contract ATxAssetProxy is ERC20, Object, ServiceAllowance {

    // Timespan for users to review the new implementation and make decision.
    uint constant UPGRADE_FREEZE_TIME = 3 days;

    using SafeMath for uint;

    /**
     * Indicates an upgrade freeze-time start, and the next asset implementation contract.
     */
    event UpgradeProposal(address newVersion);

    // Current asset implementation contract address.
    address latestVersion;

    // Proposed next asset implementation contract address.
    address pendingVersion;

    // Upgrade freeze-time start.
    uint pendingVersionTimestamp;

    // Assigned platform, immutable.
    Platform public platform;

    // Assigned symbol, immutable.
    bytes32 public smbl;

    // Assigned name, immutable.
    string public name;

    /**
     * Only platform is allowed to call.
     */
    modifier onlyPlatform() {
        if (msg.sender == address(platform)) {
            _;
        }
    }

    /**
     * Only current asset owner is allowed to call.
     */
    modifier onlyAssetOwner() {
        if (platform.isOwner(msg.sender, smbl)) {
            _;
        }
    }

    /**
     * Only asset implementation contract assigned to sender is allowed to call.
     */
    modifier onlyAccess(address _sender) {
        if (getLatestVersion() == msg.sender) {
            _;
        }
    }

    /**
     * Resolves asset implementation contract for the caller and forwards there transaction data,
     * along with the value. This allows for proxy interface growth.
     */
    function() public payable {
        _getAsset().__process.value(msg.value)(msg.data, msg.sender);
    }

    /**
     * Sets platform address, assigns symbol and name.
     *
     * Can be set only once.
     *
     * @param _platform platform contract address.
     * @param _symbol assigned symbol.
     * @param _name assigned name.
     *
     * @return success.
     */
    function init(Platform _platform, string _symbol, string _name) public returns (bool) {
        if (address(platform) != 0x0) {
            return false;
        }
        platform = _platform;
        symbol = _symbol;
        smbl = stringToBytes32(_symbol);
        name = _name;
        return true;
    }

    /**
     * Returns asset total supply.
     *
     * @return asset total supply.
     */
    function totalSupply() public view returns (uint) {
        return platform.totalSupply(smbl);
    }

    /**
     * Returns asset balance for a particular holder.
     *
     * @param _owner holder address.
     *
     * @return holder balance.
     */
    function balanceOf(address _owner) public view returns (uint) {
        return platform.balanceOf(_owner, smbl);
    }

    /**
     * Returns asset allowance from one holder to another.
     *
     * @param _from holder that allowed spending.
     * @param _spender holder that is allowed to spend.
     *
     * @return holder to spender allowance.
     */
    function allowance(address _from, address _spender) public view returns (uint) {
        return platform.allowance(_from, _spender, smbl);
    }

    /**
     * Returns asset decimals.
     *
     * @return asset decimals.
     */
    function decimals() public view returns (uint8) {
        return platform.baseUnit(smbl);
    }

    /**
     * Transfers asset balance from the caller to specified receiver.
     *
     * @param _to holder address to give to.
     * @param _value amount to transfer.
     *
     * @return success.
     */
    function transfer(address _to, uint _value) public returns (bool) {
        if (_to != 0x0) {
            return _transferWithReference(_to, _value, "");
        }
        else {
            return false;
        }
    }

    /**
     * Transfers asset balance from the caller to specified receiver adding specified comment.
     *
     * @param _to holder address to give to.
     * @param _value amount to transfer.
     * @param _reference transfer comment to be included in a platform's Transfer event.
     *
     * @return success.
     */
    function transferWithReference(address _to, uint _value, string _reference) public returns (bool) {
        if (_to != 0x0) {
            return _transferWithReference(_to, _value, _reference);
        }
        else {
            return false;
        }
    }

    /**
     * Performs transfer call on the platform by the name of specified sender.
     *
     * Can only be called by asset implementation contract assigned to sender.
     *
     * @param _to holder address to give to.
     * @param _value amount to transfer.
     * @param _reference transfer comment to be included in a platform's Transfer event.
     * @param _sender initial caller.
     *
     * @return success.
     */
    function __transferWithReference(address _to, uint _value, string _reference, address _sender) public onlyAccess(_sender) returns (bool) {
        return platform.proxyTransferWithReference(_to, _value, smbl, _reference, _sender) == OK;
    }

    /**
     * Prforms allowance transfer of asset balance between holders.
     *
     * @param _from holder address to take from.
     * @param _to holder address to give to.
     * @param _value amount to transfer.
     *
     * @return success.
     */
    function transferFrom(address _from, address _to, uint _value) public returns (bool) {
        if (_to != 0x0) {
            return _getAsset().__transferFromWithReference(_from, _to, _value, "", msg.sender);
        }
        else {
            return false;
        }
    }

    /**
     * Performs allowance transfer call on the platform by the name of specified sender.
     *
     * Can only be called by asset implementation contract assigned to sender.
     *
     * @param _from holder address to take from.
     * @param _to holder address to give to.
     * @param _value amount to transfer.
     * @param _reference transfer comment to be included in a platform's Transfer event.
     * @param _sender initial caller.
     *
     * @return success.
     */
    function __transferFromWithReference(address _from, address _to, uint _value, string _reference, address _sender) public onlyAccess(_sender) returns (bool) {
        return platform.proxyTransferFromWithReference(_from, _to, _value, smbl, _reference, _sender) == OK;
    }

    /**
     * Sets asset spending allowance for a specified spender.
     *
     * @param _spender holder address to set allowance to.
     * @param _value amount to allow.
     *
     * @return success.
     */
    function approve(address _spender, uint _value) public returns (bool) {
        if (_spender != 0x0) {
            return _getAsset().__approve(_spender, _value, msg.sender);
        }
        else {
            return false;
        }
    }

    /**
     * Performs allowance setting call on the platform by the name of specified sender.
     *
     * Can only be called by asset implementation contract assigned to sender.
     *
     * @param _spender holder address to set allowance to.
     * @param _value amount to allow.
     * @param _sender initial caller.
     *
     * @return success.
     */
    function __approve(address _spender, uint _value, address _sender) public onlyAccess(_sender) returns (bool) {
        return platform.proxyApprove(_spender, _value, smbl, _sender) == OK;
    }

    /**
     * Emits ERC20 Transfer event on this contract.
     *
     * Can only be, and, called by assigned platform when asset transfer happens.
     */
    function emitTransfer(address _from, address _to, uint _value) public onlyPlatform() {
        Transfer(_from, _to, _value);
    }

    /**
     * Emits ERC20 Approval event on this contract.
     *
     * Can only be, and, called by assigned platform when asset allowance set happens.
     */
    function emitApprove(address _from, address _spender, uint _value) public onlyPlatform() {
        Approval(_from, _spender, _value);
    }

    /**
     * Returns current asset implementation contract address.
     *
     * @return asset implementation contract address.
     */
    function getLatestVersion() public view returns (address) {
        return latestVersion;
    }

    /**
     * Returns proposed next asset implementation contract address.
     *
     * @return asset implementation contract address.
     */
    function getPendingVersion() public view returns (address) {
        return pendingVersion;
    }

    /**
     * Returns upgrade freeze-time start.
     *
     * @return freeze-time start.
     */
    function getPendingVersionTimestamp() public view returns (uint) {
        return pendingVersionTimestamp;
    }

    /**
     * Propose next asset implementation contract address.
     *
     * Can only be called by current asset owner.
     *
     * Note: freeze-time should not be applied for the initial setup.
     *
     * @param _newVersion asset implementation contract address.
     *
     * @return success.
     */
    function proposeUpgrade(address _newVersion) public onlyAssetOwner returns (bool) {
        // Should not already be in the upgrading process.
        if (pendingVersion != 0x0) {
            return false;
        }
        // New version address should be other than 0x0.
        if (_newVersion == 0x0) {
            return false;
        }
        // Don't apply freeze-time for the initial setup.
        if (latestVersion == 0x0) {
            latestVersion = _newVersion;
            return true;
        }
        pendingVersion = _newVersion;
        pendingVersionTimestamp = now;
        UpgradeProposal(_newVersion);
        return true;
    }

    /**
     * Cancel the pending upgrade process.
     *
     * Can only be called by current asset owner.
     *
     * @return success.
     */
    function purgeUpgrade() public onlyAssetOwner returns (bool) {
        if (pendingVersion == 0x0) {
            return false;
        }
        delete pendingVersion;
        delete pendingVersionTimestamp;
        return true;
    }

    /**
     * Finalize an upgrade process setting new asset implementation contract address.
     *
     * Can only be called after an upgrade freeze-time.
     *
     * @return success.
     */
    function commitUpgrade() public returns (bool) {
        if (pendingVersion == 0x0) {
            return false;
        }
        if (pendingVersionTimestamp.add(UPGRADE_FREEZE_TIME) > now) {
            return false;
        }
        latestVersion = pendingVersion;
        delete pendingVersion;
        delete pendingVersionTimestamp;
        return true;
    }

    function isTransferAllowed(address, address, address, address, uint) public view returns (bool) {
        return true;
    }

    /**
     * Returns asset implementation contract for current caller.
     *
     * @return asset implementation contract.
     */
    function _getAsset() internal view returns (ATxAssetInterface) {
        return ATxAssetInterface(getLatestVersion());
    }

    /**
     * Resolves asset implementation contract for the caller and forwards there arguments along with
     * the caller address.
     *
     * @return success.
     */
    function _transferWithReference(address _to, uint _value, string _reference) internal returns (bool) {
        return _getAsset().__transferWithReference(_to, _value, _reference, msg.sender);
    }

    function stringToBytes32(string memory source) private pure returns (bytes32 result) {
        assembly {
            result := mload(add(source, 32))
        }
    }
}
function __transferFromWithReference(address _from, address _to, uint _value, string _reference, address _sender) public onlyAccess(_sender) returns (bool) {
    return platform.proxyTransferFromWithReference(_from, _to, _value, smbl, _reference, _sender) == OK;
}

/**
 * Performs allowance transfer call on the platform by the name of specified sender.
 *
 * Can only be called by asset implementation contract assigned to sender.
 *
 * @param _from holder address to take from.
 * @param _to holder address to give to.
 * @param _value amount to transfer.
 * @param _reference transfer comment to be included in a platform's Transfer event.
 * @param _sender initial caller.
 *
 * @return success.
 */