pragma solidity ^0.5.0;


/**
 * @title Proxy
 * @dev Gives the possibility to delegate any call to a foreign implementation.
 */
contract Proxy {
    /**
    * @dev Fallback function allowing to perform a delegatecall to the given implementation.
    * This function will return whatever the implementation call returns
    */
    function () external payable {
        address _impl = implementation();
        require(_impl != address(0));

        assembly {
            let ptr := mload(0x40)
            calldatacopy(ptr, 0, calldatasize)
            let result := delegatecall(gas, _impl, ptr, calldatasize, 0, 0)
            let size := returndatasize
            returndatacopy(ptr, 0, size)

            switch result
            case 0 { revert(ptr, size) }
            default { return(ptr, size) }
        }
    }

    /**
    * @dev Tells the address of the implementation where every call will be delegated.
    * @return address of the implementation to which it will be delegated
    */
    function implementation() public view returns (address);
}

/**
 * @title UpgradeabilityProxy
 * @dev This contract represents a proxy where the implementation address to which it will delegate can be upgraded
 */
contract UpgradeabilityProxy is Proxy {
    /**
    * @dev This event will be emitted every time the implementation gets upgraded
    * @param implementation representing the address of the upgraded implementation
    */
    event Upgraded(address indexed implementation);

    // Storage position of the address of the current implementation
    bytes32 private constant IMPLEMENTATION_POSITION = keccak256("offchain.proxy.implementation");

    /**
    * @dev Constructor function
    */
    constructor() public {}

    /**
    * @dev Tells the address of the current implementation
    * @return address of the current implementation
    */
    function implementation() public view returns (address impl) {
        bytes32 position = IMPLEMENTATION_POSITION;
        assembly {
            impl := sload(position)
        }
    }

    /**
    * @dev Sets the address of the current implementation
    * @param _newImplementation address representing the new implementation to be set
    */
    function _setImplementation(address _newImplementation) internal {
        bytes32 position = IMPLEMENTATION_POSITION;
        assembly {
            sstore(position, _newImplementation)
        }
    }

    /**
    * @dev Upgrades the implementation address
    * @param _newImplementation representing the address of the new implementation to be set
    */
    function _upgradeTo(address _newImplementation) internal {
        address currentImplementation = implementation();
        require(currentImplementation != _newImplementation);
        _setImplementation(_newImplementation);
        emit Upgraded(_newImplementation);
    }
}

/**
 * @title OwnedUpgradeabilityProxy
 * @dev This contract combines an upgradeability proxy with basic authorization control functionalities
 */
contract OwnedUpgradeabilityProxy is UpgradeabilityProxy {
    /**
    * @dev Event to show ownership has been transferred
    * @param previousOwner representing the address of the previous owner
    * @param newOwner representing the address of the new owner
    */
    event ProxyOwnershipTransferred(address previousOwner, address newOwner);

    // Storage position of the owner of the contract
    bytes32 private constant PROXY_OWNER_POSITION = keccak256("offchain.proxy.owner");

    /**
    * @dev the constructor sets the original owner of the contract to the sender account.
    */
    constructor(address _implementation) public {
        _setUpgradeabilityOwner(msg.sender);
        _upgradeTo(_implementation);
    }

    /**
    * @dev Throws if called by any account other than the owner.
    */
    modifier onlyProxyOwner() {
        require(msg.sender == proxyOwner());
        _;
    }

    /**
    * @dev Tells the address of the owner
    * @return the address of the owner
    */
    function proxyOwner() public view returns (address owner) {
        bytes32 position = PROXY_OWNER_POSITION;
        assembly {
            owner := sload(position)
        }
    }

    /**
    * @dev Allows the current owner to transfer control of the contract to a newOwner.
    * @param _newOwner The address to transfer ownership to.
    */
    function transferProxyOwnership(address _newOwner) public onlyProxyOwner {
        require(_newOwner != address(0));
        _setUpgradeabilityOwner(_newOwner);
        emit ProxyOwnershipTransferred(proxyOwner(), _newOwner);
    }

    /**
    * @dev Allows the proxy owner to upgrade the current version of the proxy.
    * @param _implementation representing the address of the new implementation to be set.
    */
    function upgradeTo(address _implementation) public onlyProxyOwner {
        _upgradeTo(_implementation);
    }

    /**
     * @dev Sets the address of the owner
    */
    function _setUpgradeabilityOwner(address _newProxyOwner) internal {
        bytes32 position = PROXY_OWNER_POSITION;
        assembly {
            sstore(position, _newProxyOwner)
        }
    }
}