How to handle timestamp in Solidity

Question

I have written a smart contract which gets the block.timestamp and limits the caller to call the contract until the 2 hours passed as following:

mapping(address => uint256) public coffeKitchenLatestAqcuiredBalances;

function requestStarCoinFromCoffeeKitchenFaucet() public {
    address callerAddress = msg.sender;
    uint256 userLastRetrieveTime = coffeKitchenLatestAqcuiredBalances[callerAddress];
    if (userLastRetrieveTime != 0){
        uint256 epochNow = block.timestamp;
        require(userLastRetrieveTime < epochNow - 7200,"You need to wait for 2 hours from your last call");
    }
}

However I did not manage to extract to timestamp to limit the call time should be from 8AM to 6PM.

How can I format the epoch timestamp and check it on the smart contract call?

Answer 1

A great example of retrieving the hour from timestamp is in this library.

Since you might not want to import the whole library for just one function, here's a minimal implementation:

pragma solidity ^0.8;

library TimestampHelper {
    uint constant SECONDS_PER_DAY = 24 * 60 * 60;
    uint constant SECONDS_PER_HOUR = 60 * 60;

    function getHour(uint timestamp) internal pure returns (uint hour) {
        uint secs = timestamp % SECONDS_PER_DAY;
        hour = secs / SECONDS_PER_HOUR;
    }
}

contract MyContract {
    function foo() external view {
        uint currentHour = TimestampHelper.getHour(block.timestamp);
        require(
            currentHour >= 8 && currentHour <= 18,
            "We're closed now. Opened from 8 AM to 6 PM UTC."
        );
    }
}