//SPDX-License-Identifier: UNLICENSED

pragma solidity >=0.6;

contract purchase{
    address public shipper;
    address payable private seller;
    address payable private buyer;
    uint public proposalTime;
    uint public status; // 0 is Start, 1 is Paid, 2 is Shipped
    
    constructor (address s) {
        shipper = s; // the seller must indicate who is the shipper now, otherwise later he might cheat and indicate himself as shipper
        seller = payable(msg.sender); // this identifies the sender, to give him the money
        status = 0;
    }
    
    function propose_and_pay() payable public{
        require(status==0);  // this blocks other users from making proposals (for simplicity, one purchase at the time)
        buyer=payable(msg.sender); // this identifies the buyer, to give back the mondey in case
        status = 1;
        proposalTime = block.timestamp;  // let's remember the time to start the clock
    }
    
    function getContractBalance() view public returns(uint){
        return address(this).balance;
    }
    
    function accept_and_ship() public{
        require(msg.sender==seller);
        require(status==1);
        status=2;  // we change the status so the shipper can now decide what is happening
    }
    
    function reject() public{
        require(msg.sender==seller);
        require(status==1);
        status=0;        
        buyer.transfer(address(this).balance);  // money sent back to buyter because the seller does not want to go on
    }
    
    function delivered() public{
        require(msg.sender==shipper);
        require(status==2);
        status=0;        // purchase ends and we are ready for another purchase
        seller.transfer(address(this).balance);  // money sent to seller
    }
    
    function not_delivered() public{
        require(msg.sender==shipper);
        require(status==2);
        status=0;        // purchase ends and we are ready for another purchase
        buyer.transfer(address(this).balance);  // money sent back to buyer
    }
    
    function reclaim() public{ // too much time has passed
        require(msg.sender==buyer);  // only the buyer can request money back
        require(status==2 || status==1);
        require(block.timestamp >= proposalTime + 40);  // 40 seconds must have passed
        status=0;        // purchase ends and we are ready for another purchase
        buyer.transfer(address(this).balance);  // money sent back to buyer
    }
    
}