/*
 * 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.math3.distribution;

import org.apache.commons.math3.exception.NumberIsTooLargeException;
import org.apache.commons.math3.exception.OutOfRangeException;

/**
 * Base interface for distributions on the reals.
 *
 * @since 3.0
 */
public interface RealDistribution {
    /**
     * For a random variable {@code X} whose values are distributed according to this distribution,
     * this method returns {@code P(X = x)}. In other words, this method represents the probability
     * mass function (PMF) for the distribution.
     *
     * @param x the point at which the PMF is evaluated
     * @return the value of the probability mass function at point {@code x}
     */
    double probability(double x);

    /**
     * Returns the probability density function (PDF) of this distribution evaluated at the
     * specified point {@code x}. In general, the PDF is the derivative of the {@link
     * #cumulativeProbability(double) CDF}. If the derivative does not exist at {@code x}, then an
     * appropriate replacement should be returned, e.g. {@code Double.POSITIVE_INFINITY}, {@code
     * Double.NaN}, or the limit inferior or limit superior of the difference quotient.
     *
     * @param x the point at which the PDF is evaluated
     * @return the value of the probability density function at point {@code x}
     */
    double density(double x);

    /**
     * For a random variable {@code X} whose values are distributed according to this distribution,
     * this method returns {@code P(X <= x)}. In other words, this method represents the
     * (cumulative) distribution function (CDF) for this distribution.
     *
     * @param x the point at which the CDF is evaluated
     * @return the probability that a random variable with this distribution takes a value less than
     *     or equal to {@code x}
     */
    double cumulativeProbability(double x);

    /**
     * For a random variable {@code X} whose values are distributed according to this distribution,
     * this method returns {@code P(x0 < X <= x1)}.
     *
     * @param x0 the exclusive lower bound
     * @param x1 the inclusive upper bound
     * @return the probability that a random variable with this distribution takes a value between
     *     {@code x0} and {@code x1}, excluding the lower and including the upper endpoint
     * @throws NumberIsTooLargeException if {@code x0 > x1}
     * @deprecated As of 3.1. In 4.0, this method will be renamed {@code probability(double x0,
     *     double x1)}.
     */
    @Deprecated
    double cumulativeProbability(double x0, double x1) throws NumberIsTooLargeException;

    /**
     * Computes the quantile function of this distribution. For a random variable {@code X}
     * distributed according to this distribution, the returned value is
     *
     * <ul>
     *   <li><code>inf{x in R | P(X<=x) >= p}</code> for {@code 0 < p <= 1},
     *   <li><code>inf{x in R | P(X<=x) > 0}</code> for {@code p = 0}.
     * </ul>
     *
     * @param p the cumulative probability
     * @return the smallest {@code p}-quantile of this distribution (largest 0-quantile for {@code p
     *     = 0})
     * @throws OutOfRangeException if {@code p < 0} or {@code p > 1}
     */
    double inverseCumulativeProbability(double p) throws OutOfRangeException;

    /**
     * Use this method to get the numerical value of the mean of this distribution.
     *
     * @return the mean or {@code Double.NaN} if it is not defined
     */
    double getNumericalMean();

    /**
     * Use this method to get the numerical value of the variance of this distribution.
     *
     * @return the variance (possibly {@code Double.POSITIVE_INFINITY} as for certain cases in
     *     {@link TDistribution}) or {@code Double.NaN} if it is not defined
     */
    double getNumericalVariance();

    /**
     * Access the lower bound of the support. This method must return the same value as {@code
     * inverseCumulativeProbability(0)}. In other words, this method must return
     *
     * <p><code>inf {x in R | P(X <= x) > 0}</code>.
     *
     * @return lower bound of the support (might be {@code Double.NEGATIVE_INFINITY})
     */
    double getSupportLowerBound();

    /**
     * Access the upper bound of the support. This method must return the same value as {@code
     * inverseCumulativeProbability(1)}. In other words, this method must return
     *
     * <p><code>inf {x in R | P(X <= x) = 1}</code>.
     *
     * @return upper bound of the support (might be {@code Double.POSITIVE_INFINITY})
     */
    double getSupportUpperBound();

    /**
     * Whether or not the lower bound of support is in the domain of the density function. Returns
     * true iff {@code getSupporLowerBound()} is finite and {@code density(getSupportLowerBound())}
     * returns a non-NaN, non-infinite value.
     *
     * @return true if the lower bound of support is finite and the density function returns a
     *     non-NaN, non-infinite value there
     * @deprecated to be removed in 4.0
     */
    @Deprecated
    boolean isSupportLowerBoundInclusive();

    /**
     * Whether or not the upper bound of support is in the domain of the density function. Returns
     * true iff {@code getSupportUpperBound()} is finite and {@code density(getSupportUpperBound())}
     * returns a non-NaN, non-infinite value.
     *
     * @return true if the upper bound of support is finite and the density function returns a
     *     non-NaN, non-infinite value there
     * @deprecated to be removed in 4.0
     */
    @Deprecated
    boolean isSupportUpperBoundInclusive();

    /**
     * Use this method to get information about whether the support is connected, i.e. whether all
     * values between the lower and upper bound of the support are included in the support.
     *
     * @return whether the support is connected or not
     */
    boolean isSupportConnected();

    /**
     * Reseed the random generator used to generate samples.
     *
     * @param seed the new seed
     */
    void reseedRandomGenerator(long seed);

    /**
     * Generate a random value sampled from this distribution.
     *
     * @return a random value.
     */
    double sample();

    /**
     * Generate a random sample from the distribution.
     *
     * @param sampleSize the number of random values to generate
     * @return an array representing the random sample
     * @throws org.apache.commons.math3.exception.NotStrictlyPositiveException if {@code sampleSize}
     *     is not positive
     */
    double[] sample(int sampleSize);
}