/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.mahout.math.drm.logical

import scala.reflect.ClassTag
import org.apache.mahout.math.drm.DrmLike
import scala.util.Random

/**
 * Composition of unary elementwise functions.
 */
case class OpAewUnaryFuncFusion[K](
    override var A: DrmLike[K],
    var ff:List[OpAewUnaryFunc[K]] = Nil
    ) extends AbstractUnaryOp[K,K] with TEwFunc {

  override protected[mahout] lazy val partitioningTag: Long =
    if (A.canHaveMissingRows)
      Random.nextLong()
    else A.partitioningTag

  /** Stuff like `A +1` is always supposed to fix this */
  override protected[mahout] lazy val canHaveMissingRows: Boolean = false

  /**
    * Explicit extraction of key class Tag since traits don't support context bound access; but actual
    * implementation knows it
    */
  override def keyClassTag: ClassTag[K] = A.keyClassTag

  /** R-like syntax for number of rows. */
  def nrow: Long = A.nrow

  /** R-like syntax for number of columns */
  def ncol: Int = A.ncol

  /** Apply to degenerate elements? */
  override def evalZeros: Boolean = ff.exists(_.evalZeros)

  /** the function itself */
  override def f: (Double) => Double = {

    // Make sure composed collection becomes an attribute of this closure because we will be sending
    // it to the backend.
    val composedFunc = ff.map(_.f)

    // Create functional closure and return.
    (x: Double) => (composedFunc :\ x) { case (f, xarg) => f(xarg)}

  }
}

