/*
 * Copyright (c) Rich Hickey. All rights reserved.
 * The use and distribution terms for this software are covered by the
 * Common Public License 1.0 (http://opensource.org/licenses/cpl.php)
 * which can be found in the file CPL.TXT at the root of this distribution.
 * By using this software in any fashion, you are agreeing to be bound by
 * the terms of this license.
 * You must not remove this notice, or any other, from this software.
 */

package com.codecommit.collection

import Vector._

/**
 * A straight port of Clojure's <code>PersistentVector</code> class.
 *
 * @author Daniel Spiewak
 * @author Rich Hickey
 */
class Vector[+T] private (val length: Int, shift: Int, root: Array[AnyRef], tail: Array[AnyRef]) extends RandomAccessSeq[T] { outer =>
  private val tailOff = length - tail.length
  
  /*
   * The design of this data structure inherantly requires heterogenous arrays.
   * It is *possible* to design around this, but the result is comparatively
   * quite inefficient.  With respect to this fact, I have left the original
   * (somewhat dynamically-typed) implementation in place.
   */
  
  private[collection] def this() = this(0, 5, EmptyArray, EmptyArray)
  
  def apply(i: Int): T = {
    if (i >= 0 && i < length) {
      if (i >= tailOff) {
			  tail(i & 0x01f).asInstanceOf[T]
      } else {
        var arr = root
        var level = shift
        
        while (level > 0) {
          arr = arr((i >>> level) & 0x01f).asInstanceOf[Array[AnyRef]]
          level -= 5
        }
        
        arr(i & 0x01f).asInstanceOf[T]
      }
		} else throw new IndexOutOfBoundsException(i.toString)
  }
  
  def update[A >: T](i: Int, obj: A): Vector[A] = {
    if (i >= 0 && i < length) {
      if (i >= tailOff) {
        val newTail = new Array[AnyRef](tail.length)
        Array.copy(tail, 0, newTail, 0, tail.length)
        newTail(i & 0x01f) = obj.asInstanceOf[AnyRef]
        
        new Vector[A](length, shift, root, newTail)
			} else {
        new Vector[A](length, shift, doAssoc(shift, root, i, obj), tail)
      }
		} else if (i == length) {
		  this + obj
    } else throw new IndexOutOfBoundsException(i.toString)
  }
  
  private def doAssoc[A >: T](level: Int, arr: Array[AnyRef], i: Int, obj: A): Array[AnyRef] = {
    val ret = new Array[AnyRef](arr.length)
    Array.copy(arr, 0, ret, 0, arr.length)
    
    if (level == 0) {
      ret(i & 0x01f) = obj.asInstanceOf[AnyRef]
		} else {
      val subidx = (i >>> level) & 0x01f
      ret(subidx) = doAssoc(level - 5, arr(subidx).asInstanceOf[Array[AnyRef]], i, obj)
		}
    
    ret
  }
  
  override def ++[A >: T](other: Iterable[A]) = other.foldLeft(this:Vector[A]) { _ + _ }
  
  def +[A >: T](obj: A): Vector[A] = {
    if (tail.length < 32) {
      val newTail = new Array[AnyRef](tail.length + 1)
      Array.copy(tail, 0, newTail, 0, tail.length)
      newTail(tail.length) = obj.asInstanceOf[AnyRef]
      
      new Vector[A](length + 1, shift, root, newTail)
		} else {
      var (newRoot, expansion) = pushTail(shift - 5, root, tail, null)
      var newShift = shift
      
      if (expansion != null) {
        newRoot = array(newRoot, expansion)
        newShift += 5
      }
      
      new Vector[A](length + 1, newShift, newRoot, array(obj.asInstanceOf[AnyRef]))
    }
  }
  
  private def pushTail(level: Int, arr: Array[AnyRef], tailNode: Array[AnyRef], expansion: AnyRef): (Array[AnyRef], AnyRef) = {
    val newChild = if (level == 0) tailNode else {
      val (newChild, subExpansion) = pushTail(level - 5, arr(arr.length - 1).asInstanceOf[Array[AnyRef]], tailNode, expansion)
      
      if (subExpansion == null) {
        val ret = new Array[AnyRef](arr.length)
        Array.copy(arr, 0, ret, 0, arr.length)
        
        ret(arr.length - 1) = newChild
        
        return (ret, null)
			} else subExpansion
		}
    
    // expansion
    if (arr.length == 32) {
      (arr, array(newChild)) 
    } else {
      val ret = new Array[AnyRef](arr.length + 1)
      Array.copy(arr, 0, ret, 0, arr.length)
      ret(arr.length) = newChild
      
      (ret, null)
    }
  }
  
  /**
   * Removes the <i>tail</i> element of this vector.
   */
  def pop: Vector[T] = {
    if (length == 0) {
      throw new IllegalStateException("Can't pop empty vector")
    } else if (length == 1) {
      EmptyVector
    } else if (tail.length > 1) {
      val newTail = new Array[AnyRef](tail.length - 1)
      Array.copy(tail, 0, newTail, 0, newTail.length)
      
      new Vector[T](length - 1, shift, root, newTail)
		} else {
      var (newRoot, pTail) = popTail(shift - 5, root, null)
      var newShift = shift
      
      if (newRoot == null) {
        newRoot = EmptyArray
      }
      
      if (shift > 5 && newRoot.length == 1) {
        newRoot = newRoot(0).asInstanceOf[Array[AnyRef]]
        newShift -= 5
      }
      
      new Vector[T](length - 1, newShift, newRoot, pTail.asInstanceOf[Array[AnyRef]])
    }
  }
  
  private def popTail(shift: Int, arr: Array[AnyRef], pTail: AnyRef): (Array[AnyRef], AnyRef) = {
    val newPTail = if (shift > 0) {
      val (newChild, subPTail) = popTail(shift - 5, arr(arr.length - 1).asInstanceOf[Array[AnyRef]], pTail)
      
      if (newChild != null) {
        val ret = new Array[AnyRef](arr.length)
        Array.copy(arr, 0, ret, 0, arr.length)
        
        ret(arr.length - 1) = newChild
        
        return (ret, subPTail)
			}
      subPTail
		} else if (shift == 0) {
      arr(arr.length - 1)
    } else pTail
    
    // contraction
    if (arr.length == 1) {
      (null, newPTail)
    } else {    
      val ret = new Array[AnyRef](arr.length - 1)
      Array.copy(arr, 0, ret, 0, ret.length)
      
      (ret, newPTail)
    }
  }
  
  override def filter(p: (T)=>Boolean) = {
    var back = new Vector[T]
    var i = 0
    
    while (i < length) {
      val e = apply(i)
      if (p(e)) back += e
      
      i += 1
    }
    
    back
  }
  
  override def flatMap[A](f: (T)=>Iterable[A]) = {
    var back = new Vector[A]
    var i = 0
    
    while (i < length) {
      f(apply(i)) foreach { back += _ }
      i += 1
    }
    
    back
  }
  
  override def map[A](f: (T)=>A) = {
    var back = new Vector[A]
    var i = 0
    
    while (i < length) {
      back += f(apply(i))
      i += 1
    }
    
    back
  }
  
  override def reverse: Vector[T] = new VectorProjection[T] {
    override val length = outer.length
    
    override def apply(i: Int) = outer.apply(length - i - 1)
  }
  
  override def subseq(from: Int, end: Int) = subVector(from, end)
  
  def subVector(from: Int, end: Int): Vector[T] = {
    if (from < 0) {
      throw new IndexOutOfBoundsException(from.toString)
    } else if (end >= length) {
      throw new IndexOutOfBoundsException(end.toString)
    } else if (end <= from) {
      throw new IllegalArgumentException("Invalid range: " + from + ".." + end)
    } else {
      new VectorProjection[T] {
        override val length = end - from
        
        override def apply(i: Int) = outer.apply(i + from)
      }
    }
  }
  
  def zip[A](that: Vector[A]) = {
    var back = new Vector[(T, A)]
    var i = 0
    
    val limit = Math.min(length, that.length)
    while (i < limit) {
      back += (apply(i), that(i))
      i += 1
    }
    
    back
  }
  
  def zipWithIndex = {
    var back = new Vector[(T, Int)]
    var i = 0
    
    while (i < length) {
      back += (apply(i), i)
      i += 1
    }
    
    back
  }
  
  override def equals(other: Any) = other match {
    case vec:Vector[T] => {
      var back = length == vec.length
      var i = 0
      
      while (i < length) {
        back &&= apply(i) == vec.apply(i)
        i += 1
      }
      
      back
    }
    
    case _ => false
  }
  
  override def hashCode = foldLeft(0) { _ ^ _.hashCode }
}

object Vector {
  private[collection] val EmptyArray = new Array[AnyRef](0)
  
  def apply[T](elems: T*) = elems.foldLeft(EmptyVector:Vector[T]) { _ + _ }
  
  def unapplySeq[T](vec: Vector[T]): Option[Seq[T]] = Some(vec)
  
  @inline
  private[collection] def array(elems: AnyRef*) = {
    val back = new Array[AnyRef](elems.length)
    Array.copy(elems, 0, back, 0, back.length)
    
    back
  }
}

object EmptyVector extends Vector[Nothing]

private[collection] abstract class VectorProjection[+T] extends Vector[T] {
  override val length: Int
  override def apply(i: Int): T
  
  override def +[A >: T](e: A) = innerCopy + e
  
  override def update[A >: T](i: Int, e: A) = {
    if (i < 0) {
      throw new IndexOutOfBoundsException(i.toString)
    } else if (i > length) {
      throw new IndexOutOfBoundsException(i.toString)
    } else innerCopy(i) = e
  }
  
  private lazy val innerCopy = foldLeft(EmptyVector:Vector[T]) { _ + _ }
}