import type { ChallengeResponse } from '@/shared/api'
import { sha256 } from '@noble/hashes/sha2.js'
import { t } from '@/shared/i18n'

type PowJob = { challenge: ChallengeResponse; payload: string }
const scope = globalThis as unknown as {
  onmessage: ((event: MessageEvent<PowJob>) => void) | null
  postMessage: (message: { nonce: number } | { error: string }) => void
}

scope.onmessage = ({ data: { challenge, payload } }) => {
  if (!Number.isInteger(challenge.difficulty) || challenge.difficulty < 0 || challenge.difficulty > 256) {
    scope.postMessage({ error: t('pow.invalid') })
    return
  }
  const encoder = new TextEncoder()
  const prefix = encoder.encode(`pow.v1\n${challenge.context}\0`)
  const bytes = encoder.encode(payload)
  const buffer = new Uint8Array(prefix.length + 4 + 1 + 8 + 1 + 8 + 1 + 8 + bytes.length + 1 + 8)
  buffer.set(prefix)
  const view = new DataView(buffer.buffer)
  let offset = prefix.length
  view.setUint32(offset, challenge.difficulty, false)
  offset += 5
  view.setBigUint64(offset, BigInt(challenge.issued_at), false)
  offset += 9
  view.setBigUint64(offset, BigInt(challenge.expires_at), false)
  offset += 9
  view.setBigUint64(offset, BigInt(bytes.length), false)
  offset += 8
  buffer.set(bytes, offset)
  offset += bytes.length + 1
  const full = Math.floor(challenge.difficulty / 8)
  const rest = challenge.difficulty % 8
  const deadline = Math.min(challenge.expires_at * 1000, Date.now() + 75_000)
  for (let nonce = 0; nonce <= Number.MAX_SAFE_INTEGER; nonce++) {
    if (nonce % 1024 === 0 && Date.now() >= deadline) {
      scope.postMessage({ error: t('pow.timeout') })
      return
    }
    view.setBigUint64(offset, BigInt(nonce), false)
    const hash = sha256(buffer)
    let valid = true
    for (let index = 0; index < full; index++) {
      if (hash[index] !== 0) {
        valid = false
        break
      }
    }
    if (valid && (!rest || (hash[full] & (255 << (8 - rest))) === 0)) {
      scope.postMessage({ nonce })
      return
    }
  }
  scope.postMessage({ error: t('pow.failed') })
}