/* NSC -- new Scala compiler
 * Copyright 2005-2016 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala
package tools.nsc
package interpreter

import PartialFunction.cond
import scala.language.implicitConversions
import scala.beans.BeanProperty
import scala.collection.mutable
import scala.concurrent.{ExecutionContext, Future}
import scala.reflect.runtime.{universe => ru}
import scala.reflect.{ClassTag, classTag}
import scala.reflect.internal.util.{BatchSourceFile, SourceFile}
import scala.tools.nsc.io.AbstractFile
import scala.tools.nsc.typechecker.{StructuredTypeStrings, TypeStrings}
import scala.tools.nsc.util._
import ScalaClassLoader.URLClassLoader
import scala.tools.nsc.util.Exceptional.unwrap
import java.net.URL
import scala.tools.util.PathResolver

/** An interpreter for Scala code.
 *
 *  The main public entry points are compile(), interpret(), and bind().
 *  The compile() method loads a complete Scala file.  The interpret() method
 *  executes one line of Scala code at the request of the user.  The bind()
 *  method binds an object to a variable that can then be used by later
 *  interpreted code.
 *
 *  The overall approach is based on compiling the requested code and then
 *  using a Java classloader and Java reflection to run the code
 *  and access its results.
 *
 *  In more detail, a single compiler instance is used
 *  to accumulate all successfully compiled or interpreted Scala code.  To
 *  "interpret" a line of code, the compiler generates a fresh object that
 *  includes the line of code and which has public member(s) to export
 *  all variables defined by that code.  To extract the result of an
 *  interpreted line to show the user, a second "result object" is created
 *  which imports the variables exported by the above object and then
 *  exports members called "$eval" and "$print". To accommodate user expressions
 *  that read from variables or methods defined in previous statements, "import"
 *  statements are used.
 *
 *  This interpreter shares the strengths and weaknesses of using the
 *  full compiler-to-Java.  The main strength is that interpreted code
 *  behaves exactly as does compiled code, including running at full speed.
 *  The main weakness is that redefining classes and methods is not handled
 *  properly, because rebinding at the Java level is technically difficult.
 *
 *  @author Moez A. Abdel-Gawad
 *  @author Lex Spoon
 */
class IMain(initialSettings: Settings, protected val out: JPrintWriter) extends Imports with PresentationCompilation {
  imain =>

  def this(initialSettings: Settings) = this(initialSettings, IMain.defaultOut)

  object replOutput extends ReplOutput(settings.Yreploutdir) { }

  @deprecated("Use replOutput.dir instead", "2.11.0")
  def virtualDirectory = replOutput.dir
  // Used in a test case.
  def showDirectory() = replOutput.show(out)

  lazy val isClassBased: Boolean = settings.Yreplclassbased.value

  private[nsc] var printResults               = true        // whether to print result lines
  private[nsc] var totalSilence               = false       // whether to print anything
  private var _initializeComplete             = false       // compiler is initialized
  private var _isInitialized: Future[Boolean] = null        // set up initialization future
  private var bindExceptions                  = true        // whether to bind the lastException variable
  private var _executionWrapper               = ""          // code to be wrapped around all lines
  var partialInput: String                    = ""          // code accumulated in multi-line REPL input
  private var label                           = "<console>" // compilation unit name for reporting

  /** We're going to go to some trouble to initialize the compiler asynchronously.
   *  It's critical that nothing call into it until it's been initialized or we will
   *  run into unrecoverable issues, but the perceived repl startup time goes
   *  through the roof if we wait for it.  So we initialize it with a future and
   *  use a lazy val to ensure that any attempt to use the compiler object waits
   *  on the future.
   */
  private var _classLoader: util.AbstractFileClassLoader = null                              // active classloader
  private val _compiler: ReplGlobal                 = newCompiler(settings, reporter)   // our private compiler

  private var _runtimeClassLoader: URLClassLoader = null              // wrapper exposing addURL

  def compilerClasspath: Seq[java.net.URL] = (
    if (isInitializeComplete) global.classPath.asURLs
    else new PathResolver(settings).resultAsURLs  // the compiler's classpath
  )
  def settings = initialSettings
  // Run the code body with the given boolean settings flipped to true.
  def withoutWarnings[T](body: => T): T = beQuietDuring {
    val saved = settings.nowarn.value
    if (!saved)
      settings.nowarn.value = true

    try body
    finally if (!saved) settings.nowarn.value = false
  }
  // Apply a temporary label for compilation (for example, script name)
  def withLabel[A](temp: String)(body: => A): A = {
    val saved = label
    label = temp
    try body finally label = saved
  }

  // the expanded prompt but without color escapes and without leading newline, for purposes of indenting
  lazy val formatting = Formatting.forPrompt(replProps.promptText)
  lazy val reporter: ReplReporter = new ReplReporter(this)

  import formatting.indentCode
  import reporter.{ printMessage, printUntruncatedMessage }

  // This exists mostly because using the reporter too early leads to deadlock.
  private def echo(msg: String) { Console println msg }
  private def _initSources = List(new BatchSourceFile("<init>", "class $repl_$init { }"))
  private def _initialize() = {
    try {
      // if this crashes, REPL will hang its head in shame
      val run = new _compiler.Run()
      assert(run.typerPhase != NoPhase, "REPL requires a typer phase.")
      run compileSources _initSources
      _initializeComplete = true
      true
    }
    catch AbstractOrMissingHandler()
  }
  private val logScope = scala.sys.props contains "scala.repl.scope"
  private def scopelog(msg: String) = if (logScope) Console.err.println(msg)

  // argument is a thunk to execute after init is done
  def initialize(postInitSignal: => Unit) {
    synchronized {
      if (_isInitialized == null) {
        _isInitialized =
          Future(try _initialize() finally postInitSignal)(ExecutionContext.global)
      }
    }
  }
  def initializeSynchronous(): Unit = {
    if (!isInitializeComplete) {
      _initialize()
      assert(global != null, global)
    }
  }
  def isInitializeComplete = _initializeComplete

  lazy val global: Global = {
    if (!isInitializeComplete) _initialize()
    _compiler
  }

  import global._
  import definitions.{ ObjectClass, termMember, dropNullaryMethod}

  lazy val runtimeMirror = ru.runtimeMirror(classLoader)

  private def noFatal(body: => Symbol): Symbol = try body catch { case _: FatalError => NoSymbol }

  def getClassIfDefined(path: String)  = (
           noFatal(runtimeMirror staticClass path)
    orElse noFatal(rootMirror staticClass path)
  )
  def getModuleIfDefined(path: String) = (
           noFatal(runtimeMirror staticModule path)
    orElse noFatal(rootMirror staticModule path)
  )

  implicit class ReplTypeOps(tp: Type) {
    def andAlso(fn: Type => Type): Type = if (tp eq NoType) tp else fn(tp)
  }

  // TODO: If we try to make naming a lazy val, we run into big time
  // scalac unhappiness with what look like cycles.  It has not been easy to
  // reduce, but name resolution clearly takes different paths.
  object naming extends {
    val global: imain.global.type = imain.global
  } with Naming {
    // make sure we don't overwrite their unwisely named res3 etc.
    def freshUserTermName(): TermName = {
      val name = newTermName(freshUserVarName())
      if (replScope containsName name) freshUserTermName()
      else name
    }
    def isInternalTermName(name: Name) = isInternalVarName("" + name)
  }
  import naming._

  object deconstruct extends {
    val global: imain.global.type = imain.global
  } with StructuredTypeStrings

  lazy val memberHandlers = new {
    val intp: imain.type = imain
  } with MemberHandlers
  import memberHandlers._

  /** Temporarily be quiet */
  def beQuietDuring[T](body: => T): T = {
    val saved = printResults
    printResults = false
    try body
    finally printResults = saved
  }
  def beSilentDuring[T](operation: => T): T = {
    val saved = totalSilence
    totalSilence = true
    try operation
    finally totalSilence = saved
  }

  def quietRun[T](code: String) = beQuietDuring(interpret(code))

  /** takes AnyRef because it may be binding a Throwable or an Exceptional */
  private def withLastExceptionLock[T](body: => T, alt: => T): T = {
    assert(bindExceptions, "withLastExceptionLock called incorrectly.")
    bindExceptions = false

    try     beQuietDuring(body)
    catch   logAndDiscard("withLastExceptionLock", alt)
    finally bindExceptions = true
  }

  def executionWrapper = _executionWrapper
  def setExecutionWrapper(code: String) = _executionWrapper = code
  def clearExecutionWrapper() = _executionWrapper = ""

  /** interpreter settings */
  lazy val isettings = new ISettings(this)

  /** Instantiate a compiler.  Overridable. */
  protected def newCompiler(settings: Settings, reporter: reporters.Reporter): ReplGlobal = {
    settings.outputDirs setSingleOutput replOutput.dir
    settings.exposeEmptyPackage.value = true
    new Global(settings, reporter) with ReplGlobal { override def toString: String = "<global>" }
  }

  /**
   * Adds all specified jars to the compile and runtime classpaths.
   *
   * @note  Currently only supports jars, not directories.
   * @param urls The list of items to add to the compile and runtime classpaths.
   */
  def addUrlsToClassPath(urls: URL*): Unit = {
    new Run //  force some initialization
    urls.foreach(_runtimeClassLoader.addURL) // Add jars to runtime classloader
    global.extendCompilerClassPath(urls: _*) // Add jars to compile-time classpath
  }

  /** Parent classloader.  Overridable. */
  protected def parentClassLoader: ClassLoader = {
    val replClassLoader = this.getClass.getClassLoader() // might be null if we're on the boot classpath
    settings.explicitParentLoader.orElse(Option(replClassLoader)).getOrElse(ClassLoader.getSystemClassLoader)
  }

  /* A single class loader is used for all commands interpreted by this Interpreter.
     It would also be possible to create a new class loader for each command
     to interpret.  The advantages of the current approach are:

       - Expressions are only evaluated one time.  This is especially
         significant for I/O, e.g. "val x = Console.readLine"

     The main disadvantage is:

       - Objects, classes, and methods cannot be rebound.  Instead, definitions
         shadow the old ones, and old code objects refer to the old
         definitions.
  */
  def resetClassLoader() = {
    repldbg("Setting new classloader: was " + _classLoader)
    _classLoader = null
    ensureClassLoader()
  }
  final def ensureClassLoader() {
    if (_classLoader == null)
      _classLoader = makeClassLoader()
  }
  def classLoader: util.AbstractFileClassLoader = {
    ensureClassLoader()
    _classLoader
  }

  def backticked(s: String): String = (
    (s split '.').toList map {
      case "_"                               => "_"
      case s if nme.keywords(newTermName(s)) => s"`$s`"
      case s                                 => s
    } mkString "."
  )
  def readRootPath(readPath: String) = getModuleIfDefined(readPath)

  abstract class PhaseDependentOps {
    def shift[T](op: => T): T

    def path(name: => Name): String = shift(path(symbolOfName(name)))
    def path(sym: Symbol): String = backticked(shift(sym.fullName))
    def sig(sym: Symbol): String  = shift(sym.defString)
  }
  object typerOp extends PhaseDependentOps {
    def shift[T](op: => T): T = exitingTyper(op)
  }
  object flatOp extends PhaseDependentOps {
    def shift[T](op: => T): T = exitingFlatten(op)
  }

  def originalPath(name: String): String = originalPath(TermName(name))
  def originalPath(name: Name): String   = translateOriginalPath(typerOp path name)
  def originalPath(sym: Symbol): String  = translateOriginalPath(typerOp path sym)
  /** For class based repl mode we use an .INSTANCE accessor. */
  val readInstanceName = if(isClassBased) ".INSTANCE" else ""
  def translateOriginalPath(p: String): String = {
    val readName = java.util.regex.Matcher.quoteReplacement(sessionNames.read)
    p.replaceFirst(readName, readName + readInstanceName)
  }
  def flatPath(sym: Symbol): String      = flatOp shift sym.javaClassName

  def translatePath(path: String) = {
    val sym = if (path endsWith "$") symbolOfTerm(path.init) else symbolOfIdent(path)
    sym.toOption map flatPath
  }

  /** If path represents a class resource in the default package,
   *  see if the corresponding symbol has a class file that is a REPL artifact
   *  residing at a different resource path. Translate X.class to $line3/$read$$iw$$iw$X.class.
   */
  def translateSimpleResource(path: String): Option[String] = {
    if (!(path contains '/') && (path endsWith ".class")) {
      val name = path stripSuffix ".class"
      val sym = if (name endsWith "$") symbolOfTerm(name.init) else symbolOfIdent(name)
      def pathOf(s: String) = s"${s.replace('.', '/')}.class"
      sym.toOption map (s => pathOf(flatPath(s)))
    } else {
      None
    }
  }
  def translateEnclosingClass(n: String) = symbolOfTerm(n).enclClass.toOption map flatPath

  /** If unable to find a resource foo.class, try taking foo as a symbol in scope
   *  and use its java class name as a resource to load.
   *
   *  $intp.classLoader classBytes "Bippy" or $intp.classLoader getResource "Bippy.class" just work.
   */
  private class TranslatingClassLoader(parent: ClassLoader) extends util.AbstractFileClassLoader(replOutput.dir, parent) {
    override protected def findAbstractFile(name: String): AbstractFile = super.findAbstractFile(name) match {
      case null if _initializeComplete => translateSimpleResource(name) map super.findAbstractFile orNull
      case file => file
    }
  }
  private def makeClassLoader(): util.AbstractFileClassLoader =
    new TranslatingClassLoader({
      _runtimeClassLoader = new URLClassLoader(compilerClasspath, parentClassLoader)
      _runtimeClassLoader
    })

  // Set the current Java "context" class loader to this interpreter's class loader
  def setContextClassLoader() = classLoader.setAsContext()

  def allDefinedNames: List[Name]  = exitingTyper(replScope.toList.map(_.name).sorted)
  def unqualifiedIds: List[String] = allDefinedNames map (_.decode) sorted

  /** Most recent tree handled which wasn't wholly synthetic. */
  private def mostRecentlyHandledTree: Option[Tree] = {
    prevRequests.reverse foreach { req =>
      req.handlers.reverse foreach {
        case x: MemberDefHandler if x.definesValue && !isInternalTermName(x.name) => return Some(x.member)
        case _ => ()
      }
    }
    None
  }

  private def updateReplScope(sym: Symbol, isDefined: Boolean) {
    def log(what: String) {
      val mark = if (sym.isType) "t " else "v "
      val name = exitingTyper(sym.nameString)
      val info = cleanTypeAfterTyper(sym)
      val defn = sym defStringSeenAs info

      scopelog(f"[$mark$what%6s] $name%-25s $defn%s")
    }
    if (ObjectClass isSubClass sym.owner) return
    // unlink previous
    replScope lookupAll sym.name foreach { sym =>
      log("unlink")
      replScope unlink sym
    }
    val what = if (isDefined) "define" else "import"
    log(what)
    replScope enter sym
  }

  def recordRequest(req: Request) {
    if (req == null)
      return

    prevRequests += req

    // warning about serially defining companions.  It'd be easy
    // enough to just redefine them together but that may not always
    // be what people want so I'm waiting until I can do it better.
    exitingTyper {
      req.defines filterNot (s => req.defines contains s.companionSymbol) foreach { newSym =>
        val oldSym = replScope lookup newSym.name.companionName
        if (Seq(oldSym, newSym).permutations exists { case Seq(s1, s2) => s1.isClass && s2.isModule }) {
          replwarn(s"warning: previously defined $oldSym is not a companion to $newSym.")
          replwarn("Companions must be defined together; you may wish to use :paste mode for this.")
        }
      }
    }
    exitingTyper {
      req.imports foreach (sym => updateReplScope(sym, isDefined = false))
      req.defines foreach (sym => updateReplScope(sym, isDefined = true))
    }
  }

  private[nsc] def replwarn(msg: => String) {
    if (!settings.nowarnings)
      printMessage(msg)
  }

  def compileSourcesKeepingRun(sources: SourceFile*) = {
    val run = new Run()
    assert(run.typerPhase != NoPhase, "REPL requires a typer phase.")
    reporter.reset()
    run compileSources sources.toList
    (!reporter.hasErrors, run)
  }

  /** Compile an nsc SourceFile.  Returns true if there are
   *  no compilation errors, or false otherwise.
   */
  def compileSources(sources: SourceFile*): Boolean =
    compileSourcesKeepingRun(sources: _*)._1

  /** Compile a string.  Returns true if there are no
   *  compilation errors, or false otherwise.
   */
  def compileString(code: String): Boolean =
    compileSources(new BatchSourceFile("<script>", code))

  /** Build a request from the user. `trees` is `line` after being parsed.
   */
  private[interpreter] def buildRequest(line: String, trees: List[Tree]): Request = {
    executingRequest = new Request(line, trees)
    executingRequest
  }

  private def safePos(t: Tree, alt: Int): Int =
    try t.pos.start
    catch { case _: UnsupportedOperationException => alt }

  // Given an expression like 10 * 10 * 10 we receive the parent tree positioned
  // at a '*'.  So look at each subtree and find the earliest of all positions.
  private def earliestPosition(tree: Tree): Int = {
    var pos = Int.MaxValue
    tree foreach { t =>
      pos = math.min(pos, safePos(t, Int.MaxValue))
    }
    pos
  }

  private[interpreter] def requestFromLine(line: String, synthetic: Boolean = false): Either[IR.Result, Request] = {
    val content = line

    val trees: List[global.Tree] = parse(content) match {
      case parse.Incomplete(_)     => return Left(IR.Incomplete)
      case parse.Error(_)          => return Left(IR.Error)
      case parse.Success(trees) => trees
    }
    repltrace(
      trees map (t => {
        // [Eugene to Paul] previously it just said `t map ...`
        // because there was an implicit conversion from Tree to a list of Trees
        // however Martin and I have removed the conversion
        // (it was conflicting with the new reflection API),
        // so I had to rewrite this a bit
        val subs = t collect { case sub => sub }
        subs map (t0 =>
          "  " + safePos(t0, -1) + ": " + t0.shortClass + "\n"
        ) mkString ""
      }) mkString "\n"
    )
    // If the last tree is a bare expression, pinpoint where it begins using the
    // AST node position and snap the line off there.  Rewrite the code embodied
    // by the last tree as a ValDef instead, so we can access the value.
    val last = trees.lastOption.getOrElse(EmptyTree)
    last match {
      case _:Assign                        => // we don't want to include assignments
      case _:TermTree | _:Ident | _:Select => // ... but do want other unnamed terms.
        val varName  = if (synthetic) freshInternalVarName() else freshUserVarName()
        val rewrittenLine = (
          // In theory this would come out the same without the 1-specific test, but
          // it's a cushion against any more sneaky parse-tree position vs. code mismatches:
          // this way such issues will only arise on multiple-statement repl input lines,
          // which most people don't use.
          if (trees.size == 1) "val " + varName + " =\n" + content
          else {
            // The position of the last tree
            val lastpos0 = earliestPosition(last)
            // Oh boy, the parser throws away parens so "(2+2)" is mispositioned,
            // with increasingly hard to decipher positions as we move on to "() => 5",
            // (x: Int) => x + 1, and more.  So I abandon attempts to finesse and just
            // look for semicolons and newlines, which I'm sure is also buggy.
            val (raw1, raw2) = content splitAt lastpos0
            repldbg("[raw] " + raw1 + "   <--->   " + raw2)

            val adjustment = (raw1.reverse takeWhile (ch => (ch != ';') && (ch != '\n'))).size
            val lastpos = lastpos0 - adjustment

            // the source code split at the laboriously determined position.
            val (l1, l2) = content splitAt lastpos
            repldbg("[adj] " + l1 + "   <--->   " + l2)

            val prefix   = if (l1.trim == "") "" else l1 + ";\n"
            // Note to self: val source needs to have this precise structure so that
            // error messages print the user-submitted part without the "val res0 = " part.
            val combined   = prefix + "val " + varName + " =\n" + l2

            repldbg(List(
              "    line" -> line,
              " content" -> content,
              "     was" -> l2,
              "combined" -> combined) map {
                case (label, s) => label + ": '" + s + "'"
              } mkString "\n"
            )
            combined
          }
        )
        // Rewriting    "foo ; bar ; 123"
        // to           "foo ; bar ; val resXX = 123"
        requestFromLine(rewrittenLine, synthetic) match {
          case Right(req) => return Right(req withOriginalLine line)
          case x          => return x
        }
      case _ =>
    }
    Right(buildRequest(line, trees))
  }

  // dealias non-public types so we don't see protected aliases like Self
  def dealiasNonPublic(tp: Type) = tp match {
    case TypeRef(_, sym, _) if sym.isAliasType && !sym.isPublic => tp.dealias
    case _                                                      => tp
  }

  /**
   *  Interpret one line of input. All feedback, including parse errors
   *  and evaluation results, are printed via the supplied compiler's
   *  reporter. Values defined are available for future interpreted strings.
   *
   *  The return value is whether the line was interpreter successfully,
   *  e.g. that there were no parse errors.
   */
  def interpret(line: String): IR.Result = interpret(line, synthetic = false)
  def interpretSynthetic(line: String): IR.Result = interpret(line, synthetic = true)
  def interpret(line: String, synthetic: Boolean): IR.Result = {
    def loadAndRunReq(req: Request) = classLoader.asContext {
      val (result, succeeded) = req.loadAndRun

      /** To our displeasure, ConsoleReporter offers only printMessage,
       *  which tacks a newline on the end.  Since that breaks all the
       *  output checking, we have to take one off to balance.
       */
      if (succeeded) {
        if (printResults && result != "")
          printMessage(result stripSuffix "\n")
        else if (isReplDebug) // show quiet-mode activity
          printMessage(result.trim.lines map ("[quiet] " + _) mkString "\n")

        // Book-keeping.  Have to record synthetic requests too,
        // as they may have been issued for information, e.g. :type
        recordRequest(req)
        IR.Success
      }
      else {
        // don't truncate stack traces
        printUntruncatedMessage(result)
        IR.Error
      }
    }

    compile(line, synthetic) match {
      case Left(result) => result
      case Right(req)   => loadAndRunReq(req)
    }
  }

  // create a Request and compile it
  private[interpreter] def compile(line: String, synthetic: Boolean): Either[IR.Result, Request] = {
    if (global == null) Left(IR.Error)
    else requestFromLine(line, synthetic) match {
      case Right(null)                => Left(IR.Error)       // disallowed statement type
      case Right(req) if !req.compile => Left(IR.Error)       // compile error
      case ok @ Right(req)            => ok
      case err @ Left(result)         => err
    }
  }

  /** Bind a specified name to a specified value.  The name may
   *  later be used by expressions passed to interpret.
   *
   *  A fresh `ReadEvalPrint`, which defines a `line` package, is used to compile
   *  a custom `eval` object that wraps the bound value.
   *
   *  If the bound value is successfully installed, then bind the name
   *  by interpreting `val name = $line42.$eval.value`.
   *
   *  @param name      the variable name to bind
   *  @param boundType the type of the variable, as a string
   *  @param value     the object value to bind to it
   *  @return          an indication of whether the binding succeeded
   */
  def bind(name: String, boundType: String, value: Any, modifiers: List[String] = Nil): IR.Result = {
    val bindRep = new ReadEvalPrint()
    bindRep.compile(s"""
        |object ${bindRep.evalName} {
        |  var value: $boundType = _
        |  def set(x: _root_.scala.Any) = value = x.asInstanceOf[$boundType]
        |}
      """.stripMargin
    )
    bindRep.callEither("set", value) match {
      case Left(ex) =>
        repldbg("Set failed in bind(%s, %s, %s)".format(name, boundType, value))
        repldbg(util.stackTraceString(ex))
        IR.Error
      case Right(_) =>
        val mods = if (modifiers.isEmpty) "" else modifiers.mkString("", " ", " ")
        val line = s"${mods}val $name = ${ bindRep.evalPath }.value"
        repldbg(s"Interpreting: $line")
        interpret(line)
    }
  }
  def directBind(name: String, boundType: String, value: Any): IR.Result = {
    val result = bind(name, boundType, value)
    if (result == IR.Success)
      directlyBoundNames += newTermName(name)
    result
  }
  def directBind(p: NamedParam): IR.Result                                    = directBind(p.name, p.tpe, p.value)
  def directBind[T: ru.TypeTag : ClassTag](name: String, value: T): IR.Result = directBind((name, value))

  def rebind(p: NamedParam): IR.Result = {
    val name     = p.name
    val newType  = p.tpe
    val tempName = freshInternalVarName()

    quietRun("val %s = %s".format(tempName, name))
    quietRun("val %s = %s.asInstanceOf[%s]".format(name, tempName, newType))
  }
  def quietBind(p: NamedParam): IR.Result                               = beQuietDuring(bind(p))
  def bind(p: NamedParam): IR.Result                                    = bind(p.name, p.tpe, p.value)
  def bind[T: ru.TypeTag : ClassTag](name: String, value: T): IR.Result = bind((name, value))

  /** Reset this interpreter, forgetting all user-specified requests. */
  def reset() {
    clearExecutionWrapper()
    resetClassLoader()
    resetAllCreators()
    prevRequests.clear()
    resetReplScope()
    replOutput.dir.clear()
  }

  /** This instance is no longer needed, so release any resources
   *  it is using.  The reporter's output gets flushed.
   */
  def close() {
    reporter.flush()
  }

  /** Here is where we:
   *
   *  1) Read some source code, and put it in the "read" object.
   *  2) Evaluate the read object, and put the result in the "eval" object.
   *  3) Create a String for human consumption, and put it in the "print" object.
   *
   *  Read! Eval! Print! Some of that not yet centralized here.
   */
  class ReadEvalPrint(val lineId: Int) {
    def this() = this(freshLineId())

    val packageName = sessionNames.line + lineId
    val readName    = sessionNames.read
    val evalName    = sessionNames.eval
    val printName   = sessionNames.print
    val resultName  = sessionNames.result

    def bindError(t: Throwable) = {
      if (!bindExceptions) // avoid looping if already binding
        throw t

      val unwrapped = unwrap(t)

      // Example input: $line3.$read$$iw$$iw$
      val classNameRegex = (naming.lineRegex + ".*").r
      def isWrapperInit(x: StackTraceElement) = cond(x.getClassName) {
        case classNameRegex() if x.getMethodName == nme.CONSTRUCTOR.decoded => true
      }
      val stackTrace = unwrapped stackTracePrefixString (!isWrapperInit(_))

      withLastExceptionLock[String]({
        directBind[Throwable]("lastException", unwrapped)(StdReplTags.tagOfThrowable, classTag[Throwable])
        stackTrace
      }, stackTrace)
    }

    // TODO: split it out into a package object and a regular
    // object and we can do that much less wrapping.
    def packageDecl = "package " + packageName

    def pathToInstance(name: String)   = packageName + "." + name + readInstanceName
    def pathTo(name: String)   = packageName + "." + name
    def packaged(code: String) = packageDecl + "\n\n" + code

    def readPathInstance  = pathToInstance(readName)
    def readPath = pathTo(readName)
    def evalPath = pathTo(evalName)

    def call(name: String, args: Any*): AnyRef = {
      val m = evalMethod(name)
      repldbg("Invoking: " + m)
      if (args.nonEmpty)
        repldbg("  with args: " + args.mkString(", "))

      m.invoke(evalClass, args.map(_.asInstanceOf[AnyRef]): _*)
    }

    def callEither(name: String, args: Any*): Either[Throwable, AnyRef] =
      try Right(call(name, args: _*))
      catch { case ex: Throwable => Left(ex) }

    class EvalException(msg: String, cause: Throwable) extends RuntimeException(msg, cause) { }

    private def evalError(path: String, ex: Throwable) =
      throw new EvalException("Failed to load '" + path + "': " + ex.getMessage, ex)

    private def load(path: String): Class[_] = {
      try Class.forName(path, true, classLoader)
      catch { case ex: Throwable => evalError(path, unwrap(ex)) }
    }

    lazy val evalClass = load(evalPath)

    def evalEither = callEither(resultName) match {
      case Right(result)                 => Right(result)
      case Left(_: NullPointerException) => Right(null)
      case Left(e)                       => Left(unwrap(e))
    }

    def compile(source: String): Boolean = compileAndSaveRun(label, source)

    /** The innermost object inside the wrapper, found by
      * following accessPath into the outer one.
      */
    def resolvePathToSymbol(fullAccessPath: String): Symbol = {
      val accessPath = fullAccessPath.stripPrefix(readPath)
      val readRoot = readRootPath(readPath) // the outermost wrapper
      (accessPath split '.').foldLeft(readRoot: Symbol) {
        case (sym, "")    => sym
        case (sym, name)  => exitingTyper(termMember(sym, name))
      }
    }
    /** We get a bunch of repeated warnings for reasons I haven't
     *  entirely figured out yet.  For now, squash.
     */
    private def updateRecentWarnings(run: Run) {
      def loop(xs: List[(Position, String)]): List[(Position, String)] = xs match {
        case Nil                  => Nil
        case ((pos, msg)) :: rest =>
          val filtered = rest filter { case (pos0, msg0) =>
            (msg != msg0) || (pos.lineContent.trim != pos0.lineContent.trim) || {
              // same messages and same line content after whitespace removal
              // but we want to let through multiple warnings on the same line
              // from the same run.  The untrimmed line will be the same since
              // there's no whitespace indenting blowing it.
              (pos.lineContent == pos0.lineContent)
            }
          }
          ((pos, msg)) :: loop(filtered)
      }
      val warnings = loop(run.reporting.allConditionalWarnings.map{ case (pos, (msg, since@_)) => (pos, msg) })
      if (warnings.nonEmpty)
        mostRecentWarnings = warnings
    }
    private def evalMethod(name: String) = evalClass.getMethods filter (_.getName == name) match {
      case Array()       => null
      case Array(method) => method
      case xs            => sys.error("Internal error: eval object " + evalClass + ", " + xs.mkString("\n", "\n", ""))
    }
    private def compileAndSaveRun(label: String, code: String) = {
      showCodeIfDebugging(code)
      val (success, run) = compileSourcesKeepingRun(new BatchSourceFile(label, packaged(code)))
      updateRecentWarnings(run)
      success
    }
  }

  /** One line of code submitted by the user for interpretation */
  class Request(val line: String, val trees: List[Tree], generousImports: Boolean = false) {
    def defines    = defHandlers flatMap (_.definedSymbols)
    def imports    = importedSymbols
    def value      = Some(handlers.last) filter (h => h.definesValue) map (h => definedSymbols(h.definesTerm.get)) getOrElse NoSymbol
    val lineRep = new ReadEvalPrint()

    private var _originalLine: String = null
    def withOriginalLine(s: String): this.type = { _originalLine = s ; this }
    def originalLine = if (_originalLine == null) line else _originalLine

    /** handlers for each tree in this request */
    val handlers: List[MemberHandler] = trees map (memberHandlers chooseHandler _)
    val definesClass = handlers.exists {
      case _: ClassHandler => true
      case _ => false
    }

    def defHandlers = handlers collect { case x: MemberDefHandler => x }

    /** list of names used by this expression */
    val referencedNames: List[Name] = handlers flatMap (_.referencedNames)

    /** def and val names */
    def termNames = handlers flatMap (_.definesTerm)
    def typeNames = handlers flatMap (_.definesType)
    def importedSymbols = handlers flatMap {
      case x: ImportHandler => x.importedSymbols
      case _                => Nil
    }

    /** Code to import bound names from previous lines - accessPath is code to
      * append to objectName to access anything bound by request.
      */
    lazy val ComputedImports(headerPreamble, importsPreamble, importsTrailer, accessPath) =
      exitingTyper(importsCode(referencedNames.toSet, ObjectSourceCode, definesClass, generousImports))

    /** the line of code to compute */
    def toCompute = line

    /** The path of the value that contains the user code. */
    def fullAccessPath = s"${lineRep.readPathInstance}$accessPath"

    /** The path of the given member of the wrapping instance. */
    def fullPath(vname: String) = s"$fullAccessPath.`$vname`"

    /** generate the source code for the object that computes this request */
    abstract class Wrapper extends IMain.CodeAssembler[MemberHandler] {
      def path = originalPath("$intp")
      def envLines = {
        if (!isReplPower) Nil // power mode only for now
        else {
          val escapedLine = Constant(originalLine).escapedStringValue
          List(s"""def $$line = $escapedLine """, """def $trees = _root_.scala.Nil""")
        }
      }
      def preamble = s"""
        |$headerPreamble
        |${preambleHeader format lineRep.readName}
        |${envLines mkString ("  ", ";\n  ", ";\n")}
        |$importsPreamble
        |${indentCode(toCompute)}""".stripMargin
      def preambleLength = preamble.length - toCompute.length - 1

      val generate = (m: MemberHandler) => m extraCodeToEvaluate Request.this

      /** A format string with %s for $read, specifying the wrapper definition. */
      def preambleHeader: String

      /** Like preambleHeader for an import wrapper. */
      def prewrap: String = preambleHeader + "\n"

      /** Like postamble for an import wrapper. */
      def postwrap: String
    }

    class ObjectBasedWrapper extends Wrapper {
      def preambleHeader = "object %s {"

      def postamble = importsTrailer + "\n}"

      def postwrap = "}\n"
    }

    class ClassBasedWrapper extends Wrapper {
      def preambleHeader = "sealed class %s extends _root_.java.io.Serializable { "

      /** Adds an object that instantiates the outer wrapping class. */
      def postamble  = s"""
                          |$importsTrailer
                          |}
                          |object ${lineRep.readName} {
                          |   val INSTANCE = new ${lineRep.readName}();
                          |}
                          |""".stripMargin

      import nme.{ INTERPRETER_IMPORT_WRAPPER => iw }

      /** Adds a val that instantiates the wrapping class. */
      def postwrap = s"}\nval $iw = new $iw\n"
    }

    private[interpreter] lazy val ObjectSourceCode: Wrapper =
      if (isClassBased) new ClassBasedWrapper else new ObjectBasedWrapper

    private object ResultObjectSourceCode extends IMain.CodeAssembler[MemberHandler] {
      /** We only want to generate this code when the result
       *  is a value which can be referred to as-is.
       */
      val evalResult = Request.this.value match {
        case NoSymbol => ""
        case sym      => "lazy val %s = %s".format(lineRep.resultName, originalPath(sym))
      }
      // first line evaluates object to make sure constructor is run
      // initial "" so later code can uniformly be: + etc
      val preamble = """
      |object %s {
      |  %s
      |  lazy val %s: _root_.java.lang.String = %s {
      |    %s
      |    (""
      """.stripMargin.format(
        lineRep.evalName, evalResult, lineRep.printName,
        executionWrapper, fullAccessPath
      )

      val postamble = """
      |    )
      |  }
      |}
      """.stripMargin
      val generate = (m: MemberHandler) => m resultExtractionCode Request.this
    }

    /** Compile the object file.  Returns whether the compilation succeeded.
     *  If all goes well, the "types" map is computed. */
    lazy val compile: Boolean = {
      // error counting is wrong, hence interpreter may overlook failure - so we reset
      reporter.reset()

      // compile the object containing the user's code
      lineRep.compile(ObjectSourceCode(handlers)) && {
        // extract and remember types
        typeOf
        typesOfDefinedTerms

        // Assign symbols to the original trees
        // TODO - just use the new trees.
        defHandlers foreach { dh =>
          val name = dh.member.name
          definedSymbols get name foreach { sym =>
            dh.member setSymbol sym
            repldbg("Set symbol of " + name + " to " + symbolDefString(sym))
          }
        }

        // compile the result-extraction object
        val handls = if (printResults) handlers else Nil
        withoutWarnings(lineRep compile ResultObjectSourceCode(handls))
      }
    }

    lazy val resultSymbol = lineRep.resolvePathToSymbol(fullAccessPath)

    def applyToResultMember[T](name: Name, f: Symbol => T) = exitingTyper(f(resultSymbol.info.nonPrivateDecl(name)))

    /* typeOf lookup with encoding */
    def lookupTypeOf(name: Name) = typeOf.getOrElse(name, typeOf(global.encode(name.toString)))

    private def typeMap[T](f: Type => T) =
      mapFrom[Name, Name, T](termNames ++ typeNames)(x => f(cleanMemberDecl(resultSymbol, x)))

    /** Types of variables defined by this request. */
    lazy val compilerTypeOf = typeMap[Type](x => x) withDefaultValue NoType
    /** String representations of same. */
    lazy val typeOf         = typeMap[String](tp => exitingTyper(tp.toString))

    lazy val definedSymbols = (
      termNames.map(x => x -> applyToResultMember(x, x => x)) ++
      typeNames.map(x => x -> compilerTypeOf(x).typeSymbolDirect)
    ).toMap[Name, Symbol] withDefaultValue NoSymbol

    lazy val typesOfDefinedTerms = mapFrom[Name, Name, Type](termNames)(x => applyToResultMember(x, _.tpe))

    /** load and run the code using reflection */
    def loadAndRun: (String, Boolean) = {
      try   { ("" + (lineRep call sessionNames.print), true) }
      catch { case ex: Throwable => (lineRep.bindError(ex), false) }
    }

    override def toString = "Request(line=%s, %s trees)".format(line, trees.size)
  }

  override def finalize = close

  /** Returns the name of the most recent interpreter result.
   *  Mostly this exists so you can conveniently invoke methods on
   *  the previous result.
   */
  def mostRecentVar: String =
    if (mostRecentlyHandledTree.isEmpty) ""
    else "" + (mostRecentlyHandledTree.get match {
      case x: ValOrDefDef           => x.name
      case Assign(Ident(name), _)   => name
      case ModuleDef(_, name, _)    => name
      case _                        => naming.mostRecentVar
    })

  private var mostRecentWarnings: List[(global.Position, String)] = Nil
  def lastWarnings = mostRecentWarnings

  private lazy val importToGlobal  = global mkImporter ru
  private lazy val importToRuntime = ru.internal createImporter global
  private lazy val javaMirror = ru.rootMirror match {
    case x: ru.JavaMirror => x
    case _                => null
  }
  private implicit def importFromRu(sym: ru.Symbol): Symbol = importToGlobal importSymbol sym
  private implicit def importToRu(sym: Symbol): ru.Symbol   = importToRuntime importSymbol sym

  def classOfTerm(id: String): Option[JClass] = symbolOfTerm(id) match {
    case NoSymbol => None
    case sym      => Some(javaMirror runtimeClass importToRu(sym).asClass)
  }

  def typeOfTerm(id: String): Type = symbolOfTerm(id).tpe

  def valueOfTerm(id: String): Option[Any] = exitingTyper {
    def value() = {
      val sym0    = symbolOfTerm(id)
      val sym     = (importToRuntime importSymbol sym0).asTerm
      val module  = runtimeMirror.reflectModule(sym.owner.companionSymbol.asModule).instance
      val module1 = runtimeMirror.reflect(module)
      val invoker = module1.reflectField(sym)

      invoker.get
    }

    try Some(value()) catch { case _: Exception => None }
  }

  /** It's a bit of a shotgun approach, but for now we will gain in
   *  robustness. Try a symbol-producing operation at phase typer, and
   *  if that is NoSymbol, try again at phase flatten. I'll be able to
   *  lose this and run only from exitingTyper as soon as I figure out
   *  exactly where a flat name is sneaking in when calculating imports.
   */
  def tryTwice(op: => Symbol): Symbol = exitingTyper(op) orElse exitingFlatten(op)

  def symbolOfIdent(id: String): Symbol  = symbolOfType(id) orElse symbolOfTerm(id)
  def symbolOfType(id: String): Symbol   = tryTwice(replScope lookup TypeName(id))
  def symbolOfTerm(id: String): Symbol   = tryTwice(replScope lookup TermName(id))
  def symbolOfName(id: Name): Symbol     = replScope lookup id

  def runtimeClassAndTypeOfTerm(id: String): Option[(JClass, Type)] = {
    classOfTerm(id) flatMap { clazz =>
      clazz.supers find (!_.isScalaAnonymous) map { nonAnon =>
        (nonAnon, runtimeTypeOfTerm(id))
      }
    }
  }

  def runtimeTypeOfTerm(id: String): Type = {
    typeOfTerm(id) andAlso { tpe =>
      val clazz      = classOfTerm(id) getOrElse { return NoType }
      val staticSym  = tpe.typeSymbol
      val runtimeSym = getClassIfDefined(clazz.getName)

      if ((runtimeSym != NoSymbol) && (runtimeSym != staticSym) && (runtimeSym isSubClass staticSym))
        runtimeSym.info
      else NoType
    }
  }

  def cleanTypeAfterTyper(sym: => Symbol): Type = {
    exitingTyper(
      dealiasNonPublic(
        dropNullaryMethod(
          sym.tpe_*
        )
      )
    )
  }
  def cleanMemberDecl(owner: Symbol, member: Name): Type =
    cleanTypeAfterTyper(owner.info nonPrivateDecl member)

  object exprTyper extends {
    val repl: IMain.this.type = imain
  } with ExprTyper { }

  /** Parse a line into and return parsing result (error, incomplete or success with list of trees) */
  object parse {
    abstract sealed class Result { def trees: List[Tree] }
    case class Error(trees: List[Tree]) extends Result
    case class Incomplete(trees: List[Tree]) extends Result
    case class Success(trees: List[Tree]) extends Result

    def apply(line: String): Result = debugging(s"""parse("$line")""") {
      var isIncomplete = false
      def parse = withoutWarnings {
        reporter.reset()
        val trees = newUnitParser(line, label).parseStats()
        if (reporter.hasErrors) Error(trees)
        else if (isIncomplete) Incomplete(trees)
        else Success(trees)
      }
      currentRun.parsing.withIncompleteHandler((_, _) => isIncomplete = true)(parse)
    }
    // code has a named package
    def packaged(line: String): Boolean = {
      def parses = {
        reporter.reset()
        val tree = newUnitParser(line).parse()
        !reporter.hasErrors && {
          tree match { case PackageDef(Ident(id), _) => id != nme.EMPTY_PACKAGE_NAME case _ => false }
        }
      }
      beSilentDuring(parses)
    }
  }

  def symbolOfLine(code: String): Symbol =
    exprTyper.symbolOfLine(code)

  def typeOfExpression(expr: String, silent: Boolean = true): Type =
    exprTyper.typeOfExpression(expr, silent)

  protected def onlyTerms(xs: List[Name]): List[TermName] = xs collect { case x: TermName => x }
  protected def onlyTypes(xs: List[Name]): List[TypeName] = xs collect { case x: TypeName => x }

  def definedTerms      = onlyTerms(allDefinedNames) filterNot isInternalTermName
  def definedTypes      = onlyTypes(allDefinedNames)
  def definedSymbolList = prevRequestList flatMap (_.defines) filterNot (s => isInternalTermName(s.name))

  // Terms with user-given names (i.e. not res0 and not synthetic)
  def namedDefinedTerms = definedTerms filterNot (x => isUserVarName("" + x) || directlyBoundNames(x))

  private var _replScope: Scope = _
  private def resetReplScope() {
    _replScope = newScope
  }
  def replScope = {
    if (_replScope eq null)
      _replScope = newScope

    _replScope
  }

  private var executingRequest: Request = _
  private val prevRequests       = mutable.ListBuffer[Request]()
  private val directlyBoundNames = mutable.Set[Name]()

  def allHandlers     = prevRequestList flatMap (_.handlers)
  def lastRequest     = if (prevRequests.isEmpty) null else prevRequests.last
  def prevRequestList = prevRequests.toList
  def importHandlers  = allHandlers collect { case x: ImportHandler => x }

  def withoutUnwrapping(op: => Unit): Unit = {
    val saved = isettings.unwrapStrings
    isettings.unwrapStrings = false
    try op
    finally isettings.unwrapStrings = saved
  }

  def withoutTruncating[A](body: => A): A = reporter withoutTruncating body

  def symbolDefString(sym: Symbol) = {
    TypeStrings.quieter(
      exitingTyper(sym.defString),
      sym.owner.name + ".this.",
      sym.owner.fullName + "."
    )
  }

  def showCodeIfDebugging(code: String) {
    /** Secret bookcase entrance for repl debuggers: end the line
     *  with "// show" and see what's going on.
     */
    def isShow = code.lines exists (_.trim endsWith "// show")
    if (isReplDebug || isShow) {
      beSilentDuring(parse(code)) match {
        case parse.Success(ts) =>
          ts foreach { t =>
            withoutUnwrapping(echo(asCompactString(t)))
          }
        case _ =>
      }
    }
  }

  // debugging
  def debugging[T](msg: String)(res: T) = {
    repldbg(msg + " " + res)
    res
  }
}

/** Utility methods for the Interpreter. */
object IMain {
  /** Dummy identifier fragment inserted at the cursor before presentation compilation. Needed to support completion of `global.def<TAB>` */
  val DummyCursorFragment = "_CURSOR_"

  // The two name forms this is catching are the two sides of this assignment:
  //
  // $line3.$read.$iw.$iw.Bippy =
  //   $line3.$read$$iw$$iw$Bippy@4a6a00ca
  private def removeLineWrapper(s: String) = s.replaceAll("""\$line\d+[./]\$(read|eval|print)[$.]""", "")
  private def removeIWPackages(s: String)  = s.replaceAll("""\$(iw|read|eval|print)[$.]""", "")
  def stripString(s: String)               = removeIWPackages(removeLineWrapper(s))

  trait CodeAssembler[T] {
    def preamble: String
    def generate: T => String
    def postamble: String

    def apply(contributors: List[T]): String = stringFromWriter { code =>
      code println preamble
      contributors map generate foreach (code println _)
      code println postamble
    }
  }

  trait StrippingWriter {
    def isStripping: Boolean
    def stripImpl(str: String): String
    def strip(str: String): String = if (isStripping) stripImpl(str) else str
  }
  trait TruncatingWriter {
    def maxStringLength: Int
    def isTruncating: Boolean
    def truncate(str: String): String = {
      if (isTruncating && (maxStringLength != 0 && str.length > maxStringLength))
        (str take maxStringLength - 3) + "..."
      else str
    }
  }
  abstract class StrippingTruncatingWriter(out: JPrintWriter)
          extends JPrintWriter(out)
             with StrippingWriter
             with TruncatingWriter {
    self =>

    def clean(str: String): String = truncate(strip(str))
    override def write(str: String) = super.write(clean(str))
  }
  class ReplStrippingWriter(intp: IMain) extends StrippingTruncatingWriter(intp.out) {
    import intp._
    def maxStringLength    = isettings.maxPrintString
    def isStripping        = isettings.unwrapStrings
    def isTruncating       = reporter.truncationOK

    def stripImpl(str: String): String = naming.unmangle(str)
  }
  private[interpreter] def defaultSettings = new Settings()
  private[scala] def defaultOut = new NewLinePrintWriter(new ConsoleWriter, true)

  /** construct an interpreter that reports to Console */
  def apply(initialSettings: Settings = defaultSettings, out: JPrintWriter = defaultOut) = new IMain(initialSettings, out)
}

