package cse1030;

import java.util.Collection;

/**
 * The class <code>DistanceUtility</code> contains constants and
 * methods to convert between kilometres and miles.
 * 
 * @author CSE1030Z
 */
public class DistanceUtility {
  /**
   * The number of kilometres in a mile.
   */
  public static final double KILOMETRES_PER_MILE = 1.609344;

  /**
   * The number of miles in a kilometre.
   */
  public static final double MILES_PER_KILOMETRES = 1.0 / KILOMETRES_PER_MILE;
  
  /**
   * Converts distances in kilometres to miles.
   * 
   * @param km  The distance to convert. If <code>km</code>
   *            is negative then the returned distance is
   *            also negative.
   * @return  Distance in miles.
   */
  public static double kilometresToMiles(double km) {
    double result = km / KILOMETRES_PER_MILE;
    return result;
  }
  
  /**
   * Converts distances in miles to kilometres.
   * 
   * @param miles  The distance to convert. If <code>miles</code>
   *            is negative then the returned distance is
   *            also negative.
   * @return  Distance in kilometres.
   */
  public static double milesToKilometres(double miles) {
    double result = miles * KILOMETRES_PER_MILE;
    return result;
  }
  
  /**
   * Converts distances in kilometres to miles for arrays.
   * If an element of the array argument is negative the
   * corresponding element of the returned array is also
   * negative.
   * 
   * @param km  The distances to convert.
   * @pre.      <code>km.length > 0</code>
   * @return  Distances in miles in an array with
   *          <code>length == km.length</code>.
   */
  public static double[] kilometresToMiles(double[] km) {
    double miles[] = new double[km.length];
    for (int i = 0; i < km.length; i++) {
      miles[i] = kilometresToMiles(km[i]);
    }
    return miles;
  }
  
  /**
   * Converts distances in miles to kilometres for arrays.
   * If an element of the array argument is negative the
   * corresponding element of the returned array is also
   * negative.
   * 
   * @param miles  The distances to convert.
   * @pre.      <code>miles.length > 0</code>
   * @return  Distances in kilometres in an array with
   *          <code>length == miles.length</code>.
   */
  public static double[] milesToKilometres(double[] miles) {
    double km[] = new double[miles.length];
    for (int i = 0; i < miles.length; i++) {
      km[i] = milesToKilometres(miles[i]);
    }
    return km;
  }
  
  /**
   * Converts distances in kilometres to miles for a Collection.
   * If an element of the collection is negative the
   * corresponding element of the returned array is also
   * negative.
   * 
   * @param km  The distances to convert.
   * @pre.      <code>km.size() > 0</code>
   * @return  Distances in miles in an array with
   *          <code>length == km.size()</code>.
   */
  public static double[] kilometresToMiles(Collection<? extends Number> km) {
    double[] miles = new double[km.size()];
    int i = 0;
    for (Number n : km) {
      miles[i] = kilometresToMiles(n.doubleValue());
      i++;
    }
    return miles;
  }
  
  /**
   * Converts distances in miles to kilometres for a Collection.
   * If an element of the collection is negative the
   * corresponding element of the returned array is also
   * negative.
   * 
   * @param miles  The distances to convert.
   * @pre.      <code>miles.size() > 0</code>
   * @return  Distances in kilometres in an array with
   *          <code>length == miles.size()</code>.
   */
  public static double[] milesToKilometres(Collection<? extends Number> miles) {
    double[] km = new double[miles.size()];
    int i = 0;
    for (Number n : miles) {
      km[i] = milesToKilometres(n.doubleValue());
      i++;
    }
    return km;
  }
}