pragma solidity ^0.4.18;
library SafeMath {
    function add(uint a, uint b) internal pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function sub(uint a, uint b) internal pure returns (uint c) {
        require(b <= a);
        c = a - b;
    }
    function mul(uint a, uint b) internal pure returns (uint c) {
        c = a * b;
        require(a == 0 || c / a == b);
    }
    function div(uint a, uint b) internal pure returns (uint c) {
        require(b > 0);
        c = a / b;
    }
}
library ExtendedMath {
    function limitLessThan(uint a, uint b) internal pure returns (uint c) {
        if(a > b) return b;
        return a;
    }
}
contract ERC20Interface {
    function totalSupply() public constant returns (uint);
    function balanceOf(address tokenOwner) public constant returns (uint balance);
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);
    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}
contract ApproveAndCallFallBack {
    function receiveApproval(address from, uint256 tokens, address token, bytes data) public;
}
contract Owned {
    address public owner;
    address public newOwner;
    event OwnershipTransferred(address indexed _from, address indexed _to);
    function Owned() public {
        owner = msg.sender;
    }
    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }
    function transferOwnership(address _newOwner) public onlyOwner {
        newOwner = _newOwner;
    }
    function acceptOwnership() public {
        require(msg.sender == newOwner);
        OwnershipTransferred(owner, newOwner);
        owner = newOwner;
        newOwner = address(0);
    }
}
contract BanksCoin is ERC20Interface, Owned {
    using SafeMath for uint;
    using ExtendedMath for uint;
    string public symbol;
    string public  name;
    uint8 public decimals;
    uint public _totalSupply;
    uint public latestDifficultyPeriodStarted;
    uint public epochCount;
    uint public _BLOCKS_PER_READJUSTMENT = 10;// 10 blocks per adjustment, scheduled for every 20 days
    uint public  _MINIMUM_TARGET = 2**10;
    uint public  _MAXIMUM_TARGET = 2**204;// BTC started at 2^224, BKC starts at 2^204= 2^20 relative to BTC: 1.05m
    uint public miningTarget;
    bytes32 public challengeNumber;
    uint public rewardEra;
    uint public maxSupplyForEra;
    address public lastRewardTo;
    uint public lastRewardAmount;
    uint public lastRewardEthBlockNumber;
    bool locked = false;
    mapping(bytes32 => bytes32) solutionForChallenge;
    uint public tokensMinted;
    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;
    event Mint(address indexed from, uint reward_amount, uint epochCount, bytes32 newChallengeNumber);
    function BanksCoin() public onlyOwner{
        symbol = "BKC";
        name = "BanksCoin";
        decimals = 8;
        _totalSupply = 1000000 * 10**uint(decimals);// Total supply is 1,000,000 
        if(locked) revert();
        locked = true;
        tokensMinted = 0;
        rewardEra = 0;
        maxSupplyForEra = _totalSupply; // 1 million to mint in 1 era
        miningTarget = _MAXIMUM_TARGET;
        latestDifficultyPeriodStarted = block.number;
        _startNewMiningEpoch();
    }
        function mint(uint256 nonce, bytes32 challenge_digest) public returns (bool success) {
            bytes32 digest =  keccak256(challengeNumber, msg.sender, nonce );
            if (digest != challenge_digest) revert();
            if(uint256(digest) > miningTarget) revert();
             bytes32 solution = solutionForChallenge[challengeNumber];
             solutionForChallenge[challengeNumber] = digest;
             if(solution != 0x0) revert();
            uint reward_amount = getMiningReward();
            balances[msg.sender] = balances[msg.sender].add(reward_amount);
            tokensMinted = tokensMinted.add(reward_amount);
            assert(tokensMinted <= maxSupplyForEra);
            lastRewardTo = msg.sender;
            lastRewardAmount = reward_amount;
            lastRewardEthBlockNumber = block.number;
             _startNewMiningEpoch();
              Mint(msg.sender, reward_amount, epochCount, challengeNumber );
           return true;
        }
    function _startNewMiningEpoch() internal {
      if( tokensMinted.add(getMiningReward()) > maxSupplyForEra && rewardEra < 1) // This will be evoked in thousands of years
      {
        rewardEra = rewardEra + 1;
      }
      maxSupplyForEra = _totalSupply;
      epochCount = epochCount.add(1);
      if(epochCount % _BLOCKS_PER_READJUSTMENT == 0)
      {
        _reAdjustDifficulty();
      }
      challengeNumber = block.blockhash(block.number - 1);
    }
    function _reAdjustDifficulty() internal {
        uint ethBlocksSinceLastDifficultyPeriod = block.number - latestDifficultyPeriodStarted;
        uint epochsMined = _BLOCKS_PER_READJUSTMENT;// 1000 every 2000 days
        uint targetEthBlocksPerDiffPeriod = epochsMined * 13190; // 13.1 seconds per block, 4.58 per minute, 274.81 per hour, 13190.83 per two days
        if( ethBlocksSinceLastDifficultyPeriod < targetEthBlocksPerDiffPeriod )
        {
          uint excess_block_pct = (targetEthBlocksPerDiffPeriod.mul(100)).div( ethBlocksSinceLastDifficultyPeriod );
          uint excess_block_pct_extra = excess_block_pct.sub(100).limitLessThan(1000);
          miningTarget = miningTarget.sub(miningTarget.div(2000).mul(excess_block_pct_extra));
        }else{
          uint shortage_block_pct = (ethBlocksSinceLastDifficultyPeriod.mul(100)).div( targetEthBlocksPerDiffPeriod );
          uint shortage_block_pct_extra = shortage_block_pct.sub(100).limitLessThan(1000);
          miningTarget = miningTarget.add(miningTarget.div(2000).mul(shortage_block_pct_extra));
        }
        latestDifficultyPeriodStarted = block.number;
        if(miningTarget < _MINIMUM_TARGET)
        {
          miningTarget = _MINIMUM_TARGET;
        }
        if(miningTarget > _MAXIMUM_TARGET)
        {
          miningTarget = _MAXIMUM_TARGET;
        }
    }
    function getChallengeNumber() public constant returns (bytes32) {
        return challengeNumber;
    }
     function getMiningDifficulty() public constant returns (uint) {
        return _MAXIMUM_TARGET.div(miningTarget);
    }
    function getMiningTarget() public constant returns (uint) {
       return miningTarget;
   }
    function getMiningReward() public constant returns (uint) {
         return (1 * 10**uint(decimals) ).div( 2**rewardEra ) ; // One BKC per reward, 2^0=1
    }
    function getMintDigest(uint256 nonce, bytes32 challenge_number) public view returns (bytes32 digesttest) {
        bytes32 digest = keccak256(challenge_number,msg.sender,nonce);
        return digest;
      }
      function checkMintSolution(uint256 nonce, bytes32 challenge_digest, bytes32 challenge_number, uint testTarget) public view returns (bool success) {
          bytes32 digest = keccak256(challenge_number,msg.sender,nonce);
          if(uint256(digest) > testTarget) revert();
          return (digest == challenge_digest);
        }
    function totalSupply() public constant returns (uint) {
        return _totalSupply  - balances[address(0)];
    }
    function balanceOf(address tokenOwner) public constant returns (uint balance) {
        return balances[tokenOwner];
    }
    function transfer(address to, uint tokens) public returns (bool success) {
        balances[msg.sender] = balances[msg.sender].sub(tokens);
        balances[to] = balances[to].add(tokens);
        Transfer(msg.sender, to, tokens);
        return true;
    }
    function approve(address spender, uint tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        Approval(msg.sender, spender, tokens);
        return true;
    }
    function transferFrom(address from, address to, uint tokens) public returns (bool success) {
        balances[from] = balances[from].sub(tokens);
        allowed[from][msg.sender] = allowed[from][msg.sender].sub(tokens);
        balances[to] = balances[to].add(tokens);
        Transfer(from, to, tokens);
        return true;
    }
    function allowance(address tokenOwner, address spender) public constant returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }
    function approveAndCall(address spender, uint tokens, bytes data) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        Approval(msg.sender, spender, tokens);
        ApproveAndCallFallBack(spender).receiveApproval(msg.sender, tokens, this, data);
        return true;
    }
    function () public payable {
        revert();
    }
    function transferAnyERC20Token(address tokenAddress, uint tokens) public onlyOwner returns (bool success) {
        return ERC20Interface(tokenAddress).transfer(owner, tokens);
    }
}

{
  "compilationTarget": {
    "BanksCoin.sol": "BanksCoin"
  },
  "libraries": {},
  "optimizer": {
    "enabled": false,
    "runs": 200
  },
  "remappings": []
}