sbt/project/SbtLauncherPlugin.scala

import sbt._
import Keys._


object SbtLauncherPlugin extends AutoPlugin {
  override def requires = plugins.IvyPlugin

  object autoImport {
    val SbtLaunchConfiguration = config("sbt-launch")
    val sbtLaunchJar = taskKey[File]("constructs an sbt-launch.jar for this version of sbt.")
    val rawSbtLaunchJar = taskKey[File]("The released version of the sbt-launcher we use to bundle this application.")
  }
  import autoImport._

  override def projectConfigurations: Seq[Configuration] = Seq(SbtLaunchConfiguration)
  override def projectSettings: Seq[Setting[_]] = Seq(
    libraryDependencies += Dependencies.rawLauncher % SbtLaunchConfiguration.name,
    rawSbtLaunchJar := {
      Classpaths.managedJars(SbtLaunchConfiguration, Set("jar"), update.value).headOption match {
        case Some(jar) => jar.data
        case None => sys.error(s"Could not resolve sbt launcher!, dependencies := ${libraryDependencies.value}")
      }
    },
    sbtLaunchJar := {
      val propFiles = (resources in Compile).value
      val propFileLocations =
         for(file <- propFiles; if file.getName != "resources") yield {
           if(file.getName == "sbt.boot.properties") "sbt/sbt.boot.properties" -> file
           else file.getName -> file
         }
      // TODO - We need to inject the appropriate boot.properties file for this version of sbt.
      rebundle(rawSbtLaunchJar.value, propFileLocations.toMap, target.value / "sbt-launch.jar")
    }
  )



  def rebundle(jar: File, overrides: Map[String, File], target: File): File = {
    // TODO - Check if we should rebuild the jar or not....
    IO.withTemporaryDirectory { dir =>
      IO.unzip(jar, dir)
      IO.copy(overrides.map({ case (n, f) => (f, dir / n)}), overwrite = true)
      // TODO - is the ok for creating a jar?
      IO.zip((dir.*** --- dir) pair relativeTo(dir), target)
    }
    target
  }

}