add signature to all generated files and remove files not regenerated…

… in current run, fixes #16

src/main/scala/spray/boilerplate/BoilerplatePlugin.scala

@@ -6,34 +6,41 @@
  */
 package spray.boilerplate
 
+import java.io.FileInputStream
+
 import sbt._
 import Keys._
+import sbt.plugins.JvmPlugin
 
 object BoilerplatePlugin extends AutoPlugin {
   override def trigger: PluginTrigger = noTrigger
-  override def `requires`: Plugins = empty
+  override def `requires`: Plugins = JvmPlugin
 
   object autoImport {
     val boilerplateGenerate = taskKey[Seq[File]]("Generates boilerplate from template files")
     val boilerplateSource = settingKey[File]("Default directory containing boilerplate template sources.")
+    val boilerplateSignature = settingKey[String](
+      "Function that creates signature string to prepend to the generated file (given an input file name). " +
+        "Will be used to detect boilerplate-generated files")
   }
 
   import autoImport._
 
   override def projectSettings: Seq[Def.Setting[_]] =
-    inConfig(Compile)(rawBoilerplateSettings) ++ inConfig(Test)(rawBoilerplateSettings)
+    inConfig(Compile)(rawBoilerplateSettings) ++ inConfig(Test)(rawBoilerplateSettings) ++ Seq(
+      boilerplateSignature := "// auto-generated by sbt-boilerplate\n")
 
   private def rawBoilerplateSettings: Seq[Setting[_]] = {
     val inputFilter = "*.template"
     Seq(
       boilerplateSource := sourceDirectory.value / "boilerplate",
       watchSources in Defaults.ConfigGlobal ++= ((boilerplateSource.value ** inputFilter) --- (boilerplateSource.value ** excludeFilter.value ** inputFilter)).get,
-      boilerplateGenerate := generateFromTemplates(streams.value, boilerplateSource.value, sourceManaged.value),
+      boilerplateGenerate := generateFromTemplates(streams.value, boilerplateSignature.value, boilerplateSource.value, sourceManaged.value),
       mappings in packageSrc ++= managedSources.value pair (Path.relativeTo(sourceManaged.value) | Path.flat),
       sourceGenerators <+= boilerplateGenerate)
   }
 
-  def generateFromTemplates(streams: TaskStreams, sourceDir: File, targetDir: File): Seq[File] = {
+  def generateFromTemplates(streams: TaskStreams, signature: String, sourceDir: File, targetDir: File): Seq[File] = {
     val files = sourceDir ** "*.template"
 
     def changeExtension(f: File): File = {
@@ -49,16 +56,48 @@ object BoilerplatePlugin extends AutoPlugin {
       case (orig, target) ⇒ (orig, changeExtension(target))
     }
 
+    val newFiles = mapping.map(_._2)
+    clearTargetDir(streams, targetDir, signature, newFiles)
     mapping foreach {
       case (templateFile, target) ⇒
         if (templateFile.lastModified > target.lastModified) {
           streams.log.info("Generating '%s'" format target.getName)
           val template = IO.read(templateFile)
-          IO.write(target, Generator.generateFromTemplate(template, 22))
+          IO.write(target,
+            signature + Generator.generateFromTemplate(template, 22))
         } else
           streams.log.debug("Template '%s' older than target. Ignoring." format templateFile.getName)
     }
 
-    mapping.map(_._2)
+    newFiles
+  }
+
+  def clearTargetDir(streams: TaskStreams, targetDir: File, signature: String, newFiles: Seq[File]): Seq[File] = {
+    val fileSet = newFiles.toSet
+
+    val buffer = new Array[Byte](signature.getBytes("utf8").size)
+    def containsSignature(file: File): Boolean = {
+      val f = new FileInputStream(file)
+      try {
+        val read = f.read(buffer)
+        (read != buffer.length) || // if we haven't read the full signature assume we had read it
+          new String(buffer, "utf8") == signature
+      } finally f.close()
+    }
+
+    val toRemove =
+      targetDir.***
+        // apply filters with increasing effort
+        .filter(f ⇒ f.exists && f.isFile)
+        .filter(_.length >= signature.length)
+        .filter(!fileSet(_))
+        .filter(containsSignature)
+        .get
+
+    toRemove.foreach { f ⇒
+      streams.log.debug(s"Removing $f that was formerly created by sbt-boilerplate (but won't be created anew).")
+      f.delete
+    }
+    toRemove
   }
 }