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course...Auction.sol

pragma solidity ^0.4.17;
contract Auction {
    
    // Data
    //Structure to hold details of the item
    struct Item {
        uint itemId; // id of the item
        uint[] itemTokens;  //tokens bid in favor of the item
       
    }
    
   //Structure to hold the details of a persons
    struct Person {
        uint remainingTokens; // tokens remaining with bidder
        uint personId; // it serves as tokenId as well
        address addr;//address of the bidder
    }
 
    mapping(address => Person) tokenDetails; //address to person 
    Person [4] bidders;//Array containing 4 person objects
    
    Item [3] public items;//Array containing 3 item objects
    address[3] public winners;//Array for address of winners
    address public beneficiary;//owner of the smart contract
    
    uint bidderCount=0;//counter
    
    //functions

    function Auction() public payable{    //constructor
                
        //Part 1 Task 1. Initialize beneficiary with address of smart contract’s owner
        //Hint. In the constructor,"msg.sender" is the address of the owner.
        // ** Start code here. 1 line approximately. **/
        beneficiary = msg.sender;
          //** End code here. **/
        uint[] memory emptyArray;
        items[0] = Item({itemId:0,itemTokens:emptyArray});
        
        //Part 1 Task 2. Initialize two items with at index 1 and 2. 
        // ** Start code here. 2 lines approximately. **/
        items[1] = Item({itemId:11,itemTokens:emptyArray});
        items[2] = Item({itemId:2,itemTokens:emptyArray});
        //** End code here**/
    }
    

    function register() public payable{
        
        
        bidders[bidderCount].personId = bidderCount;
        
        //Part 1 Task 3. Initialize the address of the bidder 
        /*Hint. Here the bidders[bidderCount].addr should be initialized with address of the registrant.*/

        // ** Start code here. 1 line approximately. **/
        bidders[bidderCount].addr = msg.sender;
        //** End code here. **
        
        bidders[bidderCount].remainingTokens = 5; // only 5 tokens
        tokenDetails[msg.sender]=bidders[bidderCount];
        bidderCount++;
    }
    
    function bid(uint _itemId, uint _count) public payable{
        /*
            Bids tokens to a particular item.
            Arguments:
            _itemId -- uint, id of the item
            _count -- uint, count of tokens to bid for the item
        */
        
        /*
        Part 1 Task 4. Implement the three conditions below.
            4.1 If the number of tokens remaining with the bidder is < count of tokens bidded, revert.
            4.2 If there are no tokens remaining with the bidder, revert.
            4.3 If the id of the item for which bid is placed, is greater than 2, revert.

        Hint: "tokenDetails[msg.sender].remainingTokens" gives the details of the number of tokens remaining with the bidder.
        */
        
        // ** Start code here. 2 lines approximately. **/
        if (tokenDetails[msg.sender].remainingTokens < _count ||
                tokenDetails[msg.sender].remainingTokens <=0 ||  
                _itemId > 2 ) return;
                
        //** End code here. **
        
        /*Part 1 Task 5. Decrement the remainingTokens by the number of tokens bid and store the value in balance variable.
        Hint. "tokenDetails[msg.sender].remainingTokens" should be decremented by "_count". */
 
        // ** Start code here. 1 line approximately. **
        
        uint balance= tokenDetails[msg.sender].remainingTokens - _count;
        //** End code here. **
        
        tokenDetails[msg.sender].remainingTokens=balance;
        bidders[tokenDetails[msg.sender].personId].remainingTokens=balance;//updating the same balance in bidders map.
        
        Item storage bidItem = items[_itemId];
        for(uint i=0; i<_count;i++) {
            bidItem.itemTokens.push(tokenDetails[msg.sender].personId);    
        }
    }
    
    // Part 2 Task 1. Create a modifier named "onlyOwner" to ensure that only owner is allowed to reveal winners
    //Hint : Use require to validate if "msg.sender" is equal to the "beneficiary".
    modifier onlyOwner {
        // ** Start code here. 2 lines approximately. **
        require(msg.sender == beneficiary);
        _;
        //** End code here. **
    }
    
    
    function revealWinners() public onlyOwner{
        
        /* 
            Iterate over all the items present in the auction.
            If at least on person has placed a bid, randomly select          the winner */

        for (uint id = 0; id < 3; id++) {
            Item storage currentItem=items[id];
            if(currentItem.itemTokens.length != 0){
            // generate random# from block number 
            uint randomIndex = (block.number / currentItem.itemTokens.length)% currentItem.itemTokens.length; 
            // Obtain the winning tokenId

            uint winnerId = currentItem.itemTokens[randomIndex];
                
            /* Part 1 Task 6. Assign the winners.
            Hint." bidders[winnerId] " will give you the person object with the winnerId.
            you need to assign the address of the person obtained above to winners[id] */

            // ** Start coding here *** 1 line approximately.
            winners[id] = bidders[winnerId].addr;
                    
            //** end code here*
                
            }
        }
    } 

  //Miscellaneous methods: Below methods are used to assist Grading. Please DONOT CHANGE THEM.
    function getPersonDetails(uint id) public constant returns(uint,uint,address){
        return (bidders[id].remainingTokens,bidders[id].personId,bidders[id].addr);
    }

}