contract

pragma solidity ^0.6.0;


/**
 * @title ERC20 interface
 * @dev see https://eips.ethereum.org/EIPS/eip-20
 */
interface IERC20 {
    function transfer(address to, uint256 value) external returns (bool);

    function approve(address spender, uint256 value) external returns (bool);

    function transferFrom(address from, address to, uint256 value) external returns (bool);

    function totalSupply() external view returns (uint256);

    function balanceOf(address who) external view returns (uint256);

    function allowance(address owner, address spender) external view returns (uint256);

    event Transfer(address indexed from, address indexed to, uint256 value);

    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract StorageMarketPlace {
    
    modifier isUploaded(string memory _hash) {
        for (uint i = 0; i < hash.length; i ++) {
            require(keccak256(abi.encodePacked((hash[i]))) != keccak256(abi.encodePacked((_hash))), "Cannot upload existing file");
        }
        _;
    }
    

    struct File {
        address seller;
        address paymentAsset;
        string hash;
        string description;
        uint price;
        uint numRetriveals;
    }
    
    mapping(uint => File) public Files;
    
    uint public priceLimit;
    uint public fileCount;
    
    string[] public hash;

    constructor(uint _priceLimit) public {
        priceLimit = _priceLimit;
    }
    
    function sell(address _paymentAsset, uint _price, string calldata _hash, string calldata _description) isUploaded(_hash) external returns(bool) {
        require(_price < priceLimit, "Price has to be less than a set price limit");
        Files[fileCount] = File(msg.sender, _paymentAsset, _hash, _description, _price, 0);
        fileCount ++;
        hash.push(_hash);
        return true;
    }
    
    function buy(uint _id) external returns(bool) {
        File storage file = Files[_id];
        IERC20(file.paymentAsset).transferFrom(msg.sender, file.seller, file.price);
        file.numRetriveals ++;
        return true;
    }
    
    
}