Smart Contracts

5BLOCK uses two smart contracts: PokemonCards (NFT) and TradeMarket (marketplace).

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PokemonCards.sol

ERC-721 NFT contract for Pokemon trading cards.

Constants

Constant	Value	Description
MAX_CARDS_PER_WALLET	4	Maximum cards a wallet can own
LOCK_DURATION	10 minutes	Lock period after acquisition
MAX_POKEMON_ID	151	Highest valid Pokemon ID (Gen 1)
MIN_POKEMON_ID	1	Lowest valid Pokemon ID

Key Functions

mint(pokemonId, rarityTier, value, uri)

Creates a new card NFT.

function mint(
    uint256 pokemonId,
    uint8 rarityTier,
    uint256 value,
    string calldata uri
) external returns (uint256 tokenId)

• Validates pokemonId (1-151)
• Checks caller has < 4 cards
• Stores metadata on-chain
• Locks card for 10 minutes

getCardMeta(tokenId)

Returns on-chain metadata for a card.

struct CardMeta {
    uint256 createdAt;
    uint256 lastTransferAt;
    uint256 lockUntil;
    uint256 pokemonId;
    uint8 rarityTier;
    uint256 value;
}

getPreviousOwners(tokenId)

Returns array of all previous owners (provenance).

isLocked(tokenId)

Returns true if card cannot be traded yet.

Events

Event	Emitted When
CardMinted	New card created
CardTransferred	Card changes owner
CardLocked	Lock period starts/resets

Mint Flow

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TradeMarket.sol

Marketplace for peer-to-peer card trading.

Constants

Constant	Value	Description
COOLDOWN_DURATION	5 minutes	Time between trade actions

Offer Structure

struct Offer {
    address maker;
    uint256 makerTokenId;
    uint256 takerTokenId;
    OfferStatus status;  // Open, Cancelled, Accepted
    uint256 createdAt;
}

Key Functions

createOffer(makerTokenId, takerTokenId)

Creates a trade offer.

• Maker must own makerTokenId
• takerTokenId must exist
• Card must not be locked
• Cooldown must have passed

cancelOffer(offerId)

Cancels an open offer (maker only).

acceptOffer(offerId)

Accepts an offer and executes the swap.

• Caller must own takerTokenId
• Both cards must not be locked
• Performs atomic swap via transferFrom

getOpenOffers()

Returns all offers with Open status.

Events

Event	Emitted When
TradeCreated	New offer created
TradeCancelled	Offer cancelled
TradeAccepted	Trade executed

Trade Flow

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Security Features

ReentrancyGuard

Both contracts inherit from OpenZeppelin's ReentrancyGuard to prevent reentrancy attacks.

Ownership Validation

Every state-changing function validates the caller owns the relevant token.

Lock Mechanism

10-minute lock after any transfer prevents:

• Rapid flipping
• Flash loan exploits
• Market manipulation

Cooldown

5-minute cooldown between trade actions prevents:

• Spam attacks
• DoS via offer flooding

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Testing

Tests are located in:

• test/PokemonCards.test.ts
• test/TradeMarket.test.ts

Run tests:

pnpm test

Coverage target: >80%

Tests cover:

• Happy paths for all functions
• All revert conditions
• Edge cases (max cards, lock expiry, etc.)