/* NSC -- new Scala compiler
 * Copyright 2005-2010 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala.tools.nsc
package typechecker

import symtab.Flags._

/*
 *  @author  Martin Odersky
 *  @version 1.0
 */
trait Unapplies extends ast.TreeDSL
{
  self: Analyzer =>

  import global._
  import definitions._
  import CODE.{ CASE => _, _ }
  
  private def isVarargs(vd: ValDef) = treeInfo isRepeatedParamType vd.tpt
  private def isByName(vd: ValDef)  = treeInfo isByNameParamType vd.tpt
  private def toIdent(x: DefTree)   = Ident(x.name) setPos x.pos.focus

  /** returns type list for return type of the extraction */
  def unapplyTypeList(ufn: Symbol, ufntpe: Type) = {
    assert(ufn.isMethod)
    //Console.println("utl "+ufntpe+" "+ufntpe.typeSymbol)
    ufn.name match {
      case nme.unapply    => unapplyTypeListFromReturnType(ufntpe)
      case nme.unapplySeq => unapplyTypeListFromReturnTypeSeq(ufntpe)
      case _              => throw new TypeError(ufn+" is not an unapply or unapplySeq")
    }
  }
  /** (the inverse of unapplyReturnTypeSeq)
   *  for type Boolean, returns Nil
   *  for type Option[T] or Some[T]:
   *   - returns T0...Tn if n>0 and T <: Product[T0...Tn]]
   *   - returns T otherwise
   */
  def unapplyTypeListFromReturnType(tp1: Type): List[Type] = {
    val tp = unapplyUnwrap(tp1)    
    tp.typeSymbol match {                             // unapplySeqResultToMethodSig
      case BooleanClass             => Nil
      case OptionClass | SomeClass  =>
        val prod = tp.typeArgs.head
        getProductArgs(prod) match {
          case Some(xs) if xs.size > 1  => xs         // n > 1
          case _                        => List(prod) // special n == 0 ||  n == 1
        }
      case _                        =>
        throw new TypeError("result type "+tp+" of unapply not in {Boolean, Option[_], Some[_]}")
    }
  }

  /** let type be the result type of the (possibly polymorphic) unapply method
   *  for type Option[T] or Some[T] 
   *  -returns T0...Tn-1,Tn* if n>0 and T <: Product[T0...Tn-1,Seq[Tn]]], 
   *  -returns R* if T = Seq[R]
   */
  def unapplyTypeListFromReturnTypeSeq(tp1: Type): List[Type] = {
    val tp = unapplyUnwrap(tp1)
    tp.typeSymbol match {
      case OptionClass | SomeClass  =>
        val ts = unapplyTypeListFromReturnType(tp1)
        val last1 = (ts.last baseType SeqClass) match {
          case TypeRef(pre, seqClass, args) => typeRef(pre, RepeatedParamClass, args) // XXX seqClass or SeqClass?
          case _                            => throw new TypeError("last not seq")
        }
        ts.init ::: List(last1)
      case _                        =>
        throw new TypeError("result type "+tp+" of unapply not in {Option[_], Some[_]}")
    }
  }

  /** returns type of the unapply method returning T_0...T_n
   *  for n == 0, boolean
   *  for n == 1, Some[T0]
   *  else Some[Product[Ti]]
   */
  def unapplyReturnTypeExpected(argsLength: Int) = argsLength match {
    case 0 => BooleanClass.tpe
    case 1 => optionType(WildcardType)
    case n => optionType(productType((List fill n)(WildcardType)))
  }

  /** returns unapply or unapplySeq if available */
  def unapplyMember(tp: Type): Symbol = (tp member nme.unapply) match {
    case NoSymbol => tp member nme.unapplySeq
    case unapp    => unapp
  }
  /** returns unapply member's parameter type. */
  def unapplyParameterType(extractor: Symbol) = {
    val ps = extractor.tpe.params
    if (ps.length == 1) ps.head.tpe.typeSymbol
    else NoSymbol
  }

  def copyUntyped[T <: Tree](tree: T): T =
    returning[T](tree.duplicate)(UnTyper traverse _)

  def copyUntypedInvariant(td: TypeDef): TypeDef = {
    val copy = treeCopy.TypeDef(td, td.mods &~ (COVARIANT | CONTRAVARIANT), td.name, td.tparams, td.rhs)
    
    returning[TypeDef](copy.duplicate)(UnTyper traverse _)
  }

  private def classType(cdef: ClassDef, tparams: List[TypeDef]): Tree = {
    val tycon = REF(cdef.symbol)
    if (tparams.isEmpty) tycon else AppliedTypeTree(tycon, tparams map toIdent)
  }

  private def constrParamss(cdef: ClassDef): List[List[ValDef]] = {
    val DefDef(_, _, _, vparamss, _, _) = treeInfo firstConstructor cdef.impl.body
    vparamss map (_ map copyUntyped[ValDef])
  }

  /** The return value of an unapply method of a case class C[Ts]
   *  @param param  The name of the parameter of the unapply method, assumed to be of type C[Ts]
   *  @param caseclazz  The case class C[Ts]
   */
  private def caseClassUnapplyReturnValue(param: Name, caseclazz: Symbol) = {
    def caseFieldAccessorValue(selector: Symbol): Tree = Ident(param) DOT selector
    
    caseclazz.caseFieldAccessors match {
      case Nil      => TRUE
      case xs       => SOME(xs map caseFieldAccessorValue: _*)
    }
  }

  /** The module corresponding to a case class; without any member definitions
   */
  def caseModuleDef(cdef: ClassDef): ModuleDef = {
    // > MaxFunctionArity is caught in Namers, but for nice error reporting instead of
    // an abrupt crash we trim the list here.
    def primaries      = constrParamss(cdef).head take MaxFunctionArity map (_.tpt)
    def inheritFromFun = !cdef.mods.isAbstract && cdef.tparams.isEmpty && constrParamss(cdef).length == 1
    def createFun      = gen.scalaFunctionConstr(primaries, toIdent(cdef), abstractFun = true)
    def parents        = if (inheritFromFun) List(createFun) else Nil
        
    companionModuleDef(cdef, parents)
  }

  def companionModuleDef(cdef: ClassDef, parents: List[Tree] = Nil): ModuleDef = atPos(cdef.pos.focus) {
    val allParents = parents ::: List( gen.scalaScalaObjectConstr)
    ModuleDef(
      Modifiers(cdef.mods.flags & AccessFlags | SYNTHETIC, cdef.mods.privateWithin),
      cdef.name.toTermName,
      Template(allParents, emptyValDef, NoMods, Nil, List(Nil), Nil, cdef.impl.pos.focus))
  }

  private val caseMods = Modifiers(SYNTHETIC | CASE)
  
  /** The apply method corresponding to a case class
   */
  def caseModuleApplyMeth(cdef: ClassDef): DefDef = {
    val tparams   = cdef.tparams map copyUntypedInvariant
    val cparamss  = constrParamss(cdef)
    atPos(cdef.pos.focus)(
      DefDef(caseMods, nme.apply, tparams, cparamss, classType(cdef, tparams),
        New(classType(cdef, tparams), cparamss map (_ map gen.paramToArg)))
    )
  }

  /** The unapply method corresponding to a case class
   */
  def caseModuleUnapplyMeth(cdef: ClassDef): DefDef = {
    val tparams   = cdef.tparams map copyUntypedInvariant
    val paramName = newTermName("x$0")
    val method    = constrParamss(cdef) match {
      case xs :: _ if !xs.isEmpty && isVarargs(xs.last) => nme.unapplySeq
      case _                                            => nme.unapply
    }
    val cparams   = List(ValDef(Modifiers(PARAM | SYNTHETIC), paramName, classType(cdef, tparams), EmptyTree))
    val ifNull    = if (constrParamss(cdef).head.size == 0) FALSE else REF(NoneModule)
    val body      = nullSafe({ case Ident(x) => caseClassUnapplyReturnValue(x, cdef.symbol) }, ifNull)(Ident(paramName))

    atPos(cdef.pos.focus)(
      DefDef(caseMods, method, tparams, List(cparams), TypeTree(), body)
    )
  }

  def caseClassCopyMeth(cdef: ClassDef): Option[DefDef] = {    
    def isDisallowed(vd: ValDef) = isVarargs(vd) || isByName(vd)
    val cparamss  = constrParamss(cdef)
    val flat      = cparamss flatten
    
    if (flat.isEmpty || (cdef.symbol hasFlag ABSTRACT) || (flat exists isDisallowed)) None
    else {
      val tparams = cdef.tparams map copyUntypedInvariant
      // the parameter types have to be exactly the same as the constructor's parameter types; so it's
      // not good enough to just duplicated the (untyped) tpt tree; the parameter types are removed here
      // and re-added in ``finishWith'' in the namer.
      def paramWithDefault(vd: ValDef) =
        treeCopy.ValDef(vd, vd.mods | DEFAULTPARAM, vd.name, atPos(vd.pos.focus)(TypeTree() setOriginal vd.tpt), toIdent(vd))
      
      val paramss   = cparamss map (_ map paramWithDefault)
      val classTpe  = classType(cdef, tparams)
      
      Some(atPos(cdef.pos.focus)(
        DefDef(Modifiers(SYNTHETIC), nme.copy, tparams, paramss, classTpe,
          New(classTpe, paramss map (_ map toIdent)))
      ))
    }
  }
}
