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/*
 * Scala (https://www.scala-lang.org)
 *
 * Copyright EPFL and Lightbend, Inc.
 *
 * Licensed under Apache License 2.0
 * (http://www.apache.org/licenses/LICENSE-2.0).
 *
 * See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership.
 */

package scala.collection

/**
  * Trait that overrides operations on sequences in order
  * to take advantage of strict builders.
  */
trait StrictOptimizedSeqOps [+A, +CC[_], +C]
  extends Any
    with SeqOps[A, CC, C]
    with StrictOptimizedIterableOps[A, CC, C] {

  override def distinctBy[B](f: A => B): C = {
    val builder = newSpecificBuilder
    val seen = mutable.HashSet.empty[B]
    val it = this.iterator
    while (it.hasNext) {
      val next = it.next()
      if (seen.add(f(next))) builder += next
    }
    builder.result()
  }

  override def prepended[B >: A](elem: B): CC[B] = {
    val b = iterableFactory.newBuilder[B]
    b.sizeHint(this, delta = 1)
    b += elem
    b ++= this
    b.result()
  }

  override def appended[B >: A](elem: B): CC[B] = {
    val b = iterableFactory.newBuilder[B]
    b.sizeHint(this, delta = 1)
    b ++= this
    b += elem
    b.result()
  }

  override def appendedAll[B >: A](suffix: IterableOnce[B]): CC[B] =
    strictOptimizedConcat(suffix, iterableFactory.newBuilder)

  override def prependedAll[B >: A](prefix: IterableOnce[B]): CC[B] = {
    val b = iterableFactory.newBuilder[B]
    b ++= prefix
    b ++= this
    b.result()
  }

  override def padTo[B >: A](len: Int, elem: B): CC[B] = {
    val b = iterableFactory.newBuilder[B]
    val L = size
    b.sizeHint(math.max(L, len))
    var diff = len - L
    b ++= this
    while (diff > 0) {
      b += elem
      diff -= 1
    }
    b.result()
  }

  override def diff[B >: A](that: Seq[B]): C =
    if (isEmpty || that.isEmpty) coll
    else {
      val occ = occCounts(that)
      val b = newSpecificBuilder
      for (x <- this) {
        occ.updateWith(x) {
          case None => {
            b.addOne(x)
            None
          }
          case Some(1) => None
          case Some(n) => Some(n - 1)
        }
      }
      b.result()
    }

  override def intersect[B >: A](that: Seq[B]): C =
    if (isEmpty || that.isEmpty) empty
    else {
      val occ = occCounts(that)
      val b = newSpecificBuilder
      for (x <- this) {
        occ.updateWith(x) {
          case None => None
          case Some(n) => {
            b.addOne(x)
            if (n == 1) None else Some(n - 1)
          }
        }
      }
      b.result()
    }
}