app/packer/PackerProcessMonitor.scala

package packer

import java.io.{InputStreamReader, BufferedReader}

import event.EventBus
import event.BakeEvent.{AmiCreated, Log, PackerProcessExited}
import models.{BakeLog, BakeId}
import org.joda.time.DateTime

import scala.annotation.tailrec
import scala.concurrent.Promise
import scala.util.control.NonFatal

object PackerProcessMonitor {

  /** Monitors the given Packer process and consumes its output stream. Sends
    * updates to the listener and completes the promise with the process's exit
    * value
    */
  def monitorProcess(
      process: Process,
      exitValuePromise: Promise[Int],
      bakeId: BakeId,
      eventBus: EventBus
  ): Unit = {
    try {
      val bufferedReader = new BufferedReader(
        new InputStreamReader(process.getInputStream)
      )

      // When this returns it means the stream has closed, which means the process has exited
      processNextLine(process, bufferedReader, bakeId, eventBus)

      process.waitFor()
      val exitValue = process.exitValue()
      eventBus.publish(PackerProcessExited(bakeId, exitValue))
      exitValuePromise.trySuccess(exitValue)
    } catch {
      case NonFatal(e) => exitValuePromise.tryFailure(e)
    }
  }

  @tailrec
  private def processNextLine(
      process: Process,
      reader: BufferedReader,
      bakeId: BakeId,
      eventBus: EventBus,
      logNumber: Int = 0
  ): Unit = {
    val line = reader.readLine()
    if (line != null) {
      var nextLogNumber = logNumber
      PackerOutputParser.parseLine(line).foreach {
        case PackerOutputParser.UiOutput(logLevel, messageParts) =>
          val bakeLog =
            BakeLog(bakeId, logNumber, DateTime.now, logLevel, messageParts)
          eventBus.publish(Log(bakeId, bakeLog))
          nextLogNumber += 1
        case PackerOutputParser.AmiCreated(amiId) =>
          eventBus.publish(AmiCreated(bakeId, amiId))
      }
      processNextLine(process, reader, bakeId, eventBus, nextLogNumber)
    }
    // if line is null it means the stream has closed, so stop recursing and return
  }

}