package dotty.tools.dotc.util

import collection.mutable.ListBuffer

abstract class SimpleMap[K <: AnyRef, +V >: Null <: AnyRef] extends (K => V) {
  def size: Int
  def apply(k: K): V
  def remove(k: K): SimpleMap[K, V]
  def updated[V1 >: V <: AnyRef](k: K, v: V1): SimpleMap[K, V1]
  def contains(k: K): Boolean = apply(k) != null
  def mapValuesNow[V1 >: V <: AnyRef](f: (K, V1) => V1): SimpleMap[K, V1]
  def foreachBinding(f: (K, V) => Unit): Unit
  def map2[T](f: (K, V) => T): List[T] = {
    val buf = new ListBuffer[T]
    foreachBinding((k, v) => buf += f(k, v))
    buf.toList
  }
  def keys: List[K] = map2((k, v) => k)
  def toList: List[(K, V)] = map2((k, v) => (k, v))
  override def toString = {
    def assocToString(key: K, value: V) = s"$key -> $value"
    map2(assocToString) mkString ("(", ", ", ")")
  }
}

object SimpleMap {

  private val CompactifyThreshold = 4

  private object myEmpty extends SimpleMap[AnyRef, Null] {
    def size = 0
    def apply(k: AnyRef) = null
    def remove(k: AnyRef) = this
    def updated[V1 >: Null <: AnyRef](k: AnyRef, v: V1) = new Map1(k, v)
    def mapValuesNow[V1 >: Null <: AnyRef](f: (AnyRef, V1) => V1) = this
    def foreachBinding(f: (AnyRef, Null) => Unit) = ()
  }

  def Empty[K <: AnyRef] = myEmpty.asInstanceOf[SimpleMap[K, Null]]

  class Map1[K <: AnyRef, +V >: Null <: AnyRef] (k1: K, v1: V) extends SimpleMap[K, V] {
    def size = 1
    def apply(k: K) =
      if (k == k1) v1
      else null
    def remove(k: K) =
      if (k == k1) Empty.asInstanceOf[SimpleMap[K, V]]
      else this
    def updated[V1 >: V <: AnyRef](k: K, v: V1) =
      if (k == k1) new Map1(k, v)
      else new Map2(k1, v1, k, v)
    def mapValuesNow[V1 >: V <: AnyRef](f: (K, V1) => V1) = {
      val w1 = f(k1, v1)
      if (v1 eq w1) this else new Map1(k1, w1)
    }
    def foreachBinding(f: (K, V) => Unit) = f(k1, v1)
  }

  class Map2[K <: AnyRef, +V >: Null <: AnyRef] (k1: K, v1: V, k2: K, v2: V) extends SimpleMap[K, V] {
    def size = 2
    def apply(k: K) =
      if (k == k1) v1
      else if (k == k2) v2
      else null
    def remove(k: K) =
      if (k == k1) new Map1(k2, v2)
      else if (k == k2) new Map1(k1, v1)
      else this
    def updated[V1 >: V <: AnyRef](k: K, v: V1) =
      if (k == k1) new Map2(k, v, k2, v2)
      else if (k == k2) new Map2(k1, v1, k, v)
      else new Map3(k1, v1, k2, v2, k, v)
    def mapValuesNow[V1 >: V <: AnyRef](f: (K, V1) => V1) = {
      val w1 = f(k1, v1); val w2 = f(k2, v2)
      if ((v1 eq w1) && (v2 eq w2)) this
      else new Map2(k1, w1, k2, w2)
    }
    def foreachBinding(f: (K, V) => Unit) = { f(k1, v1); f(k2, v2) }
  }

  class Map3[K <: AnyRef, +V >: Null <: AnyRef] (k1: K, v1: V, k2: K, v2: V, k3: K, v3: V) extends SimpleMap[K, V] {
    def size = 3
    def apply(k: K) =
      if (k == k1) v1
      else if (k == k2) v2
      else if (k == k3) v3
      else null
    def remove(k: K) =
      if (k == k1) new Map2(k2, v2, k3, v3)
      else if (k == k2) new Map2(k1, v1, k3, v3)
      else if (k == k3) new Map2(k1, v1, k2, v2)
      else this
    def updated[V1 >: V <: AnyRef](k: K, v: V1) =
      if (k == k1) new Map3(k, v, k2, v2, k3, v3)
      else if (k == k2) new Map3(k1, v1, k, v, k3, v3)
      else if (k == k3) new Map3(k1, v1, k2, v2, k, v)
      else new Map4(k1, v1, k2, v2, k3, v3, k, v)
    def mapValuesNow[V1 >: V <: AnyRef](f: (K, V1) => V1) = {
      val w1 = f(k1, v1); val w2 = f(k2, v2); val w3 = f(k3, v3)
      if ((v1 eq w1) && (v2 eq w2) && (v3 eq w3)) this
      else new Map3(k1, w1, k2, w2, k3, w3)
    }
    def foreachBinding(f: (K, V) => Unit) = { f(k1, v1); f(k2, v2); f(k3, v3) }
  }

  class Map4[K <: AnyRef, +V >: Null <: AnyRef] (k1: K, v1: V, k2: K, v2: V, k3: K, v3: V, k4: K, v4: V) extends SimpleMap[K, V] {
    def size = 4
    def apply(k: K) =
      if (k == k1) v1
      else if (k == k2) v2
      else if (k == k3) v3
      else if (k == k4) v4
      else null
    def remove(k: K) =
      if (k == k1) new Map3(k2, v2, k3, v3, k4, v4)
      else if (k == k2) new Map3(k1, v1, k3, v3, k4, v4)
      else if (k == k3) new Map3(k1, v1, k2, v2, k4, v4)
      else if (k == k4) new Map3(k1, v1, k2, v2, k3, v3)
      else this
    def updated[V1 >: V <: AnyRef](k: K, v: V1) =
      if (k == k1) new Map4(k, v, k2, v2, k3, v3, k4, v4)
      else if (k == k2) new Map4(k1, v1, k, v, k3, v3, k4, v4)
      else if (k == k3) new Map4(k1, v1, k2, v2, k, v, k4, v4)
      else if (k == k4) new Map4(k1, v1, k2, v2, k3, v3, k, v)
      else new MapMore(Array[AnyRef](k1, v1, k2, v2, k3, v3, k4, v4, k, v))
    def mapValuesNow[V1 >: V <: AnyRef](f: (K, V1) => V1) = {
      val w1 = f(k1, v1); val w2 = f(k2, v2); val w3 = f(k3, v3); val w4 = f(k4, v4)
      if ((v1 eq w1) && (v2 eq w2) && (v3 eq w3) && (v4 eq w4)) this
      else new Map4(k1, w1, k2, w2, k3, w3, k4, w4)
    }
    def foreachBinding(f: (K, V) => Unit) = { f(k1, v1); f(k2, v2); f(k3, v3); f(k4, v4) }
  }

  class MapMore[K <: AnyRef, +V >: Null <: AnyRef](bindings: Array[AnyRef]) extends SimpleMap[K, V] {
    private def key(i: Int): K = bindings(i).asInstanceOf[K]
    private def value(i: Int): V = bindings(i + 1).asInstanceOf[V]

    def size = bindings.length / 2

    def apply(k: K): V = {
      var i = 0
      while (i < bindings.length) {
        if (bindings(i) eq k) return value(i)
        i += 2
      }
      null
    }

    def remove(k: K): SimpleMap[K, V] = {
      var i = 0
      while (i < bindings.length) {
        if (bindings(i) eq k) return {
          if (size == CompactifyThreshold) {
            var m: SimpleMap[K, V] = Empty[K]
            for (j <- 0 until bindings.length by 2)
              if (j != i) m = m.updated(key(j), value(j))
            m
          } else {
            val bindings1 = new Array[AnyRef](bindings.length - 2)
            Array.copy(bindings, 0, bindings1, 0, i)
            Array.copy(bindings, i + 2, bindings1, i, bindings1.length - i)
            new MapMore(bindings1)
          }
        }
        i += 2
      }
      this
    }

    def updated[V1 >: V <: AnyRef](k: K, v: V1): SimpleMap[K, V] = {
      var i = 0
      while (i < bindings.length) {
        if (bindings(i) eq k)
          return {
            if (v eq bindings(i + 1)) this
            else {
              val bindings1 = bindings.clone
              bindings1(i + 1) = v
              new MapMore(bindings1)
            }
          }
        i += 2
      }
      val bindings2 = new Array[AnyRef](bindings.length + 2)
      Array.copy(bindings, 0, bindings2, 0, bindings.length)
      bindings2(bindings.length) = k
      bindings2(bindings.length + 1) = v
      new MapMore(bindings2)
    }

    override def contains(k: K): Boolean = {
      var i = 0
      while (i < bindings.length) {
        if (bindings(i) eq k) return true
        i += 2
      }
      false
    }

    def mapValuesNow[V1 >: V <: AnyRef](f: (K, V1) => V1) = {
      var bindings1: Array[AnyRef] = bindings
      var i = 0
      while (i < bindings.length) {
        val v = value(i)
        val v1 = f(key(i), v)
        if ((v1 ne v) && (bindings1 eq bindings))
          bindings1 = bindings.clone
        bindings1(i) = bindings(i)
        bindings1(i + 1) = v1
        i += 2
      }
      if (bindings1 eq bindings) this else new MapMore(bindings1)
    }

    def foreachBinding(f: (K, V) => Unit) = {
      var i = 0
      while (i < bindings.length) {
        f(key(i), value(i))
        i += 2
      }
    }
  }
}