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/*
 * 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.flink.ml

/**
 * Convenience methods to handle Flink's [[org.apache.flink.ml.math.Matrix]] and [[Vector]]
 * abstraction.
 */
package object math {
  implicit class RichMatrix(matrix: Matrix) extends Iterable[(Int, Int, Double)] {

    override def iterator: Iterator[(Int, Int, Double)] = {
      new Iterator[(Int, Int, Double)] {
        var index = 0

        override def hasNext: Boolean = {
          index < matrix.numRows * matrix.numCols
        }

        override def next(): (Int, Int, Double) = {
          val row = index % matrix.numRows
          val column = index / matrix.numRows

          index += 1

          (row, column, matrix(row, column))
        }
      }
    }

    def valueIterator: Iterator[Double] = {
      val it = iterator

      new Iterator[Double] {
        override def hasNext: Boolean = it.hasNext

        override def next(): Double = it.next._3
      }
    }

  }

  implicit class RichVector(vector: Vector) extends Iterable[(Int, Double)] {

    override def iterator: Iterator[(Int, Double)] = {
      new Iterator[(Int, Double)] {
        var index = 0

        override def hasNext: Boolean = {
          index < vector.size
        }

        override def next(): (Int, Double) = {
          val resultIndex = index

          index += 1

          (resultIndex, vector(resultIndex))
        }
      }
    }

    def valueIterator: Iterator[Double] = {
      val it = iterator

      new Iterator[Double] {
        override def hasNext: Boolean = it.hasNext

        override def next(): Double = it.next._2
      }
    }
  }

  /** Stores the vector values in a dense array
    *
    * @param vector
    * @return Array containing the vector values
    */
  def vector2Array(vector: Vector): Array[Double] = {
    vector match {
      case dense: DenseVector => dense.data.clone

      case sparse: SparseVector =>
        val result = new Array[Double](sparse.size)

        for((index, value) <- sparse) {
          result(index) = value
        }

        result

    }
  }
}