/* Copyright 2022-2026 Thales Alenia Space
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS 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.orekit.frames;
  
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.concurrent.locks.ReentrantLock;
  import java.util.function.Function;
  
  import org.orekit.time.AbsoluteDate;
  
  /** Thread-safe cached provider for frame transforms.
   * <p>
   * This provider is based on a thread-safe Least Recently Used cache
   * using date as it access key, hence saving computation time on
   * transform building.
   * </p>
   * <p>
   * This class is thread-safe.
   * </p>
   * @author Luc Maisonobe
   * @since 13.0.3
   */
  public class CachedTransformProvider {
  
      /** Origin frame. */
      private final Frame origin;
  
      /** Destination frame. */
      private final Frame destination;
  
      /** Number of transforms kept in the date-based cache. */
      private final int cacheSize;
  
      /** Generator for full transforms. */
      private final Function<AbsoluteDate, Transform> fullGenerator;
  
      /** Generator for kinematic transforms. */
      private final Function<AbsoluteDate, KinematicTransform> kinematicGenerator;
  
      /** Generator for static transforms. */
      private final Function<AbsoluteDate, StaticTransform> staticGenerator;
  
      /** Lock for concurrent access. */
      private final ReentrantLock lock;
  
      /** Transforms LRU cache. */
      private final Map<AbsoluteDate, Transform> fullCache;
  
      /** Transforms LRU cache. */
      private final Map<AbsoluteDate, KinematicTransform> kinematicCache;
  
      /** Transforms LRU cache. */
      private final Map<AbsoluteDate, StaticTransform> staticCache;
  
      /** Simple constructor.
       * @param origin             origin frame
       * @param destination        destination frame
       * @param fullGenerator      generator for full transforms
       * @param kinematicGenerator generator for kinematic transforms
       * @param staticGenerator    generator for static transforms
       * @param cacheSize          number of transforms kept in the date-based cache
       */
      public CachedTransformProvider(final Frame origin, final Frame destination,
                                     final Function<AbsoluteDate, Transform> fullGenerator,
                                     final Function<AbsoluteDate, KinematicTransform> kinematicGenerator,
                                     final Function<AbsoluteDate, StaticTransform> staticGenerator,
                                     final int cacheSize) {
  
          this.origin             = origin;
          this.destination        = destination;
          this.cacheSize          = cacheSize;
          this.fullGenerator      = fullGenerator;
          this.kinematicGenerator = kinematicGenerator;
          this.staticGenerator    = staticGenerator;
          this.lock               = new ReentrantLock();
  
          // cache for full transforms
          this.fullCache = new LinkedHashMap<>(cacheSize, 0.75f, true) {
              /**
               * {@inheritDoc}
               */
              @Override
              protected boolean removeEldestEntry(final Map.Entry<AbsoluteDate, Transform> eldest) {
                  return size() > cacheSize;
             }
         };
 
         // cache for kinematic transforms
         this.kinematicCache = new LinkedHashMap<>(cacheSize, 0.75f, true) {
             /**
              * {@inheritDoc}
              */
             @Override
             protected boolean removeEldestEntry(final Map.Entry<AbsoluteDate, KinematicTransform> eldest) {
                 return size() > cacheSize;
             }
         };
 
         // cache for static transforms
         this.staticCache = new LinkedHashMap<>(cacheSize, 0.75f, true) {
             /**
              * {@inheritDoc}
              */
             @Override
             protected boolean removeEldestEntry(final Map.Entry<AbsoluteDate, StaticTransform> eldest) {
                 return size() > cacheSize;
             }
         };
 
     }
 
     /** Get origin frame.
      * @return origin frame
      */
     public Frame getOrigin() {
         return origin;
     }
 
     /** Get destination frame.
      * @return destination frame
      */
     public Frame getDestination() {
         return destination;
     }
 
     /** Get the nmber of transforms kept in the date-based cache.
      * @return nmber of transforms kept in the date-based cache
      */
     public int getCacheSize() {
         return cacheSize;
     }
 
     /** Get the {@link Transform} corresponding to specified date.
      * @param date current date
      * @return transform at specified date
      */
     public Transform getTransform(final AbsoluteDate date) {
         lock.lock();
         try {
             return fullCache.computeIfAbsent(date, fullGenerator);
         } finally {
             lock.unlock();
         }
     }
 
     /** Get the {@link Transform} corresponding to specified date.
      * @param date current date
      * @return transform at specified date
      */
     public KinematicTransform getKinematicTransform(final AbsoluteDate date) {
         lock.lock();
         try {
             return kinematicCache.computeIfAbsent(date, kinematicGenerator);
         } finally {
             lock.unlock();
         }
     }
 
     /** Get the {@link Transform} corresponding to specified date.
      * @param date current date
      * @return transform at specified date
      */
     public StaticTransform getStaticTransform(final AbsoluteDate date) {
         lock.lock();
         try {
             return staticCache.computeIfAbsent(date, staticGenerator);
         } finally {
             lock.unlock();
         }
     }
 
 }