Stringify version for debug

function debugVersion(
  versionSet: VersionSet,
  ver: Version,
  key: string
): string {
  const debuglist: number[][][] = [
    [[], [], []],
    [[], [], []],
    [[], [], []],
    [[], [], []],
    [[], [], []],
    [[], [], []],
  ]

  for (let level = 0; level < Config.kNumLevels; level++) {
    for (let file of versionSet._base.files[level]) {
      debuglist[level][0].push(file.number)
    }
    for (let file of versionSet._levels[level].addedFiles.iterator()) {
      debuglist[level][1].push(file.number)
    }

    for (let file of versionSet._levels[level].deletedFiles) {
      debuglist[level][2].push(file)
    }
  }

  function stringifyBuilderState(): string {
    let result = ''
    let level = 0
    for (let levelFiles of debuglist) {
      result += `level=${level} baseFiles=${levelFiles[0].join(
        ','
      )} addedFiles=${levelFiles[1].join(
        ','
      )} deletedFiles=${levelFiles[2].join(',')} \n`
      level++
    }
    return result
  }

  function stringifyVersion(ver: Version): string {
    let result = ''
    let level = 0
    for (let levelFiles of ver.files) {
      result += `level=${level} files=${levelFiles
        .map(file => file.number)
        .join(',')}\n`
      level++
    }
    return result
  }

  return key + '\n' + stringifyBuilderState() + '\n' + stringifyVersion(ver)
}