@zk-kit/incremental-merkle-tree/src/update.ts

Incremental Merkle tree implementation in TypeScript.

import checkParameter from "./checkParameter"
import { HashFunction, Node } from "./types"

export default function update(
    index: number,
    value: Node,
    depth: number,
    arity: number,
    nodes: Node[][],
    zeroes: Node[],
    hash: HashFunction
): Node {
    checkParameter(index, "index", "number")

    if (index < 0 || index >= nodes[0].length) {
        throw new Error("The leaf does not exist in this tree")
    }

    let node = value

    for (let level = 0; level < depth; level += 1) {
        const position = index % arity
        const levelStartIndex = index - position
        const levelEndIndex = levelStartIndex + arity

        const children = []
        nodes[level][index] = node

        for (let i = levelStartIndex; i < levelEndIndex; i += 1) {
            if (i < nodes[level].length) {
                children.push(nodes[level][i])
            } else {
                children.push(zeroes[level])
            }
        }

        node = hash(children)
        index = Math.floor(index / arity)
    }

    return node
}