/*
  Akropolis Token, https://akropolis.io
*/
pragma solidity ^0.4.24;

// File: openzeppelin-solidity/contracts/math/SafeMath.sol

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  function mul(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
    // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (_a == 0) {
      return 0;
    }

    c = _a * _b;
    assert(c / _a == _b);
    return c;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  function div(uint256 _a, uint256 _b) internal pure returns (uint256) {
    // assert(_b > 0); // Solidity automatically throws when dividing by 0
    // uint256 c = _a / _b;
    // assert(_a == _b * c + _a % _b); // There is no case in which this doesn't hold
    return _a / _b;
  }

  /**
  * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
    assert(_b <= _a);
    return _a - _b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
    c = _a + _b;
    assert(c >= _a);
    return c;
  }
}

// File: contracts/helpers/Ownable.sol

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions". This adds two-phase
 * ownership control to OpenZeppelin's Ownable class. In this model, the original owner 
 * designates a new owner but does not actually transfer ownership. The new owner then accepts 
 * ownership and completes the transfer.
 */
contract Ownable {
    address public owner;
    address public pendingOwner;


    event OwnershipTransferred(
      address indexed previousOwner,
      address indexed newOwner
    );


    /**
    * @dev The Ownable constructor sets the original `owner` of the contract to the sender
    * account.
    */
    constructor() public {
        owner = msg.sender;
        pendingOwner = address(0);
    }

    /**
    * @dev Throws if called by any account other than the owner.
    */
    modifier onlyOwner() {
        require(msg.sender == owner, "Account is not owner");
        _;
    }

    /**
    * @dev Throws if called by any account other than the owner.
    */
    modifier onlyPendingOwner() {
        require(msg.sender == pendingOwner, "Account is not pending owner");
        _;
    }

    /**
    * @dev Allows the current owner to transfer control of the contract to a newOwner.
    * @param _newOwner The address to transfer ownership to.
    */
    function transferOwnership(address _newOwner) public onlyOwner {
        require(_newOwner != address(0), "Empty address");
        pendingOwner = _newOwner;
    }

    /**
    * @dev Allows the pendingOwner address to finalize the transfer.
    */
    function claimOwnership() onlyPendingOwner public {
        emit OwnershipTransferred(owner, pendingOwner);
        owner = pendingOwner;
        pendingOwner = address(0);
    }
}

// File: contracts/token/dataStorage/AllowanceSheet.sol

/**
* @title AllowanceSheet
* @notice A wrapper around an allowance mapping. 
*/
contract AllowanceSheet is Ownable {
    using SafeMath for uint256;

    mapping (address => mapping (address => uint256)) public allowanceOf;

    function addAllowance(address _tokenHolder, address _spender, uint256 _value) public onlyOwner {
        allowanceOf[_tokenHolder][_spender] = allowanceOf[_tokenHolder][_spender].add(_value);
    }

    function subAllowance(address _tokenHolder, address _spender, uint256 _value) public onlyOwner {
        allowanceOf[_tokenHolder][_spender] = allowanceOf[_tokenHolder][_spender].sub(_value);
    }

    function setAllowance(address _tokenHolder, address _spender, uint256 _value) public onlyOwner {
        allowanceOf[_tokenHolder][_spender] = _value;
    }
}

// File: contracts/token/dataStorage/BalanceSheet.sol

/**
* @title BalanceSheet
* @notice A wrapper around the balanceOf mapping. 
*/
contract BalanceSheet is Ownable {
    using SafeMath for uint256;

    mapping (address => uint256) public balanceOf;
    uint256 public totalSupply;

    function addBalance(address _addr, uint256 _value) public onlyOwner {
        balanceOf[_addr] = balanceOf[_addr].add(_value);
    }

    function subBalance(address _addr, uint256 _value) public onlyOwner {
        balanceOf[_addr] = balanceOf[_addr].sub(_value);
    }

    function setBalance(address _addr, uint256 _value) public onlyOwner {
        balanceOf[_addr] = _value;
    }

    function addTotalSupply(uint256 _value) public onlyOwner {
        totalSupply = totalSupply.add(_value);
    }

    function subTotalSupply(uint256 _value) public onlyOwner {
        totalSupply = totalSupply.sub(_value);
    }

    function setTotalSupply(uint256 _value) public onlyOwner {
        totalSupply = _value;
    }
}

// File: contracts/token/dataStorage/TokenStorage.sol

/**
* @title TokenStorage
*/
contract TokenStorage {
    /**
        Storage
    */
    BalanceSheet public balances;
    AllowanceSheet public allowances;


    string public name;   //name of Token                
    uint8  public decimals;        //decimals of Token        
    string public symbol;   //Symbol of Token

    /**
    * @dev a TokenStorage consumer can set its storages only once, on construction
    *
    **/
    constructor (address _balances, address _allowances, string _name, uint8 _decimals, string _symbol) public {
        balances = BalanceSheet(_balances);
        allowances = AllowanceSheet(_allowances);

        name = _name;
        decimals = _decimals;
        symbol = _symbol;
    }

    /**
    * @dev claim ownership of balance sheet passed into constructor.
    **/
    function claimBalanceOwnership() public {
        balances.claimOwnership();
    }

    /**
    * @dev claim ownership of allowance sheet passed into constructor.
    **/
    function claimAllowanceOwnership() public {
        allowances.claimOwnership();
    }
}

// File: zos-lib/contracts/upgradeability/Proxy.sol

/**
 * @title Proxy
 * @dev Implements delegation of calls to other contracts, with proper
 * forwarding of return values and bubbling of failures.
 * It defines a fallback function that delegates all calls to the address
 * returned by the abstract _implementation() internal function.
 */
contract Proxy {
  /**
   * @dev Fallback function.
   * Implemented entirely in `_fallback`.
   */
  function () payable external {
    _fallback();
  }

  /**
   * @return The Address of the implementation.
   */
  function _implementation() internal view returns (address);

  /**
   * @dev Delegates execution to an implementation contract.
   * This is a low level function that doesn't return to its internal call site.
   * It will return to the external caller whatever the implementation returns.
   * @param implementation Address to delegate.
   */
  function _delegate(address implementation) internal {
    assembly {
      // Copy msg.data. We take full control of memory in this inline assembly
      // block because it will not return to Solidity code. We overwrite the
      // Solidity scratch pad at memory position 0.
      calldatacopy(0, 0, calldatasize)

      // Call the implementation.
      // out and outsize are 0 because we don't know the size yet.
      let result := delegatecall(gas, implementation, 0, calldatasize, 0, 0)

      // Copy the returned data.
      returndatacopy(0, 0, returndatasize)

      switch result
      // delegatecall returns 0 on error.
      case 0 { revert(0, returndatasize) }
      default { return(0, returndatasize) }
    }
  }

  /**
   * @dev Function that is run as the first thing in the fallback function.
   * Can be redefined in derived contracts to add functionality.
   * Redefinitions must call super._willFallback().
   */
  function _willFallback() internal {
  }

  /**
   * @dev fallback implementation.
   * Extracted to enable manual triggering.
   */
  function _fallback() internal {
    _willFallback();
    _delegate(_implementation());
  }
}

// File: openzeppelin-solidity/contracts/AddressUtils.sol

/**
 * Utility library of inline functions on addresses
 */
library AddressUtils {

  /**
   * Returns whether the target address is a contract
   * @dev This function will return false if invoked during the constructor of a contract,
   * as the code is not actually created until after the constructor finishes.
   * @param _addr address to check
   * @return whether the target address is a contract
   */
  function isContract(address _addr) internal view returns (bool) {
    uint256 size;
    // XXX Currently there is no better way to check if there is a contract in an address
    // than to check the size of the code at that address.
    // See https://ethereum.stackexchange.com/a/14016/36603
    // for more details about how this works.
    // TODO Check this again before the Serenity release, because all addresses will be
    // contracts then.
    // solium-disable-next-line security/no-inline-assembly
    assembly { size := extcodesize(_addr) }
    return size > 0;
  }

}

// File: zos-lib/contracts/upgradeability/UpgradeabilityProxy.sol

/**
 * @title UpgradeabilityProxy
 * @dev This contract implements a proxy that allows to change the
 * implementation address to which it will delegate.
 * Such a change is called an implementation upgrade.
 */
contract UpgradeabilityProxy is Proxy {
  /**
   * @dev Emitted when the implementation is upgraded.
   * @param implementation Address of the new implementation.
   */
  event Upgraded(address implementation);

  /**
   * @dev Storage slot with the address of the current implementation.
   * This is the keccak-256 hash of "org.zeppelinos.proxy.implementation", and is
   * validated in the constructor.
   */
  bytes32 private constant IMPLEMENTATION_SLOT = 0x7050c9e0f4ca769c69bd3a8ef740bc37934f8e2c036e5a723fd8ee048ed3f8c3;

  /**
   * @dev Contract constructor.
   * @param _implementation Address of the initial implementation.
   */
  constructor(address _implementation) public {
    assert(IMPLEMENTATION_SLOT == keccak256("org.zeppelinos.proxy.implementation"));

    _setImplementation(_implementation);
  }

  /**
   * @dev Returns the current implementation.
   * @return Address of the current implementation
   */
  function _implementation() internal view returns (address impl) {
    bytes32 slot = IMPLEMENTATION_SLOT;
    assembly {
      impl := sload(slot)
    }
  }

  /**
   * @dev Upgrades the proxy to a new implementation.
   * @param newImplementation Address of the new implementation.
   */
  function _upgradeTo(address newImplementation) internal {
    _setImplementation(newImplementation);
    emit Upgraded(newImplementation);
  }

  /**
   * @dev Sets the implementation address of the proxy.
   * @param newImplementation Address of the new implementation.
   */
  function _setImplementation(address newImplementation) private {
    require(AddressUtils.isContract(newImplementation), "Cannot set a proxy implementation to a non-contract address");

    bytes32 slot = IMPLEMENTATION_SLOT;

    assembly {
      sstore(slot, newImplementation)
    }
  }
}

// File: contracts/token/TokenProxy.sol

/**
* @title TokenProxy
* @notice A proxy contract that serves the latest implementation of TokenProxy.
*/
contract TokenProxy is UpgradeabilityProxy, TokenStorage, Ownable {
    constructor(address _implementation, address _balances, address _allowances, string _name, uint8 _decimals, string _symbol) 
    UpgradeabilityProxy(_implementation) 
    TokenStorage(_balances, _allowances, _name, _decimals, _symbol) public {
    }

    /**
    * @dev Upgrade the backing implementation of the proxy.
    * Only the admin can call this function.
    * @param newImplementation Address of the new implementation.
    */
    function upgradeTo(address newImplementation) public onlyOwner {
        _upgradeTo(newImplementation);
    }

    /**
    * @return The address of the implementation.
    */
    function implementation() public view returns (address) {
        return _implementation();
    }
}