/**
 * 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.lucene.spatial.geometry;

/**
 * Enum representing difference distance units, currently only kilometers and
 * miles
 */
public enum DistanceUnits {

  MILES("miles", 3959, 24902),
  KILOMETERS("km", 6371, 40076);

  private static final double MILES_KILOMETRES_RATIO = 1.609344;

  private final String unit;
  
  private final double earthCircumference;
  
  private final double earthRadius;

  /**
   * Creates a new DistanceUnit that represents the given unit
   *
   * @param unit Distance unit in String form
   * @param earthRadius Radius of the Earth in the specific distance unit
   * @param earthCircumfence Circumference of the Earth in the specific distance unit
   */
  DistanceUnits(String unit, double earthRadius, double earthCircumfence) {
    this.unit = unit;
    this.earthCircumference = earthCircumfence;
    this.earthRadius = earthRadius;
  }

  /**
   * Returns the DistanceUnit which represents the given unit
   *
   * @param unit Unit whose DistanceUnit should be found
   * @return DistanceUnit representing the unit
   * @throws IllegalArgumentException if no DistanceUnit which represents the given unit is found
   */
  public static DistanceUnits findDistanceUnit(String unit) {
    if (MILES.getUnit().equalsIgnoreCase(unit) || unit.equalsIgnoreCase("mi")) {
      return MILES;
    }

    if (KILOMETERS.getUnit().equalsIgnoreCase(unit)) {
      return KILOMETERS;
    }

    throw new IllegalArgumentException("Unknown distance unit " + unit);
  }

  /**
   * Converts the given distance in given DistanceUnit, to a distance in the unit represented by {@code this} 
   *
   * @param distance Distance to convert
   * @param from Unit to convert the distance from
   * @return Given distance converted to the distance in the given unit
   */
  public double convert(double distance, DistanceUnits from) {
    if (from == this) {
      return distance;
    }
    return (this == MILES) ? distance / MILES_KILOMETRES_RATIO : distance * MILES_KILOMETRES_RATIO;
  }

  /**
   * Returns the string representation of the distance unit
   *
   * @return String representation of the distance unit
   */
  public String getUnit() {
    return unit;
  }
  
  /**
   * Returns the <a href="http://en.wikipedia.org/wiki/Earth_radius">average earth radius</a>
   *
   * @return the average earth radius
   */
  public double earthRadius() {
    return earthRadius;
  }
  
  /**
   * Returns the <a href="http://www.lyberty.com/encyc/articles/earth.html">circumference of the Earth</a>
   * 
   * @return  the circumference of the Earth
   */
  public double earthCircumference() {
    return earthCircumference;
  }
}