/*
    * 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.commons.math4.legacy.ode;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.commons.math4.legacy.exception.DimensionMismatchException;
  import org.apache.commons.math4.legacy.exception.MaxCountExceededException;
  
  
  /**
   * This class represents a combined set of first order differential equations,
   * with at least a primary set of equations expandable by some sets of secondary
   * equations.
   * <p>
   * One typical use case is the computation of the Jacobian matrix for some ODE.
   * In this case, the primary set of equations corresponds to the raw ODE, and we
   * add to this set another bunch of secondary equations which represent the Jacobian
   * matrix of the primary set.
   * </p>
   * <p>
   * We want the integrator to use <em>only</em> the primary set to estimate the
   * errors and hence the step sizes. It should <em>not</em> use the secondary
   * equations in this computation. The {@link AbstractIntegrator integrator} will
   * be able to know where the primary set ends and so where the secondary sets begin.
   * </p>
   *
   * @see FirstOrderDifferentialEquations
   * @see JacobianMatrices
   *
   * @since 3.0
   */
  
  public class ExpandableStatefulODE {
  
      /** Primary differential equation. */
      private final FirstOrderDifferentialEquations primary;
  
      /** Mapper for primary equation. */
      private final EquationsMapper primaryMapper;
  
      /** Time. */
      private double time;
  
      /** State. */
      private final double[] primaryState;
  
      /** State derivative. */
      private final double[] primaryStateDot;
  
      /** Components of the expandable ODE. */
      private List<SecondaryComponent> components;
  
      /** Build an expandable set from its primary ODE set.
       * @param primary the primary set of differential equations to be integrated.
       */
      public ExpandableStatefulODE(final FirstOrderDifferentialEquations primary) {
          final int n          = primary.getDimension();
          this.primary         = primary;
          this.primaryMapper   = new EquationsMapper(0, n);
          this.time            = Double.NaN;
          this.primaryState    = new double[n];
          this.primaryStateDot = new double[n];
          this.components      = new ArrayList<>();
      }
  
      /** Get the primary set of differential equations.
       * @return primary set of differential equations
       */
      public FirstOrderDifferentialEquations getPrimary() {
          return primary;
      }
  
      /** Return the dimension of the complete set of equations.
       * <p>
       * The complete set of equations correspond to the primary set plus all secondary sets.
       * </p>
       * @return dimension of the complete set of equations
       */
      public int getTotalDimension() {
          if (components.isEmpty()) {
              // there are no secondary equations, the complete set is limited to the primary set
              return primaryMapper.getDimension();
          } else {
             // there are secondary equations, the complete set ends after the last set
             final EquationsMapper lastMapper = components.get(components.size() - 1).mapper;
             return lastMapper.getFirstIndex() + lastMapper.getDimension();
         }
     }
 
     /** Get the current time derivative of the complete state vector.
      * @param t current value of the independent <I>time</I> variable
      * @param y array containing the current value of the complete state vector
      * @param yDot placeholder array where to put the time derivative of the complete state vector
      * @exception MaxCountExceededException if the number of functions evaluations is exceeded
      * @exception DimensionMismatchException if arrays dimensions do not match equations settings
      */
     public void computeDerivatives(final double t, final double[] y, final double[] yDot)
         throws MaxCountExceededException, DimensionMismatchException {
 
         // compute derivatives of the primary equations
         primaryMapper.extractEquationData(y, primaryState);
         primary.computeDerivatives(t, primaryState, primaryStateDot);
 
         // Add contribution for secondary equations
         for (final SecondaryComponent component : components) {
             component.mapper.extractEquationData(y, component.state);
             component.equation.computeDerivatives(t, primaryState, primaryStateDot,
                                                   component.state, component.stateDot);
             component.mapper.insertEquationData(component.stateDot, yDot);
         }
 
         primaryMapper.insertEquationData(primaryStateDot, yDot);
     }
 
     /** Add a set of secondary equations to be integrated along with the primary set.
      * @param secondary secondary equations set
      * @return index of the secondary equation in the expanded state
      */
     public int addSecondaryEquations(final SecondaryEquations secondary) {
 
         final int firstIndex;
         if (components.isEmpty()) {
             // lazy creation of the components list
             components = new ArrayList<>();
             firstIndex = primary.getDimension();
         } else {
             final SecondaryComponent last = components.get(components.size() - 1);
             firstIndex = last.mapper.getFirstIndex() + last.mapper.getDimension();
         }
 
         components.add(new SecondaryComponent(secondary, firstIndex));
 
         return components.size() - 1;
     }
 
     /** Get an equations mapper for the primary equations set.
      * @return mapper for the primary set
      * @see #getSecondaryMappers()
      */
     public EquationsMapper getPrimaryMapper() {
         return primaryMapper;
     }
 
     /** Get the equations mappers for the secondary equations sets.
      * @return equations mappers for the secondary equations sets
      * @see #getPrimaryMapper()
      */
     public EquationsMapper[] getSecondaryMappers() {
         final EquationsMapper[] mappers = new EquationsMapper[components.size()];
         for (int i = 0; i < mappers.length; ++i) {
             mappers[i] = components.get(i).mapper;
         }
         return mappers;
     }
 
     /** Set current time.
      * @param time current time
      */
     public void setTime(final double time) {
         this.time = time;
     }
 
     /** Get current time.
      * @return current time
      */
     public double getTime() {
         return time;
     }
 
     /** Set primary part of the current state.
      * @param primaryState primary part of the current state
      * @throws DimensionMismatchException if the dimension of the array does not
      * match the primary set
      */
     public void setPrimaryState(final double[] primaryState) throws DimensionMismatchException {
 
         // safety checks
         if (primaryState.length != this.primaryState.length) {
             throw new DimensionMismatchException(primaryState.length, this.primaryState.length);
         }
 
         // set the data
         System.arraycopy(primaryState, 0, this.primaryState, 0, primaryState.length);
     }
 
     /** Get primary part of the current state.
      * @return primary part of the current state
      */
     public double[] getPrimaryState() {
         return primaryState.clone();
     }
 
     /** Get primary part of the current state derivative.
      * @return primary part of the current state derivative
      */
     public double[] getPrimaryStateDot() {
         return primaryStateDot.clone();
     }
 
     /** Set secondary part of the current state.
      * @param index index of the part to set as returned by {@link
      * #addSecondaryEquations(SecondaryEquations)}
      * @param secondaryState secondary part of the current state
      * @throws DimensionMismatchException if the dimension of the partial state does not
      * match the selected equations set dimension
      */
     public void setSecondaryState(final int index, final double[] secondaryState)
         throws DimensionMismatchException {
 
         // get either the secondary state
         double[] localArray = components.get(index).state;
 
         // safety checks
         if (secondaryState.length != localArray.length) {
             throw new DimensionMismatchException(secondaryState.length, localArray.length);
         }
 
         // set the data
         System.arraycopy(secondaryState, 0, localArray, 0, secondaryState.length);
     }
 
     /** Get secondary part of the current state.
      * @param index index of the part to set as returned by {@link
      * #addSecondaryEquations(SecondaryEquations)}
      * @return secondary part of the current state
      */
     public double[] getSecondaryState(final int index) {
         return components.get(index).state.clone();
     }
 
     /** Get secondary part of the current state derivative.
      * @param index index of the part to set as returned by {@link
      * #addSecondaryEquations(SecondaryEquations)}
      * @return secondary part of the current state derivative
      */
     public double[] getSecondaryStateDot(final int index) {
         return components.get(index).stateDot.clone();
     }
 
     /** Set the complete current state.
      * @param completeState complete current state to copy data from
      * @throws DimensionMismatchException if the dimension of the complete state does not
      * match the complete equations sets dimension
      */
     public void setCompleteState(final double[] completeState)
         throws DimensionMismatchException {
 
         // safety checks
         if (completeState.length != getTotalDimension()) {
             throw new DimensionMismatchException(completeState.length, getTotalDimension());
         }
 
         // set the data
         primaryMapper.extractEquationData(completeState, primaryState);
         for (final SecondaryComponent component : components) {
             component.mapper.extractEquationData(completeState, component.state);
         }
     }
 
     /** Get the complete current state.
      * @return complete current state
      * @throws DimensionMismatchException if the dimension of the complete state does not
      * match the complete equations sets dimension
      */
     public double[] getCompleteState() throws DimensionMismatchException {
 
         // allocate complete array
         double[] completeState = new double[getTotalDimension()];
 
         // set the data
         primaryMapper.insertEquationData(primaryState, completeState);
         for (final SecondaryComponent component : components) {
             component.mapper.insertEquationData(component.state, completeState);
         }
 
         return completeState;
     }
 
     /** Components of the compound stateful ODE. */
     private static final class SecondaryComponent {
 
         /** Secondary differential equation. */
         private final SecondaryEquations equation;
 
         /** Mapper between local and complete arrays. */
         private final EquationsMapper mapper;
 
         /** State. */
         private final double[] state;
 
         /** State derivative. */
         private final double[] stateDot;
 
         /** Simple constructor.
          * @param equation secondary differential equation
          * @param firstIndex index to use for the first element in the complete arrays
          */
         SecondaryComponent(final SecondaryEquations equation, final int firstIndex) {
             final int n   = equation.getDimension();
             this.equation = equation;
             mapper        = new EquationsMapper(firstIndex, n);
             state         = new double[n];
             stateDot      = new double[n];
         }
     }
 }