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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.rest.guards;

import java.text.*;
import java.util.*;
import java.util.regex.*;

import org.apache.juneau.internal.*;

import static org.apache.juneau.internal.StateMachineState.*;

/**
 * Utility class for matching JEE user roles against string expressions.
 *
 * <p>
 * Supports the following expression constructs:
 * <ul>
 *    <li><js>"foo"</js> - Single arguments.
 *    <li><js>"foo,bar,baz"</js> - Multiple OR'ed arguments.
 *    <li><js>"foo | bar | bqz"</js> - Multiple OR'ed arguments, pipe syntax.
 *    <li><js>"foo || bar || bqz"</js> - Multiple OR'ed arguments, Java-OR syntax.
 *    <li><js>"fo*"</js> - Patterns including <js>'*'</js> and <js>'?'</js>.
 *    <li><js>"fo* &amp; *oo"</js> - Multiple AND'ed arguments, ampersand syntax.
 *    <li><js>"fo* &amp;&amp; *oo"</js> - Multiple AND'ed arguments, Java-AND syntax.
 *    <li><js>"fo* || (*oo || bar)"</js> - Parenthesis.
 * </ul>
 *
 * <ul class='notes'>
 *    <li>AND operations take precedence over OR operations (as expected).
 *    <li>Whitespace is ignored.
 *    <li><jk>null</jk> or empty expressions always match as <jk>false</jk>.
 * </ul>
 */
public class RoleMatcher {

   private final Exp exp;
   private static final AsciiSet
      WS = AsciiSet.create(" \t"),
      OP = AsciiSet.create(",|&"),
      META = AsciiSet.create("*?");

   /**
    * Constructor.
    *
    * @param expression The string expression.
    * @throws ParseException If the expression is malformed.
    */
   public RoleMatcher(String expression) throws ParseException {
      this.exp = parse(expression);
   }

   /**
    * Returns <jk>true</jk> if the specified string matches this expression.
    *
    * @param roles The user roles.
    * @return
    *    <jk>true</jk> if the specified string matches this expression.
    *    <br>Always <jk>false</jk> if the string is <jk>null</jk>.
    */
   public boolean matches(Set<String> roles) {
      return roles != null && exp.matches(roles);
   }

   @Override /* Object */
   public String toString() {
      return exp.toString();
   }

   /**
    * Returns all the tokens used in this expression.
    *
    * @return All the tokens used in this expression.
    */
   public Set<String> getRolesInExpression() {
      Set<String> set = new TreeSet<>();
      exp.appendTokens(set);
      return set;
   }

   private Exp parse(String expression) throws ParseException {
      if (StringUtils.isEmptyOrBlank(expression))
         return new Never();

      expression = expression.trim();

      List<Exp> ors = new ArrayList<>();
      List<Exp> ands = new ArrayList<>();

      StateMachineState state = S01;
      int i = 0, mark = -1;
      int pDepth = 0;
      boolean error = false;

      for (i = 0; i < expression.length(); i++) {
         char c = expression.charAt(i);
         if (state == S01) {
            // S01 = Looking for start
            if (! WS.contains(c)) {
               if (c == '(') {
                  state = S02;
                  pDepth = 0;
                  mark = i+1;
               } else if (OP.contains(c)) {
                  error = true;
                  break;
               } else {
                  state = S03;
                  mark = i;
               }
            }
         } else if (state == S02) {
            // S02 = Found [(], looking for [)].
            if (c == '(')
               pDepth++;
            if (c == ')') {
               if (pDepth > 0)
                  pDepth--;
               else {
                  ands.add(parse(expression.substring(mark, i)));
                  mark = -1;
                  state = S04;
               }
            }
         } else if (state == S03) {
            // S03 = Found [A], looking for end of A.
            if (WS.contains(c) || OP.contains(c)) {
               ands.add(parseOperand(expression.substring(mark, i)));
               mark = -1;
               if (WS.contains(c)) {
                  state = S04;
               } else {
                  i--;
                  state = S05;
               }
            }
         } else if (state == S04) {
            // S04 = Found [A ], looking for & or | or ,.
            if (! WS.contains(c)) {
               if (OP.contains(c)) {
                  i--;
                  state = S05;
               } else {
                  error = true;
                  break;
               }
            }
         } else if (state == S05) {
            // S05 = Found & or | or ,.
            if (c == '&') {
               //ands.add(operand);
               state = S06;
            } else /* (c == '|' || c == ',') */ {
                if (ands.size() == 1) {
                   ors.add(ands.get(0));
                } else {
                   ors.add(new And(ands));
                }
                ands.clear();
                if (c == '|') {
                   state = S07;
                } else {
                   state = S01;
                }
            }
         } else if (state == S06) {
            // S06 = Found &, looking for & or other
            if (! WS.contains(c)) {
               if (c != '&')
                  i--;
               state = S01;
            }
         } else /* (state == S07) */ {
            // S07 = Found |, looking for | or other
            if (! WS.contains(c)) {
               if (c != '|')
                  i--;
               state = S01;
            }
         }
      }

      if (error)
         throw new ParseException("Invalid character in expression '"+expression+"' at position " + i + ". state=" + state, i);

      if (state == S01)
         throw new ParseException("Could not find beginning of clause in '"+expression+"'", i);
      if (state == S02)
         throw new ParseException("Could not find matching parenthesis in expression '"+expression+"'", i);
      if (state == S05 || state == S06 || state == S07)
         throw new ParseException("Dangling clause in expression '"+expression+"'", i);

      if (mark != -1)
         ands.add(parseOperand(expression.substring(mark, expression.length())));
      if (ands.size() == 1)
         ors.add(ands.get(0));
      else
         ors.add(new And(ands));

      if (ors.size() == 1)
         return ors.get(0);
      return new Or(ors);
   }

   private static Exp parseOperand(String operand) {
      boolean hasMeta = false;
      for (int i = 0; i < operand.length() && ! hasMeta; i++) {
         char c = operand.charAt(i);
         hasMeta |= META.contains(c);
      }
      return hasMeta ? new Match(operand) : new Eq(operand);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Expression classes
   //-----------------------------------------------------------------------------------------------------------------

   abstract static class Exp {

      abstract boolean matches(Set<String> roles);

      void appendTokens(Set<String> set) {}
   }

   static class Never extends Exp {
      @Override
      boolean matches(Set<String> roles) {
         return false;
      }

      @Override /* Object */
      public String toString() {
         return "(NEVER)";
      }
   }

   static class And extends Exp {
      Exp[] clauses;

      And(List<Exp> clauses) {
         this.clauses = clauses.toArray(new Exp[clauses.size()]);
      }

      @Override /* Exp */
      boolean matches(Set<String> roles) {
         for (Exp e : clauses)
            if (! e.matches(roles))
               return false;
         return true;
      }

      @Override /* Exp */
      void appendTokens(Set<String> set) {
         for (Exp clause : clauses)
            clause.appendTokens(set);
      }

      @Override /* Object */
      public String toString() {
         return "(& " + StringUtils.join(clauses, " ") + ')';
      }
   }

   static class Or extends Exp {
      Exp[] clauses;

      Or(List<Exp> clauses) {
         this.clauses = clauses.toArray(new Exp[clauses.size()]);
      }

      @Override
      boolean matches(Set<String> roles) {
         for (Exp e : clauses)
            if (e.matches(roles))
               return true;
         return false;
      }

      @Override /* Exp */
      void appendTokens(Set<String> set) {
         for (Exp clause : clauses)
            clause.appendTokens(set);
      }

      @Override /* Object */
      public String toString() {
         return "(| " + StringUtils.join(clauses, " ") + ')';
      }
   }

   static class Eq extends Exp {
      final String operand;

      Eq(String operand) {
         this.operand = operand;
      }

      @Override /* Exp */
      boolean matches(Set<String> roles) {
         for (String role : roles)
            if (operand.equals(role))
               return true;
         return false;
      }

      @Override /* Exp */
      void appendTokens(Set<String> set) {
         set.add(operand);
      }

      @Override /* Object */
      public String toString() {
         return "[= " + operand + "]";
      }
   }

   static class Match extends Exp {
      final Pattern p;
      final String operand;

      Match(String operand) {
         this.operand = operand;
         p = StringUtils.getMatchPattern(operand);
      }

      @Override /* Exp */
      boolean matches(Set<String> roles) {
         for (String role : roles)
            if (p.matcher(role).matches())
               return true;
         return false;
      }

      @Override /* Exp */
      void appendTokens(Set<String> set) {
         set.add(operand);
      }

      @Override /* Object */
      public String toString() {
         return "[* " + p.pattern().replaceAll("\\\\[QE]", "") + "]";
      }
   }
}