabs/nba-smart-contracts/blob/master/contracts/TopShotShardedCollection.cdc

are under the Unlicense https://github.com/onflow/flow-NFT/blob/master/LICENSE

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