src/MessageHandler/deleteSet.js

import { deleteItemRange } from '../Struct/Delete.js'
import ID from '../Util/ID/ID.js'

export function stringifyDeleteSet (y, decoder, strBuilder) {
  let dsLength = decoder.readUint32()
  for (let i = 0; i < dsLength; i++) {
    let user = decoder.readVarUint()
    strBuilder.push(' -' + user + ':')
    let dvLength = decoder.readVarUint()
    for (let j = 0; j < dvLength; j++) {
      let from = decoder.readVarUint()
      let len = decoder.readVarUint()
      let gc = decoder.readUint8() === 1
      strBuilder.push(`clock: ${from}, length: ${len}, gc: ${gc}`)
    }
  }
  return strBuilder
}

export function writeDeleteSet (y, encoder) {
  let currentUser = null
  let currentLength
  let lastLenPos

  let numberOfUsers = 0
  let laterDSLenPus = encoder.pos
  encoder.writeUint32(0)

  y.ds.iterate(null, null, function (n) {
    var user = n._id.user
    var clock = n._id.clock
    var len = n.len
    var gc = n.gc
    if (currentUser !== user) {
      numberOfUsers++
      // a new user was found
      if (currentUser !== null) { // happens on first iteration
        encoder.setUint32(lastLenPos, currentLength)
      }
      currentUser = user
      encoder.writeVarUint(user)
      // pseudo-fill pos
      lastLenPos = encoder.pos
      encoder.writeUint32(0)
      currentLength = 0
    }
    encoder.writeVarUint(clock)
    encoder.writeVarUint(len)
    encoder.writeUint8(gc ? 1 : 0)
    currentLength++
  })
  if (currentUser !== null) { // happens on first iteration
    encoder.setUint32(lastLenPos, currentLength)
  }
  encoder.setUint32(laterDSLenPus, numberOfUsers)
}

export function readDeleteSet (y, decoder) {
  let dsLength = decoder.readUint32()
  for (let i = 0; i < dsLength; i++) {
    let user = decoder.readVarUint()
    let dv = []
    let dvLength = decoder.readUint32()
    for (let j = 0; j < dvLength; j++) {
      let from = decoder.readVarUint()
      let len = decoder.readVarUint()
      let gc = decoder.readUint8() === 1
      dv.push([from, len, gc])
    }
    if (dvLength > 0) {
      let pos = 0
      let d = dv[pos]
      let deletions = []
      y.ds.iterate(new ID(user, 0), new ID(user, Number.MAX_VALUE), function (n) {
        // cases:
        // 1. d deletes something to the right of n
        //  => go to next n (break)
        // 2. d deletes something to the left of n
        //  => create deletions
        //  => reset d accordingly
        //  *)=> if d doesn't delete anything anymore, go to next d (continue)
        // 3. not 2) and d deletes something that also n deletes
        //  => reset d so that it doesn't contain n's deletion
        //  *)=> if d does not delete anything anymore, go to next d (continue)
        while (d != null) {
          var diff = 0 // describe the diff of length in 1) and 2)
          if (n._id.clock + n.len <= d[0]) {
            // 1)
            break
          } else if (d[0] < n._id.clock) {
            // 2)
            // delete maximum the len of d
            // else delete as much as possible
            diff = Math.min(n._id.clock - d[0], d[1])
            // deleteItemRange(y, user, d[0], diff, true)
            deletions.push([user, d[0], diff])
          } else {
            // 3)
            diff = n._id.clock + n.len - d[0] // never null (see 1)
            if (d[2] && !n.gc) {
              // d marks as gc'd but n does not
              // then delete either way
              // deleteItemRange(y, user, d[0], Math.min(diff, d[1]), true)
              deletions.push([user, d[0], Math.min(diff, d[1])])
            }
          }
          if (d[1] <= diff) {
            // d doesn't delete anything anymore
            d = dv[++pos]
          } else {
            d[0] = d[0] + diff // reset pos
            d[1] = d[1] - diff // reset length
          }
        }
      })
      // TODO: It would be more performant to apply the deletes in the above loop
      // Adapt the Tree implementation to support delete while iterating
      for (let i = deletions.length - 1; i >= 0; i--) {
        const del = deletions[i]
        deleteItemRange(y, del[0], del[1], del[2], true)
      }
      // for the rest.. just apply it
      for (; pos < dv.length; pos++) {
        d = dv[pos]
        deleteItemRange(y, user, d[0], d[1], true)
        // deletions.push([user, d[0], d[1], d[2]])
      }
    }
  }
}