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/*
 * Copyright (c) 2016 Jacob Rachiele
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 * and associated documentation files (the "Software"), to deal in the Software without restriction
 * including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense
 * and/or sell copies of the Software, and to permit persons to whom the Software is furnished to
 * do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED
 * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
 * USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * Contributors:
 *
 * Jacob Rachiele
 */
package linear;

import com.google.common.collect.ImmutableList;
import math.FieldElement;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * An immutable and thread-safe implementation of a vector backed by a list of {@link FieldElement}s.
 *
 * @author Jacob Rachiele
 */
final class FieldVector> {

  private final List elements;

  /**
   * Create a new vector using the provided list of elements.
   *
   * @param elements a list of elements constituting the elements of the new vector.
   */
  FieldVector(List elements) {
    this.elements = ImmutableList.copyOf(elements);
  }

  /**
   * Create a new vector using the provided elements.
   *
   * @param elements the elements of the new vector.
   */
  @SafeVarargs
  FieldVector(T... elements) {
    this.elements = ImmutableList.copyOf(Arrays.asList(elements.clone()));
  }

  /**
   * The elements of the vector as a list of field elements.
   *
   * @return the elements of the vector as a list of field element.
   */
  List elements() {
    return this.elements;
  }

  /**
   * Return the element at index i, where indexing begins at 0.
   *
   * @param i the index of the element.
   * @return the element at index i, where indexing begins at 0.
   */
  T at(final int i) {
    return this.elements.get(i);
  }

  /**
   * The number of elements in this vector.
   *
   * @return the number of elements in this vector.
   */
  int size() {
    return this.elements.size();
  }

  /**
   * Add this vector to the given vector and return the result in a new vector.
   *
   * @param other the vector to add to this vector.
   * @return this vector added to the given vector.
   */
  FieldVector plus(final FieldVector other) {
    final List summed = new ArrayList<>(this.size());
    for (int i = 0; i < this.size(); i++) {
      summed.add(this.elements.get(i).plus(other.elements.get(i)));
    }
    return new FieldVector<>(summed);
  }

  /**
   * Subtract the given vector from this vector and return the result in a new vector.
   *
   * @param other the vector to subtract from this vector.
   * @return this vector subtracted by the given vector.
   */
  FieldVector minus(final FieldVector other) {
    final List differenced = new ArrayList<>(this.size());
    for (int i = 0; i < this.size(); i++) {
      differenced.add(this.elements.get(i).minus(other.elements.get(i)));
    }
    return new FieldVector<>(differenced);
  }

  /**
   * Scale this vector by the given scalar and return the result in a new vector.
   *
   * @param alpha the scalar to scale this vector by.
   * @return this vector scaled by the given scalar.
   */
  FieldVector scaledBy(final T alpha) {
    final List scaled = new ArrayList<>(this.size());
    for (int i = 0; i < this.size(); i++) {
      scaled.add(this.elements.get(i).times(alpha));
    }
    return new FieldVector<>(scaled);
  }

  FieldVector axpy(final FieldVector other, final T alpha) {
    final List result = new ArrayList<>(this.size());
    for (int i = 0; i < this.size(); i++) {
      result.add(this.elements.get(i).times(alpha).plus(other.elements.get(i)));
    }
    return new FieldVector<>(result);
  }

  /**
   * Compute the dot product of this vector with the given vector.
   *
   * @param other the vector to take the dot product with.
   * @return the dot product of this vector with the given vector.
   */
  T dotProduct(final FieldVector other) {
    if (this.size() > 0) {
      T product = this.elements.get(0).times(other.elements.get(0).conjugate());
      for (int t = 1; t < this.elements.size(); t++) {
        product = product.plus(this.elements.get(t).times(other.elements.get(t).conjugate()));
      }
      return product;
    }
    throw new IllegalStateException("The dot product is undefined for zero length vectors.");
  }

  /**
   * Compute the L2 length of this vector.
   *
   * @return the L2 length of this vector.
   */
  double norm() {
    return Math.sqrt(sumOfSquares());
  }

  private double sumOfSquares() {
    double sum = 0.0;
    if (this.size() > 0) {
      sum = Math.pow(this.elements.get(0).abs(), 2);
      for (int i = 1; i < this.elements.size(); i++) {
        sum += Math.pow(this.elements.get(i).abs(), 2);
      }
    }
    return sum;
  }


  @Override
  public String toString() {
    return "elements: " + elements;
  }

  @Override
  public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((elements == null) ? 0 : elements.hashCode());
    return result;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj)
      return true;
    if (obj == null)
      return false;
    if (getClass() != obj.getClass())
      return false;
    FieldVector other = (FieldVector) obj;
    if (elements == null) {
      if (other.elements != null)
        return false;
    } else if (!elements.equals(other.elements))
      return false;
    return true;
  }
}