function getTokensForContribution(uint weiContribution) public constant 
         returns(uint tokenAmount, uint weiRemainder)
    {
         
         uint256 bonus = 0;
         
         
         uint crowdsaleEnd = sale.end;
        
         
         require(block.timestamp <= crowdsaleEnd);

         
         uint periodPriceInWei = sale.priceInWei;

         
         
         tokenAmount = weiContribution / periodPriceInWei;
         
	 	
            if (block.timestamp < 1521234001) {
                
                bonus = tokenAmount * 20 / 100;
            } else if (block.timestamp < 1521925201) {
                
                bonus = tokenAmount * 15 / 100;
            } else {
                
                bonus = tokenAmount * 10 / 100;
            }
		 

            
        tokenAmount = tokenAmount + bonus;
        
         
         weiRemainder = weiContribution % periodPriceInWei;
    }