nip13.ts

import { bytesToHex } from '@noble/hashes/utils'
import { type UnsignedEvent, type Event } from './pure.ts'
import { sha256 } from '@noble/hashes/sha256'

import { utf8Encoder } from './utils.ts'

/** Get POW difficulty from a Nostr hex ID. */
export function getPow(hex: string): number {
  let count = 0

  for (let i = 0; i < 64; i += 8) {
    const nibble = parseInt(hex.substring(i, i + 8), 16)
    if (nibble === 0) {
      count += 32
    } else {
      count += Math.clz32(nibble)
      break
    }
  }

  return count
}

/**
 * Mine an event with the desired POW. This function mutates the event.
 * Note that this operation is synchronous and should be run in a worker context to avoid blocking the main thread.
 */
export function minePow(unsigned: UnsignedEvent, difficulty: number): Omit<Event, 'sig'> {
  let count = 0

  const event = unsigned as Omit<Event, 'sig'>
  const tag = ['nonce', count.toString(), difficulty.toString()]

  event.tags.push(tag)

  while (true) {
    const now = Math.floor(new Date().getTime() / 1000)

    if (now !== event.created_at) {
      count = 0
      event.created_at = now
    }

    tag[1] = (++count).toString()

    event.id = fastEventHash(event)

    if (getPow(event.id) >= difficulty) {
      break
    }
  }

  return event
}

export function fastEventHash(evt: UnsignedEvent): string {
  return bytesToHex(
    sha256(utf8Encoder.encode(JSON.stringify([0, evt.pubkey, evt.created_at, evt.kind, evt.tags, evt.content]))),
  )
}