Help wanted with tranche based bonus in a crowdsale

[abcoathup]

Hi @Roodiger welcome to the community

You can take inspiration from the IncreasingPriceCrowdsale.sol

You could override the _getTokenAmount function of Crowdsale to use the current rate and then have a function getCurrentRate which has your rate calculation based on how many tokens have been sold.

I have created an example crowdsale contract below. The getCurrentRate function would need to be updated to include the rate calculation you want to use. Currently it just multiplies the _initialRate by one.

I recommend that any such contract be fully tested and audited.
For testing, I suggest using the following guide:

Test smart contracts like a rockstar

One does not simply test your dapp. Among many other things while developing a decentralized application, testing it is something you always need to do. What most people still don’t do is automate those tests, which leads to a huge loss of time and drains the energy to code. Automated tests have been around for a while and they have been gaining lots of traction in the last decade. Whilst blockchain and smart contract development are fairly new, we can still automate tests for these. We can, s…

pragma solidity ^0.5.0;

import "openzeppelin-solidity/contracts/crowdsale/Crowdsale.sol";
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";

/**
 * @title MyCrowdsale
 * @dev This is a crowdsale.
 */
contract MyCrowdsale is Crowdsale {

    using SafeMath for uint256;

    uint256 private _initialRate;

    constructor (
        uint256 initialRate,
        address payable wallet,
        IERC20 token
    )
        public
        Crowdsale(initialRate, wallet, token) {
        _initialRate = initialRate;
    }

    /**
     * The base rate function is overridden to revert, since this crowdsale doesn't use it, and
     * all calls to it are a mistake.
     */
    function rate() public view returns (uint256) {
        revert("MyCrowdsale: rate() called");
    }

    /**
     * @return the initial rate of the crowdsale.
     */
    function initialRate() public view returns (uint256) {
        return _initialRate;
    }

    /**
     * @dev Returns the current rate of tokens per wei.
     * @return The number of tokens a buyer gets per wei
     */
    function getCurrentRate() public view returns (uint256) {
        // calculate the current rate
        return _initialRate.mul(1);
    }

    /**
     * @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);
    }
}