pragma solidity ^0.4.4;

/**
 * @title Contract for object that have an owner
 */
contract Owned {
    /**
     * Contract owner address
     */
    address public owner;

    /**
     * @dev Delegate contract to another person
     * @param _owner New owner address 
     */
    function setOwner(address _owner) onlyOwner
    { owner = _owner; }

    /**
     * @dev Owner check modifier
     */
    modifier onlyOwner { if (msg.sender != owner) throw; _; }
}

/**
 * @title Common pattern for destroyable contracts 
 */
contract Destroyable {
    address public hammer;

    /**
     * @dev Hammer setter
     * @param _hammer New hammer address
     */
    function setHammer(address _hammer) onlyHammer
    { hammer = _hammer; }

    /**
     * @dev Destroy contract and scrub a data
     * @notice Only hammer can call it 
     */
    function destroy() onlyHammer
    { suicide(msg.sender); }

    /**
     * @dev Hammer check modifier
     */
    modifier onlyHammer { if (msg.sender != hammer) throw; _; }
}

/**
 * @title Generic owned destroyable contract
 */
contract Object is Owned, Destroyable {
    function Object() {
        owner  = msg.sender;
        hammer = msg.sender;
    }
}

// Standard token interface (ERC 20)
// https://github.com/ethereum/EIPs/issues/20
contract ERC20 
{
// Functions:
    /// @return total amount of tokens
    uint256 public totalSupply;

    /// @param _owner The address from which the balance will be retrieved
    /// @return The balance
    function balanceOf(address _owner) constant returns (uint256);

    /// @notice send `_value` token to `_to` from `msg.sender`
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transfer(address _to, uint256 _value) returns (bool);

    /// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
    /// @param _from The address of the sender
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transferFrom(address _from, address _to, uint256 _value) returns (bool);

    /// @notice `msg.sender` approves `_addr` to spend `_value` tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @param _value The amount of wei to be approved for transfer
    /// @return Whether the approval was successful or not
    function approve(address _spender, uint256 _value) returns (bool);

    /// @param _owner The address of the account owning tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @return Amount of remaining tokens allowed to spent
    function allowance(address _owner, address _spender) constant returns (uint256);

// Events:
    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}

/**
 * @title Token contract represents any asset in digital economy
 */
contract Token is Object, ERC20 {
    /* Short description of token */
    string public name;
    string public symbol;

    /* Total count of tokens exist */
    uint public totalSupply;

    /* Fixed point position */
    uint8 public decimals;
    
    /* Token approvement system */
    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowances;
 
    /**
     * @dev Get balance of plain address
     * @param _owner is a target address
     * @return amount of tokens on balance
     */
    function balanceOf(address _owner) constant returns (uint256)
    { return balances[_owner]; }
 
    /**
     * @dev Take allowed tokens
     * @param _owner The address of the account owning tokens
     * @param _spender The address of the account able to transfer the tokens
     * @return Amount of remaining tokens allowed to spent
     */
    function allowance(address _owner, address _spender) constant returns (uint256)
    { return allowances[_owner][_spender]; }

    /* Token constructor */
    function Token(string _name, string _symbol, uint8 _decimals, uint _count) {
        name        = _name;
        symbol      = _symbol;
        decimals    = _decimals;
        totalSupply = _count;
        balances[msg.sender] = _count;
    }
 
    /**
     * @dev Transfer self tokens to given address
     * @param _to destination address
     * @param _value amount of token values to send
     * @notice `_value` tokens will be sended to `_to`
     * @return `true` when transfer done
     */
    function transfer(address _to, uint _value) returns (bool) {
        if (balances[msg.sender] >= _value) {
            balances[msg.sender] -= _value;
            balances[_to]        += _value;
            Transfer(msg.sender, _to, _value);
            return true;
        }
        return false;
    }

    /**
     * @dev Transfer with approvement mechainsm
     * @param _from source address, `_value` tokens shold be approved for `sender`
     * @param _to destination address
     * @param _value amount of token values to send 
     * @notice from `_from` will be sended `_value` tokens to `_to`
     * @return `true` when transfer is done
     */
    function transferFrom(address _from, address _to, uint256 _value) returns (bool) {
        var avail = allowances[_from][msg.sender]
                  > balances[_from] ? balances[_from]
                                    : allowances[_from][msg.sender];
        if (avail >= _value) {
            allowances[_from][msg.sender] -= _value;
            balances[_from] -= _value;
            balances[_to]   += _value;
            Transfer(_from, _to, _value);
            return true;
        }
        return false;
    }

    /**
     * @dev Give to target address ability for self token manipulation without sending
     * @param _spender target address (future requester)
     * @param _value amount of token values for approving
     */
    function approve(address _spender, uint256 _value) returns (bool) {
        allowances[msg.sender][_spender] += _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
     * @dev Reset count of tokens approved for given address
     * @param _spender target address (future requester)
     */
    function unapprove(address _spender)
    { allowances[msg.sender][_spender] = 0; }
}