BufferRandomizer

The BufferRandomizer contract randomizes integer weights and can apply optional buffs if a user sacrifices a Non-Fungible Token (NFT). These buffs are determined by the NFT tier, which defines a multiplier and a buff value that can be added to the pool of weights for a single randomization.

Setup

The contract is initialized with three arrays buffs, NFT addresses, and NFT tiers.

• buffs: An array of integer weights (buffs) that the contract can randomize.
• nftAddresses: An array of NFT contract addresses. Each address has a corresponding tier.
• tiers: An array of tiers.

Tier Struct

• tier: The tier of the NFT. This is used to organize the buff and multiplier.
• mul: The multiplier for the buff. This is used to determine the buff and multiplier.
• buff: The buff value. This is used to determine the buff and multiplier.

   struct Tier {
	uint8 tier;
	uint8 mul;
	int16 buff;
   }

Functions

• getRandomWeight: Returns a random weight from the pool of weights.
• getRandomBuff: Returns a base value multiplied by a random weight from the pool of weights, optionally modified by a buff associated with an NFT. If the NFT address is not zero, the contract uses the _getRandomWeightWithNFTBuffer function, otherwise it uses _getRandomWeight.
• addBuff: Adds a buff to the pool of weights. Only callable by the owner.
• removeBuffAndReplace: Removes a buff from the pool of weights by index and replaces it with the last buff in the array. Only callable by the owner.
• removeBuffAndShift: Removes a buff from the pool of weights by index and shifts all subsequent buffs to fill the gap. Only callable by the owner.
• getBuffs: Returns the entire pool of weights.
• getBuff: Returns a buff from the pool of weights by index.
• addAcceptedNFT: Adds an NFT and its associated tier to the contract. Only callable by the owner.
• getTier: Returns the tier associated with an NFT address.

Errors

• NotOwner: Emitted when a function restricted to the owner is called by a different address.
• IndexOutOfBounds: Emitted when an index is out of the bounds of the buffs array.
• InvalidBaseValue: Emitted when the base value in getRandomBuff is zero.
• InvalidTier: Emitted when the NFT tier is zero in _getRandomWeightWithNFTBuffer.
• InvalidWeights: Emitted when there are no weights in the pool in getRandomBuff.

Notes

• The contract uses integer weights instead of probabilities or percentages. This allows for more variability in weights while avoiding the complexities of fractional arithmetic in Solidity.
• Buffs associated with NFTs are optional and only applied if the user sacrifices an NFT.
• The contract burns the NFT when applying a buff.
• The contract owner can add and remove weights.

More notes - This may not be suitable for all use cases

• The randomness in this contract is not truly random, as it uses the keccak256 hash function for pseudo-randomness. This is ok for most lower value use cases, but if you need true randomness, you should use an oracle.
• This contract suffers from Modulo Bias and don't try to fix it. You can change the weights such this is minimized. I don't think this is a big deal for most use cases.