contracts/AssetProxy.sol

pragma solidity 0.5.8;

import './EToken2Interface.sol';
import './AssetInterface.sol';
import './ERC20Interface.sol';
import './AssetProxyInterface.sol';
import '../dependencies/contracts/Bytes32.sol';
import '../dependencies/contracts/ReturnData.sol';


/**
 * @title EToken2 Asset Proxy.
 *
 * Proxy implements ERC20 interface and acts as a gateway to a single EToken2 asset.
 * Proxy adds etoken2Symbol and caller(sender) when forwarding requests to EToken2.
 * Every request that is made by caller first sent to the specific asset implementation
 * contract, which then calls back to be forwarded onto EToken2.
 *
 * Calls flow: Caller ->
 *             Proxy.func(...) ->
 *             Asset._performFunc(..., Caller.address) ->
 *             Proxy._forwardFunc(..., Caller.address) ->
 *             Platform.proxyFunc(..., symbol, Caller.address)
 *
 * Generic call flow: Caller ->
 *             Proxy.unknownFunc(...) ->
 *             Asset._performGeneric(..., Caller.address) ->
 *             Asset.unknownFunc(...)
 *
 * Asset implementation contract is mutable, but each user have an option to stick with
 * old implementation, through explicit decision made in timely manner, if he doesn't agree
 * with new rules.
 * Each user have a possibility to upgrade to latest asset contract implementation, without the
 * possibility to rollback.
 *
 * Note: all the non constant functions return false instead of throwing in case if state change
 * didn't happen yet.
 */
contract AssetProxy is ERC20Interface, AssetProxyInterface, Bytes32, ReturnData {
    // Assigned EToken2, immutable.
    EToken2Interface public etoken2;

    // Assigned symbol, immutable.
    bytes32 public etoken2Symbol;

    // Assigned name, immutable. For UI.
    string public name;
    string public symbol;

    /**
     * Sets EToken2 address, assigns symbol and name.
     *
     * Can be set only once.
     *
     * @param _etoken2 EToken2 contract address.
     * @param _symbol assigned symbol.
     * @param _name assigned name.
     *
     * @return success.
     */
    function init(EToken2Interface _etoken2, string memory _symbol, string memory _name)
        public returns(bool)
    {
        if (address(etoken2) != address(0)) {
            return false;
        }
        etoken2 = _etoken2;
        etoken2Symbol = _bytes32(_symbol);
        name = _name;
        symbol = _symbol;
        return true;
    }

    /**
     * Only EToken2 is allowed to call.
     */
    modifier onlyEToken2() {
        if (msg.sender == address(etoken2)) {
            _;
        }
    }

    /**
     * Only current asset owner is allowed to call.
     */
    modifier onlyAssetOwner() {
        if (etoken2.isOwner(msg.sender, etoken2Symbol)) {
            _;
        }
    }

    /**
     * Returns asset implementation contract for current caller.
     *
     * @return asset implementation contract.
     */
    function _getAsset() internal view returns(AssetInterface) {
        return AssetInterface(getVersionFor(msg.sender));
    }

    /**
     * Recovers tokens on proxy contract
     *
     * @param _asset type of tokens to recover.
     * @param _value tokens that will be recovered.
     * @param _receiver address where to send recovered tokens.
     *
     * @return success.
     */
    function recoverTokens(ERC20Interface _asset, address _receiver, uint _value)
    public onlyAssetOwner() returns(bool) {
        return _asset.transfer(_receiver, _value);
    }

    /**
     * Returns asset total supply.
     *
     * @return asset total supply.
     */
    function totalSupply() public view returns(uint) {
        return etoken2.totalSupply(etoken2Symbol);
    }

    /**
     * Returns asset balance for a particular holder.
     *
     * @param _owner holder address.
     *
     * @return holder balance.
     */
    function balanceOf(address _owner) public view returns(uint) {
        return etoken2.balanceOf(_owner, etoken2Symbol);
    }

    /**
     * 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 etoken2.allowance(_from, _spender, etoken2Symbol);
    }

    /**
     * Returns asset decimals.
     *
     * @return asset decimals.
     */
    function decimals() public view returns(uint8) {
        return etoken2.baseUnit(etoken2Symbol);
    }

    /**
     * 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) {
        return transferWithReference(_to, _value, '');
    }

    /**
     * Transfers asset balance from the caller to specified receiver adding specified comment.
     * Resolves asset implementation contract for the caller and forwards there arguments along with
     * the caller address.
     *
     * @param _to holder address to give to.
     * @param _value amount to transfer.
     * @param _reference transfer comment to be included in a EToken2's Transfer event.
     *
     * @return success.
     */
    function transferWithReference(address _to, uint _value, string memory _reference)
    public returns(bool) {
        return _getAsset()._performTransferWithReference(
            _to, _value, _reference, msg.sender);
    }

    /**
     * Transfers asset balance from the caller to specified ICAP.
     *
     * @param _icap recipient ICAP to give to.
     * @param _value amount to transfer.
     *
     * @return success.
     */
    function transferToICAP(bytes32 _icap, uint _value) public returns(bool) {
        return transferToICAPWithReference(_icap, _value, '');
    }

    /**
     * Transfers asset balance from the caller to specified ICAP adding specified comment.
     * Resolves asset implementation contract for the caller and forwards there arguments along with
     * the caller address.
     *
     * @param _icap recipient ICAP to give to.
     * @param _value amount to transfer.
     * @param _reference transfer comment to be included in a EToken2's Transfer event.
     *
     * @return success.
     */
    function transferToICAPWithReference(
        bytes32 _icap,
        uint _value,
        string memory _reference)
    public returns(bool) {
        return _getAsset()._performTransferToICAPWithReference(
            _icap, _value, _reference, msg.sender);
    }

    /**
     * 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) {
        return transferFromWithReference(_from, _to, _value, '');
    }

    /**
     * Prforms allowance transfer of asset balance between holders adding specified comment.
     * Resolves asset implementation contract for the caller and forwards there arguments along with
     * the caller address.
     *
     * @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 EToken2's Transfer event.
     *
     * @return success.
     */
    function transferFromWithReference(
        address _from,
        address _to,
        uint _value,
        string memory _reference)
    public returns(bool) {
        return _getAsset()._performTransferFromWithReference(
            _from,
            _to,
            _value,
            _reference,
            msg.sender
        );
    }

    /**
     * Performs transfer call on the EToken2 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 EToken2's Transfer event.
     * @param _sender initial caller.
     *
     * @return success.
     */
    function _forwardTransferFromWithReference(
        address _from,
        address _to,
        uint _value,
        string memory _reference,
        address _sender)
    public onlyImplementationFor(_sender) returns(bool) {
        return etoken2.proxyTransferFromWithReference(
            _from,
            _to,
            _value,
            etoken2Symbol,
            _reference,
            _sender
        );
    }

    /**
     * Prforms allowance transfer of asset balance between holders.
     *
     * @param _from holder address to take from.
     * @param _icap recipient ICAP address to give to.
     * @param _value amount to transfer.
     *
     * @return success.
     */
    function transferFromToICAP(address _from, bytes32 _icap, uint _value)
    public returns(bool) {
        return transferFromToICAPWithReference(_from, _icap, _value, '');
    }

    /**
     * Prforms allowance transfer of asset balance between holders adding specified comment.
     * Resolves asset implementation contract for the caller and forwards there arguments along with
     * the caller address.
     *
     * @param _from holder address to take from.
     * @param _icap recipient ICAP address to give to.
     * @param _value amount to transfer.
     * @param _reference transfer comment to be included in a EToken2's Transfer event.
     *
     * @return success.
     */
    function transferFromToICAPWithReference(
        address _from,
        bytes32 _icap,
        uint _value,
        string memory _reference)
    public returns(bool) {
        return _getAsset()._performTransferFromToICAPWithReference(
            _from,
            _icap,
            _value,
            _reference,
            msg.sender
        );
    }

    /**
     * Performs allowance transfer to ICAP call on the EToken2 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 _icap recipient ICAP address to give to.
     * @param _value amount to transfer.
     * @param _reference transfer comment to be included in a EToken2's Transfer event.
     * @param _sender initial caller.
     *
     * @return success.
     */
    function _forwardTransferFromToICAPWithReference(
        address _from,
        bytes32 _icap,
        uint _value,
        string memory _reference,
        address _sender)
    public onlyImplementationFor(_sender) returns(bool) {
        return etoken2.proxyTransferFromToICAPWithReference(
            _from,
            _icap,
            _value,
            _reference,
            _sender
        );
    }

    /**
     * Sets asset spending allowance for a specified spender.
     * Resolves asset implementation contract for the caller and forwards there arguments along with
     * the caller address.
     *
     * @param _spender holder address to set allowance to.
     * @param _value amount to allow.
     *
     * @return success.
     */
    function approve(address _spender, uint _value) public returns(bool) {
        return _getAsset()._performApprove(_spender, _value, msg.sender);
    }

    /**
     * Performs allowance setting call on the EToken2 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 _forwardApprove(address _spender, uint _value, address _sender)
    public onlyImplementationFor(_sender) returns(bool) {
        return etoken2.proxyApprove(_spender, _value, etoken2Symbol, _sender);
    }

    /**
     * Emits ERC20 Transfer event on this contract.
     *
     * Can only be, and, called by assigned EToken2 when asset transfer happens.
     */
    function emitTransfer(address _from, address _to, uint _value) public onlyEToken2() {
        emit Transfer(_from, _to, _value);
    }

    /**
     * Emits ERC20 Approval event on this contract.
     *
     * Can only be, and, called by assigned EToken2 when asset allowance set happens.
     */
    function emitApprove(address _from, address _spender, uint _value) public onlyEToken2() {
        emit Approval(_from, _spender, _value);
    }

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

    // Interface functions to allow specifying ICAP addresses as strings.
    function transferToICAP(string memory _icap, uint _value) public returns(bool) {
        return transferToICAPWithReference(_icap, _value, '');
    }

    function transferToICAPWithReference(string memory _icap, uint _value, string memory _reference)
    public returns(bool) {
        return transferToICAPWithReference(_bytes32(_icap), _value, _reference);
    }

    function transferFromToICAP(address _from, string memory _icap, uint _value)
        public returns(bool)
    {
        return transferFromToICAPWithReference(_from, _icap, _value, '');
    }

    function transferFromToICAPWithReference(
        address _from,
        string memory _icap,
        uint _value,
        string memory _reference)
    public returns(bool) {
        return transferFromToICAPWithReference(_from, _bytes32(_icap), _value, _reference);
    }

    /**
     * Indicates an upgrade freeze-time start, and the next asset implementation contract.
     */
    event UpgradeProposed(address newVersion);
    event UpgradePurged(address newVersion);
    event UpgradeCommited(address newVersion);
    event OptedOut(address sender, address version);
    event OptedIn(address sender, address version);

    // Current asset implementation contract address.
    address internal latestVersion;

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

    // Upgrade freeze-time start.
    uint internal pendingVersionTimestamp;

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

    // Asset implementation contract address that user decided to stick with.
    // 0x0 means that user uses latest version.
    mapping(address => address) internal userOptOutVersion;

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

    /**
     * Returns asset implementation contract address assigned to sender.
     *
     * @param _sender sender address.
     *
     * @return asset implementation contract address.
     */
    function getVersionFor(address _sender) public view returns(address) {
        return userOptOutVersion[_sender] == address(0) ?
            latestVersion : userOptOutVersion[_sender];
    }

    /**
     * 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 != address(0)) {
            return false;
        }
        // New version address should be other than 0x0.
        if (_newVersion == address(0)) {
            return false;
        }
        // Don't apply freeze-time for the initial setup.
        if (latestVersion == address(0)) {
            latestVersion = _newVersion;
            return true;
        }
        pendingVersion = _newVersion;
        // solhint-disable-next-line not-rely-on-time
        pendingVersionTimestamp = now;
        emit UpgradeProposed(_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 == address(0)) {
            return false;
        }
        emit UpgradePurged(pendingVersion);
        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 == address(0)) {
            return false;
        }
        // solhint-disable-next-line not-rely-on-time
        if (pendingVersionTimestamp + UPGRADE_FREEZE_TIME > now) {
            return false;
        }
        latestVersion = pendingVersion;
        delete pendingVersion;
        delete pendingVersionTimestamp;
        emit UpgradeCommited(latestVersion);
        return true;
    }

    /**
     * Disagree with proposed upgrade, and stick with current asset implementation
     * until further explicit agreement to upgrade.
     *
     * @return success.
     */
    function optOut() public returns(bool) {
        if (userOptOutVersion[msg.sender] != address(0)) {
            return false;
        }
        userOptOutVersion[msg.sender] = latestVersion;
        emit OptedOut(msg.sender, latestVersion);
        return true;
    }

    /**
     * Implicitly agree to upgrade to current and future asset implementation upgrades,
     * until further explicit disagreement.
     *
     * @return success.
     */
    function optIn() public returns(bool) {
        delete userOptOutVersion[msg.sender];
        emit OptedIn(msg.sender, latestVersion);
        return true;
    }

    // Backwards compatibility.
    function multiAsset() public view returns(EToken2Interface) {
        return etoken2;
    }
}