pragma solidity ^0.4.23;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 * Name : AlphaChain (ACH)
 * Decimals : 18
 * TotalSupply : 20000000000
 *
 */
library SafeMath {

    /**
    * @dev Multiplies two numbers, throws on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
        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;
    }
}

contract ForeignToken {
    function balanceOf(address _owner) constant public returns (uint256);
    function transfer(address _to, uint256 _value) public returns (bool);
}

contract ERC20Basic {
    uint256 public totalSupply;
    function balanceOf(address who) public constant returns (uint256);
    function transfer(address to, uint256 value) public returns (bool);
    event Transfer(address indexed from, address indexed to, uint256 value);
}

contract ERC20 is ERC20Basic {
    function allowance(address owner, address spender) public constant returns (uint256);
    function transferFrom(address from, address to, uint256 value) public returns (bool);
    function approve(address spender, uint256 value) public returns (bool);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract AlphaChain is ERC20 {

    using SafeMath for uint256;
    address owner = msg.sender;

    mapping (address => uint256) balances;
    mapping (address => mapping (address => uint256)) allowed;

    string public constant name = "AlphaChain";
    string public constant symbol = "ACH";
    uint public constant decimals = 18;

    uint256 public totalSupply = 20000000000e18;
    uint256 public totalDistributed = 15000000000e18;
    uint256 public tokensPerEth = 2000000e18;
    uint256 public constant MIN_CONTRIBUTION = 1 ether / 100; // 0.01 Ether
    uint256 public constant MAX_CONTRIBUTION = 1 ether ; // 1 Ether


    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    event Distr(address indexed to, uint256 amount);
    event DistrFinished();

    event Airdrop(address indexed _owner, uint _amount, uint _balance);

    event TokensPerEthUpdated(uint _tokensPerEth);

    event Burn(address indexed burner, uint256 value);

    bool public distributionFinished = false;

    modifier canDistr() {
        require(!distributionFinished);
        _;
    }

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }


    function AlphaChainConstructor () public {
        owner = msg.sender;
        distr(owner, totalDistributed);
    }

    function transferOwnership(address newOwner) onlyOwner public {
        if (newOwner != address(0)) {
            owner = newOwner;
        }
    }


    function finishDistribution() onlyOwner canDistr public returns (bool) {
        distributionFinished = true;
        emit DistrFinished();
        return true;
    }

    function distr(address _to, uint256 _amount) canDistr private returns (bool) {
        totalDistributed = totalDistributed.add(_amount);
        balances[_to] = balances[_to].add(_amount);
        emit Distr(_to, _amount);
        emit Transfer(address(0), _to, _amount);

        return true;
    }

    function doAirdrop(address _participant, uint _amount) internal {

        require( _amount > 0 );

        require( totalDistributed < totalSupply );

        balances[_participant] = balances[_participant].add(_amount);
        totalDistributed = totalDistributed.add(_amount);

        if (totalDistributed >= totalSupply) {
            distributionFinished = true;
        }

        // log
        emit Airdrop(_participant, _amount, balances[_participant]);
        emit Transfer(address(0), _participant, _amount);
    }

    function adminClaimAirdrop(address _participant, uint _amount) public onlyOwner {
        doAirdrop(_participant, _amount);
    }

    function adminClaimAirdropMultiple(address[] _addresses, uint _amount) public onlyOwner {
        for (uint i = 0; i < _addresses.length; i++) doAirdrop(_addresses[i], _amount);
    }

    function updateTokensPerEth(uint _tokensPerEth) public onlyOwner {
        tokensPerEth = _tokensPerEth;
        emit TokensPerEthUpdated(_tokensPerEth);
    }

    function () external payable {
        getTokens();
     }

    function getTokens() payable canDistr  public {
        uint256 tokens = 0;

        require( msg.value >= MIN_CONTRIBUTION );
        require( msg.value <= MAX_CONTRIBUTION );
        require( msg.value > 0 );
        uint256 bonusTokens = 0;
        
        tokens = tokensPerEth.mul(msg.value) / 1 ether;
        if (msg.value >= 1 ether){bonusTokens = tokens.div(2);}
        else if (msg.value >= 0.5 ether){bonusTokens = tokens.div(4);}
        else if (msg.value >= 0.25 ether){bonusTokens = tokens.div(10);}
        else if (msg.value >= 0.05 ether){bonusTokens = tokens.div(20);}
        
        tokens += bonusTokens;
            
        address investor = msg.sender;

        if (tokens > 0) {
            distr(investor, tokens);
        }

        if (totalDistributed >= totalSupply) {
            distributionFinished = true;
        }
    }

    function balanceOf(address _owner) constant public returns (uint256) {
        return balances[_owner];
    }

    // mitigates the ERC20 short address attack
    modifier onlyPayloadSize(uint size) {
        assert(msg.data.length >= size + 4);
        _;
    }

    function transfer(address _to, uint256 _amount) onlyPayloadSize(2 * 32) public returns (bool success) {

        require(_to != address(0));
        require(_amount <= balances[msg.sender]);

        balances[msg.sender] = balances[msg.sender].sub(_amount);
        balances[_to] = balances[_to].add(_amount);
        emit Transfer(msg.sender, _to, _amount);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _amount) onlyPayloadSize(3 * 32) public returns (bool success) {

        require(_to != address(0));
        require(_amount <= balances[_from]);
        require(_amount <= allowed[_from][msg.sender]);

        balances[_from] = balances[_from].sub(_amount);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_amount);
        balances[_to] = balances[_to].add(_amount);
        emit Transfer(_from, _to, _amount);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool success) {
        // mitigates the ERC20 spend/approval race condition
        if (_value != 0 && allowed[msg.sender][_spender] != 0) { return false; }
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function allowance(address _owner, address _spender) constant public returns (uint256) {
        return allowed[_owner][_spender];
    }

    function getTokenBalance(address tokenAddress, address who) constant public returns (uint){
        ForeignToken t = ForeignToken(tokenAddress);
        uint bal = t.balanceOf(who);
        return bal;
    }

    function withdraw() onlyOwner public {
        address myAddress = this;
        uint256 etherBalance = myAddress.balance;
        owner.transfer(etherBalance);
    }

    function burn(uint256 _value) onlyOwner public {
        require(_value <= balances[msg.sender]);
        address burner = msg.sender;
        balances[burner] = balances[burner].sub(_value);
        totalSupply = totalSupply.sub(_value);
        totalDistributed = totalDistributed.sub(_value);
        emit Burn(burner, _value);
    }

    function withdrawForeignTokens(address _tokenContract) onlyOwner public returns (bool) {
        ForeignToken token = ForeignToken(_tokenContract);
        uint256 amount = token.balanceOf(address(this));
        return token.transfer(owner, amount);
    }
}