package dotty.tools
package dotc
package core

import Types._, Contexts._, Symbols._, Decorators._
import util.SimpleMap
import collection.mutable
import printing.{Printer, Showable}
import printing.Texts._
import config.Config
import config.Printers._
import collection.immutable.BitSet
import reflect.ClassTag

object OrderingConstraint {

  /** The type of `Constraint#boundsMap` */
  type ParamBounds = SimpleMap[PolyType, Array[Type]]
  
  /** The type of `Constraint#lowerMap`, `Constraint#upperMap` */
  type ParamOrdering = SimpleMap[PolyType, Array[List[PolyParam]]]
  
  /** A new constraint with given maps */
  private def newConstraint(boundsMap: ParamBounds, lowerMap: ParamOrdering, upperMap: ParamOrdering)(implicit ctx: Context) : OrderingConstraint = {
    val result = new OrderingConstraint(boundsMap, lowerMap, upperMap)
    if (Config.checkConstraintsNonCyclic) result.checkNonCyclic()
    ctx.runInfo.recordConstraintSize(result, result.boundsMap.size)
    result
  }
  
  /** A lens for updating a single entry array in one of the three constraint maps */
  abstract class ConstraintLens[T <: AnyRef: ClassTag] {
    def entries(c: OrderingConstraint, poly: PolyType): Array[T] 
    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[T])(implicit ctx: Context): OrderingConstraint
    def initial: T
    
    def apply(c: OrderingConstraint, poly: PolyType, idx: Int) = {
      val es = entries(c, poly)
      if (es == null) initial else es(idx)
    }
 
    /** The `current` constraint but with the entry for `param` updated to `entry`.
     *  `current` is used linearly. If it is different from `prev` it is
     *  known to be dead after the call. Hence it is OK to update destructively
     *  parts of `current` which are not shared by `prev`.
     */
    def update(prev: OrderingConstraint, current: OrderingConstraint, 
        poly: PolyType, idx: Int, entry: T)(implicit ctx: Context): OrderingConstraint = {
      var es = entries(current, poly)
      if (es != null && (es(idx) eq entry)) current
      else {
        val result = 
          if (es == null) {
            es = Array.fill(poly.paramNames.length)(initial)
            updateEntries(current, poly, es)
          }
          else if (es ne entries(prev, poly))
            current // can re-use existing entries array.
          else {
            es = es.clone
            updateEntries(current, poly, es)
          }
        es(idx) = entry
        result
      }
    }
    
    def update(prev: OrderingConstraint, current: OrderingConstraint, 
        param: PolyParam, entry: T)(implicit ctx: Context): OrderingConstraint =
      update(prev, current, param.binder, param.paramNum, entry)
      
    def map(prev: OrderingConstraint, current: OrderingConstraint, 
        poly: PolyType, idx: Int, f: T => T)(implicit ctx: Context): OrderingConstraint = 
     update(prev, current, poly, idx, f(apply(current, poly, idx)))

    def map(prev: OrderingConstraint, current: OrderingConstraint, 
        param: PolyParam, f: T => T)(implicit ctx: Context): OrderingConstraint = 
      map(prev, current, param.binder, param.paramNum, f)
  }

  val boundsLens = new ConstraintLens[Type] {
    def entries(c: OrderingConstraint, poly: PolyType): Array[Type] = 
      c.boundsMap(poly)
    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[Type])(implicit ctx: Context): OrderingConstraint = 
      newConstraint(c.boundsMap.updated(poly, entries), c.lowerMap, c.upperMap)
    def initial = NoType
  }
  
  val lowerLens = new ConstraintLens[List[PolyParam]] {
    def entries(c: OrderingConstraint, poly: PolyType): Array[List[PolyParam]] = 
      c.lowerMap(poly)
    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[List[PolyParam]])(implicit ctx: Context): OrderingConstraint = 
      newConstraint(c.boundsMap, c.lowerMap.updated(poly, entries), c.upperMap)
    def initial = Nil
  }

  val upperLens = new ConstraintLens[List[PolyParam]] {
    def entries(c: OrderingConstraint, poly: PolyType): Array[List[PolyParam]] = 
      c.upperMap(poly)
    def updateEntries(c: OrderingConstraint, poly: PolyType, entries: Array[List[PolyParam]])(implicit ctx: Context): OrderingConstraint = 
      newConstraint(c.boundsMap, c.lowerMap, c.upperMap.updated(poly, entries))
    def initial = Nil
  }
}

import OrderingConstraint._

/** Constraint over undetermined type parameters that keeps separate maps to 
 *  reflect parameter orderings.
 *  @param boundsMap a map from PolyType to arrays.
 *               Each array contains twice the number of entries as there a type parameters
 *               in the PolyType. The first half of the array contains the type bounds that constrain the
 *               polytype's type parameters. The second half might contain type variables that
 *               track the corresponding parameters, or is left empty (filled with nulls).
 *               An instantiated type parameter is represented by having its instance type in
 *               the corresponding array entry.
 *               
 *  @param lowerMap a map from PolyTypes to arrays. Each array entry corresponds
 *               to a parameter P of the polytype; it contains all constrained parameters
 *               Q that are known to be smaller than P, i.e. P <: Q. 
 *  @param upperMap a map from PolyTypes to arrays. Each array entry corresponds
 *               to a parameter P of the polytype; it contains all constrained parameters
 *               Q that are known to be greater than P, i.e. Q <: P. 
 */
class OrderingConstraint(private val boundsMap: ParamBounds, 
                         private val lowerMap : ParamOrdering, 
                         private val upperMap : ParamOrdering) extends Constraint {
  
  type This = OrderingConstraint
    
  
// ----------- Basic indices --------------------------------------------------
  
  /** The number of type parameters in the given entry array */
  private def paramCount(entries: Array[Type]) = entries.length >> 1

  /** The type variable corresponding to parameter numbered `n`, null if none was created */
  private def typeVar(entries: Array[Type], n: Int): Type =
    entries(paramCount(entries) + n)

  /** The `boundsMap` entry corresponding to `param` */
  def entry(param: PolyParam): Type = {
    val entries = boundsMap(param.binder)
    if (entries == null) NoType
    else entries(param.paramNum)
  }
    
// ----------- Contains tests --------------------------------------------------

  def contains(pt: PolyType): Boolean = boundsMap(pt) != null

  def contains(param: PolyParam): Boolean = {
    val entries = boundsMap(param.binder)
    entries != null && entries(param.paramNum).isInstanceOf[TypeBounds]
  }

  def contains(tvar: TypeVar): Boolean = {
    val origin = tvar.origin
    val entries = boundsMap(origin.binder)
    val pnum = origin.paramNum
    entries != null && isBounds(entries(pnum)) && (typeVar(entries, pnum) eq tvar)
  }

  private def isBounds(tp: Type) = tp.isInstanceOf[TypeBounds]
  
// ---------- Dependency handling ----------------------------------------------
    
  def lower(param: PolyParam): List[PolyParam] = lowerLens(this, param.binder, param.paramNum)
  def upper(param: PolyParam): List[PolyParam] = upperLens(this, param.binder, param.paramNum)
    
  def minLower(param: PolyParam): List[PolyParam] = {
    val all = lower(param)
    all.filterNot(p => all.exists(isLess(p, _)))
  }
  
  def minUpper(param: PolyParam): List[PolyParam] = {
    val all = upper(param)
    all.filterNot(p => all.exists(isLess(_, p)))
  }
  
  def exclusiveLower(param: PolyParam, butNot: PolyParam): List[PolyParam] =
    lower(param).filterNot(isLess(_, butNot))
    
  def exclusiveUpper(param: PolyParam, butNot: PolyParam): List[PolyParam] =
    upper(param).filterNot(isLess(butNot, _))
  
// ---------- Info related to PolyParams -------------------------------------------

  def isLess(param1: PolyParam, param2: PolyParam): Boolean =
    upper(param1).contains(param2)

  def nonParamBounds(param: PolyParam): TypeBounds = 
    entry(param).asInstanceOf[TypeBounds]
    
  def fullLowerBound(param: PolyParam)(implicit ctx: Context): Type =
    (nonParamBounds(param).lo /: minLower(param))(_ | _)

  def fullUpperBound(param: PolyParam)(implicit ctx: Context): Type = 
    (nonParamBounds(param).hi /: minUpper(param))(_ & _)
    
  def fullBounds(param: PolyParam)(implicit ctx: Context): TypeBounds =
    nonParamBounds(param).derivedTypeBounds(fullLowerBound(param), fullUpperBound(param))

  def typeVarOfParam(param: PolyParam): Type = {
    val entries = boundsMap(param.binder)
    if (entries == null) NoType
    else {
      val tvar = typeVar(entries, param.paramNum)
      if (tvar != null) tvar else NoType
    }
  }  

// ---------- Adding PolyTypes --------------------------------------------------
   
  /** The bound type `tp` without dependent parameters
   *  NoType if type consists only of dependent parameters.
   *  @param seenFromBelow   If true, `bound` is an upper bound, else a lower bound.
   */
  private def stripParams(tp: Type, paramBuf: mutable.ListBuffer[PolyParam], 
      isUpper: Boolean)(implicit ctx: Context): Type = tp match {
    case param: PolyParam if contains(param) => 
      if (!paramBuf.contains(param)) paramBuf += param
      NoType
    case tp: AndOrType if isUpper == tp.isAnd =>
      val tp1 = stripParams(tp.tp1, paramBuf, isUpper)
      val tp2 = stripParams(tp.tp2, paramBuf, isUpper)
      if (tp1.exists)
        if (tp2.exists) tp.derivedAndOrType(tp1, tp2)
        else tp1
      else tp2
    case _ =>
      tp
  } 
  
  /** The bound type `tp` without dependent parameters.
   *  A top or bottom type if type consists only of dependent parameters.
   *  @param seenFromBelow   If true, `bound` is an upper bound, else a lower bound.
   */
  private def normalizedType(tp: Type, paramBuf: mutable.ListBuffer[PolyParam], 
      isUpper: Boolean)(implicit ctx: Context): Type = 
    stripParams(tp, paramBuf, isUpper)
      .orElse(if (isUpper) defn.AnyType else defn.NothingType)
  
  def add(poly: PolyType, tvars: List[TypeVar])(implicit ctx: Context): This = {
    assert(!contains(poly))
    val nparams = poly.paramNames.length
    val entries1 = new Array[Type](nparams * 2)
    poly.paramBounds.copyToArray(entries1, 0)
    tvars.copyToArray(entries1, nparams)
    newConstraint(boundsMap.updated(poly, entries1), lowerMap, upperMap).init(poly)
  }
    
  private def init(poly: PolyType)(implicit ctx: Context): This = {
    var current = this
    val loBuf, hiBuf = new mutable.ListBuffer[PolyParam]
    var i = 0
    while (i < poly.paramNames.length) {
      val param = PolyParam(poly, i)
      val bounds = nonParamBounds(param)
      val lo = normalizedType(bounds.lo, loBuf, isUpper = false)
      val hi = normalizedType(bounds.hi, hiBuf, isUpper = true)
      current = boundsLens.update(this, current, poly, i, bounds.derivedTypeBounds(lo, hi))
      current = (current /: loBuf)(order(_, _, param))
      current = (current /: hiBuf)(order(_, param, _))
      loBuf.clear()
      hiBuf.clear()
      i += 1
    }
    if (Config.checkConstraintsNonCyclic) checkNonCyclic()
    current
  }
  
// ---------- Updates ------------------------------------------------------------
  
  /** An updated partial order matrix that incorporates `less` and also reflects that `param` relates
   *  to `p2` wrt <:< if `inOrder` is true, `>:>` otherwise.
   */
  private def order(current: This, param1: PolyParam, param2: PolyParam)(implicit ctx: Context): This =
    if (param1 == param2 || current.isLess(param1, param2)) this
    else {
      assert(contains(param1))
      assert(contains(param2))
      val newUpper = param2 :: exclusiveUpper(param2, param1)
      val newLower = param1 :: exclusiveLower(param1, param2)
      val current1 = (current /: newLower)(upperLens.map(this, _, _, newUpper ::: _))
      val current2 = (current1 /: newUpper)(lowerLens.map(this, _, _, newLower ::: _))
      current2
    }

  def addLess(param1: PolyParam, param2: PolyParam)(implicit ctx: Context): This =
    order(this, param1, param2)
      
  def updateEntry(param: PolyParam, tp: Type)(implicit ctx: Context): This =
    boundsLens.update(this, this, param, tp)
    
  def unify(p1: PolyParam, p2: PolyParam)(implicit ctx: Context): This = {
    val p1Bounds = (nonParamBounds(p1) & nonParamBounds(p2)).substParam(p2, p1)
    updateEntry(p1, p1Bounds).replace(p2, p1)
  }
  
  def narrowBound(param: PolyParam, bound: Type, isUpper: Boolean)(implicit ctx: Context): This = {
    val oldBounds @ TypeBounds(lo, hi) = nonParamBounds(param) 
    val newBounds = 
      if (isUpper) oldBounds.derivedTypeBounds(lo, hi & bound)
      else oldBounds.derivedTypeBounds(lo | bound, hi)
    updateEntry(param, newBounds)
  }

// ---------- Removals ------------------------------------------------------------

  /** Drop parameter `PolyParam(poly, n)` from `bounds`,
   *  replacing with Nothing in the lower bound and by `Any` in the upper bound.
   */
  private def dropParamIn(bounds: TypeBounds, poly: PolyType, n: Int)(implicit ctx: Context): TypeBounds = {
    def drop(tp: Type): Type = tp match {
      case tp: AndOrType =>
        val tp1 = drop(tp.tp1)
        val tp2 = drop(tp.tp2)
        if (!tp1.exists) tp2
        else if (!tp2.exists) tp1
        else tp
      case PolyParam(`poly`, `n`) => NoType
      case _ => tp
    }
    def approx(tp: Type, limit: Type): Type = {
      val tp1 = drop(tp)
      if (tp1.exists || !tp.exists) tp1 else limit
    }
    bounds.derivedTypeBounds(
        approx(bounds.lo, defn.NothingType), approx(bounds.hi, defn.AnyType))
  }

  def replace(param: PolyParam, tp: Type)(implicit ctx: Context): OrderingConstraint = {
    val replacement = tp.dealias.stripTypeVar
    if (param == replacement) this 
    else {
      assert(replacement.isValueType)
      val poly = param.binder
      val idx = param.paramNum
      def removeParam(ps: List[PolyParam]) = 
        ps.filterNot(p => p.binder.eq(poly) && p.paramNum == idx)
      def replaceParam(tp: Type, atPoly: PolyType, atIdx: Int) = tp match {
        case bounds: TypeBounds =>
          val bounds1 = tp.substParam(param, replacement).asInstanceOf[TypeBounds]
          if (bounds1 eq bounds) bounds
          else dropParamIn(bounds1, atPoly, atIdx)
        case _ => tp
      }
      var current = this
      if (isRemovable(poly, idx)) current = remove(poly) 
      else {
        current = updateEntry(param, replacement)
        lowerLens.update(this, current, poly, idx, Nil)
        upperLens.update(this, current, poly, idx, Nil)
      }
      current.foreachParam {(p, i) =>
        current = boundsLens.map(this, current, p, i, replaceParam(_, p, i))
        current = lowerLens.map(this, current, p, i, removeParam)
        current = upperLens.map(this, current, p, i, removeParam)
      }
      current
    }
  }

  def remove(pt: PolyType)(implicit ctx: Context): This = 
    newConstraint(boundsMap.remove(pt), lowerMap.remove(pt), upperMap.remove(pt))

  def isRemovable(pt: PolyType, removedParam: Int = -1): Boolean = {
    val entries = boundsMap(pt)
    var noneLeft = true
    var i = paramCount(entries)
    while (noneLeft && i > 0) {
      i -= 1
      if (i != removedParam && isBounds(entries(i))) noneLeft = false
      else typeVar(entries, i) match {
        case tv: TypeVar =>
          if (!tv.inst.exists) noneLeft = false // need to keep line around to compute instType
        case _ =>
      }
    }
    noneLeft
  }

// ---------- Exploration --------------------------------------------------------

  def domainPolys: List[PolyType] = boundsMap.keys

  def domainParams: List[PolyParam] = 
    for {
      (poly, entries) <- boundsMap.toList
      n <- 0 until paramCount(entries)
      if isBounds(entries(n))
    } yield PolyParam(poly, n)

  def forallParams(p: PolyParam => Boolean): Boolean = {
    boundsMap.foreachBinding { (poly, entries) =>
      for (i <- 0 until paramCount(entries))
        if (isBounds(entries(i)) && !p(PolyParam(poly, i))) return false
    }
    true
  }
  
  def foreachParam(p: (PolyType, Int) => Unit): Unit =
    boundsMap.foreachBinding { (poly, entries) =>
      0.until(poly.paramNames.length).foreach(p(poly, _))
    }

  def foreachTypeVar(op: TypeVar => Unit): Unit =
    boundsMap.foreachBinding { (poly, entries) =>
      for (i <- 0 until paramCount(entries)) {
        typeVar(entries, i) match {
          case tv: TypeVar if !tv.inst.exists => op(tv)
          case _ =>
        }
      }
    }

  private var myUninstVars: mutable.ArrayBuffer[TypeVar] = _

  /** The uninstantiated typevars of this constraint */
  def uninstVars: collection.Seq[TypeVar] = {
    if (myUninstVars == null) {
      myUninstVars = new mutable.ArrayBuffer[TypeVar]
      boundsMap.foreachBinding { (poly, entries) =>
        for (i <- 0 until paramCount(entries)) {
          typeVar(entries, i) match {
            case tv: TypeVar if !tv.inst.exists && isBounds(entries(i)) => myUninstVars += tv
            case _ =>
          }
        }
      }
    }
    myUninstVars
  }

// ---------- Cyclic checking -------------------------------------------

  def checkNonCyclic()(implicit ctx: Context): Unit =
    domainParams.foreach(checkNonCyclic)
  
  private def checkNonCyclic(param: PolyParam)(implicit ctx: Context): Unit =
    assert(!isLess(param, param), i"cyclic constraint involving $param in $this")
  
// ---------- toText -----------------------------------------------------

  override def toText(printer: Printer): Text = {
    def entryText(tp: Type) = tp match {
      case tp: TypeBounds => 
        tp.toText(printer)
      case _ => 
        " := " ~ tp.toText(printer)
    }
    val indent = 3
    val header: Text = "Constraint("
    val uninstVarsText = " uninstVars = " ~
      Text(uninstVars map (_.toText(printer)), ", ") ~ ";"
    val constrainedText =
      " constrained types = " ~ Text(domainPolys map (_.toText(printer)), ", ")
    val boundsText =
      " bounds = " ~ {
        val assocs =
          for (param <- domainParams)
          yield (" " * indent) ~ param.toText(printer) ~ entryText(entry(param))
        Text(assocs, "\n")
      }
    val orderingText =
      " ordering = " ~ {
        val deps =
          for {
            param <- domainParams
            ups = minUpper(param)
            if ups.nonEmpty
          }
          yield 
            (" " * indent) ~ param.toText(printer) ~ " <: " ~
              Text(ups.map(_.toText(printer)), ", ")
        Text(deps, "\n")
      }
    Text.lines(List(header, uninstVarsText, constrainedText, boundsText, orderingText, ")"))
  }
}