refer to:
https://docs.soliditylang.org/en/latest/units-and-global-variables.html
msg.value
msg.sender
this 代表当前合约
1 wei = 1
1 gwei = 1e9
1 ether = 1e18
时间的单位是秒
1 minutes = 60
1 hours = 3600
下面都是copy来的：
blockhash(uint blockNumber) returns (bytes32): hash of the given block when blocknumber is one of the 256 most recent blocks; otherwise returns zero
blobhash(uint index) returns (bytes32): versioned hash of the index-th blob associated with the current transaction. A versioned hash consists of a single byte representing the version (currently 0x01), followed by the last 31 bytes of the SHA256 hash of the KZG commitment (EIP-4844).
block.basefee (uint): current block’s base fee (EIP-3198 and EIP-1559)
block.blobbasefee (uint): current block’s blob base fee (EIP-7516 and EIP-4844)
block.chainid (uint): current chain id
block.coinbase (address payable): current block miner’s address
block.difficulty (uint): current block difficulty (EVM < Paris). For other EVM versions it behaves as a deprecated alias for block.prevrandao (EIP-4399 )
block.gaslimit (uint): current block gaslimit
block.number (uint): current block number
block.prevrandao (uint): random number provided by the beacon chain (EVM >= Paris)
block.timestamp (uint): current block timestamp as seconds since unix epoch
gasleft() returns (uint256): remaining gas
msg.data (bytes calldata): complete calldata
msg.sender (address): sender of the message (current call)
msg.sig (bytes4): first four bytes of the calldata (i.e. function identifier)
msg.value (uint): number of wei sent with the message
tx.gasprice (uint): gas price of the transaction
tx.origin (address): sender of the transaction (full call chain)