function decodeDocumentChanges()

in backend/columnar.js [945:981]

• 34 lines of code
• 13 McCabe index (conditional complexity)

function decodeDocumentChanges(changes, expectedHeads) {
  let heads = {} // change hashes that are not a dependency of any other change
  for (let i = 0; i < changes.length; i++) {
    let change = changes[i]
    change.deps = []
    for (let index of change.depsNum.map(d => d.depsIndex)) {
      if (!changes[index] || !changes[index].hash) {
        throw new RangeError(`No hash for index ${index} while processing index ${i}`)
      }
      const hash = changes[index].hash
      change.deps.push(hash)
      if (heads[hash]) delete heads[hash]
    }
    change.deps.sort()
    delete change.depsNum

    if (change.extraLen_datatype !== VALUE_TYPE.BYTES) {
      throw new RangeError(`Bad datatype for extra bytes: ${VALUE_TYPE.BYTES}`)
    }
    change.extraBytes = change.extraLen
    delete change.extraLen_datatype

    // Encoding and decoding again to compute the hash of the change
    changes[i] = decodeChange(encodeChange(change))
    heads[changes[i].hash] = true
  }

  const actualHeads = Object.keys(heads).sort()
  let headsEqual = (actualHeads.length === expectedHeads.length), i = 0
  while (headsEqual && i < actualHeads.length) {
    headsEqual = (actualHeads[i] === expectedHeads[i])
    i++
  }
  if (!headsEqual) {
    throw new RangeError(`Mismatched heads hashes: expected ${expectedHeads.join(', ')}, got ${actualHeads.join(', ')}`)
  }
}