MoodNFT 🎭

A dynamic NFT (dNFT) project that demonstrates advanced smart contract development using Foundry. MoodNFT creates unique tokens that can change their visual representation based on their current "mood" state - switching between happy and sad pixel art characters.

🌟 Project Overview

MoodNFT is an ERC-721 compliant NFT collection where each token can exist in one of two states:

• Happy 😊 - Displays a smiling pixel art character
• Sad 😢 - Displays a frowning pixel art character

The unique feature of this project is that token holders can flip the mood of their NFTs, dynamically changing the token's metadata and visual appearance.

🚀 Features

• Dynamic NFT Metadata: Token metadata changes based on mood state
• On-chain SVG Storage: Images are stored as base64-encoded SVG data on-chain
• Mood Flipping: Token owners and approved operators can change NFT moods
• Pixel Art Design: Retro-style 20x20 pixel art characters
• Gas Optimized: Efficient storage and retrieval of mood states
• Authorization Controls: Only authorized users can modify NFT moods

🛠️ Technology Stack

• Foundry: Smart contract development framework
• Solidity ^0.8.18: Smart contract programming language
• OpenZeppelin v5: Industry-standard smart contract libraries
• Base64 Encoding: For on-chain SVG storage
• Forge: Testing and deployment framework
• SVG: Scalable vector graphics for NFT images

📁 Project Structure

foundry-nft/
├── src/
│   ├── MoodNft.sol          # Main dynamic NFT contract
│   └── BasicNFT.sol         # Basic NFT implementation for reference
├── script/
│   ├── DeployMoodNft.s.sol  # Deployment script
│   └── Interactions.s.sol   # Contract interaction scripts
├── test/
│   └── unit/
│       └── MoodNftTest.t.sol # Comprehensive unit tests
├── lib/                     # Dependencies
│   ├── forge-std/           # Foundry standard library
│   ├── openzeppelin-contracts/ # OpenZeppelin contracts
│   └── foundry-devops/      # DevOps utilities
└── public/
    ├── happy.svg            # Happy mood SVG file
    └── sad.svg              # Sad mood SVG file

📋 Smart Contract Details

MoodNft.sol

The main contract inheriting from OpenZeppelin's ERC721:

Key Functions:

• mintNft(): Creates a new NFT (starts in HAPPY mood)
• flipMood(uint256 tokenId): Changes NFT mood between HAPPY/SAD
• tokenURI(uint256 tokenId): Returns dynamic metadata based on current mood

Storage:

• s_tokenCounter: Tracks total number of minted tokens
• s_tokenIdToMood: Maps token IDs to their current mood
• s_happySvgURI & s_sadSvgURI: Base64-encoded SVG data

Authorization: Uses OpenZeppelin v5's _isAuthorized() function to ensure only token owners or approved operators can flip moods.

🎨 NFT Metadata Structure

{
  "name": "MoodNFT",
  "description": "A mood NFT",
  "attributes": [
    {
      "trait_type": "moodiness",
      "value": "100"
    }
  ],
  "image": "data:image/svg+xml;base64,..."
}

🧪 Testing

Comprehensive test suite covers:

• NFT minting functionality
• Mood flipping mechanics
• Authorization controls
• Metadata generation
• SVG URI validation

Run tests:

forge test

Run tests with gas reporting:

forge test --gas-report

🚀 Deployment

Prerequisites

• Foundry installed
• Ethereum wallet with testnet ETH

Deploy to Local Network

# Start local Anvil node
anvil

# Deploy contract
forge script script/DeployMoodNft.s.sol --rpc-url http://localhost:8545 --private-key $PRIVATE_KEY --broadcast

Deploy to Testnet

forge script script/DeployMoodNft.s.sol --rpc-url $SEPOLIA_RPC_URL --private-key $PRIVATE_KEY --broadcast --verify --etherscan-api-key $ETHERSCAN_API_KEY

🔧 Usage Examples

Minting an NFT

// Mint a new NFT (starts as HAPPY)
moodNft.mintNft();

Flipping Mood

// Change NFT mood from HAPPY to SAD (or vice versa)
moodNft.flipMood(tokenId);

Viewing Token Metadata

// Get current token metadata
string memory metadata = moodNft.tokenURI(tokenId);

🛡️ Security Features

• Access Control: Only token owners and approved operators can flip moods
• Input Validation: Proper checks for token existence and ownership
• Reentrancy Protection: Uses OpenZeppelin's battle-tested contracts
• Gas Optimization: Efficient storage patterns and function calls

🔍 Gas Usage

Approximate gas costs (may vary):

• Minting: ~80,000 gas
• Mood Flipping: ~30,000 gas
• Token URI Generation: View function (no gas cost)

🤝 Contributing

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

• OpenZeppelin for secure smart contract libraries
• Foundry for the excellent development framework
• Patrick Collins for educational inspiration
• The Ethereum community for continuous innovation

📚 Learning Resources

• Foundry Book
• OpenZeppelin Documentation
• ERC-721 Standard
• Dynamic NFTs

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