NFT Marketplace Smart Contract Documentation

Overview

This NFT marketplace system consists of three main smart contracts that work together to provide a complete NFT marketplace experience:

1. CollectionManager - Handles creation and management of NFT collections
2. MainContract - Manages purchases, commissions, and promotional codes
3. NewERC721Collection - Individual ERC721 NFT collections

System Architecture

┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
│  MainContract   │◄───┤CollectionManager│◄───┤NewERC721Collection│
│                 │    │                 │    │                 │
│ - Purchases     │    │ - Create NFTs   │    │ - Mint tokens   │
│ - Commissions   │    │ - Manage info   │    │ - Token URIs    │
│ - Promo codes   │    │ - Price/Stock   │    │ - Ownership     │
└─────────────────┘    └─────────────────┘    └─────────────────┘

Contract Details

1. CollectionManager

Purpose: Manages the creation and administration of NFT collections.

Key Features

• Create new ERC721 collections
• Store collection metadata and configuration
• Update collection prices and stock quantities
• Track collections by creator

Core Functions

createCollection()

function createCollection(
    string memory _name,
    string memory _symbol,
    string memory _collectionURI,
    uint256 _price,
    uint256 _quantityInStock
) external payable

Creates a new NFT collection with specified parameters.

Parameters:

• _name: Collection name (1-64 characters)
• _symbol: Collection symbol (1-8 characters)
• _collectionURI: Base URI for metadata
• _price: Price per NFT in wei
• _quantityInStock: Initial stock quantity

Requirements:

• Name length: 1-64 characters
• Symbol length: 1-8 characters
• URI must not be empty
• Price must be greater than 0

getCollectionByAddress()

function getCollectionByAddress(address _collectionAddress) 
    external view returns (CollectionInfo memory)

Retrieves complete collection information by contract address.

changePrice() / changeQuantityInStock()

function changePrice(uint _newPrice, address _collectionAddress) 
    public payable onlyCreator(_collectionAddress)

Updates collection price or stock quantity. Only accessible by collection creator or main contract.

Data Structures

struct CollectionInfo {
    string name;
    string symbol;
    address collectionOwner;
    string collectionURI;
    uint256 price;
    uint256 quantityInStock;
    address collectionAddress;
}

Events

event CollectionCreated(
    address newCollectionAddress,
    address collectionOwner,
    string collectionURI,
    string collectionName,
    uint256 price,
    uint amountOfStock
);

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2. MainContract

Purpose: Handles NFT purchases, commission distribution, and promotional code management.

Key Features

• Individual and batch NFT purchases
• Commission calculation and distribution
• Promotional code generation and redemption
• Reentrancy protection

Core Functions

buy()

function buy(address _collectionAddress, uint256 _quantity) 
    external payable nonReentrant

Purchases NFTs from a specific collection.

Process:

1. Validates stock availability
2. Calculates total price including commission
3. Generates promotional codes
4. Updates stock quantity
5. Distributes funds to seller and platform

batchBuy()

function batchBuy(address[] memory _collectionAddresses, uint256[] memory _quantities) 
    external payable nonReentrant

Purchases multiple NFTs from different collections in a single transaction.

Limitations:

• Maximum 25 collections per transaction
• Arrays must have matching lengths

redeemCode()

function redeemCode(address _collectionAddress, bytes8 _code) 
    external payable

Redeems a promotional code to mint an NFT.

Process:

1. Validates collection existence
2. Verifies promotional code validity
3. Mints NFT to user
4. Removes used promotional code

Commission System

The platform charges a configurable commission on all sales:

• Commission rate set at contract deployment (max 100%)
• Automatically deducted from seller proceeds
• Transferred to platform owner

Promotional Code System

• Generated automatically upon purchase
• Unique codes created using blockchain entropy
• One code per NFT purchased
• Codes are user-specific and single-use

Events

event productPurchased(
    address buyer,
    address indexed collectionAddress,
    uint256 price,
    uint256 cQuantity
);

event promoCodeSuccessfullyUsed(
    address indexed user,
    address indexed collectionAddress
);

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3. NewERC721Collection

Purpose: Individual ERC721 NFT collection contract with marketplace integration.

Key Features

• Standard ERC721 functionality
• Integration with main contract for minting
• Metadata URI management
• Access control for minting

Core Functions

mint()

function mint(address _to) external onlyMainContract

Mints a new NFT to the specified address. Only callable by the main contract.

tokenURI()

function tokenURI(uint256 tokenId) public view override returns (string memory)

Returns the metadata URI for a specific token ID.

Access Control

• Only the main contract can mint new tokens
• Prevents unauthorized token creation
• Ensures integration with marketplace purchase flow

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Security Features

Access Control

• Ownable: Platform owner controls for configuration
• Creator-only: Collection creators can modify their collections
• Main contract restriction: Only main contract can mint NFTs

Reentrancy Protection

• ReentrancyGuard: Prevents reentrancy attacks on purchase functions
• Applied to all payable functions that modify state

Input Validation

• String length limits for names and symbols
• Address zero checks
• Price and quantity validations
• Array length matching for batch operations

Fund Management

• Automatic excess refunds to buyers
• Secure commission distribution
• Protected fund transfers

Usage Examples

Creating a Collection

// Deploy CollectionManager and MainContract first
CollectionManager manager = new CollectionManager(owner);
MainContract main = new MainContract(owner, 5, address(manager)); // 5% commission

// Create a collection
manager.createCollection(
    "My NFT Collection",
    "MNC",
    "https://api.example.com/metadata/",
    1 ether,
    1000
);

Purchasing NFTs

// Single purchase
mainContract.buy{value: 1 ether}(collectionAddress, 1);

// Batch purchase
address[] memory collections = [collection1, collection2];
uint256[] memory quantities = [2, 3];
mainContract.batchBuy{value: 5 ether}(collections, quantities);

Redeeming Promotional Codes

// Redeem a promotional code
mainContract.redeemCode(collectionAddress, promoCode);

Configuration

Deployment Parameters

• Commission Rate: 0-100% (set during MainContract deployment)
• Collection Limits: Name (64 chars), Symbol (8 chars)
• Batch Purchase Limit: 25 collections per transaction

Admin Functions

• setMainContract(): Update main contract address
• setCollectionManager(): Update collection manager address

Error Handling

The system includes comprehensive error handling with custom error messages:

• Collection existence validation
• Stock availability checks
• Payment sufficiency verification
• Input parameter validation
• Access control enforcement

Gas Optimization

• Efficient data structures
• Minimal external calls
• Batch operations support
• Optimized storage patterns

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License

This project is licensed under the MIT License.