zio nio and streams file IO

-zio-nio-streams-file-io.scala

object TestApp extends zio.ZIOAppDefault {
  override def run = {
    val filePath = "main.csv"

    val program = for {
      // read a csv file
      lines <- ZStream
        .fromFileName(filePath, 1024)
        .via(ZPipeline.utfDecode)
        .via(ZPipeline.splitLines)
        .runCollect

      // filter data
      filtered = lines.filter(_.contains("abc"))

      // open new file
      fileChannel <- AsynchronousFileChannel.open(
        Path("main.filtered.csv"),
        StandardOpenOption.WRITE,
        StandardOpenOption.TRUNCATE_EXISTING
      )

      // truncate new file
      _ <- fileChannel.truncate(0)

      // write header
      headerBytes = s"${lines(0)}\n".getBytes
      _ <- fileChannel.writeChunk(Chunk.from(headerBytes), 0L)

      // append data
      sink = fileChannel.sink(headerBytes.length)
      _ <- ZStream
        .fromChunk(filtered)
        .intersperse("\n")
        .via(ZPipeline.utf8Encode)
        .run(sink)

    } yield ()
    program
  }
}

easier-version.scala

object TestApp extends zio.ZIOAppDefault {
  override def run = {
    val filePath    = "main.csv"
    val newFilePath = "main.filtered.csv"

    val program = for {
      // read a csv file
      lines <- Files.readAllLines(Path(filePath), Charset.defaultCharset)

      // filter data
      filtered = lines.filter(_.contains("abc"))

      headerBytes = s"${lines(0)}\n".getBytes

      // write header
      _ <- Files.writeBytes(
        Path(newFilePath),
        Chunk.from(headerBytes),
        StandardOpenOption.WRITE,
        StandardOpenOption.TRUNCATE_EXISTING
      )

      // write data
      _ <- Files.writeLines(
        Path(newFilePath),
        filtered,
        Charset.defaultCharset,
        Set(StandardOpenOption.WRITE, StandardOpenOption.APPEND)
      )

      _ <- zio.Console.printLine("DONE")
    } yield ()
    program
  }
}