pragma solidity ^0.4.11;
contract DABToken  {
    string public constant name = "DAB Token";
    string public constant symbol = "DABT";
    uint public constant decimals = 18;
    uint256 _totalSupply = 60000000 * 10**decimals;

    function totalSupply() public returns (uint256 supply) {
        return _totalSupply;
    }

    function balanceOf(address _owner) public returns (uint256 balance) {
        return balances[_owner];
    }

    function approve(address _spender, uint256 _value) returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }

    function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
      return allowed[_owner][_spender];
    }

    mapping(address => uint256) balances;         //list of balance of each address
    mapping(address => uint256) distBalances;     //list of distributed balance of each address to calculate restricted amount
    mapping(address => mapping (address => uint256)) allowed;

    uint public baseStartTime; //All other time spots are calculated based on this time spot.

    // Initial founder address (set in constructor)
    // All deposited will be instantly forwarded to this address.

    address public founder;
    uint256 public distributed = 0;

    event AllocateFounderTokens(address indexed sender);
    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    //constructor
    constructor() public{
        founder = msg.sender;
    }

    function setStartTime(uint _startTime) {
        if (msg.sender!=founder) revert();
        baseStartTime = _startTime;
    }

    //Distribute tokens out.
    function distribute(uint256 _amount, address _to) {
        if (msg.sender!=founder) revert();
        if (distributed + _amount > _totalSupply) revert();

        distributed += _amount;
        balances[_to] += _amount;
        distBalances[_to] += _amount;
    }

    //ERC 20 Standard Token interface transfer function
    //Prevent transfers until freeze period is over.
    function transfer(address _to, uint256 _value) returns (bool success) {
        if (now < baseStartTime) revert();

        //Default assumes totalSupply can't be over max (2^256 - 1).
        //If your token leaves out totalSupply and can issue more tokens as time goes on, you need to check if it doesn't wrap.
        if (balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
            uint _freeAmount = freeAmount(msg.sender);
            if (_freeAmount < _value) {
                return false;
            } 

            balances[msg.sender] -= _value;
            balances[_to] += _value;
            Transfer(msg.sender, _to, _value);
            return true;
        } else {
            return false;
        }
    }

    function freeAmount(address user) returns (uint256 amount) {
        //0) no restriction for founder
        if (user == founder) {
            return balances[user];
        }

        //1) no free amount before base start time;
        if (now < baseStartTime) {
            return 0;
        }

        //2) calculate number of months passed since base start time;
        uint monthDiff = (now - baseStartTime) / (30 days);

        //3) if it is over 15 months, free up everything.
        if (monthDiff > 15) {
            return balances[user];
        }

        //4) calculate amount of unrestricted within distributed amount.
        uint unrestricted = distBalances[user] / 10 + distBalances[user] * 6 / 100 * monthDiff;
        if (unrestricted > distBalances[user]) {
            unrestricted = distBalances[user];
        }

        //5) calculate total free amount including those not from distribution 
        if (unrestricted + balances[user] < distBalances[user]) {
            amount = 0;
        } else {
            amount = unrestricted + (balances[user] - distBalances[user]);
        }

        return amount;
    }

    //Change founder address (where ICO is being forwarded).
    function changeFounder(address newFounder) {
        if (msg.sender!=founder) revert();
        founder = newFounder;
    }

    //ERC 20 Standard Token interface transfer function
    //Prevent transfers until freeze period is over.         
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        if (msg.sender != founder) revert();

        //same as above. Replace this line with the following if you want to protect against wrapping uints.
        if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
            uint _freeAmount = freeAmount(_from);
            if (_freeAmount < _value) {
                return false;
            } 

            balances[_to] += _value;
            balances[_from] -= _value;
            allowed[_from][msg.sender] -= _value;
            Transfer(_from, _to, _value);
            return true;
        } else { return false; }
    }

    function() payable {
        if (!founder.call.value(msg.value)()) revert(); 
    }

}