/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection
package immutable

import scala.collection.generic.{ CanBuildFrom, BitOperations }
import scala.collection.mutable.{ Builder, MapBuilder }
import scala.annotation.tailrec

/** Utility class for integer maps.
 *  @author David MacIver
 */
private[immutable] object IntMapUtils extends BitOperations.Int {
  def branchMask(i: Int, j: Int) = highestOneBit(i ^ j)

  def join[T](p1: Int, t1: IntMap[T], p2: Int, t2: IntMap[T]): IntMap[T] = {
    val m = branchMask(p1, p2)
    val p = mask(p1, m)
    if (zero(p1, m)) IntMap.Bin(p, m, t1, t2)
    else IntMap.Bin(p, m, t2, t1)
  }

  def bin[T](prefix: Int, mask: Int, left: IntMap[T], right: IntMap[T]): IntMap[T] = (left, right) match {
    case (left, IntMap.Nil) => left
    case (IntMap.Nil, right) => right
    case (left, right) => IntMap.Bin(prefix, mask, left, right)
  }
}

import IntMapUtils._

/** A companion object for integer maps.
 *
 *  @define Coll  `IntMap`
 *  @define mapCanBuildFromInfo
 *    The standard `CanBuildFrom` instance for `$Coll` objects.
 *    The created value is an instance of class `MapCanBuildFrom`.
 *  @since 2.7
 */
object IntMap {
  /** $mapCanBuildFromInfo */
  implicit def canBuildFrom[A, B] = new CanBuildFrom[IntMap[A], (Int, B), IntMap[B]] {
    def apply(from: IntMap[A]): Builder[(Int, B), IntMap[B]] = apply()
    def apply(): Builder[(Int, B), IntMap[B]] = new MapBuilder[Int, B, IntMap[B]](empty[B])
  }

  def empty[T] : IntMap[T]  = IntMap.Nil

  def singleton[T](key: Int, value: T): IntMap[T] = IntMap.Tip(key, value)

  def apply[T](elems: (Int, T)*): IntMap[T] =
    elems.foldLeft(empty[T])((x, y) => x.updated(y._1, y._2))

  private[immutable] case object Nil extends IntMap[Nothing] {
    // Important! Without this equals method in place, an infinite
    // loop from Map.equals => size => pattern-match-on-Nil => equals
    // develops.  Case objects and custom equality don't mix without
    // careful handling.
    override def equals(that : Any) = that match {
      case _: this.type => true
      case _: IntMap[_] => false // The only empty IntMaps are eq Nil
      case _            => super.equals(that)
    }
  }

  private[immutable] case class Tip[+T](key: Int, value: T) extends IntMap[T]{
    def withValue[S](s: S) =
      if (s.asInstanceOf[AnyRef] eq value.asInstanceOf[AnyRef]) this.asInstanceOf[IntMap.Tip[S]]
      else IntMap.Tip(key, s)
  }
  private[immutable] case class Bin[+T](prefix: Int, mask: Int, left: IntMap[T], right: IntMap[T]) extends IntMap[T] {
    def bin[S](left: IntMap[S], right: IntMap[S]): IntMap[S] = {
      if ((this.left eq left) && (this.right eq right)) this.asInstanceOf[IntMap.Bin[S]]
      else IntMap.Bin[S](prefix, mask, left, right)
    }
  }

}

import IntMap._

// Iterator over a non-empty IntMap.
private[immutable] abstract class IntMapIterator[V, T](it: IntMap[V]) extends AbstractIterator[T] {

  // Basically this uses a simple stack to emulate conversion over the tree. However
  // because we know that Ints are at least 32 bits we can have at most 32 IntMap.Bins and
  // one IntMap.Tip sitting on the tree at any point. Therefore we know the maximum stack
  // depth is 33 and
  var index = 0
  var buffer = new Array[AnyRef](33)

  def pop = {
    index -= 1
    buffer(index).asInstanceOf[IntMap[V]]
  }

  def push(x: IntMap[V]) {
    buffer(index) = x.asInstanceOf[AnyRef]
    index += 1
  }
  push(it)

  /**
   * What value do we assign to a tip?
   */
  def valueOf(tip: IntMap.Tip[V]): T

  def hasNext = index != 0
  final def next: T =
    pop match {
      case IntMap.Bin(_,_, t@IntMap.Tip(_, _), right) => {
        push(right)
        valueOf(t)
      }
      case IntMap.Bin(_, _, left, right) => {
        push(right)
        push(left)
        next
      }
      case t@IntMap.Tip(_, _) => valueOf(t)
      // This should never happen. We don't allow IntMap.Nil in subtrees of the IntMap
      // and don't return an IntMapIterator for IntMap.Nil.
      case IntMap.Nil => sys.error("Empty maps not allowed as subtrees")
    }
}

private[immutable] class IntMapEntryIterator[V](it: IntMap[V]) extends IntMapIterator[V, (Int, V)](it) {
  def valueOf(tip: IntMap.Tip[V]) = (tip.key, tip.value)
}

private[immutable] class IntMapValueIterator[V](it: IntMap[V]) extends IntMapIterator[V, V](it) {
  def valueOf(tip: IntMap.Tip[V]) = tip.value
}

private[immutable] class IntMapKeyIterator[V](it: IntMap[V]) extends IntMapIterator[V, Int](it) {
  def valueOf(tip: IntMap.Tip[V]) = tip.key
}

import IntMap._

/** Specialised immutable map structure for integer keys, based on
 *  [[http://ittc.ku.edu/~andygill/papers/IntMap98.pdf Fast Mergeable Integer Maps]]
 *  by Okasaki and Gill. Essentially a trie based on binary digits of the integers.
 *
 *  '''Note:''' This class is as of 2.8 largely superseded by HashMap.
 *
 *  @tparam T    type of the values associated with integer keys.
 *
 *  @since 2.7
 *  @define Coll `immutable.IntMap`
 *  @define coll immutable integer map
 *  @define mayNotTerminateInf
 *  @define willNotTerminateInf
 */
sealed abstract class IntMap[+T] extends AbstractMap[Int, T]
   with Map[Int, T]
   with MapLike[Int, T, IntMap[T]] {

  override def empty: IntMap[T] = IntMap.Nil

  override def toList = {
    val buffer = new scala.collection.mutable.ListBuffer[(Int, T)]
    foreach(buffer += _)
    buffer.toList
  }

  /**
   * Iterator over key, value pairs of the map in unsigned order of the keys.
   *
   * @return an iterator over pairs of integer keys and corresponding values.
   */
  def iterator: Iterator[(Int, T)] = this match {
    case IntMap.Nil => Iterator.empty
    case _ => new IntMapEntryIterator(this)
  }

  /**
   * Loops over the key, value pairs of the map in unsigned order of the keys.
   */
  override final def foreach[U](f: ((Int, T)) => U): Unit = this match {
    case IntMap.Bin(_, _, left, right) => { left.foreach(f); right.foreach(f) }
    case IntMap.Tip(key, value) => f((key, value))
    case IntMap.Nil =>
  }

  override def keysIterator: Iterator[Int] = this match {
    case IntMap.Nil => Iterator.empty
    case _ => new IntMapKeyIterator(this)
  }

  /**
   * Loop over the keys of the map. The same as `keys.foreach(f)`, but may
   * be more efficient.
   *
   * @param f The loop body
   */
  final def foreachKey(f: Int => Unit): Unit = this match {
    case IntMap.Bin(_, _, left, right) => { left.foreachKey(f); right.foreachKey(f) }
    case IntMap.Tip(key, _) => f(key)
    case IntMap.Nil =>
  }

  override def valuesIterator: Iterator[T] = this match {
    case IntMap.Nil => Iterator.empty
    case _ => new IntMapValueIterator(this)
  }

  /**
   * Loop over the values of the map. The same as `values.foreach(f)`, but may
   * be more efficient.
   *
   * @param f The loop body
   */
  final def foreachValue(f: T => Unit): Unit = this match {
    case IntMap.Bin(_, _, left, right) => { left.foreachValue(f); right.foreachValue(f) }
    case IntMap.Tip(_, value) => f(value)
    case IntMap.Nil =>
  }

  override def stringPrefix = "IntMap"

  override def isEmpty = this == IntMap.Nil

  override def filter(f: ((Int, T)) => Boolean): IntMap[T] = this match {
    case IntMap.Bin(prefix, mask, left, right) => {
      val (newleft, newright) = (left.filter(f), right.filter(f))
      if ((left eq newleft) && (right eq newright)) this
      else bin(prefix, mask, newleft, newright)
    }
    case IntMap.Tip(key, value) =>
      if (f((key, value))) this
      else IntMap.Nil
    case IntMap.Nil => IntMap.Nil
  }

  def transform[S](f: (Int, T) => S): IntMap[S] = this match {
    case b@IntMap.Bin(prefix, mask, left, right) => b.bin(left.transform(f), right.transform(f))
    case t@IntMap.Tip(key, value) => t.withValue(f(key, value))
    case IntMap.Nil => IntMap.Nil
  }

  final override def size: Int = this match {
    case IntMap.Nil => 0
    case IntMap.Tip(_, _) => 1
    case IntMap.Bin(_, _, left, right) => left.size + right.size
  }

  final def get(key: Int): Option[T] = this match {
    case IntMap.Bin(prefix, mask, left, right) => if (zero(key, mask)) left.get(key) else right.get(key)
    case IntMap.Tip(key2, value) => if (key == key2) Some(value) else None
    case IntMap.Nil => None
  }

  final override def getOrElse[S >: T](key: Int, default: => S): S = this match {
    case IntMap.Nil => default
    case IntMap.Tip(key2, value) => if (key == key2) value else default
    case IntMap.Bin(prefix, mask, left, right) =>
      if (zero(key, mask)) left.getOrElse(key, default) else right.getOrElse(key, default)
  }

  final override def apply(key: Int): T = this match {
    case IntMap.Bin(prefix, mask, left, right) => if (zero(key, mask)) left(key) else right(key)
    case IntMap.Tip(key2, value) => if (key == key2) value else sys.error("Key not found")
    case IntMap.Nil => sys.error("key not found")
  }

  def + [S >: T] (kv: (Int, S)): IntMap[S] = updated(kv._1, kv._2)

  override def updated[S >: T](key: Int, value: S): IntMap[S] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      if (!hasMatch(key, prefix, mask)) join(key, IntMap.Tip(key, value), prefix, this)
      else if (zero(key, mask)) IntMap.Bin(prefix, mask, left.updated(key, value), right)
      else IntMap.Bin(prefix, mask, left, right.updated(key, value))
    case IntMap.Tip(key2, value2) =>
      if (key == key2) IntMap.Tip(key, value)
      else join(key, IntMap.Tip(key, value), key2, this)
    case IntMap.Nil => IntMap.Tip(key, value)
  }

  /**
   * Updates the map, using the provided function to resolve conflicts if the key is already present.
   *
   * Equivalent to:
   * {{{
   *   this.get(key) match {
   *     case None => this.update(key, value)
   *     case Some(oldvalue) => this.update(key, f(oldvalue, value)
   *   }
   * }}}
   *
   * @tparam S     The supertype of values in this `LongMap`.
   * @param key    The key to update
   * @param value  The value to use if there is no conflict
   * @param f      The function used to resolve conflicts.
   * @return       The updated map.
   */
  def updateWith[S >: T](key: Int, value: S, f: (T, S) => S): IntMap[S] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      if (!hasMatch(key, prefix, mask)) join(key, IntMap.Tip(key, value), prefix, this)
      else if (zero(key, mask)) IntMap.Bin(prefix, mask, left.updateWith(key, value, f), right)
      else IntMap.Bin(prefix, mask, left, right.updateWith(key, value, f))
    case IntMap.Tip(key2, value2) =>
      if (key == key2) IntMap.Tip(key, f(value2, value))
      else join(key, IntMap.Tip(key, value), key2, this)
    case IntMap.Nil => IntMap.Tip(key, value)
  }

  def - (key: Int): IntMap[T] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      if (!hasMatch(key, prefix, mask)) this
      else if (zero(key, mask)) bin(prefix, mask, left - key, right)
      else bin(prefix, mask, left, right - key)
    case IntMap.Tip(key2, _) =>
      if (key == key2) IntMap.Nil
      else this
    case IntMap.Nil => IntMap.Nil
  }

  /**
   * A combined transform and filter function. Returns an `IntMap` such that
   * for each `(key, value)` mapping in this map, if `f(key, value) == None`
   * the map contains no mapping for key, and if `f(key, value)`.
   *
   * @tparam S  The type of the values in the resulting `LongMap`.
   * @param f   The transforming function.
   * @return    The modified map.
   */
  def modifyOrRemove[S](f: (Int, T) => Option[S]): IntMap[S] = this match {
    case IntMap.Bin(prefix, mask, left, right) =>
      val newleft = left.modifyOrRemove(f)
      val newright = right.modifyOrRemove(f)
      if ((left eq newleft) && (right eq newright)) this.asInstanceOf[IntMap[S]]
      else bin(prefix, mask, newleft, newright)
    case IntMap.Tip(key, value) => f(key, value) match {
      case None =>
        IntMap.Nil
      case Some(value2) =>
        //hack to preserve sharing
        if (value.asInstanceOf[AnyRef] eq value2.asInstanceOf[AnyRef]) this.asInstanceOf[IntMap[S]]
        else IntMap.Tip(key, value2)
      }
    case IntMap.Nil =>
      IntMap.Nil
  }

  /**
   * Forms a union map with that map, using the combining function to resolve conflicts.
   *
   * @tparam S      The type of values in `that`, a supertype of values in `this`.
   * @param that    The map to form a union with.
   * @param f       The function used to resolve conflicts between two mappings.
   * @return        Union of `this` and `that`, with identical key conflicts resolved using the function `f`.
   */
  def unionWith[S >: T](that: IntMap[S], f: (Int, S, S) => S): IntMap[S] = (this, that) match{
    case (IntMap.Bin(p1, m1, l1, r1), that@(IntMap.Bin(p2, m2, l2, r2))) =>
      if (shorter(m1, m2)) {
        if (!hasMatch(p2, p1, m1)) join[S](p1, this, p2, that) // TODO: remove [S] when scala/bug#5548 is fixed
        else if (zero(p2, m1)) IntMap.Bin(p1, m1, l1.unionWith(that, f), r1)
        else IntMap.Bin(p1, m1, l1, r1.unionWith(that, f))
      } else if (shorter(m2, m1)){
        if (!hasMatch(p1, p2, m2)) join[S](p1, this, p2, that) // TODO: remove [S] when scala/bug#5548 is fixed
        else if (zero(p1, m2)) IntMap.Bin(p2, m2, this.unionWith(l2, f), r2)
        else IntMap.Bin(p2, m2, l2, this.unionWith(r2, f))
      }
      else {
        if (p1 == p2) IntMap.Bin(p1, m1, l1.unionWith(l2,f), r1.unionWith(r2, f))
        else join[S](p1, this, p2, that) // TODO: remove [S] when scala/bug#5548 is fixed
      }
    case (IntMap.Tip(key, value), x) => x.updateWith[S](key, value, (x, y) => f(key, y, x))
    case (x, IntMap.Tip(key, value)) => x.updateWith[S](key, value, (x, y) => f(key, x, y))
    case (IntMap.Nil, x) => x
    case (x, IntMap.Nil) => x
  }

  /**
   * Forms the intersection of these two maps with a combining function. The
   * resulting map is a map that has only keys present in both maps and has
   * values produced from the original mappings by combining them with `f`.
   *
   * @tparam S      The type of values in `that`.
   * @tparam R      The type of values in the resulting `LongMap`.
   * @param that    The map to intersect with.
   * @param f       The combining function.
   * @return        Intersection of `this` and `that`, with values for identical keys produced by function `f`.
   */
  def intersectionWith[S, R](that: IntMap[S], f: (Int, T, S) => R): IntMap[R] = (this, that) match {
    case (IntMap.Bin(p1, m1, l1, r1), that@IntMap.Bin(p2, m2, l2, r2)) =>
      if (shorter(m1, m2)) {
        if (!hasMatch(p2, p1, m1)) IntMap.Nil
        else if (zero(p2, m1)) l1.intersectionWith(that, f)
        else r1.intersectionWith(that, f)
      } else if (m1 == m2) bin(p1, m1, l1.intersectionWith(l2, f), r1.intersectionWith(r2, f))
        else {
        if (!hasMatch(p1, p2, m2)) IntMap.Nil
        else if (zero(p1, m2)) this.intersectionWith(l2, f)
        else this.intersectionWith(r2, f)
      }
    case (IntMap.Tip(key, value), that) => that.get(key) match {
      case None => IntMap.Nil
      case Some(value2) => IntMap.Tip(key, f(key, value, value2))
    }
    case (_, IntMap.Tip(key, value)) => this.get(key) match {
      case None => IntMap.Nil
      case Some(value2) => IntMap.Tip(key, f(key, value2, value))
    }
    case (_, _) => IntMap.Nil
  }

  /**
   * Left biased intersection. Returns the map that has all the same mappings
   * as this but only for keys which are present in the other map.
   *
   * @tparam R      The type of values in `that`.
   * @param that    The map to intersect with.
   * @return        A map with all the keys both in `this` and `that`, mapped to corresponding values from `this`.
   */
  def intersection[R](that: IntMap[R]): IntMap[T] =
    this.intersectionWith(that, (key: Int, value: T, value2: R) => value)

  def ++[S >: T](that: IntMap[S]) =
    this.unionWith[S](that, (key, x, y) => y)

  /**
   * The entry with the lowest key value considered in unsigned order.
   */
  @tailrec
  final def firstKey: Int = this match {
    case Bin(_, _, l, r) => l.firstKey
    case Tip(k, v) => k
    case IntMap.Nil => sys.error("Empty set")
  }

  /**
   * The entry with the highest key value considered in unsigned order.
   */
  @tailrec
  final def lastKey: Int = this match {
    case Bin(_, _, l, r) => r.lastKey
    case Tip(k, v) => k
    case IntMap.Nil => sys.error("Empty set")
  }
}
