code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 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 java.util.ArrayDeque;
  import java.util.Deque;
  
  import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
  
  /**
   * <p>
   * Restricts the number of boolean operators ({@code &amp;&amp;}, {@code ||},
   * {@code &amp;}, {@code |} and {@code ^}) in an expression.
   * </p>
   * <p>
   * Rationale: Too many conditions leads to code that is difficult to read
   * and hence debug and maintain.
   * </p>
   * <p>
   * Note that the operators {@code &amp;} and {@code |} are not only integer bitwise
   * operators, they are also the
   * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-15.html#jls-15.22.2">
   * non-shortcut versions</a> of the boolean operators {@code &amp;&amp;} and {@code ||}.
   * </p>
   * <p>
   * Note that {@code &amp;}, {@code |} and {@code ^} are not checked if they are part
   * of constructor or method call because they can be applied to non-boolean
   * variables and Checkstyle does not know types of methods from different classes.
   * </p>
   * <ul>
   * <li>
   * Property {@code max} - Specify the maximum number of boolean operations
   * allowed in one expression.
   * Type is {@code int}.
   * Default value is {@code 3}.
   * </li>
   * <li>
   * Property {@code tokens} - tokens to check
   * Type is {@code java.lang.String[]}.
   * Validation type is {@code tokenSet}.
   * Default value is:
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LAND">
   * LAND</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BAND">
   * BAND</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LOR">
   * LOR</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BOR">
   * BOR</a>,
   * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#BXOR">
   * BXOR</a>.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name="BooleanExpressionComplexity"/&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * public class Test
   * {
   * public static void main(String ... args)
   * {
   * boolean a = true;
   * boolean b = false;
   *
   * boolean c = (a &amp; b) | (b ^ a);       // OK, 1(&amp;) + 1(|) + 1(^) = 3 (max allowed 3)
   *
   * boolean d = (a &amp; b) ^ (a || b) | a;  // violation, 1(&amp;) + 1(^) + 1(||) + 1(|) = 4
   * }
   * }
   * </pre>
   * <p>
   * To configure the check with 5 allowed operation in boolean expression:
   * </p>
   * <pre>
   * &lt;module name="BooleanExpressionComplexity"&gt;
   *   &lt;property name="max" value="5"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * public class Test
   * {
   *  public static void main(String ... args)
   *  {
   *   boolean a = true;
   *   boolean b = false;
   *
   *   boolean c = (a &amp; b) | (b ^ a) | (a ^ b);   // OK, 1(&amp;) + 1(|) + 1(^) + 1(|) + 1(^) = 5
   *
   *   boolean d = (a | b) ^ (a | b) ^ (a || b) &amp; b; // violation,
   *                                               // 1(|) + 1(^) + 1(|) + 1(^) + 1(||) + 1(&amp;) = 6
   *  }
   * }
   * </pre>
   * <p>
   * To configure the check to ignore {@code &amp;} and {@code |}:
   * </p>
   * <pre>
   * &lt;module name="BooleanExpressionComplexity"&gt;
   *   &lt;property name="tokens" value="BXOR,LAND,LOR"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>Code Example:</p>
   * <pre>
   * public class Test
   * {
   *  public static void main(String ... args)
   *   {
   *     boolean a = true;
   *     boolean b = false;
   *
   *     boolean c = (!a &amp;&amp; b) | (a || !b) ^ a;    // OK, 1(&amp;&amp;) + 1(||) + 1(^) = 3
   *                                                // | is ignored here
   *
   *     boolean d = a ^ (a || b) ^ (b || a) &amp; a; // violation, 1(^) + 1(||) + 1(^) + 1(||) = 4
   *                                               // &amp; is ignored here
   *    }
   *  }
   * </pre>
   *
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code booleanExpressionComplexity}
   * </li>
   * </ul>
   *
   * @since 3.4
   */
  @FileStatefulCheck
  public final class BooleanExpressionComplexityCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "booleanExpressionComplexity";
  
      /** Default allowed complexity. */
      private static final int DEFAULT_MAX = 3;
  
      /** Stack of contexts. */
      private final Deque<Context> contextStack = new ArrayDeque<>();
      /** Specify the maximum number of boolean operations allowed in one expression. */
      private int max;
      /** Current context. */
      private Context context = new Context(false);
  
      /** Creates new instance of the check. */
      public BooleanExpressionComplexityCheck() {
          max = DEFAULT_MAX;
      }
  
      @Override
      public int[] getDefaultTokens() {
          return new int[] {
              TokenTypes.CTOR_DEF,
              TokenTypes.METHOD_DEF,
              TokenTypes.EXPR,
              TokenTypes.LAND,
              TokenTypes.BAND,
              TokenTypes.LOR,
              TokenTypes.BOR,
              TokenTypes.BXOR,
              TokenTypes.COMPACT_CTOR_DEF,
          };
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.CTOR_DEF,
              TokenTypes.METHOD_DEF,
              TokenTypes.EXPR,
              TokenTypes.COMPACT_CTOR_DEF,
          };
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return new int[] {
              TokenTypes.CTOR_DEF,
              TokenTypes.METHOD_DEF,
              TokenTypes.EXPR,
              TokenTypes.LAND,
              TokenTypes.BAND,
              TokenTypes.LOR,
              TokenTypes.BOR,
              TokenTypes.BXOR,
              TokenTypes.COMPACT_CTOR_DEF,
          };
      }
  
      /**
       * Setter to specify the maximum number of boolean operations allowed in one expression.
       *
       * @param max new maximum allowed complexity.
       */
      public void setMax(int max) {
          this.max = max;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          switch (ast.getType()) {
              case TokenTypes.CTOR_DEF:
              case TokenTypes.METHOD_DEF:
              case TokenTypes.COMPACT_CTOR_DEF:
                  visitMethodDef(ast);
                  break;
              case TokenTypes.EXPR:
                  visitExpr();
                  break;
              case TokenTypes.BOR:
                  if (!isPipeOperator(ast) && !isPassedInParameter(ast)) {
                      context.visitBooleanOperator();
                  }
                  break;
              case TokenTypes.BAND:
              case TokenTypes.BXOR:
                  if (!isPassedInParameter(ast)) {
                      context.visitBooleanOperator();
                  }
                  break;
              case TokenTypes.LAND:
              case TokenTypes.LOR:
                  context.visitBooleanOperator();
                  break;
              default:
                  throw new IllegalArgumentException("Unknown type: " + ast);
          }
      }
  
      /**
       * Checks if logical operator is part of constructor or method call.
       *
       * @param logicalOperator logical operator
       * @return true if logical operator is part of constructor or method call
       */
      private static boolean isPassedInParameter(DetailAST logicalOperator) {
          return logicalOperator.getParent().getParent().getType() == TokenTypes.ELIST;
      }
  
      /**
       * Checks if {@link TokenTypes#BOR binary OR} is applied to exceptions
       * in
       * <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20">
       * multi-catch</a> (pipe-syntax).
       *
       * @param binaryOr {@link TokenTypes#BOR binary or}
       * @return true if binary or is applied to exceptions in multi-catch.
       */
      private static boolean isPipeOperator(DetailAST binaryOr) {
          return binaryOr.getParent().getType() == TokenTypes.TYPE;
      }
  
      @Override
      public void leaveToken(DetailAST ast) {
          switch (ast.getType()) {
              case TokenTypes.CTOR_DEF:
              case TokenTypes.METHOD_DEF:
              case TokenTypes.COMPACT_CTOR_DEF:
                  leaveMethodDef();
                  break;
              case TokenTypes.EXPR:
                  leaveExpr(ast);
                  break;
              default:
                  // Do nothing
          }
      }
  
      /**
       * Creates new context for a given method.
       *
       * @param ast a method we start to check.
       */
      private void visitMethodDef(DetailAST ast) {
          contextStack.push(context);
          final boolean check = !CheckUtil.isEqualsMethod(ast);
          context = new Context(check);
      }
  
      /** Removes old context. */
      private void leaveMethodDef() {
          context = contextStack.pop();
      }
  
      /** Creates and pushes new context. */
      private void visitExpr() {
          contextStack.push(context);
          context = new Context(context.isChecking());
      }
  
      /**
       * Restores previous context.
       *
       * @param ast expression we leave.
       */
      private void leaveExpr(DetailAST ast) {
          context.checkCount(ast);
          context = contextStack.pop();
      }
  
      /**
       * Represents context (method/expression) in which we check complexity.
       *
       */
      private final class Context {
  
          /**
           * Should we perform check in current context or not.
           * Usually false if we are inside equals() method.
           */
          private final boolean checking;
          /** Count of boolean operators. */
          private int count;
  
          /**
           * Creates new instance.
           *
           * @param checking should we check in current context or not.
           */
          private Context(boolean checking) {
              this.checking = checking;
          }
  
          /**
           * Getter for checking property.
           *
           * @return should we check in current context or not.
           */
          public boolean isChecking() {
              return checking;
          }
  
          /** Increases operator counter. */
          public void visitBooleanOperator() {
              ++count;
          }
  
          /**
           * Checks if we violate maximum allowed complexity.
           *
           * @param ast a node we check now.
           */
          public void checkCount(DetailAST ast) {
              if (checking && count > max) {
                  final DetailAST parentAST = ast.getParent();
  
                  log(parentAST, MSG_KEY, count, max);
              }
          }
  
      }
  
  }
  