////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2020 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
////////////////////////////////////////////////////////////////////////////////

package com.puppycrawl.tools.checkstyle.checks.metrics;

import com.puppycrawl.tools.checkstyle.api.TokenTypes;

/**
 * <p>
 * Checks the number of other classes a given class relies on. Also the square
 * of this has been shown to indicate the amount of maintenance required
 * in functional programs (on a file basis) at least.
 * </p>
 * <p>
 * This check processes files in the following way:
 * </p>
 * <ol>
 * <li>
 * Iterates over all tokens that might contain type reference.
 * </li>
 * <li>
 * If a class was imported with direct import (i.e. {@code import java.math.BigDecimal}),
 * or the class was referenced with the package name (i.e. {@code java.math.BigDecimal value})
 * and the package was added to the {@code excludedPackages} parameter,
 * the class does not increase complexity.
 * </li>
 * <li>
 * If a class name was added to the {@code excludedClasses} parameter,
 * the class does not increase complexity.
 * </li>
 * </ol>
 * <ul>
 * <li>
 * Property {@code max} - Specify the maximum threshold allowed.
 * Default value is {@code 20}.
 * </li>
 * <li>
 * Property {@code excludedClasses} - Specify user-configured class names to ignore.
 * Default value is {@code ArrayIndexOutOfBoundsException, ArrayList, Boolean, Byte,
 * Character, Class, Deprecated, Deque, Double, Exception, Float, FunctionalInterface,
 * HashMap, HashSet, IllegalArgumentException, IllegalStateException,
 * IndexOutOfBoundsException, Integer, LinkedList, List, Long, Map, NullPointerException,
 * Object, Override, Queue, RuntimeException, SafeVarargs, SecurityException, Set, Short,
 * SortedMap, SortedSet, String, StringBuffer, StringBuilder, SuppressWarnings, Throwable,
 * TreeMap, TreeSet, UnsupportedOperationException, Void, boolean, byte, char, double,
 * float, int, long, short, void}.
 * </li>
 * <li>
 * Property {@code excludeClassesRegexps} - Specify user-configured regular
 * expressions to ignore classes.
 * Default value is {@code ^$}.
 * </li>
 * <li>
 * Property {@code excludedPackages} - Specify user-configured packages to ignore.
 * All excluded packages should end with a period, so it also appends a dot to a package name.
 * Default value is {@code {}}.
 * </li>
 * </ul>
 * <p>
 * To configure the check:
 * </p>
 * <pre>
 * &lt;module name="ClassFanOutComplexity"/&gt;
 * </pre>
 * <p>
 * Example:
 * </p>
 * <p>
 * The check passes without violations in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 *   Place place = new Place(); // Counted, 3
 * }
 * </pre>
 * <p>
 * The check results in a violation in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 *   // mention of 18 other user defined classes
 *   Place place = new Place(); // violation, total is 21
 * }
 * </pre>
 * <p>
 * To configure the check with a threshold of 2:
 * </p>
 * <pre>
 * &lt;module name="ClassFanOutComplexity"&gt;
 *   &lt;property name="max" value="2"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>
 * Example:
 * </p>
 * <p>
 * The check passes without violations in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 * }
 * </pre>
 * <p>
 * The check results in a violation in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 *   Place place = new Place(); // violation, total is 3
 * }
 * </pre>
 * <p>
 * To configure the check with three excluded classes {@code HashMap},
 * {@code HashSet} and {@code Place}:
 * </p>
 * <pre>
 * &lt;module name="ClassFanOutComplexity"&gt;
 *   &lt;property name="excludedClasses" value="HashMap, HashSet, Place"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>
 * Example:
 * </p>
 * <p>
 * The check passes without violations in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set counted 1, HashSet ignored
 *   Map map = new HashMap(); // Map counted 2, HashMap ignored
 *   Date date = new Date(); // Counted, 3
 *   Time time = new Time(); // Counted, 4
 *   // mention of 16 other user defined classes
 *   Place place = new Place(); // Ignored
 * }
 * </pre>
 * <p>
 * The check results in a violation in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set counted 1, HashSet ignored
 *   Map map = new HashMap(); // Map counted 2, HashMap ignored
 *   Date date = new Date(); // Counted, 3
 *   Time time = new Time(); // Counted, 4
 *   // mention of 16 other user defined classes
 *   Space space = new Space(); // violation, total is 21
 * }
 * </pre>
 * <p>
 * To configure the check to exclude classes with a regular expression
 * {@code .*Reader$}:
 * </p>
 * <pre>
 * &lt;module name="ClassFanOutComplexity"&gt;
 *   &lt;property name="excludeClassesRegexps" value=".*Reader$"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>
 * Example:
 * </p>
 * <p>
 * The check passes without violations in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 *   // mention of 18 other user defined classes
 *   BufferedReader br; // Ignored
 * }
 * </pre>
 * <p>
 * The check results in a violation in the following:
 * </p>
 * <pre>
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 *   // mention of 18 other user defined classes
 *   File file; // violation, total is 21
 * }
 * </pre>
 * <p>
 * To configure the check with an excluded package {@code java.io}:
 * </p>
 * <pre>
 * &lt;module name="ClassFanOutComplexity"&gt;
 *   &lt;property name="excludedPackages" value="java.io"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>
 * Example:
 * </p>
 * <p>
 * The check passes without violations in the following:
 * </p>
 * <pre>
 * import java.io.BufferedReader;
 *
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 *   // mention of 18 other user defined classes
 *   BufferedReader br; // Ignored
 * }
 * </pre>
 * <p>
 * The check results in a violation in the following:
 * </p>
 * <pre>
 * import java.util.StringTokenizer;
 *
 * class InputClassComplexity {
 *   Set set = new HashSet(); // Set, HashSet ignored due to default excludedClasses property
 *   Map map = new HashMap(); // Map, HashMap ignored due to default excludedClasses property
 *   Date date = new Date(); // Counted, 1
 *   Time time = new Time(); // Counted, 2
 *   // mention of 18 other user defined classes
 *   StringTokenizer st; // violation, total is 21
 * }
 * </pre>
 * <p>
 * Override property {@code excludedPackages} to mark some packages as excluded.
 * Each member of {@code excludedPackages} should be a valid identifier:
 * </p>
 * <ul>
 * <li>
 * {@code java.util} - valid, excludes all classes inside {@code java.util},
 * but not from the subpackages.
 * </li>
 * <li>
 * {@code java.util.} - invalid, should not end with a dot.
 * </li>
 * <li>
 * {@code java.util.*} - invalid, should not end with a star.
 * </li>
 * </ul>
 * <p>
 * Note, that checkstyle will ignore all classes from the {@code java.lang}
 * package and its subpackages, even if the {@code java.lang} was not listed
 * in the {@code excludedPackages} parameter.
 * </p>
 * <p>
 * Also note, that {@code excludedPackages} will not exclude classes, imported
 * via wildcard (e.g. {@code import java.math.*}). Instead of wildcard import
 * you should use direct import (e.g. {@code import java.math.BigDecimal}).
 * </p>
 * <p>
 * Also note, that checkstyle will not exclude classes within the same file even
 * if it was listed in the {@code excludedPackages} parameter.
 * For example, assuming the config is
 * </p>
 * <pre>
 * &lt;module name="ClassFanOutComplexity"&gt;
 *   &lt;property name="excludedPackages" value="a.b"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>
 * And the file {@code a.b.Foo.java} is:
 * </p>
 * <pre>
 * package a.b;
 *
 * import a.b.Bar;
 * import a.b.c.Baz;
 *
 * class Foo {
 *   Bar bar; // Will be ignored, located inside ignored a.b package
 *   Baz baz; // Will not be ignored, located inside a.b.c package
 *   Data data; // Will not be ignored, same file
 *
 *   class Data {
 *     Foo foo; // Will not be ignored, same file
 *   }
 * }
 * </pre>
 * <p>
 * The {@code bar} member will not be counted, since the {@code a.b}
 * added to the {@code excludedPackages}. The {@code baz} member will be counted,
 * since the {@code a.b.c} was not added to the {@code excludedPackages}.
 * The {@code data} and {@code foo} members will be counted, as they are inside same file.
 * </p>
 *
 * @since 3.4
 */
public final class ClassFanOutComplexityCheck extends AbstractClassCouplingCheck {

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_KEY = "classFanOutComplexity";

    /** Default value of max value. */
    private static final int DEFAULT_MAX = 20;

    /** Creates new instance of this check. */
    public ClassFanOutComplexityCheck() {
        super(DEFAULT_MAX);
    }

    @Override
    public int[] getRequiredTokens() {
        return new int[] {
            TokenTypes.PACKAGE_DEF,
            TokenTypes.IMPORT,
            TokenTypes.CLASS_DEF,
            TokenTypes.EXTENDS_CLAUSE,
            TokenTypes.IMPLEMENTS_CLAUSE,
            TokenTypes.ANNOTATION,
            TokenTypes.INTERFACE_DEF,
            TokenTypes.ENUM_DEF,
            TokenTypes.TYPE,
            TokenTypes.LITERAL_NEW,
            TokenTypes.LITERAL_THROWS,
            TokenTypes.ANNOTATION_DEF,
        };
    }

    @Override
    public int[] getAcceptableTokens() {
        return getRequiredTokens();
    }

    @Override
    protected String getLogMessageId() {
        return MSG_KEY;
    }

}