pragma solidity ^0.4.24;

/**
 * ERC20 contract interface.
 */
contract ERC20 {
    function totalSupply() public view returns (uint);
    function decimals() public view returns (uint);
    function balanceOf(address tokenOwner) public view returns (uint balance);
    function allowance(address tokenOwner, address spender) public view 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);
}

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

    /**
    * @dev Multiplies two numbers, reverts on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b);

        return c;
    }

    /**
    * @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0); // Solidity only automatically asserts 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 c;
    }

    /**
    * @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
    * @dev Adds two numbers, reverts on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }

    /**
    * @dev Divides two numbers and returns the remainder (unsigned integer modulo),
    * reverts when dividing by zero.
    */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }

    /**
    * @dev Returns ceil(a / b).
    */
    function ceil(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a / b;
        if(a % b == 0) {
            return c;
        }
        else {
            return c + 1;
        }
    }
}

/**
 * @title KyberNetwork
 * @dev Interface for KyberNetwork main contract.
 */
contract KyberNetwork {

    function getExpectedRate(
        ERC20 src,
        ERC20 dest,
        uint srcQty
    )
        public
        view
        returns (uint expectedRate, uint slippageRate);

    function trade(
        ERC20 src,
        uint srcAmount,
        ERC20 dest,
        address destAddress,
        uint maxDestAmount,
        uint minConversionRate,
        address walletId
    )
        public
        payable
        returns(uint);
}

/**
 * @title TokenPriceProvider
 * @dev Simple contract returning the price in ETH for ERC20 tokens listed on KyberNetworks. 
 * @author Olivier Van Den Biggelaar - <olivier@argent.xyz>
 */
contract TokenPriceProvider {

    using SafeMath for uint256;

    // Mock token address for ETH
    address constant internal ETH_TOKEN_ADDRESS = 0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE;
    // Address of Kyber's trading contract
    address constant internal KYBER_NETWORK_ADDRESS = 0x818E6FECD516Ecc3849DAf6845e3EC868087B755;

    mapping(address => uint256) public cachedPrices;

    function syncPrice(ERC20 token) public {
        uint256 expectedRate;
        (expectedRate,) = kyberNetwork().getExpectedRate(token, ERC20(ETH_TOKEN_ADDRESS), 10000);
        cachedPrices[token] = expectedRate;
    }

    //
    // Convenience functions
    //

    function syncPriceForTokenList(ERC20[] tokens) public {
        for(uint16 i = 0; i < tokens.length; i++) {
            syncPrice(tokens[i]);
        }
    }

    /**
     * @dev Converts the value of _amount tokens in ether.
     * @param _amount the amount of tokens to convert (in 'token wei' twei)
     * @param _token the ERC20 token contract
     * @return the ether value (in wei) of _amount tokens with contract _token
     */
    function getEtherValue(uint256 _amount, address _token) public view returns (uint256) {
        uint256 decimals = ERC20(_token).decimals();
        uint256 price = cachedPrices[_token];
        return price.mul(_amount).div(10**decimals);
    }

    //
    // Internal
    //

    function kyberNetwork() internal view returns (KyberNetwork) {
        return KyberNetwork(KYBER_NETWORK_ADDRESS);
    }
}