import { sha256 } from "@noble/hashes/sha2.js"
import { encodeVarInt, FINGERPRINT_SIZE } from "./utils"

export class Accumulator {
  #buf!: Uint8Array

  constructor() {
    this.setToZero()
  }

  setToZero() {
    this.#buf = new Uint8Array(32)
  }

  add(otherBuf: Uint8Array) {
    let currCarry = 0,
      nextCarry = 0
    const p = new DataView(this.#buf.buffer)
    const po = new DataView(otherBuf.buffer)

    for (let i = 0; i < 8; i++) {
      const offset = i * 4
      const orig = p.getUint32(offset, true)
      const otherV = po.getUint32(offset, true)

      let next = orig

      next += currCarry
      next += otherV
      if (next > 4294967295) nextCarry = 1

      p.setUint32(offset, next & 4294967295, true)
      currCarry = nextCarry
      nextCarry = 0
    }
  }

  negate() {
    const p = new DataView(this.#buf.buffer)

    for (let i = 0; i < 8; i++) {
      const offset = i * 4
      p.setUint32(offset, ~p.getUint32(offset, true))
    }

    const one = new Uint8Array(32)
    one[0] = 1
    this.add(one)
  }

  getFingerprint(n: number) {
    const varInt = encodeVarInt(n)
    const copy = new Uint8Array(this.#buf.length + varInt.length)
    copy.set(this.#buf)
    copy.set(varInt, this.#buf.length)

    const hash = sha256(copy)
    return hash.subarray(0, FINGERPRINT_SIZE)
  }
}