package dotty.tools
package dotc
package typer

import core._
import ast._
import Contexts._, Types._, Flags._, Denotations._, Names._, StdNames._, NameOps._, Symbols._
import Trees._
import annotation.unchecked
import util.Positions._
import util.Stats
import Decorators._
import ErrorReporting.InfoString

object Inferencing {

  import tpd._

  /** A trait defining an `isCompatible` method. */
  trait Compatibility {

    /** Is there an implicit conversion from `tp` to `pt`? */
    def viewExists(tp: Type, pt: Type)(implicit ctx: Context): Boolean

    /** A type `tp` is compatible with a type `pt` if one of the following holds:
     *    1. `tp` is a subtype of `pt`
     *    2. `pt` is by name parameter type, and `tp` is compatible with its underlying type
     *    3. there is an implicit conversion from `tp` to `pt`.
     */
    def isCompatible(tp: Type, pt: Type)(implicit ctx: Context): Boolean = (
      (tp <:< pt)
      || (pt isRef defn.ByNameParamClass) && (tp <:< pt.typeArgs.head)
      || viewExists(tp, pt))
  }

  class SelectionProto(name: Name, proto: Type)
  extends RefinedType(WildcardType, name)(_ => proto) with ProtoType with Compatibility {
    override def viewExists(tp: Type, pt: Type)(implicit ctx: Context): Boolean = false
    override def isMatchedBy(tp1: Type)(implicit ctx: Context) = {
      def testCompatible(mbrType: Type)(implicit ctx: Context) =
        isCompatible(normalize(mbrType), /*(new WildApprox) apply (needed?)*/ proto)
      name == nme.WILDCARD || {
        val mbr = tp1.member(name)
        mbr.exists && mbr.hasAltWith(m => testCompatible(m.info)(ctx.fresh.withExploreTyperState))
      }
    }
    override def toString = "Proto" + super.toString
  }

  /** Create a selection proto-type, but only one level deep;
   *  treat constructors specially
   */
  def selectionProto(name: Name, tp: Type) =
    if (name.isConstructorName) WildcardType
    else {
      val rtp = tp match {
        case tp: ProtoType => WildcardType
        case _ => tp
      }
      new SelectionProto(name, rtp)
    }

  object AnySelectionProto extends SelectionProto(nme.WILDCARD, WildcardType)

  case class FunProto(args: List[untpd.Tree], override val resultType: Type, typer: Typer)(implicit ctx: Context) extends UncachedGroundType with ProtoType {
    private var myTypedArgs: List[Tree] = null

    def isMatchedBy(tp: Type)(implicit ctx: Context) =
      typer.isApplicableToTrees(tp, typedArgs, resultType)

    def argsAreTyped: Boolean = myTypedArgs != null

    def typedArgs: List[Tree] = {
      if (myTypedArgs == null)
        myTypedArgs = args mapconserve (typer.typed(_))
      myTypedArgs
    }
  }

  case class ViewProto(argType: Type, override val resultType: Type)(implicit ctx: Context) extends CachedGroundType with ProtoType {
    def isMatchedBy(tp: Type)(implicit ctx: Context) =
      ctx.typer.isApplicableToTypes(tp, argType :: Nil, resultType)
    override def namedPartsWith(p: NamedType => Boolean)(implicit ctx: Context): Set[NamedType] =
      argType.namedPartsWith(p) | resultType.namedPartsWith(p)
    override def computeHash = doHash(argType, resultType)
  }

  case class PolyProto(nargs: Int, override val resultType: Type) extends UncachedGroundType

  object AnyFunctionProto extends UncachedGroundType with ProtoType {
    def isMatchedBy(tp: Type)(implicit ctx: Context) = true
  }

  /** The normalized form of a type
   *   - unwraps polymorphic types, tracking their parameters in the current constraint
   *   - skips implicit parameters
   *   - converts non-dependent method types to the corresponding function types
   *   - dereferences parameterless method types
   */
  def normalize(tp: Type)(implicit ctx: Context): Type = Stats.track("normalize") {
    tp.widenSingleton match {
      case pt: PolyType => normalize(ctx.track(pt).resultType)
      case mt: MethodType if !mt.isDependent =>
        if (mt.isImplicit) mt.resultType
        else defn.FunctionType(mt.paramTypes, mt.resultType)
      case et: ExprType => et.resultType
      case _ => tp
    }
  }

  /** Is type fully defined, meaning the type does not contain wildcard types
   *  or uninstantiated type variables. As a side effect, this will minimize
   *  any uninstantiated type variables, provided that
   *   - the instance type for the variable is not Nothing or Null
   *   - the overall result of `isFullYDefined` is `true`.
   *  Variables that are succesfully minimized do not count as uninstantiated.
   */
  def isFullyDefined(tp: Type, forceIt: Boolean = false)(implicit ctx: Context): Boolean = {
    val nestedCtx = ctx.fresh.withNewTyperState
    val result = new IsFullyDefinedAccumulator(forceIt)(nestedCtx).traverse(tp)
    if (result) nestedCtx.typerState.commit()
    result
  }

  private class IsFullyDefinedAccumulator(forceIt: Boolean)(implicit ctx: Context) extends TypeAccumulator[Boolean] {
    def traverse(tp: Type): Boolean = apply(true, tp)
    def apply(x: Boolean, tp: Type) = !x || isOK(tp) && foldOver(x, tp)
    def isOK(tp: Type): Boolean = tp match {
      case _: WildcardType =>
        false
      case tvar: TypeVar if forceIt && !tvar.isInstantiated =>
        val inst = tvar.instantiate(fromBelow = true)
        println(i"forced instantiation of ${tvar.origin} = $inst")
        inst != defn.NothingType && inst != defn.NullType
      case _ =>
        true
    }
  }

  def widenForSelector(tp: Type)(implicit ctx: Context): Type = tp.widen match {
    case tp: TypeRef if tp.symbol.isAbstractOrAliasType => widenForSelector(tp.bounds.hi)
    case tp => tp
  }

  def checkBounds(args: List[Tree], poly: PolyType, pos: Position)(implicit ctx: Context): Unit = {

  }

  def checkStable(tp: Type, pos: Position)(implicit ctx: Context): Type = {
    if (!tp.isStable)
      ctx.error(i"Prefix $tp is not stable", pos)
    tp
  }

  def checkClassTypeWithStablePrefix(tp: Type, pos: Position)(implicit ctx: Context): ClassSymbol = tp.dealias match {
    case tp: TypeRef if tp.symbol.isClass =>
      checkStable(tp.prefix, pos)
      tp.symbol.asClass
    case /* _: RefinedType |*/ _: TypeVar | _: AnnotatedType =>
      checkClassTypeWithStablePrefix(tp.asInstanceOf[TypeProxy].underlying, pos)
    case _ =>
      ctx.error(i"$tp is not a class type", pos)
      defn.ObjectClass
  }

  def checkInstantiatable(cls: ClassSymbol, pos: Position): Unit = {
    ???
  }

  implicit class Infer(val ictx: Context) extends AnyVal {

    implicit private def ctx = ictx
    private def state = ctx.typerState

    /** Add all parameters in given polytype `pt` to the constraint's domain.
     *  If the constraint contains already some of these parameters in its domain,
     *  make a copy of the polytype and add the copy's type parameters instead.
     *  Return either the original polytype, or the copy, if one was made.
     */
    def track(pt: PolyType): PolyType = {
      val tracked =
        if (state.constraint contains pt) pt.copy(pt.paramNames, pt.paramBounds, pt.resultType)
        else pt
      state.constraint = state.constraint + tracked
      tracked
    }

    /** Interpolate those undetermined type variables whose position
     *  is included in the position `pos` of the current tree.
     *  If such a variable appears covariantly in type `tp` or does not appear at all,
     *  approximate it by its lower bound. Otherwise, if it appears contravariantly
     *  in type `tp` approximate it by its upper bound.
     */
    def interpolateUndetVars(tp: Type, pos: Position): Unit = Stats.track("interpolateUndetVars") {
      val vs = tp.variances(tvar =>
        (ctx.typerState.undetVars contains tvar) && (pos contains tvar.pos))
      for ((tvar, v) <- vs)
        if (v == 1) {
          println(s"interpolate covariant ${tvar.show} in ${tp.show}")
          tvar.instantiate(fromBelow = true)
        }
        else if (v == -1) {
          println(s"interpolate contrvariant ${tvar.show} in ${tp.show}")
          tvar.instantiate(fromBelow = false)
        }
      for (tvar <- ctx.typerState.undetVars if (pos contains tvar.pos) && !(vs contains tvar)) {
        println(s"interpolate non-occurring ${tvar.show} in ${tp.show}")
        tvar.instantiate(fromBelow = true)
      }
    }

    /** Instantiate undetermined type variables to that type `tp` is
     *  maximized and return None. If this is not possible, because a non-variant
     *  typevar is not uniquely determined, return that typevar in a Some.
     */
    def maximizeType(tp: Type): Option[TypeVar] = Stats.track("maximizeType") {
      val vs = tp.variances(tvar => ctx.typerState.undetVars contains tvar)
      var result: Option[TypeVar] = None
      for ((tvar, v) <- vs)
        if (v == 1) tvar.instantiate(fromBelow = false)
        else if (v == -1) tvar.instantiate(fromBelow = true)
        else {
          val bounds @ TypeBounds(lo, hi) = ctx.typerState.constraint(tvar.origin)
          if (hi <:< lo) tvar.instantiate(fromBelow = false)
          else result = Some(tvar)
        }
      result
    }

    /** Create new type variables for the parameters of a poly type.
     *  @param pos   The position of the new type variables (relevant for
     *  interpolateUndetVars
     */
    def newTypeVars(pt: PolyType, pos: Position): List[TypeVar] = {
      val state = ctx.typerState
      val tvars =
        for (n <- (0 until pt.paramNames.length).toList)
        yield new TypeVar(PolyParam(pt, n), state, pos)
      state.constraint = state.constraint.updated(pt,
        state.constraint(pt) map (_.substParams(pt, tvars)))
      tvars
    }

    def isSubTypes(actuals: List[Type], formals: List[Type])(implicit ctx: Context): Boolean = formals match {
      case formal :: formals1 =>
        actuals match {
          case actual :: actuals1 => actual <:< formal && isSubTypes(actuals1, formals1)
          case _ => false
        }
      case nil =>
        actuals.isEmpty
    }

/* not needed right now
    def formalParameters[T](mtp: MethodType, actuals: List[T])(isRepeated: T => Boolean)(implicit ctx: Context) =
      if (mtp.isVarArgs && !(actuals.nonEmpty && isRepeated(actuals.last))) {
        val leading = mtp.paramTypes.init
        val repeated = mtp.paramTypes.last.typeArgs.head
        val trailing = List.fill(actuals.length - leading.length)(repeated)
        leading ++ trailing
      }
      else mtp.paramTypes
  */
  }
}