麦加双币协议

pragma solidity ^0.8.0;
 
contract MeccaProtocol {
    IERC20 public tokenA;
    IERC20 public tokenB;
    
    enum NodeTier { BASIC, STANDARD, PREMIUM }
    
    struct Node {
        address owner;
        NodeTier tier;
        uint256 rewards;
    }
    
    mapping(address => Node) public nodes;
    
    function purchaseNode(NodeTier _tier) external payable {
        uint256 price = getNodePrice(_tier);
        require(msg.value >= price, 400">"Insufficient payment");
        
        nodes[msg.sender] = Node({
            owner: msg.sender,
            tier: _tier,
            rewards: 0
        });
    }
}