nip10.ts

import type {Event} from './event'
import type {EventPointer, ProfilePointer} from './nip19'

export type NIP10Result = {
  /**
   * Pointer to the root of the thread.
   */
  root: EventPointer | undefined

  /**
   * Pointer to a "parent" event that parsed event replies to (responded to).
   */
  reply: EventPointer | undefined

  /**
   * Pointers to events which may or may not be in the reply chain.
   */
  mentions: EventPointer[]

  /**
   * List of pubkeys that are involved in the thread in no particular order.
   */
  profiles: ProfilePointer[]
}

export function parse(event: Pick<Event, 'tags'>): NIP10Result {
  const result: NIP10Result = {
    reply: undefined,
    root: undefined,
    mentions: [],
    profiles: []
  }

  const eTags: string[][] = []

  for (const tag of event.tags) {
    if (tag[0] === 'e' && tag[1]) {
      eTags.push(tag)
    }

    if (tag[0] === 'p' && tag[1]) {
      result.profiles.push({
        pubkey: tag[1],
        relays: tag[2] ? [tag[2]] : []
      })
    }
  }

  for (let eTagIndex = 0; eTagIndex < eTags.length; eTagIndex++) {
    const eTag = eTags[eTagIndex]

    const [_, eTagEventId, eTagRelayUrl, eTagMarker] = eTag as [
      string,
      string,
      undefined | string,
      undefined | string
    ]

    const eventPointer: EventPointer = {
      id: eTagEventId,
      relays: eTagRelayUrl ? [eTagRelayUrl] : []
    }

    const isFirstETag = eTagIndex === 0
    const isLastETag = eTagIndex === eTags.length - 1

    if (eTagMarker === 'root') {
      result.root = eventPointer
      continue
    }

    if (eTagMarker === 'reply') {
      result.reply = eventPointer
      continue
    }

    if (eTagMarker === 'mention') {
      result.mentions.push(eventPointer)
      continue
    }

    if (isFirstETag) {
      result.root = eventPointer
      continue
    }

    if (isLastETag) {
      result.reply = eventPointer
      continue
    }

    result.mentions.push(eventPointer)
  }

  return result
}