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| //SPDX-License-Identifier: GPL-3.0 | |
| pragma solidity >=0.5.0 <0.9.0; | |
| contract Lottery { | |
| address payable[] public players; | |
| address public manager; | |
| // set the manager to the address that deploys the contract in the constructor | |
| // the constructor is called only once upon creation | |
| constructor() { | |
| manager = msg.sender; | |
| } | |
| // a contract can only have one receive function declared with this syntax. No arguments. No colon; | |
| // notice that a value without a suffix is assumed to be wei. | |
| // 100000000000000000 = 0.1 ether <-- with the suffix | |
| receive() external payable{ | |
| // any code before the below line will still consume gas if fails. | |
| require(msg.sender != manager); // Prevents manager from participating | |
| require(msg.value == 0.01 ether); // minimum amount required to play | |
| players.push(payable(msg.sender)); | |
| } | |
| // The below function returns the contract's balance in wei. | |
| function getBalance() public view returns(uint) { | |
| // only the manager can see the balance of the contract | |
| require(msg.sender == manager); | |
| return address(this).balance; | |
| } | |
| function random() public view returns(uint){ | |
| // on a live deploy with high stakes, use the chainlink vrf solution to generate random numbers. | |
| return uint(keccak256(abi.encodePacked(block.difficulty, block.timestamp, players.length))); | |
| } | |
| // Declare a winner | |
| function pickWinner() public { | |
| // ensure that only the manager pick the winner. | |
| require(msg.sender == manager); | |
| require(players.length >= 3); | |
| uint r = random(); | |
| address payable winner; | |
| // now select the index of the winner using the modulus of the player length | |
| uint index = r % players.length; | |
| uint balance = getBalance(); | |
| winner = players[index]; | |
| // recall that the winner's address was declared as payable upon receiving ether. | |
| winner.transfer(balance); | |
| // reset the lottery for another round. Namely, reset the players; | |
| players = new address payable[](0); | |
| } | |
| } |
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