Solidity how to get random number with ratio

Question

I want to create my own NFT according to ERC1155 standard.

My hero has 6 parts, each part has 4 types as shown in the picture.

Now I want to create a function that takes a random number with the ratio shown in the image.

Here is simple function return random number. With _mod = 10^n it will return number of length n-1.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
contract RandomNumbers{
    function random(uint _mod) public view returns(uint){
        return uint(keccak256(abi.encodePacked(block.timestamp,block.difficulty,  
        msg.sender))) % _mod;
    }
}

I've been struggling with this for a whole day. Thanks for help.

Answer 1

Just so you know. You shouldn't use keccak256(abi.encodePacked(block.timestamp,block.difficulty,msg.sender)) to generate a random number because that actually creates a pseudo-random guessable number. Take a look at Chainlink VRF.

For the ratio you could try to check out this Data structure (GitHub): you manually set values for the leaves and then when you have your random number you can call the draw function to set the different stats.