minime/MiniMeToken.sol

pragma solidity ^0.4.4;

/*
    Copyright 2016, Jordi Baylina

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/// @title MiniMeToken Contract
/// @author Jordi Baylina
/// @dev This token contract's goal is to make it easy to clone this token to
///  spawn child tokens using the token distribution at a given block.
/// @dev It is ERC20 compliant, but still needs to under go further testing.


contract Owned {
    /// @notice The address of the owner is the only address that can call a
    ///  function with this modifier
    modifier onlyOwner { if (msg.sender != owner) throw; _; }

    address public owner;

    function Owned() { owner = msg.sender;}

    /// @notice Changes the owner of the contract
    /// @param _newOwner The new owner of the contract
    function changeOwner(address _newOwner) onlyOwner {
        owner = _newOwner;
    }
}

contract TokenCreation {
    function proxyPayment(address _owner) payable returns(bool);
}

contract MiniMeToken is Owned {

    string public name;                //The Token's name: e.g. DigixDAO Tokens
    uint8 public decimals;             //Number of decimals of the smallest unit
    string public symbol;              //An identifier: e.g. REP
    string public version = 'MMT_0.1'; //An arbitrary versioning scheme.


    /// @dev `Checkpoint` is the structure that attaches a block number to the a
    ///  given token attribute
    struct  Checkpoint {

        // `fromBlock` is the block number that the value was generated from
        uint fromBlock;

        // `value` is the amount of tokens at a specific block number
        uint value;
    }

    // `parentToken` is the Token address that was cloned. 0x0 for a root token
    MiniMeToken public parentToken;

    // `parentSnapShotBlock` is the Block number from the Parent Token that was
    //  used to determine the initial distribution of the Cloned Token.
    uint public parentSnapShotBlock;

    // `creationBlock` is the block number that the Cloned Token was created
    uint public creationBlock;

    // `balances` is the map that tracks the balance of each address
    mapping (address => Checkpoint[]) balances;

    // `allowed` tracks any extra transfer rights as in all ERC20 tokens
    mapping (address => mapping (address => uint256)) allowed;

    // Tracks the history of the `totalSupply` of the token
    Checkpoint[] totalSupplyHistory;

    // Flag that determines if the token is transferable or not.
    bool public isConstant;

    // The factory used to create new cloned tokens
    MiniMeTokenFactory public tokenFactory;

////////////////
// Constructor
////////////////

    /// @notice Constructor to create a MiniMeToken
    /// @param _tokenFactory The address of the MiniMeTokenFactory contract that
    ///  will create the Cloned token contracts
    /// @param _parentToken Address of the parent token, set to 0x0 if it is a
    ///  new token
    /// @param _parentSnapShotBlock Block of the parent token that will
    ///  determine the initial distribution of the cloned token, set to 0 if it
    ///  is a new token
    /// @param _tokenName Name of the new token
    /// @param _decimalUnits Number of decimals of the new token
    /// @param _tokenSymbol Token Symbol for the new token
    /// @param _isConstant If true, tokens will not be able to be transferred
    function MiniMeToken(
        address _tokenFactory,
        address _parentToken,
        uint _parentSnapShotBlock,
        string _tokenName,
        uint8 _decimalUnits,
        string _tokenSymbol,
        bool _isConstant
    ) {
        tokenFactory = MiniMeTokenFactory(_tokenFactory);
        name = _tokenName;                                 // Set the name
        decimals = _decimalUnits;                          // Set the decimals
        symbol = _tokenSymbol;                             // Set the symbol
        parentToken = MiniMeToken(_parentToken);
        parentSnapShotBlock = _parentSnapShotBlock;
        isConstant = _isConstant;
        creationBlock = block.number;
    }


///////////////////
// ERC20 Methods
///////////////////

    /// @notice Send `_amount` tokens to `_to` from `msg.sender`
    /// @param _to The address of the recipient
    /// @param _amount The amount of tokens to be transferred
    /// @return Whether the transfer was successful or not
    function transfer(address _to, uint256 _amount) returns (bool success) {
        if (isConstant) throw;
        return doTransfer(msg.sender, _to, _amount);
    }

    /// @notice Send `_amount` tokens to `_to` from `_from` on the condition it
    ///  is approved by `_from`
    /// @param _from The address holding the tokens being transferred
    /// @param _to The address of the recipient
    /// @param _amount The amount of tokens to be transferred
    /// @return True if the transfer was successful
    function transferFrom(address _from, address _to, uint256 _amount
    ) returns (bool success) {

        // The owner of this contract can move tokens around at will, this is
        //  important to recognize! Confirm that you trust the owner of this
        //  contract, which in most situations should be another open source
        //  smart contract or 0x0
        if (msg.sender != owner) {
            if (isConstant) throw;

            // The standard ERC 20 transferFrom functionality
            if (allowed[_from][msg.sender] < _amount) return false;
            allowed[_from][msg.sender] -= _amount;
        }
        return doTransfer(_from, _to, _amount);
    }

    function doTransfer(address _from, address _to, uint _amount
    ) internal returns(bool) {

           if (_amount == 0) {
               return true;
           }

           // Do not allow transfer to 0x0 or the token contract itself
           if ((_to == 0) || (_to == address(this))) throw;

           // If the amount being transfered is more than the balance of the
           //  account the transfer returns false
           var previousBalanceFrom = balanceOfAt(_from, block.number);
           if (previousBalanceFrom < _amount) {
               return false;
           }

           // First update the balance array with the new value for the address
           //  sending the tokens
           updateValueAtNow(balances[_from], previousBalanceFrom - _amount);

           // Then update the balance array with the new value for the address
           //  receiving the tokens
           var previousBalanceTo = balanceOfAt(_to, block.number);
           updateValueAtNow(balances[_to], previousBalanceTo + _amount);

           // An event to make the transfer easy to find on the blockchain
           Transfer(_from, _to, _amount);

           return true;
    }

    /// @param _owner The address that's balance is being requested
    /// @return The balance of `_owner` at the current block
    function balanceOf(address _owner) constant returns (uint256 balance) {
        return balanceOfAt(_owner, block.number);
    }

    /// @notice `msg.sender` approves `_spender` to spend `_amount` tokens on
    ///  its behalf
    /// @param _spender The address of the account able to transfer the tokens
    /// @param _amount The amount of tokens to be approved for transfer
    /// @return True if the approval was successful
    function approve(address _spender, uint256 _amount) returns (bool success) {
        if (isConstant) throw;
        allowed[msg.sender][_spender] = _amount;
        Approval(msg.sender, _spender, _amount);
        return true;
    }

    /// @param _owner The address of the account that owns the token
    /// @param _spender The address of the account able to transfer the tokens
    /// @return Amount of remaining tokens of _owner that _spender is allowed
    ///  to spend
    function allowance(address _owner, address _spender
    ) constant returns (uint256 remaining) {
        return allowed[_owner][_spender];
    }

    /// @notice `msg.sender` approves `_spender` to send `_amount` tokens on
    ///  its behalf, and then a function is triggered in the contract that is
    ///  being approved, `_spender`
    /// @param _spender The address of the contract able to transfer the tokens
    /// @param _amount The amount of tokens to be approved for transfer
    /// @return True if the function call was successful
    function approveAndCall(address _spender, uint256 _amount, bytes _extraData
    ) returns (bool success) {
        if (isConstant) throw;
        allowed[msg.sender][_spender] = _amount;
        Approval(msg.sender, _spender, _amount);

        // This portion is copied from ConsenSys's Standard Token Contract. It
        //  calls the receiveApproval function that is part of the contract that
        //  is being approved (`_spender`). The function should look like:
        //  `receiveApproval(address _from, uint256 _amount, address
        //  _tokenContract, bytes _extraData)` It is assumed that the call
        //  *should* succeed, otherwise one would use vanilla approve instead.
        if(!_spender.call(
            bytes4(bytes32(sha3("receiveApproval(address,uint256,address,bytes)"))),
            msg.sender,
            _amount,
            this,
            _extraData
            )) { throw;
        }
        return true;
    }

    /// @return The total amount of tokens
    function totalSupply() constant returns (uint) {
        return totalSupplyAt(block.number);
    }


////////////////
// Query balance and totalSupply in History
////////////////

    /// @notice Queries the balance of `_owner` at a specific `_blockNumber`
    /// @param _owner The address from which the balance will be retrieved
    /// @param _blockNumber The block number when the balance is queried
    /// @return The balance at `_blockNumber`
    function balanceOfAt(address _owner, uint _blockNumber) constant
        returns (uint) {

        // If the `_blockNumber` requested is before the genesis block for the
        //  the token being queried, the value returned is 0
        if (_blockNumber < creationBlock) {
            return 0;

        // These next few lines are used when the balance of the token is
        //  requested before a check point was ever created for this token, it
        //  requires that the `parentToken.balanceOfAt` be queried at the genesis
        //  block for that token as this contains initial balance of this token.
        } else if ((balances[_owner].length == 0)
            || (balances[_owner][0].fromBlock > _blockNumber)) {
            if (address(parentToken) != 0) {
                return parentToken.balanceOfAt(_owner, parentSnapShotBlock);
            } else {
                // Has no parent
                return 0;
            }

        // This will return the expected balance during normal situations
        } else {
            return getValueAt( balances[_owner], _blockNumber);
        }

    }

    /// @notice Total amount of tokens at a specific `_blockNumber`.
    /// @param _blockNumber The block number when the totalSupply is queried
    /// @return The total amount of tokens at `_blockNumber`
    function totalSupplyAt(uint _blockNumber) constant returns(uint) {

        // If the `_blockNumber` requested is before the genesis block for the
        //  the token being queried, the value returned is 0
        if (_blockNumber < creationBlock) {
            return 0;

        // These next few lines are used when the totalSupply of the token is
        //  requested before a check point was ever created for this token, it
        //  requires that the `parentToken.totalSupplyAt` be queried at the
        //  genesis block for this token as that contains totalSupply of this
        //  token at this block number.
        } else if ((totalSupplyHistory.length == 0)
            || (totalSupplyHistory[0].fromBlock > _blockNumber)) {
            if (address(parentToken) != 0) {
                return parentToken.totalSupplyAt(parentSnapShotBlock);
            } else {
                return 0;
            }

        // This will return the expected totalSupply during normal situations
        } else {
            return getValueAt( totalSupplyHistory, _blockNumber);
        }
    }

////////////////
// Clone Token Method
////////////////

    /// @notice Creates a new child token with the initial distribution being
    ///  this token at `_snapshotBlock`
    /// @param _childTokenName Name of the child token
    /// @param _childDecimalUnits Units of the child token
    /// @param _childTokenSymbol Symbol of the child token
    /// @param _snapshotBlock Block when the distribution of the parent token is
    ///  copied to set the initial distribution of the new child token;
    ///  if the block is higher than the actual block, the current block is used
    /// @param _isConstant True if transfers are not allowed in the child token
    ///  if the block is higher than the actual block, the current block is used
    /// @return The address of the new MiniMeToken Contract
    function createChildToken(
        string _childTokenName,
        uint8 _childDecimalUnits,
        string _childTokenSymbol,
        uint _snapshotBlock,
        bool _isConstant
        ) returns(address) {
        if (_snapshotBlock > block.number) _snapshotBlock = block.number;
        MiniMeToken childToken = tokenFactory.createChildToken(
            this,
            _snapshotBlock,
            _childTokenName,
            _childDecimalUnits,
            _childTokenSymbol,
            _isConstant
            );

        // An event to make the token easy to find on the blockchain
        NewChildToken(address(childToken), _snapshotBlock);
        return address(childToken);
    }

////////////////
// Generate and destroy tokens
////////////////

    /// @notice Generates `_amount` tokens that are assigned to `_owner`
    /// @param _owner The address that will be assigned the new tokens
    /// @param _amount The quantity of tokens generated
    /// @return True if the tokens are generated correctly
    function generateTokens(address _owner, uint _amount
    ) onlyOwner returns (bool) {
        uint curTotalSupply = getValueAt(totalSupplyHistory, block.number);
        updateValueAtNow(totalSupplyHistory, curTotalSupply + _amount);
        var previousBalanceTo = balanceOf(_owner);
        updateValueAtNow(balances[_owner], previousBalanceTo + _amount);
        Transfer(0, _owner, _amount);
        return true;
    }


    /// @notice Burns `_amount` tokens from `_owner`
    /// @param _owner The address that will lose the tokens
    /// @param _amount The quantity of tokens to burn
    /// @return True if the tokens are burned correctly
    function destroyTokens(address _owner, uint _amount
    ) onlyOwner returns (bool) {
        uint curTotalSupply = getValueAt(totalSupplyHistory, block.number);
        if (curTotalSupply < _amount) throw;
        updateValueAtNow(totalSupplyHistory, curTotalSupply - _amount);
        var previousBalanceFrom = balanceOf(_owner);
        if (previousBalanceFrom < _amount) throw;
        updateValueAtNow(balances[_owner], previousBalanceFrom - _amount);
        Transfer(_owner, 0, _amount);
        return true;
    }

////////////////
// Constant tokens
////////////////


    /// @notice Sets if the contract is constant or not
    /// @param _isConstant true to don't allow transfers false to allow transfer
    function setConstant(bool _isConstant) onlyOwner {
        isConstant = _isConstant;
    }

////////////////
// Internal helper functions to query and set a value in a snapshot array
////////////////

    function getValueAt(Checkpoint[] storage checkpoints, uint _block
    ) constant internal returns (uint) {
        if (checkpoints.length == 0) return 0;
        // Shorcut for the actual value
        if (_block >= checkpoints[checkpoints.length-1].fromBlock)
            return checkpoints[checkpoints.length-1].value;
        if (_block < checkpoints[0].fromBlock) return 0;

        // Binary search of the value in the array.
        uint min = 0;
        uint max = checkpoints.length-1;
        while (max > min) {
            uint mid = (max + min + 1)/ 2;
            if (checkpoints[mid].fromBlock<=_block) {
                min = mid;
            } else {
                max = mid-1;
            }
        }
        return checkpoints[min].value;
    }

    function updateValueAtNow(Checkpoint[] storage checkpoints, uint _value
    ) internal  {
        if ((checkpoints.length == 0)
        || (checkpoints[checkpoints.length -1].fromBlock < block.number)) {
               Checkpoint newCheckPoint = checkpoints[ checkpoints.length++ ];
               newCheckPoint.fromBlock =  block.number;
               newCheckPoint.value = _value;
           } else {
               Checkpoint oldCheckPoint = checkpoints[checkpoints.length-1];
               oldCheckPoint.value = _value;
           }
    }

    /// @notice The fallback function: If the contract's owner has not been set
    /// to 0, the ether is sent to the owner (normally the token creation
    /// contract) using the `proxyPayment` method.
    function ()  payable {
        if (owner == 0) throw;
        if (! TokenCreation(owner).proxyPayment.value(msg.value)(msg.sender)) {
            throw;
        }
    }


////////////////
// Events
////////////////
    event Transfer(address indexed _from, address indexed _to, uint256 _amount);
    event NewChildToken(address indexed _childToken, uint _snapshotBlock);
    event Approval(
        address indexed _owner,
        address indexed _spender,
        uint256 _amount
        );

}


////////////////
// MiniMeTokenFactory
////////////////

// This contract is used to generate child contracts from a contract.
// In solidity this is the way to create a contract from a contract of the same
//  class
contract MiniMeTokenFactory {
    function createChildToken(
        address _parentToken,
        uint _snapshotBlock,
        string _tokenName,
        uint8 _decimalUnits,
        string _tokenSymbol,
        bool _isConstant
    ) returns (MiniMeToken) {
        MiniMeToken newToken = new MiniMeToken(
            this,
            _parentToken,
            _snapshotBlock,
            _tokenName,
            _decimalUnits,
            _tokenSymbol,
            _isConstant
            );
        return newToken;
    }
}