li/cil/oc/server/computer/LuaStateFactory.scala

package li.cil.oc.server.computer

import java.io.File
import java.io.FileOutputStream
import java.nio.channels.Channels

import scala.collection.mutable.Map

import com.naef.jnlua.LuaState
import com.naef.jnlua.NativeSupport
import com.naef.jnlua.NativeSupport.Loader

/**
 * Factory singleton used to spawn new LuaState instances.
 *
 * This is realized as a singleton so that we only have to resolve shared
 * library references once during initialization and can then re-use the
 * already loaded ones.
 */
private[computer] object LuaStateFactory {
  // ----------------------------------------------------------------------- //
  // Initialization
  // ----------------------------------------------------------------------- //

  // Since we use native libraries we have to do some work. This includes
  // figuring out what we're running on, so that we can load the proper shared
  // libraries compiled for that system. It also means we have to unpack the
  // shared libraries somewhere so that we can load them, because we cannot
  // load them directly from a JAR.
  {
    val platform = System.getProperty("os.name").toLowerCase() match {
      case name if (name.startsWith("linux")) => "linux"
      case name if (name.startsWith("windows")) => "windows"
      case name if (name.startsWith("mac")) => "mac"
    }
    val libPath = "/assets/opencomputers/lib/" + System.getProperty("os.arch") + "/"

    val libExt = platform match {
      case "linux" => ".so"
      case "windows" => ".dll"
      case "mac" => ".dylib"
      case _ => ""
    }
    val tmpPath = {
      val path = System.getProperty("java.io.tmpdir")
      if (path.endsWith("/") || path.endsWith("\\")) path
      else path + "/"
    }

    val library = "native"
    val libraryUrl = classOf[Computer].getResource(libPath + library + libExt)
    if (libraryUrl == null) {
      throw new NotImplementedError("Unsupported platform.")
    }
    // Found file with proper extension. Create a temporary file.
    val file = new File(tmpPath + library + libExt)
    // Try to delete an old instance of the library, in case we have an update
    // and deleteOnExit fails (which it regularly does on Windows it seems).
    try {
      file.delete()
    }
    catch {
      case t: Throwable => // Ignore.
    }
    // Copy the file contents to the temporary file.
    try {
      val in = Channels.newChannel(libraryUrl.openStream())
      val out = new FileOutputStream(file).getChannel()
      out.transferFrom(in, 0, Long.MaxValue)
      in.close()
      out.close()
      file.deleteOnExit()
    }
    catch {
      // Java (or Windows?) locks the library file when opening it, so any
      // further tries to update it while another instance is still running
      // will fail. We still want to try each time, since the files may have
      // been updated.
      case t: Throwable => // Nothing.
    }

    // Remember the temporary file's location for the loader.
    val libraryPath = file.getAbsolutePath()

    // Register a custom library loader with JNLua to actually load the ones we
    // just extracted.
    NativeSupport.getInstance().setLoader(new Loader {
      def load() {
        System.load(libraryPath)
      }
    })
  }

  // ----------------------------------------------------------------------- //
  // Factory
  // ----------------------------------------------------------------------- //

  def createState(): Option[LuaState] = {
    val state = new LuaState(Integer.MAX_VALUE)
    try {
      // Load all libraries.
      state.openLib(LuaState.Library.BASE)
      state.openLib(LuaState.Library.BIT32)
      state.openLib(LuaState.Library.COROUTINE)
      state.openLib(LuaState.Library.DEBUG)
      state.openLib(LuaState.Library.ERIS)
      state.openLib(LuaState.Library.MATH)
      state.openLib(LuaState.Library.STRING)
      state.openLib(LuaState.Library.TABLE)
      state.pop(8)

      // Prepare table for os stuff.
      state.newTable()
      state.setGlobal("os")

      // Remove some other functions we don't need and are dangerous.
      state.pushNil()
      state.setGlobal("dofile")
      state.pushNil()
      state.setGlobal("loadfile")
      state.pushNil()
      state.setGlobal("module")
      state.pushNil()
      state.setGlobal("require")

      return Some(state)
    }
    catch {
      case ex: Throwable => {
        ex.printStackTrace()
        state.close()
        return None
      }
    }
  }
}