/* NSC -- new Scala compiler
 * Copyright 2005-2014 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala.tools.nsc
package backend.jvm
package opt

import scala.tools.asm
import asm.tree._
import scala.collection.JavaConverters._
import scala.collection.{concurrent, mutable}
import scala.tools.asm.Attribute
import scala.tools.nsc.backend.jvm.BackendReporting._
import scala.tools.nsc.io.AbstractFile
import scala.tools.nsc.util.ClassFileLookup
import BytecodeUtils._
import ByteCodeRepository._
import BTypes.InternalName
import java.util.concurrent.atomic.AtomicLong

/**
 * The ByteCodeRepository provides utilities to read the bytecode of classfiles from the compilation
 * classpath. Parsed classes are cached in the `classes` map.
 *
 * @param classPath The compiler classpath where classfiles are searched and read from.
 */
class ByteCodeRepository[BT <: BTypes](val classPath: ClassFileLookup[AbstractFile], val btypes: BT) {
  import btypes._

  /**
   * ClassNodes for classes being compiled in the current compilation run.
   */
  val compilingClasses: concurrent.Map[InternalName, ClassNode] = recordPerRunCache(concurrent.TrieMap.empty)

  /**
   * Cache for parsed ClassNodes.
   * The `Long` field encodes the age of the node in the map, which allows removing old entries when
   * the map grows too large (see limitCacheSize).
   * For Java classes in mixed compilation, the map contains an error message: no ClassNode is
   * generated by the backend and also no classfile that could be parsed.
   */
  val parsedClasses: concurrent.Map[InternalName, Either[ClassNotFound, (ClassNode, Long)]] = recordPerRunCache(concurrent.TrieMap.empty)

  private val maxCacheSize = 1500
  private val targetSize   = 500

  private object lruCounter extends AtomicLong(0l) with collection.generic.Clearable {
    def clear(): Unit = { this.set(0l) }
  }
  recordPerRunCache(lruCounter)

  /**
   * Prevent the code repository from growing too large. Profiling reveals that the average size
   * of a ClassNode is about 30 kb. I observed having 17k+ classes in the cache, i.e., 500 mb.
   */
  private def limitCacheSize(): Unit = {
    if (parsedClasses.size > maxCacheSize) {
      // OK if multiple threads get here
      val minimalLRU = parsedClasses.valuesIterator.collect({
        case Right((_, lru)) => lru
      }).toList.sorted(Ordering.Long.reverse).drop(targetSize).headOption.getOrElse(Long.MaxValue)
      parsedClasses retain {
        case (_, Right((_, lru))) => lru > minimalLRU
        case _ => false
      }
    }
  }

  def add(classNode: ClassNode, source: Source) = {
    if (source == CompilationUnit) compilingClasses(classNode.name) = classNode
    else parsedClasses(classNode.name) = Right((classNode, lruCounter.incrementAndGet()))
  }

  /**
   * The class node and source for an internal name. If the class node is not yet available, it is
   * parsed from the classfile on the compile classpath.
   */
  def classNodeAndSource(internalName: InternalName): Either[ClassNotFound, (ClassNode, Source)] = {
    classNode(internalName) map (n => {
      val source = if (compilingClasses contains internalName) CompilationUnit else Classfile
      (n, source)
    })
  }

  /**
   * The class node for an internal name. If the class node is not yet available, it is parsed from
   * the classfile on the compile classpath.
   */
  def classNode(internalName: InternalName): Either[ClassNotFound, ClassNode] = {
    compilingClasses.get(internalName).map(Right(_)) getOrElse {
      val r = parsedClasses.get(internalName) match {
        case Some(l @ Left(_)) => l
        case Some(r @ Right((classNode, _))) =>
          parsedClasses(internalName) = Right((classNode, lruCounter.incrementAndGet()))
          r
        case None =>
          limitCacheSize()
          val res = parseClass(internalName).map((_, lruCounter.incrementAndGet()))
          parsedClasses(internalName) = res
          res
      }
      r.map(_._1)
    }
  }

  /**
   * The field node for a field matching `name` and `descriptor`, accessed in class `classInternalName`.
   * The declaration of the field may be in one of the superclasses.
   *
   * @return The [[FieldNode]] of the requested field and the [[InternalName]] of its declaring
   *         class, or an error message if the field could not be found
   */
  def fieldNode(classInternalName: InternalName, name: String, descriptor: String): Either[FieldNotFound, (FieldNode, InternalName)] = {
    def fieldNodeImpl(parent: InternalName): Either[FieldNotFound, (FieldNode, InternalName)] = {
      classNode(parent) match {
        case Left(e)  => Left(FieldNotFound(name, descriptor, classInternalName, Some(e)))
        case Right(c) =>
          c.fields.asScala.find(f => f.name == name && f.desc == descriptor) match {
            case Some(f) => Right((f, parent))
            case None    =>
              if (c.superName == null) Left(FieldNotFound(name, descriptor, classInternalName, None))
              else fieldNode(c.superName, name, descriptor)
          }
      }
    }
    fieldNodeImpl(classInternalName)
  }

  /**
   * The method node for a method matching `name` and `descriptor`, accessed in class `ownerInternalNameOrArrayDescriptor`.
   * The declaration of the method may be in one of the parents.
   *
   * Note that the JVM spec performs method lookup in two steps: resolution and selection.
   *
   * Method resolution, defined in jvms-5.4.3.3 and jvms-5.4.3.4, is the first step and is identical
   * for all invocation styles (virtual, interface, special, static). If C is the receiver class
   * in the invocation instruction:
   *   1 find a matching method (name and descriptor) in C
   *   2 then in C's superclasses
   *   3 then find the maximally-specific matching superinterface methods, succeed if there's a
   *     single non-abstract one. static and private methods in superinterfaces are not considered.
   *   4 then pick a random non-static, non-private superinterface method.
   *   5 then fail.
   *
   * Note that for an `invokestatic` instruction, a method reference `B.m` may resolve to `A.m`, if
   * class `B` doesn't specify a matching method `m`, but the parent `A` does.
   *
   * Selection depends on the invocation style and is defined in jvms-6.5.
   *   - invokestatic: invokes the resolved method
   *   - invokevirtual / invokeinterface: searches for an override of the resolved method starting
   *     at the dynamic receiver type. the search procedure is basically the same as in resolution,
   *     but it fails at 4 instead of picking a superinterface method at random.
   *   - invokespecial: if C is the receiver in the invocation instruction, searches for an override
   *     of the resolved method starting at
   *       - the superclass of the current class, if C is a superclass of the current class
   *       - C otherwise
   *     again, the search procedure is the same.
   *
   * In the method here we implement method *resolution*. Whether or not the returned method is
   * actually invoked at runtime depends on the invocation instruction and the class hierarchy, so
   * the users (e.g. the inliner) have to be aware of method selection.
   *
   * Note that the returned method may be abstract (ACC_ABSTRACT), native (ACC_NATIVE) or signature
   * polymorphic (methods `invoke` and `invokeExact` in class `MehtodHandles`).
   *
   * @return The [[MethodNode]] of the requested method and the [[InternalName]] of its declaring
   *         class, or an error message if the method could not be found. An error message is also
   *         returned if method resolution results in multiple default methods.
   */
  def methodNode(ownerInternalNameOrArrayDescriptor: String, name: String, descriptor: String): Either[MethodNotFound, (MethodNode, InternalName)] = {
    def findMethod(c: ClassNode): Option[MethodNode] = c.methods.asScala.find(m => m.name == name && m.desc == descriptor)

    // https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-2.html#jvms-2.9: "In Java SE 8, the only
    // signature polymorphic methods are the invoke and invokeExact methods of the class MethodHandle.
    def isSignaturePolymorphic(owner: InternalName) = owner == coreBTypes.jliMethodHandleRef.internalName && (name == "invoke" || name == "invokeExact")

    // Note: if `owner` is an interface, in the first iteration we search for a matching member in the interface itself.
    // If that fails, the recursive invocation checks in the superclass (which is Object) with `publicInstanceOnly == true`.
    // This is specified in jvms-5.4.3.4: interface method resolution only returns public, non-static methods of Object.
    def findInSuperClasses(owner: ClassNode, publicInstanceOnly: Boolean = false): Either[ClassNotFound, Option[(MethodNode, InternalName)]] = {
      findMethod(owner) match {
        case Some(m) if !publicInstanceOnly || (isPublicMethod(m) && !isStaticMethod(m)) => Right(Some((m, owner.name)))
        case None =>
          if (isSignaturePolymorphic(owner.name)) Right(Some((owner.methods.asScala.find(_.name == name).get, owner.name)))
          else if (owner.superName == null) Right(None)
          else classNode(owner.superName).flatMap(findInSuperClasses(_, isInterface(owner)))
      }
    }

    def findInInterfaces(initialOwner: ClassNode): Either[ClassNotFound, Option[(MethodNode, InternalName)]] = {
      val visited = mutable.Set.empty[InternalName]
      val found = mutable.ListBuffer.empty[(MethodNode, ClassNode)]

      def findIn(owner: ClassNode): Option[ClassNotFound] = {
        for (i <- owner.interfaces.asScala if !visited(i)) classNode(i) match {
          case Left(e) => return Some(e)
          case Right(c) =>
            visited += i
            // abstract and static methods are excluded, see jvms-5.4.3.3
            for (m <- findMethod(c) if !isPrivateMethod(m) && !isStaticMethod(m)) found += ((m, c))
            val recusionResult = findIn(c)
            if (recusionResult.isDefined) return recusionResult
        }
        None
      }

      findIn(initialOwner)

      val result =
        if (found.size <= 1) found.headOption
        else {
          val maxSpecific = found.filterNot({
            case (method, owner) =>
              isAbstractMethod(method) || {
                val ownerTp = classBTypeFromClassNode(owner)
                found exists {
                  case (other, otherOwner) =>
                    (other ne method) && {
                      val otherTp = classBTypeFromClassNode(otherOwner)
                      otherTp.isSubtypeOf(ownerTp).get
                    }
                }
              }
          })
          // (*) note that if there's no single, non-abstract, maximally-specific method, the jvm
          // method resolution (jvms-5.4.3.3) returns any of the non-private, non-static parent
          // methods at random (abstract or concrete).
          // we chose not to do this here, to prevent the inliner from potentially inlining the
          // wrong method. in other words, we guarantee that a concrete method is only returned if
          // it resolves deterministically.
          // however, there may be multiple abstract methods inherited. in this case we *do* want
          // to return a result to allow performing accessibility checks in the inliner. note that
          // for accessibility it does not matter which of these methods is return, as they are all
          // non-private (i.e., public, protected is not possible, jvms-4.1).
          // the remaining case (when there's no max-specific method, but some non-abstract one)
          // does not occur in bytecode generated by scalac or javac. we return no result in this
          // case. this may at worst prevent some optimizations from happening.
          if (maxSpecific.size == 1) maxSpecific.headOption
          else if (found.forall(p => isAbstractMethod(p._1))) found.headOption // (*)
          else None
        }
      Right(result.map(p => (p._1, p._2.name)))
    }

    // In a MethodInsnNode, the `owner` field may be an array descriptor, for example when invoking `clone`. We don't have a method node to return in this case.
    if (ownerInternalNameOrArrayDescriptor.charAt(0) == '[') {
      Left(MethodNotFound(name, descriptor, ownerInternalNameOrArrayDescriptor, None))
    } else {
      def notFound(cnf: Option[ClassNotFound]) = Left(MethodNotFound(name, descriptor, ownerInternalNameOrArrayDescriptor, cnf))
      val res: Either[ClassNotFound, Option[(MethodNode, InternalName)]] = classNode(ownerInternalNameOrArrayDescriptor).flatMap(c =>
        findInSuperClasses(c) flatMap {
          case None => findInInterfaces(c)
          case res => Right(res)
        }
      )
      res match {
        case Left(e) => notFound(Some(e))
        case Right(None) => notFound(None)
        case Right(Some(res)) => Right(res)
      }
    }
  }

  private def parseClass(internalName: InternalName): Either[ClassNotFound, ClassNode] = {
    val fullName = internalName.replace('/', '.')
    classPath.findClassFile(fullName) map { classFile =>
      val classNode = new asm.tree.ClassNode()
      val classReader = new asm.ClassReader(classFile.toByteArray)

      // Passing the InlineInfoAttributePrototype makes the ClassReader invoke the specific `read`
      // method of the InlineInfoAttribute class, instead of putting the byte array into a generic
      // Attribute.
      // We don't need frames when inlining, but we want to keep the local variable table, so we
      // don't use SKIP_DEBUG.
      classReader.accept(classNode, Array[Attribute](InlineInfoAttributePrototype), asm.ClassReader.SKIP_FRAMES)
      // SKIP_FRAMES leaves line number nodes. Remove them because they are not correct after
      // inlining.
      // TODO: we need to remove them also for classes that are not parsed from classfiles, why not simplify and do it once when inlining?
      // OR: instead of skipping line numbers for inlined code, use write a SourceDebugExtension
      // attribute that contains JSR-45 data that encodes debugging info.
      //   http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.7.11
      //   https://jcp.org/aboutJava/communityprocess/final/jsr045/index.html
      removeLineNumberNodes(classNode)
      classNode
    } match {
      case Some(node) => Right(node)
      case None       => Left(ClassNotFound(internalName, javaDefinedClasses(internalName)))
    }
  }
}

object ByteCodeRepository {
  /**
   * The source of a ClassNode in the ByteCodeRepository. Can be either [[CompilationUnit]] if the
   * class is being compiled or [[Classfile]] if the class was parsed from the compilation classpath.
   */
  sealed trait Source
  object CompilationUnit extends Source
  object Classfile extends Source
}