/*
    * 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.scxml;
  
  import java.io.StringWriter;
  import java.util.HashSet;
  import java.util.IdentityHashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.commons.scxml.model.Data;
  import org.apache.commons.scxml.model.Datamodel;
  import org.apache.commons.scxml.model.Parallel;
  import org.apache.commons.scxml.model.Path;
  import org.apache.commons.scxml.model.State;
  import org.apache.commons.scxml.model.Transition;
  import org.apache.commons.scxml.model.TransitionTarget;
  import org.apache.commons.scxml.semantics.ErrorConstants;
  import org.w3c.dom.CharacterData;
  import org.w3c.dom.Node;
  import org.w3c.dom.Text;
  
  /***
   * Helper class, all methods static final.
   *
   */
  public final class SCXMLHelper {
  
      /***
       * Return true if the string is empty.
       *
       * @param attr The String to test
       * @return Is string empty
       */
      public static boolean isStringEmpty(final String attr) {
          if (attr == null || attr.trim().length() == 0) {
              return true;
          }
          return false;
      }
  
      /***
       * Checks whether a transition target tt (State or Parallel) is a
       * descendant of the transition target context.
       *
       * @param tt
       *            TransitionTarget to check - a potential descendant
       * @param ctx
       *            TransitionTarget context - a potential ancestor
       * @return true iff tt is a descendant of ctx, false otherwise
       */
      public static boolean isDescendant(final TransitionTarget tt,
              final TransitionTarget ctx) {
          TransitionTarget parent = tt.getParent();
          while (parent != null) {
              if (parent == ctx) {
                  return true;
              }
              parent = parent.getParent();
          }
          return false;
      }
  
      /***
       * Creates a set which contains given states and all their ancestors
       * recursively up to the upper bound. Null upperBound means root
       * of the state machine.
       *
       * @param states The Set of States
       * @param upperBounds The Set of upper bound States
       * @return transitive closure of a given state set
       */
      public static Set getAncestorClosure(final Set states,
              final Set upperBounds) {
          Set closure = new HashSet(states.size() * 2);
          for (Iterator i = states.iterator(); i.hasNext();) {
              TransitionTarget tt = (TransitionTarget) i.next();
              while (tt != null) {
                  if (!closure.add(tt)) {
                      //tt is already a part of the closure
                      break;
                 }
                 if (upperBounds != null && upperBounds.contains(tt)) {
                     break;
                 }
                 tt = tt.getParent();
             }
         }
         return closure;
     }
 
     /***
      * Checks whether a given set of states is a legal Harel State Table
      * configuration (with the respect to the definition of the OR and AND
      * states).
      *
      * @param states
      *            a set of states
      * @param errRep
      *            ErrorReporter to report detailed error info if needed
      * @return true if a given state configuration is legal, false otherwise
      */
     public static boolean isLegalConfig(final Set states,
             final ErrorReporter errRep) {
         /*
          * For every active state we add 1 to the count of its parent. Each
          * Parallel should reach count equal to the number of its children and
          * contribute by 1 to its parent. Each State should reach count exactly
          * 1. SCXML elemnt (top) should reach count exactly 1. We essentially
          * summarize up the hierarchy tree starting with a given set of
          * states = active configuration.
          */
         boolean legalConfig = true; // let's be optimists
         Map counts = new IdentityHashMap();
         Set scxmlCount = new HashSet();
         for (Iterator i = states.iterator(); i.hasNext();) {
             TransitionTarget tt = (TransitionTarget) i.next();
             TransitionTarget parent = null;
             while ((parent = tt.getParent()) != null) {
                 HashSet cnt = (HashSet) counts.get(parent);
                 if (cnt == null) {
                     cnt = new HashSet();
                     counts.put(parent, cnt);
                 }
                 cnt.add(tt);
                 tt = parent;
             }
             //top-level contribution
             scxmlCount.add(tt);
         }
         //Validate counts:
         for (Iterator i = counts.entrySet().iterator(); i.hasNext();) {
             Map.Entry entry = (Map.Entry) i.next();
             TransitionTarget tt = (TransitionTarget) entry.getKey();
             Set count = (Set) entry.getValue();
             if (tt instanceof Parallel) {
                 Parallel p = (Parallel) tt;
                 if (count.size() < p.getChildren().size()) {
                     errRep.onError(ErrorConstants.ILLEGAL_CONFIG,
                         "Not all AND states active for parallel "
                         + p.getId(), entry);
                     legalConfig = false;
                 }
             } else {
                 if (count.size() > 1) {
                     errRep.onError(ErrorConstants.ILLEGAL_CONFIG,
                         "Multiple OR states active for state "
                         + tt.getId(), entry);
                     legalConfig = false;
                 }
             }
             count.clear(); //cleanup
         }
         if (scxmlCount.size() > 1) {
             errRep.onError(ErrorConstants.ILLEGAL_CONFIG,
                     "Multiple top-level OR states active!", scxmlCount);
         }
         //cleanup
         scxmlCount.clear();
         counts.clear();
         return legalConfig;
     }
 
     /***
      * Finds the least common ancestor of transition targets tt1 and tt2 if
      * one exists.
      *
      * @param tt1 First TransitionTarget
      * @param tt2 Second TransitionTarget
      * @return closest common ancestor of tt1 and tt2 or null
      */
     public static TransitionTarget getLCA(final TransitionTarget tt1,
             final TransitionTarget tt2) {
         if (tt1 == tt2) {
             return tt1; //self-transition
         } else if (isDescendant(tt1, tt2)) {
             return tt2;
         } else if (isDescendant(tt2, tt1)) {
             return tt1;
         }
         Set parents = new HashSet();
         TransitionTarget tmp = tt1;
         while ((tmp = tmp.getParent()) != null) {
             parents.add(tmp);
         }
         tmp = tt2;
         while ((tmp = tmp.getParent()) != null) {
             //test redundant add = common ancestor
             if (!parents.add(tmp)) {
                 parents.clear();
                 return tmp;
             }
         }
         return null;
     }
 
     /***
      * Returns the set of all states (and parallels) which are exited if a
      * given transition t is going to be taken.
      * Current states are necessary to be taken into account
      * due to orthogonal states and cross-region transitions -
      * see UML specs for more details.
      *
      * @param t
      *            transition to be taken
      * @param currentStates
      *            the set of current states (simple states only)
      * @return a set of all states (including composite) which are exited if a
      *         given transition is taken
      */
     public static Set getStatesExited(final Transition t,
             final Set currentStates) {
         Set allStates = new HashSet();
         if (t.getTargets().size() == 0) {
             return allStates;
         }
         Path p = (Path) t.getPaths().get(0); // all paths have same upseg
         //the easy part
         allStates.addAll(p.getUpwardSegment());
         TransitionTarget source = t.getParent();
         for (Iterator act = currentStates.iterator(); act.hasNext();) {
             TransitionTarget a = (TransitionTarget) act.next();
             if (isDescendant(a, source)) {
                 boolean added = false;
                 added = allStates.add(a);
                 while (added && a != source) {
                     a = a.getParent();
                     added = allStates.add(a);
                 }
             }
         }
         if (p.isCrossRegion()) {
             for (Iterator regions = p.getRegionsExited().iterator();
                     regions.hasNext();) {
                 Parallel par = ((Parallel) ((State) regions.next()).
                     getParent());
                 //let's find affected states in sibling regions
                 for (Iterator siblings = par.getChildren().iterator();
                         siblings.hasNext();) {
                     State s = (State) siblings.next();
                     for (Iterator act = currentStates.iterator();
                             act.hasNext();) {
                         TransitionTarget a = (TransitionTarget) act.next();
                         if (isDescendant(a, s)) {
                             //a is affected
                             boolean added = false;
                             added = allStates.add(a);
                             while (added && a != s) {
                                 a = a.getParent();
                                 added = allStates.add(a);
                             }
                         }
                     }
                 }
             }
         }
         return allStates;
     }
 
     /***
      * According to the UML definition, two transitions
      * are conflicting if the sets of states they exit overlap.
      *
      * @param t1 a transition to check against t2
      * @param t2 a transition to check against t1
      * @param currentStates the set of current states (simple states only)
      * @return true if the t1 and t2 are conflicting transitions
      * @see #getStatesExited(Transition, Set)
      */
     public static boolean inConflict(final Transition t1,
             final Transition t2, final Set currentStates) {
         Set ts1 = getStatesExited(t1, currentStates);
         Set ts2 = getStatesExited(t2, currentStates);
         ts1.retainAll(ts2);
         if (ts1.isEmpty()) {
             return false;
         }
         return true;
     }
 
     /***
      * Whether the first argument is a subtype of the second.
      *
      * @param child The candidate subtype
      * @param parent The supertype
      * @return true if child is subtype of parent, otherwise false
      */
     public static boolean subtypeOf(final Class child, final Class parent) {
         if (child == null || parent == null) {
             return false;
         }
         for (Class current = child; current != Object.class;
                 current = current.getSuperclass()) {
             if (current == parent) {
                 return true;
             }
         }
         return false;
     }
 
     /***
      * Whether the class implements the interface.
      *
      * @param clas The candidate class
      * @param interfayce The interface
      * @return true if clas implements interfayce, otherwise false
      */
     public static boolean implementationOf(final Class clas,
             final Class interfayce) {
         if (clas == null || interfayce == null || !interfayce.isInterface()) {
             return false;
         }
         for (Class current = clas; current != Object.class;
                 current = current.getSuperclass()) {
             Class[] implementedInterfaces = current.getInterfaces();
             for (int i = 0; i < implementedInterfaces.length; i++) {
                 if (implementedInterfaces[i] == interfayce) {
                     return true;
                 }
             }
         }
         return false;
     }
 
     /***
      * Set node value, depending on its type, from a String.
      *
      * @param node A Node whose value is to be set
      * @param value The new value
      */
     public static void setNodeValue(final Node node, final String value) {
         switch(node.getNodeType()) {
             case Node.ATTRIBUTE_NODE:
                 node.setNodeValue(value);
                 break;
             case Node.ELEMENT_NODE:
                 //remove all text children
                 if (node.hasChildNodes()) {
                     Node child = node.getFirstChild();
                     while (child != null) {
                         if (child.getNodeType() == Node.TEXT_NODE) {
                             node.removeChild(child);
                         }
                         child = child.getNextSibling();
                     }
                 }
                 //create a new text node and append
                 Text txt = node.getOwnerDocument().createTextNode(value);
                 node.appendChild(txt);
                 break;
             case Node.TEXT_NODE:
             case Node.CDATA_SECTION_NODE:
                 ((CharacterData) node).setData(value);
                 break;
             default:
                 String err = "Trying to set value of a strange Node type: "
                     + node.getNodeType();
                 //Logger.logln(Logger.E, err);
                 throw new IllegalArgumentException(err);
         }
     }
 
     /***
      * Retrieve a DOM node value as a string depending on its type.
      *
      * @param node A node to be retreived
      * @return The value as a string
      */
     public static String getNodeValue(final Node node) {
         String result = "";
         if (node == null) {
             return result;
         }
         switch(node.getNodeType()) {
             case Node.ATTRIBUTE_NODE:
                 result = node.getNodeValue();
                 break;
             case Node.ELEMENT_NODE:
                 if (node.hasChildNodes()) {
                     Node child = node.getFirstChild();
                     StringBuffer buf = new StringBuffer();
                     while (child != null) {
                         if (child.getNodeType() == Node.TEXT_NODE) {
                             buf.append(((CharacterData) child).getData());
                         }
                         child = child.getNextSibling();
                     }
                     result = buf.toString();
                 }
                 break;
             case Node.TEXT_NODE:
             case Node.CDATA_SECTION_NODE:
                 result = ((CharacterData) node).getData();
                 break;
             default:
                 String err = "Trying to get value of a strange Node type: "
                     + node.getNodeType();
                 //Logger.logln(Logger.W, err );
                 throw new IllegalArgumentException(err);
         }
         return result.trim();
     }
 
     /***
      * Clone data model.
      *
      * @param ctx The context to clone to.
      * @param datamodel The datamodel to clone.
      * @param evaluator The expression evaluator.
      * @param log The error log.
      */
     public static void cloneDatamodel(final Datamodel datamodel,
             final Context ctx, final Evaluator evaluator,
             final Log log) {
         if (datamodel == null) {
             return;
         }
         List data = datamodel.getData();
         if (data == null) {
             return;
         }
         for (Iterator iter = data.iterator(); iter.hasNext();) {
             Data datum = (Data) iter.next();
             Node datumNode = datum.getNode();
             Node valueNode = null;
             if (datumNode != null) {
                 valueNode = datumNode.cloneNode(true);
             }
             // prefer "src" over "expr" over "inline"
             if (!SCXMLHelper.isStringEmpty(datum.getSrc())) {
                 ctx.setLocal(datum.getId(), valueNode);
             } else if (!SCXMLHelper.isStringEmpty(datum.
                     getExpr())) {
                 Object value = null;
                 try {
                     ctx.setLocal(NAMESPACES_KEY, datum.getNamespaces());
                     value = evaluator.eval(ctx, datum.getExpr());
                     ctx.setLocal(NAMESPACES_KEY, null);
                 } catch (SCXMLExpressionException see) {
                     if (log != null) {
                         log.error(see.getMessage(), see);
                     } else {
                         Log defaultLog = LogFactory.getLog(SCXMLHelper.class);
                         defaultLog.error(see.getMessage(), see);
                     }
                 }
                 ctx.setLocal(datum.getId(), value);
             } else {
                 ctx.setLocal(datum.getId(), valueNode);
             }
         }
     }
 
     /***
      * Escape XML strings for serialization.
      * The basic algorithm is taken from Commons Lang (see oacl.Entities.java)
      *
      * @param str A string to be escaped
      * @return The escaped string
      */
     public static String escapeXML(final String str) {
         if (str == null) {
             return null;
         }
 
         // Make the writer an arbitrary bit larger than the source string
         int len = str.length();
         StringWriter stringWriter = new StringWriter(len + 8);
 
         for (int i = 0; i < len; i++) {
             char c = str.charAt(i);
             String entityName = null; // Look for XML 1.0 predefined entities
             switch (c) {
                 case '"':
                     entityName = "quot";
                     break;
                 case '&':
                     entityName = "amp";
                     break;
                 case '\'':
                     entityName = "apos";
                     break;
                 case '<':
                     entityName = "lt";
                     break;
                 case '>':
                     entityName = "gt";
                     break;
                 default:
             }
             if (entityName == null) {
                 if (c > 0x7F) {
                     stringWriter.write("&#");
                     stringWriter.write(Integer.toString(c));
                     stringWriter.write(';');
                 } else {
                     stringWriter.write(c);
                 }
             } else {
                 stringWriter.write('&');
                 stringWriter.write(entityName);
                 stringWriter.write(';');
             }
         }
 
         return stringWriter.toString();
     }
 
     /***
      * Discourage instantiation since this is a utility class.
      */
     private SCXMLHelper() {
         super();
     }
 
     /***
      * Current document namespaces are saved under this key in the parent
      * state's context.
      */
     private static final String NAMESPACES_KEY = "_ALL_NAMESPACES";
 
 }