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pragma solidity ^0.4.24;
import "../validation/TimedCrowdsale.sol";
import "../../math/SafeMath.sol";
/**
* @title IncreasingPriceCrowdsale
* @dev Extension of Crowdsale contract that increases the price of tokens linearly in time.
* Note that what should be provided to the constructor is the initial and final _rates_, that is,
* the amount of tokens per wei contributed. Thus, the initial rate must be greater than the final rate.
*/
contract IncreasingPriceCrowdsale is TimedCrowdsale {
using SafeMath for uint256;
uint256 private _initialRate;
uint256 private _finalRate;
/**
* @dev Constructor, takes initial and final rates of tokens received per wei contributed.
* @param initialRate Number of tokens a buyer gets per wei at the start of the crowdsale
* @param finalRate Number of tokens a buyer gets per wei at the end of the crowdsale
*/
constructor(uint256 initialRate, uint256 finalRate) internal {
require(finalRate > 0);
require(initialRate > finalRate);
_initialRate = initialRate;
_finalRate = finalRate;
}
/**
* The base rate function is overridden to revert, since this crowdsale doens't use it, and
* all calls to it are a mistake.
*/
function rate() public view returns(uint256) {
revert();
}
/**
* @return the initial rate of the crowdsale.
*/
function initialRate() public view returns(uint256) {
return _initialRate;
}
/**
* @return the final rate of the crowdsale.
*/
function finalRate() public view returns (uint256) {
return _finalRate;
}
/**
* @dev Returns the rate of tokens per wei at the present time.
* Note that, as price _increases_ with time, the rate _decreases_.
* @return The number of tokens a buyer gets per wei at a given time
*/
function getCurrentRate() public view returns (uint256) {
if (!isOpen()) {
return 0;
}
// solium-disable-next-line security/no-block-members
uint256 elapsedTime = block.timestamp.sub(openingTime());
uint256 timeRange = closingTime().sub(openingTime());
uint256 rateRange = _initialRate.sub(_finalRate);
return _initialRate.sub(elapsedTime.mul(rateRange).div(timeRange));
}
/**
* @dev Overrides parent method taking into account variable rate.
* @param weiAmount The value in wei to be converted into tokens
* @return The number of tokens _weiAmount wei will buy at present time
*/
function _getTokenAmount(uint256 weiAmount)
internal view returns (uint256)
{
uint256 currentRate = getCurrentRate();
return currentRate.mul(weiAmount);
}
}