Contract 4: GameEngine - The Game Logic Hub

Combat System

function fightEnemy(uint256 tokenId) external nonReentrant {
    require(evolutionNFT.ownerOf(tokenId) == msg.sender, "Not owner");
    require(block.timestamp >= lastActionTime[tokenId] + 1 hours, "Cooldown active");
    
    uint256 currentLevel = traitFusion.getTraitAsUint(address(evolutionNFT), tokenId, "level");
    uint256 currentEnergy = traitFusion.getTraitAsUint(address(evolutionNFT), tokenId, "energy");
    
    require(currentEnergy >= 20, "Not enough energy");

What's happening here?

• Checks if player owns the NFT

• Enforces 1-hour cooldown between fights

• Gets current level and energy from TraitFusion

• Requires at least 20 energy to fight

// Consume energy
traitFusion.setTraitUint(address(evolutionNFT), tokenId, "energy", currentEnergy - 20);

// Gain XP and potentially level up
uint256 xpGain = 10 + (currentLevel / 2);
uint256 newLevel = currentLevel + (xpGain / 100);

if (newLevel > currentLevel) {
    traitFusion.setTraitUint(address(evolutionNFT), tokenId, "level", newLevel);
    // Increase strength on level up
    uint256 currentStrength = traitFusion.getTraitAsUint(address(evolutionNFT), tokenId, "strength");
    traitFusion.setTraitUint(address(evolutionNFT), tokenId, "strength", currentStrength + 5);
}

What's happening here?

• Reduces energy by 20 points

• Calculates XP gain (higher level = more XP)

• Every 100 XP = 1 level up

• When leveling up, adds 5 strength points

• This is where the evolution happens!

Real-World Data Integration

function updateSteps(uint256 tokenId, uint256 steps) external onlyRole(ORACLE_ROLE) {
    dailySteps[tokenId] = steps;
    
    // Convert steps to stamina (1 step = 0.01 stamina)
    uint256 currentStamina = traitFusion.getTraitAsUint(address(evolutionNFT), tokenId, "stamina");
    uint256 staminaBonus = steps / 100;
    uint256 newStamina = currentStamina + staminaBonus;
    if (newStamina > 200) newStamina = 200; // Cap at 200
    
    traitFusion.setTraitUint(address(evolutionNFT), tokenId, "stamina", newStamina);

What's happening here?

• Only oracle can call this (real-world data source)

• Converts real walking steps to in-game stamina

• 100 steps = 1 stamina point

• Caps stamina at 200 to prevent infinite growth

// Milestone rewards
if (steps >= 10000) {
    gameToken.mint(evolutionNFT.ownerOf(tokenId), 200 * 10**18);
    emit QuestCompleted(tokenId, "daily_10k_steps", 200);
}

What's happening here?

• If player walks 10,000+ steps, they get 200 game tokens

• Real-world activity = in-game rewards!

Loot Box System with Chainlink VRF

function openLootBox(uint256 tokenId) external nonReentrant {
    require(evolutionNFT.ownerOf(tokenId) == msg.sender, "Not owner");
    require(gameToken.balanceOf(msg.sender) >= 100 * 10**18, "Not enough GAME tokens");
    
    gameToken.burn(msg.sender, 100 * 10**18);
    
    uint256 requestId = vrfCoordinator.requestRandomWords(
        keyHash,
        subscriptionId,
        requestConfirmations,
        callbackGasLimit,
        1
    );
    
    vrfRequests[requestId] = tokenId;

What's happening here?

• Player burns 100 tokens to open loot box

• Requests truly random number from Chainlink VRF

• Maps the request ID to the token ID for later processing

function fulfillRandomWords(uint256 requestId, uint256[] memory randomWords) internal override {
    uint256 tokenId = vrfRequests[requestId];
    uint256 randomValue = randomWords[0] % 100;
    
    // Loot rarity: 0-49 = common, 50-79 = rare, 80-94 = epic, 95-99 = legendary
    if (randomValue >= 95) {
        // Legendary loot
        uint256 currentStrength = traitFusion.getTraitAsUint(address(evolutionNFT), tokenId, "strength");
        traitFusion.setTraitUint(address(evolutionNFT), tokenId, "strength", currentStrength + 50);
        traitFusion.setTraitString(address(evolutionNFT), tokenId, "loot_tier", "legendary");

What's happening here?

• Chainlink calls this function with random number

• Converts random number to percentage (0-99)

• 5% chance for legendary loot (+50 strength)

• 15% chance for epic loot (+25 strength)

• 30% chance for rare loot (+10 strength)

• 50% chance for common loot (+5 strength)