pzp-db/lib/db-tangle.js

const pull = require('pull-stream')
const p = require('node:util').promisify
const MsgV4 = require('./msg-v4')

/**
 * @typedef {string} MsgID
 * @typedef {import('./msg-v4').Msg} Msg
 */

/**
 * @typedef {{
 *   id?: never;
 *   msg?: never;
 *   received?: never;
 * }} RecDeleted
 *
 * @typedef {{
 *   id: MsgID;
 *   msg: Msg;
 *   received: number;
 * }} RecPresent
 *
 * @typedef {RecPresent | RecDeleted} Rec
 */

/**
 * @template T
 * @typedef {[T] extends [void] ?
 *   (...args: [Error] | []) => void :
 *   (...args: [Error] | [null, T]) => void
 * } CB
 */

class DBTangle extends MsgV4.Tangle {
  /** @type {(msgID: MsgID, cb: CB<Msg>) => void} */
  #getMsg

  /**
   * @param {MsgID} rootID
   * @param {(msgID: MsgID, cb: CB<Msg>) => void} getMsg
   */
  constructor(rootID, getMsg) {
    super(rootID)
    this.#getMsg = getMsg
  }

  /**
   * @param {MsgID} rootID
   * @param {AsyncIterable<Rec>} recordsIter
   * @param {(msgID: MsgID, cb: any) => void} getMsg
   * @return {Promise<DBTangle>}
   */
  static async init(rootID, recordsIter, getMsg) {
    const dbtangle = new DBTangle(rootID, getMsg)
    for await (const rec of recordsIter) {
      if (!rec.msg) continue
      dbtangle.add(rec.id, rec.msg)
    }
    return dbtangle
  }

  /**
   * Given a set of msgs (`msgIDs`) in this tangle, find all "deletable" and
   * "erasable" msgs that precede that set.
   *
   * *Deletables* are msgs that precede `msgsIDs` but are not important in any
   * validation path toward the root, and thus can be deleted.
   *
   * *Erasables* are msgs that precede `msgsIDs` and can be erased without
   * losing a validation path toward the root.
   * @param {Array<MsgID>} msgIDs
   * @returns {{ deletables: Set<MsgID>, erasables: Set<MsgID> } | null}
   */
  getDeletablesAndErasables(...msgIDs) {
    // Determine erasables
    const erasables = new Set()
    const minimum = this.getMinimumAmong(msgIDs)
    for (const msgID of minimum) {
      const trail = this.shortestPathToRoot(msgID)
      if (!trail) return null
      for (const id of trail) {
        erasables.add(id)
      }
    }

    // Determine deletables
    const deletables = new Set()
    const sorted = this.topoSort()
    for (const msgID of sorted) {
      if (erasables.has(msgID)) continue
      if (minimum.some((min) => this.precedes(msgID, min))) {
        deletables.add(msgID)
      }
    }

    return { deletables, erasables }
  }

  /**
   * @param {Array<string>=} minSet
   * @param {Array<string>=} maxSet
   * @param {CB<Array<Msg>>=} cb
   * @return {Promise<Array<Msg>>|void}
   */
  slice(minSet = [], maxSet = [], cb) {
    // @ts-ignore
    if (cb === undefined) return p(this.slice).bind(this)(minSet, maxSet)

    const minSetGood = minSet.filter((msgID) => this.has(msgID))
    const maxSetGood = maxSet.filter((msgID) => this.has(msgID))
    const minSetTight = this.getMinimumAmong(minSetGood)

    const trail = new Set()
    for (const msgID of minSetTight) {
      const path = this.shortestPathToRoot(msgID)
      if (!path) return cb(Error("Couldn't get shortest path to root when slicing dbtangle"))
      for (const msgID of path) {
        trail.add(msgID)
      }
    }

    const msgs = /**@type {Array<Msg>}*/ ([])

    pull(
      pull.values(this.topoSort()),
      pull.asyncMap((msgID, cb) => {
        this.#getMsg(msgID, (err, msg) => {
          if (err) return cb(err)
          cb(null, { id: msgID, msg })
        })
      }),
      pull.drain(
        (rec) => {
          if (trail.has(rec.id)) {
            if (rec.msg) msgs.push({ ...rec.msg, data: null })
          }
          const isMin = minSetGood.includes(rec.id)
          const isMax = maxSetGood.includes(rec.id)
          const isBeforeMin = minSetGood.some((min) =>
            this.precedes(rec.id, min)
          )
          const isAfterMax = maxSetGood.some((max) =>
            this.precedes(max, rec.id)
          )
          if (!isMin && isBeforeMin) return
          if (!isMax && isAfterMax) return
          if (rec.msg) msgs.push(rec.msg)
        },
        (err) => {
          if (err) return cb(Error('DBTangle.slice() failed', { cause: err }))
          return cb(null, msgs)
        }
      )
    )
  }
}

module.exports = DBTangle