/*
 * 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
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package org.apache.commons.math3.ode;

import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.analysis.solvers.BracketedRealFieldUnivariateSolver;
import org.apache.commons.math3.exception.MaxCountExceededException;
import org.apache.commons.math3.exception.NoBracketingException;
import org.apache.commons.math3.exception.NumberIsTooSmallException;
import org.apache.commons.math3.ode.events.FieldEventHandler;
import org.apache.commons.math3.ode.sampling.FieldStepHandler;

import java.util.Collection;

/**
 * This interface represents a first order integrator for differential equations.
 *
 * <p>The classes which are devoted to solve first order differential equations should implement
 * this interface. The problems which can be handled should implement the {@link
 * FirstOrderDifferentialEquations} interface.
 *
 * @see FirstOrderFieldDifferentialEquations
 * @param <T> the type of the field elements
 * @since 3.6
 */
public interface FirstOrderFieldIntegrator<T extends RealFieldElement<T>> {

    /**
     * Get the name of the method.
     *
     * @return name of the method
     */
    String getName();

    /**
     * Add a step handler to this integrator.
     *
     * <p>The handler will be called by the integrator for each accepted step.
     *
     * @param handler handler for the accepted steps
     * @see #getStepHandlers()
     * @see #clearStepHandlers()
     */
    void addStepHandler(FieldStepHandler<T> handler);

    /**
     * Get all the step handlers that have been added to the integrator.
     *
     * @return an unmodifiable collection of the added events handlers
     * @see #addStepHandler(FieldStepHandler)
     * @see #clearStepHandlers()
     */
    Collection<FieldStepHandler<T>> getStepHandlers();

    /**
     * Remove all the step handlers that have been added to the integrator.
     *
     * @see #addStepHandler(FieldStepHandler)
     * @see #getStepHandlers()
     */
    void clearStepHandlers();

    /**
     * Add an event handler to the integrator.
     *
     * <p>The default solver is a 5<sup>th</sup> order {@link
     * org.apache.commons.math3.analysis.solvers.FieldBracketingNthOrderBrentSolver}.
     *
     * @param handler event handler
     * @param maxCheckInterval maximal time interval between switching function checks (this
     *     interval prevents missing sign changes in case the integration steps becomes very large)
     * @param convergence convergence threshold in the event time search
     * @param maxIterationCount upper limit of the iteration count in the event time search events.
     * @see #addEventHandler(FieldEventHandler, double, double, int,
     *     org.apache.commons.math3.analysis.solvers.BracketedRealFieldUnivariateSolver)
     * @see #getEventHandlers()
     * @see #clearEventHandlers()
     */
    void addEventHandler(
            FieldEventHandler<T> handler,
            double maxCheckInterval,
            double convergence,
            int maxIterationCount);

    /**
     * Add an event handler to the integrator.
     *
     * @param handler event handler
     * @param maxCheckInterval maximal time interval between switching function checks (this
     *     interval prevents missing sign changes in case the integration steps becomes very large)
     * @param convergence convergence threshold in the event time search
     * @param maxIterationCount upper limit of the iteration count in the event time search events.
     * @param solver solver to use to locate the event
     * @see #addEventHandler(FieldEventHandler, double, double, int)
     * @see #getEventHandlers()
     * @see #clearEventHandlers()
     */
    void addEventHandler(
            FieldEventHandler<T> handler,
            double maxCheckInterval,
            double convergence,
            int maxIterationCount,
            BracketedRealFieldUnivariateSolver<T> solver);

    /**
     * Get all the event handlers that have been added to the integrator.
     *
     * @return an unmodifiable collection of the added events handlers
     * @see #addEventHandler(FieldEventHandler, double, double, int)
     * @see #clearEventHandlers()
     */
    Collection<FieldEventHandler<T>> getEventHandlers();

    /**
     * Remove all the event handlers that have been added to the integrator.
     *
     * @see #addEventHandler(FieldEventHandler, double, double, int)
     * @see #getEventHandlers()
     */
    void clearEventHandlers();

    /**
     * Get the current value of the step start time t<sub>i</sub>.
     *
     * <p>This method can be called during integration (typically by the object implementing the
     * {@link FirstOrderDifferentialEquations differential equations} problem) if the value of the
     * current step that is attempted is needed.
     *
     * <p>The result is undefined if the method is called outside of calls to <code>integrate</code>
     * .
     *
     * @return current value of the state at step start time t<sub>i</sub>
     */
    FieldODEStateAndDerivative<T> getCurrentStepStart();

    /**
     * Get the current signed value of the integration stepsize.
     *
     * <p>This method can be called during integration (typically by the object implementing the
     * {@link FirstOrderDifferentialEquations differential equations} problem) if the signed value
     * of the current stepsize that is tried is needed.
     *
     * <p>The result is undefined if the method is called outside of calls to <code>integrate</code>
     * .
     *
     * @return current signed value of the stepsize
     */
    T getCurrentSignedStepsize();

    /**
     * Set the maximal number of differential equations function evaluations.
     *
     * <p>The purpose of this method is to avoid infinite loops which can occur for example when
     * stringent error constraints are set or when lots of discrete events are triggered, thus
     * leading to many rejected steps.
     *
     * @param maxEvaluations maximal number of function evaluations (negative values are silently
     *     converted to maximal integer value, thus representing almost unlimited evaluations)
     */
    void setMaxEvaluations(int maxEvaluations);

    /**
     * Get the maximal number of functions evaluations.
     *
     * @return maximal number of functions evaluations
     */
    int getMaxEvaluations();

    /**
     * Get the number of evaluations of the differential equations function.
     *
     * <p>The number of evaluations corresponds to the last call to the <code>integrate</code>
     * method. It is 0 if the method has not been called yet.
     *
     * @return number of evaluations of the differential equations function
     */
    int getEvaluations();

    /**
     * Integrate the differential equations up to the given time.
     *
     * <p>This method solves an Initial Value Problem (IVP).
     *
     * <p>Since this method stores some internal state variables made available in its public
     * interface during integration ({@link #getCurrentSignedStepsize()}), it is <em>not</em>
     * thread-safe.
     *
     * @param equations differential equations to integrate
     * @param initialState initial state (time, primary and secondary state vectors)
     * @param finalTime target time for the integration (can be set to a value smaller than {@code
     *     t0} for backward integration)
     * @return final state, its time will be the same as {@code finalTime} if integration reached
     *     its target, but may be different if some {@link
     *     org.apache.commons.math3.ode.events.FieldEventHandler} stops it at some point.
     * @exception NumberIsTooSmallException if integration step is too small
     * @exception MaxCountExceededException if the number of functions evaluations is exceeded
     * @exception NoBracketingException if the location of an event cannot be bracketed
     */
    FieldODEStateAndDerivative<T> integrate(
            FieldExpandableODE<T> equations, FieldODEState<T> initialState, T finalTime)
            throws NumberIsTooSmallException, MaxCountExceededException, NoBracketingException;
}