MerkleProof.js

/**
 * @description Returns a cryptographic proof to show that a given 
 * wallet address is in the whitelist associated with a smart contract.
 */
import {MerkleTree} from "merkletreejs"
import keccak256 from "keccak256"
import { initializeApp } from "firebase/app"
import { getFirestore, collection, query, getDocs, where, setDoc, doc } from 'firebase/firestore/lite'
const firebaseConfig = {
    apiKey: process.env.fb_key,
    authDomain: process.env.authDomain,
    projectId: process.env.projectId,
    storageBucket: process.env.storageBucket,
    messagingSenderId: process.env.messagingSenderId,
    appId: process.env.appId,
    measurementId: process.env.measurementId
}

const fb = initializeApp(firebaseConfig)

const db = getFirestore(fb)

export const MerkleProof = async (req) => {
    const contract = req.query.contract
    const address = req.query.wallet

    // Retrieve whitelist associated with contract address
    const q = query(collection(db, "whitelists"), where("contract", "==", contract))
    const wlSnapshot = await getDocs(q)

    // If no contract exists for that address in DB
    if(wlSnapshot.docs.length === 0) {
        throw 'No contract found with that address'
    }

    // If wallet address is not on the whitelist
    let whitelist = wlSnapshot.docs[0].data().addresses
    if(!whitelist.includes(address)) {
        throw 'Wallet provided is not on whitelist'
    }

    // Create mapping of leaves and construct merkle tree
    const leafNodes = whitelist.map(addr => keccak256(addr))
    const merkleTree = new MerkleTree(leafNodes, keccak256, {sortPairs: true})
    
    // Hash wallet address using keccak256 hashing algorithm and 
    // get proof that this hash is a member of the tree
    const leaf = keccak256(address)
    const proof = merkleTree.getHexProof(leaf)

    // result.output.data will be used in smart contract call to prove to
    // smart contract that the tx sender is on the whitelist
    const result = {
        inputs: {contract: contract, wallet: address},
        output: {data: proof},
        success: true
    }

    return result
}