package org.opentrafficsim.core.geometry;
   
   import java.util.Map;
   import java.util.Map.Entry;
   import java.util.NavigableMap;
   import java.util.TreeMap;
   
   import org.djutils.exceptions.Throw;
   import org.djutils.immutablecollections.ImmutableLinkedHashSet;
  import org.djutils.immutablecollections.ImmutableNavigableSet;
  import org.djutils.immutablecollections.ImmutableSet;
  import org.djutils.immutablecollections.ImmutableTreeSet;
  
  /**
   * Container for fractional length data.
   * <p>
   * Copyright (c) 2023-2024 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
   * </p>
   * @author <a href="https://github.com/wjschakel">Wouter Schakel</a>
   */
  public class FractionalLengthData
  {
  
      /** Underlying data. */
      private final NavigableMap<Double, Double> data = new TreeMap<>();
  
      /**
       * Create FractionalLengthData.
       * @param data double...; fractional length - value pairs. Fractional lengths do not need to be in order.
       * @throws IllegalArgumentException when the number of input values is not even or 0.
       * @throws IllegalArgumentException when a fractional value is not in the range [0 ... 1].
       */
      public FractionalLengthData(final double... data) throws IllegalArgumentException
      {
          Throw.when(data.length < 2 || data.length % 2 > 0, IllegalArgumentException.class,
                  "Number of input values must be even and at least 2.");
          for (int i = 0; i < data.length; i = i + 2)
          {
              Throw.when(data[i] < 0.0 || data[i] > 1.0, IllegalArgumentException.class,
                      "Fractional length %s is outside of range [0 ... 1].", data[i]);
              this.data.put(data[i], data[i + 1]);
          }
      }
  
      /**
       * Create FractionalLengthData.
       * @param data Map&lt;Double, Double&gt;; fractional length - value pairs. Fractional lengths do not need to be in order.
       * @throws IllegalArgumentException when the input data is null or empty.
       * @throws IllegalArgumentException when a fractional value is not in the range [0 ... 1].
       */
      public FractionalLengthData(final Map<Double, Double> data) throws IllegalArgumentException
      {
          Throw.when(data == null || data.isEmpty(), IllegalArgumentException.class, "Input data is empty or null.");
          for (Entry<Double, Double> entry : data.entrySet())
          {
              Throw.when(entry.getKey() < 0.0 || entry.getKey() > 1.0, IllegalArgumentException.class,
                      "Fractional length %s is outside of range [0 ... 1].", entry.getKey());
              this.data.put(entry.getKey(), entry.getValue());
          }
      }
  
      /**
       * Returns the data at given fractional length. If only data beyond the fractional length is available, the first available
       * value is returned. If only data before the fractional length is available, the last available value is returned.
       * Otherwise data is linearly interpolated.
       * @param fractionalLength double; fractional length, may be outside range [0 ... 1].
       * @return double; interpolated or extended value.
       */
      public double get(final double fractionalLength)
      {
          Double exact = this.data.get(fractionalLength);
          if (exact != null)
          {
              return exact;
          }
          Entry<Double, Double> ceiling = this.data.ceilingEntry(fractionalLength);
          if (ceiling == null)
          {
              return this.data.lastEntry().getValue();
          }
          Entry<Double, Double> floor = this.data.floorEntry(fractionalLength);
          if (floor == null)
          {
              return this.data.firstEntry().getValue();
          }
          double w = (fractionalLength - floor.getKey()) / (ceiling.getKey() - floor.getKey());
          return (1.0 - w) * floor.getValue() + w * ceiling.getValue();
      }
  
      /**
       * Returns the derivative of the data with respect to fractional length.
       * @param fractionalLength double; fractional length, may be outside range [0 ... 1].
       * @return double; derivative of the data with respect to fractional length.
       */
      public double getDerivative(final double fractionalLength)
      {
          Entry<Double, Double> ceiling, floor;
          if (fractionalLength == 0.0)
         {
             ceiling = this.data.higherEntry(fractionalLength);
             floor = this.data.floorEntry(fractionalLength);
         }
         else
         {
             ceiling = this.data.ceilingEntry(fractionalLength);
             floor = this.data.lowerEntry(fractionalLength);
         }
         if (ceiling == null || floor == null)
         {
             return 0.0;
         }
         return (ceiling.getValue() - floor.getValue()) / (ceiling.getKey() - floor.getKey());
     }
 
     /**
      * Returns the fractional lengths in the underlying data.
      * @return ImmutableNavigableSet&lt;Double&gt;; fractional lengths in the underlying data.
      */
     public ImmutableNavigableSet<Double> getFractionalLengths()
     {
         return new ImmutableTreeSet<>(this.data.keySet());
     }
 
     /**
      * Returns the values in the underlying data.
      * @return ImmutableSet&lt;Double&gt;; values in the underlying data.
      */
     public ImmutableSet<Double> getValues()
     {
         return new ImmutableLinkedHashSet<>(this.data.values());
     }
 
     /**
      * Returns fractional lengths in array form, including 0.0 and 1.0.
      * @return double[]; fractional lengths.
      */
     public double[] getFractionalLengthsAsArray()
     {
         NavigableMap<Double, Double> full = fullRange();
         double[] fractionalLengths = new double[full.size()];
         int i = 0;
         for (double f : full.navigableKeySet())
         {
             fractionalLengths[i++] = f;
         }
         return fractionalLengths;
     }
 
     /**
      * Returns fractional lengths in array form, including values at 0.0 and 1.0.
      * @return double[]; fractional lengths.
      */
     public double[] getValuesAsArray()
     {
         NavigableMap<Double, Double> full = fullRange();
         double[] values = new double[full.size()];
         int i = 0;
         for (double f : full.navigableKeySet())
         {
             values[i++] = full.get(f);
         }
         return values;
     }
 
     /**
      * Returns the data including entries at 0.0 and 1.0.
      * @return NavigableMap&lt;Double, Double&gt;; data with fill range.
      */
     private final NavigableMap<Double, Double> fullRange()
     {
         NavigableMap<Double, Double> full = new TreeMap<>(this.data);
         full.put(0.0, full.firstEntry().getValue());
         full.put(1.0, full.lastEntry().getValue());
         return full;
     }
 
     /**
      * Returns the number of data points.
      * @return int; number of data points.
      */
     public int size()
     {
         return this.data.size();
     }
 
     /**
      * Create FractionalLengthData.
      * @param data double...; fractional length - value pairs. Fractional lengths do not need to be in order.
      * @return FractionalLengthData; fractional length data.
      * @throws IllegalArgumentException when the number of input values is not even or 0.
      * @throws IllegalArgumentException when a fractional value is not in the range [0 ... 1].
      */
     public static FractionalLengthData of(final double... data) throws IllegalArgumentException
     {
         return new FractionalLengthData(data);
     }
 
 }