content: /**
   * 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;
    }
  }
  
  