# UnreachableCodeWorker.java

    /*
    ** Module   : UnreachableCodeWorker.java
    ** Abstract : Helper routines for unreachable code processing rule-sets.
    **
    ** Copyright (c) 2005-2022, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- --JPRM-- ----------------Description-----------------
    ** 001 SIY 20050706   @21709 Created initial version.
    ** 002 SIY 20060312   @24992 Added support for NOT and parentheses in
    **                           expression evaluator.
    ** 003 GES 20090518   @42382 Import change.
    ** 004 TJD 20220504          Java 11 compatibility minor changes
    */
    /*
    ** This program is free software: you can redistribute it and/or modify
    ** it under the terms of the GNU Affero General Public License as
    ** published by the Free Software Foundation, either version 3 of the
    ** License, or (at your option) any later version.
    **
    ** This program 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 Affero General Public License for more details.
    **
    ** You may find a copy of the GNU Affero GPL version 3 at the following
    ** location: https://www.gnu.org/licenses/agpl-3.0.en.html
    **
    ** Additional terms under GNU Affero GPL version 3 section 7:
    **
    **   Under Section 7 of the GNU Affero GPL version 3, the following additional
    **   terms apply to the works covered under the License.  These additional terms
    **   are non-permissive additional terms allowed under Section 7 of the GNU
    **   Affero GPL version 3 and may not be removed by you.
    **
    **   0. Attribution Requirement.
    **
    **     You must preserve all legal notices or author attributions in the covered
    **     work or Appropriate Legal Notices displayed by works containing the covered
    **     work.  You may not remove from the covered work any author or developer
    **     credit already included within the covered work.
    **
    **   1. No License To Use Trademarks.
    **
    **     This license does not grant any license or rights to use the trademarks
    **     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
    **     of Golden Code Development Corporation. You are not authorized to use the
    **     name Golden Code, FWD, or the names of any author or contributor, for
    **     publicity purposes without written authorization.
    **
    **   2. No Misrepresentation of Affiliation.
    **
    **     You may not represent yourself as Golden Code Development Corporation or FWD.
    **
    **     You may not represent yourself for publicity purposes as associated with
    **     Golden Code Development Corporation, FWD, or any author or contributor to
    **     the covered work, without written authorization.
    **
    **   3. No Misrepresentation of Source or Origin.
    **
    **     You may not represent the covered work as solely your work.  All modified
    **     versions of the covered work must be marked in a reasonable way to make it
    **     clear that the modified work is not originating from Golden Code Development
    **     Corporation or FWD.  All modified versions must contain the notices of
    **     attribution required in this license.
    */

    package com.goldencode.p2j.convert;

    import java.util.*;

    import com.goldencode.ast.*;
    import com.goldencode.p2j.pattern.*;
    import com.goldencode.p2j.uast.*;
    import com.goldencode.p2j.util.*;

    /**
     * Helper routines for the unreachable code processing rules.  This provides
     * support for constant resolution and for simple expression evaluation
     * to statically determine if a particular conditional execution path can
     * be proven to be unreachable.
     */
    public final class UnreachableCodeWorker
    extends AbstractPatternWorker
    {
       /** Expression evaluates to <code>false</code>. */
       private static final long RES_FALSE = 2;

       /** Expression evaluates to <code>true</code>. */
       private static final long RES_TRUE = 1;

       /** Expression cannot be evaluated statically. */
       private static final long RES_UNKNOWN = 0;

       /**
        * Default constructor which initializes libraries.
        */
       public UnreachableCodeWorker()
       {
          super();
          setLibrary(new Helper());
       }

       /**
        * Resolve constant name into its value.
        *
        * @param   constant
        *          Name of the constant.
        *
        * @return  Value for the known constant name or <code>null</code> if
        *          the name is unknown.
        */
       public Object resolveConstant(String constant)
       {
          if("RES_FALSE".equalsIgnoreCase(constant))
             return Long.valueOf(RES_FALSE);

          if("RES_TRUE".equalsIgnoreCase(constant))
             return Long.valueOf(RES_TRUE);

          if("RES_UNKNOWN".equalsIgnoreCase(constant))
             return Long.valueOf(RES_UNKNOWN);

          return null;
       }

       /**
        * Provides user-level APIs necessary for unreachable code processing.
        */
       public class Helper
       {
          /** Information about known variables */
          HashMap varPool = new HashMap();

          /**
           * Add a variable to the pool of known variables. A variable consists
           * of a name and a list of values.  If the variable is already known
           * in the pool, then a new value is added to the array of known values.
           * <p>
           * At this time, all variables must be of type VAR_CHAR and the values
           * must be the Java version of the Progress STRING.
           *
           * @param   variable
           *          Variable name. Must not be <code>null</code>.
           * @param   value
           *          New variable value. Must not be <code>null</code>.
           *
           * @return  <code>true</code> if operation was successful.
           */
          public boolean addKnownVarValue(String variable, String value)
          {
             if (variable == null || value == null)
                return false;

             variable = variable.toLowerCase();

             List data = (List)varPool.get(variable);

             if (data == null)
                data = new LinkedList();

             data.add(value);

             varPool.put(variable, data);

             return true;
          }

          /**
           * Try to evaluate the expression defined by the passed AST node. If
           * this can be done then return result of evaluation.
           * <p>
           * At present only the following expressions are recognized:
           * <p>
           * <ol>
           *    <li>TRUE</li>
           *    <li>FALSE</li>
           *    <li>VAR_CHAR = STRING</li>
           *    <li>STRING = VAR_CHAR</li>
           *    <li>VAR_CHAR &lt;&gt; STRING</li>
           *    <li>STRING &lt;&gt; VAR_CHAR</li>
           * </ol>
           *
           * @param   node
           *          Expression root node.
           *
           * @return  <code>RES_UNKNOWN</code> if the expression cannot be
           *          evaluated, <code>RES_TRUE</code> if the result is
           *          <code>true</code> and <code>RES_FALSE</code> if the result
           *          is <code>false</code>.
           */
          public long tryEval(Aast node)
          {
             if (node == null ||
                 node.getType() != ProgressParserTokenTypes.EXPRESSION ||
                 node.getFirstChild() == null)
             {
                return RES_UNKNOWN;   // Result is unknown
             }

             return tryEvalNode((AnnotatedAst) node.getFirstChild());
          }

          /**
           * Try to evaluate CASE-WHEN-THEN statement expression which compares
           * a <code>VAR_CHAR</code> to a <code>STRING</code>.
           *
           * @param   var
           *          CASE statement variable name of type <code>VAR_CHAR</code>.
           *
           * @param   value
           *          THEN statement value of type <code>STRING</code>.
           *
           * @return  <code>true</code> if variable contains specified value.
           */
          public boolean tryEvalCase(String var, String value)
          {
             List list = getKnownValues(var);

             if (list == null)
                return false;

             value = character.progressToJavaString(value);

             if (list.indexOf(value) >= 0)
                return true;

             return false;
          }

          /**
           * Get list of known values of the variable for the expression
           * evaluator.
           *
           * @param   var
           *          Variable name (will be automatically translated to lower
           *          case).
           *
           * @return  Array with the variable values or <code>null</code> if no
           *          such variable defined.
           */
          private List getKnownValues(String var)
          {
             if (varPool == null)
                return null;

             return (List)varPool.get(var.toLowerCase());
          }

          /**
           * Expression evaluation worker.
           *
           * @param   node
           *          Expression root node.
           *
           * @return  <code>RES_UNKNOWN</code> if the expression cannot be
           *          evaluated, <code>RES_TRUE</code> if the result is
           *          <code>true</code> and <code>RES_FALSE</code> if the result
           *          is <code>false</code>.
           */
          private long tryEvalNode(AnnotatedAst node)
          {
             if (node == null ||
                 node.getNumberOfChildren() > 1)
             {
                return RES_UNKNOWN;
             }

             AnnotatedAst child = (AnnotatedAst) node.getFirstChild();

             int type = node.getType();

             if (child != null)
             {
                if (type == ProgressParserTokenTypes.LPARENS)
                   return tryEvalNode(child);

                if (type == ProgressParserTokenTypes.KW_NOT)
                {
                   long res = tryEvalNode(child);

                   if (res == RES_FALSE)
                      return RES_TRUE;

                   if (res == RES_TRUE)
                      return RES_FALSE;

                   return res;
                }

                return RES_UNKNOWN;
             }

             if (type == ProgressParserTokenTypes.BOOL_TRUE)
                return RES_TRUE;

             if (type == ProgressParserTokenTypes.BOOL_FALSE)
                return RES_FALSE;

             if (type == ProgressParserTokenTypes.EQUALS ||
                 type == ProgressParserTokenTypes.NOT_EQ)
             {
                boolean isEq = (type == ProgressParserTokenTypes.EQUALS);
                AnnotatedAst tmp = (AnnotatedAst) node.getFirstChild();

                if (tmp == null)
                   return RES_UNKNOWN;

                String var  = null;
                String data = null;

                while (tmp != null)
                {
                   int ttype = tmp.getType();

                   if (ttype ==  ProgressParserTokenTypes.VAR_CHAR)
                      var = tmp.getText();

                   if (ttype == ProgressParserTokenTypes.STRING)
                      data = character.progressToJavaString(tmp.getText());

                   tmp = (AnnotatedAst) tmp.getNextSibling();
                }

                if (var == null || data == null)
                   return RES_UNKNOWN;

                List list = getKnownValues(var);

                if (list == null)
                   return RES_UNKNOWN;

                if (list.indexOf(data) >= 0)
                   return isEq ? RES_TRUE : RES_FALSE;

                return isEq ? RES_FALSE : RES_TRUE;
             }

             return RES_UNKNOWN;   // Result is unknown
          }
       }
    }