function readDocumentChanges()

in backend/new.js [1605:1635]

• 29 lines of code
• 15 McCabe index (conditional complexity)

function readDocumentChanges(doc) {
  const columns = makeDecoders(doc.changesColumns, DOCUMENT_COLUMNS)
  const actorD = columns[0].decoder, seqD = columns[1].decoder
  const depsNumD = columns[5].decoder, depsIndexD = columns[6].decoder
  if (columns[0].columnId !== DOCUMENT_COLUMNS[0].columnId || DOCUMENT_COLUMNS[0].columnName !== 'actor' ||
      columns[1].columnId !== DOCUMENT_COLUMNS[1].columnId || DOCUMENT_COLUMNS[1].columnName !== 'seq' ||
      columns[5].columnId !== DOCUMENT_COLUMNS[5].columnId || DOCUMENT_COLUMNS[5].columnName !== 'depsNum' ||
      columns[6].columnId !== DOCUMENT_COLUMNS[6].columnId || DOCUMENT_COLUMNS[6].columnName !== 'depsIndex') {
    throw new RangeError('unexpected columnId')
  }

  let numChanges = 0, clock = {}, actorNums = [], headIndexes = new Set()
  while (!actorD.done) {
    const actorNum = actorD.readValue(), seq = seqD.readValue(), depsNum = depsNumD.readValue()
    const actorId = doc.actorIds[actorNum]
    if (seq !== 1 && seq !== clock[actorId] + 1) {
      throw new RangeError(`Expected seq ${clock[actorId] + 1}, got ${seq} for actor ${actorId}`)
    }
    actorNums.push(actorNum)
    clock[actorId] = seq
    headIndexes.add(numChanges)
    for (let j = 0; j < depsNum; j++) headIndexes.delete(depsIndexD.readValue())
    numChanges++
  }
  const headActors = [...headIndexes].map(index => doc.actorIds[actorNums[index]]).sort()

  for (let col of columns) col.decoder.reset()
  const encoders = columns.map(col => ({columnId: col.columnId, encoder: encoderByColumnId(col.columnId)}))
  copyColumns(encoders, columns, numChanges)
  return {clock, headActors, encoders, numChanges}
}