FleaMarket.sol

pragma solidity 0.5.11;

import "./HitchensUnorderedKeySet.sol";
contract FleaMarket {

    using HitchensUnorderedKeySetLib for HitchensUnorderedKeySetLib.Set;
    HitchensUnorderedKeySetLib.Set widgetSet;

    struct WidgetStruct {
        address contractAddress;
    }

    mapping(bytes32 => WidgetStruct) widgets;
    string public name;
    address public lastContractAddress;

    constructor() public {
        name = "FleaMarket Smart Contract";
    }

    event logNewPurchaseContract(address contractAddress);
    event logRemovePurchaseContract(address sender, bytes32 key);

    function createPurchaseContract(bytes32 key, string memory title, string memory ipfsHash) 
	        public payable returns(bool createResult)
    {
	widgetSet.insert(key); // Note that this will fail automatically if the key already exists.
        WidgetStruct storage w = widgets[key];
		
	SafeRemotePurchase c = (new SafeRemotePurchase).value(msg.value)(msg.sender, key, title, ipfsHash);	
	lastContractAddress = address(c);	
	w.contractAddress = lastContractAddress;
	
	emit logNewPurchaseContract(lastContractAddress);
	    
	return true;
   }
	
    function getContractCount() public view returns(uint contractCount) {
        return widgetSet.count();
    }
	
    function getContractKeyAtIndex(uint index) public view returns(bytes32 key) {
        return widgetSet.keyAtIndex(index);
    }

    function getContractByKey(bytes32 key) public view returns(address contractAddress) {
        require(widgetSet.exists(key), "Can't get a widget that doesn't exist.");
        WidgetStruct storage w = widgets[key];
        return(w.contractAddress);
    } 

    function removeContractByKey(bytes32 key) public {
        // Note that this will fail automatically if the key doesn't exist
        widgetSet.remove(key); 
        delete widgets[key];
        emit logRemovePurchaseContract(msg.sender, key);
    }
	
}


// based on https://solidity.readthedocs.io/en/latest/solidity-by-example.html
contract SafeRemotePurchase {
    // .....   
    
}