Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/GateActivity.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/src/java/org/lamsfoundation/lams/learningdesign/GateActivity.java,v
diff -u -r1.5 -r1.6
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/GateActivity.java	6 Apr 2005 05:02:57 -0000	1.5
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/GateActivity.java	6 Apr 2005 07:34:45 -0000	1.6
@@ -2,9 +2,12 @@
 
 import java.io.Serializable;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
 
 import org.apache.commons.lang.builder.ToStringBuilder;
+import org.lamsfoundation.lams.learningdesign.strategy.GateActivityStrategy;
+import org.lamsfoundation.lams.usermanagement.User;
 
 
 /**
@@ -25,6 +28,9 @@
     /** persistent field */
     private Boolean gateOpen;
     
+    /**
+     * The learners who are waiting at the gate.
+     */
     private Set waitingLearners;
     
     /** full constructor */
@@ -138,13 +144,6 @@
         this.waitingLearners = waitingLearners;
     }
     
-    public String toString()
-    {
-        return new ToStringBuilder(this)
-        .append("activityId", getActivityId())
-        .toString();
-    }
-    
 	public Boolean getGateOpen() 
 	{
 		return gateOpen;
@@ -155,9 +154,47 @@
 		this.gateOpen = gateOpen;
 	}
 	
-	public boolean shouldOpen()
+    //---------------------------------------------------------------------
+    // Domain service methods
+    //---------------------------------------------------------------------
+
+	/**
+	 * Add a learner into the waiting list. 
+	 * @param learner the new waiting learner.
+	 */
+	public void addWaitingLeaner(User learner)
 	{
-	    return false;
+	    if(this.waitingLearners == null)
+	        this.setWaitingLearners(new HashSet());
+	    
+	    //only add the learner if we have never added him before.
+	    if(!this.waitingLearners.contains(learner))
+	        this.waitingLearners.add(learner);	    
 	}
+	
+	/**
+	 * Delegate to strategy class to calculate whether we should open the 
+	 * gate for this learner.
+	 * @param learner the learner who wants to go through the gate.
+	 * @return the gate should be open or closed.
+	 */
+	public boolean shouldOpenGateFor(User learner, List lessonLearners)
+	{
+        //by default, we close the gate
+        if(getGateOpen()==null)
+            this.setGateOpen(new Boolean(false));
+        
+	    return ((GateActivityStrategy)simpleActivityStrategy).shouldOpenGateFor(learner,lessonLearners,this);
+	}
+	
+    //---------------------------------------------------------------------
+    // Helper methods
+    //---------------------------------------------------------------------
+    public String toString()
+    {
+        return new ToStringBuilder(this)
+        .append("activityId", getActivityId())
+        .toString();
+    }
 
 }
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/ScheduleGateActivity.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/src/java/org/lamsfoundation/lams/learningdesign/ScheduleGateActivity.java,v
diff -u -r1.11 -r1.12
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/ScheduleGateActivity.java	6 Apr 2005 05:02:57 -0000	1.11
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/ScheduleGateActivity.java	6 Apr 2005 07:34:45 -0000	1.12
@@ -5,6 +5,7 @@
 import java.util.Set;
 
 import org.apache.commons.lang.builder.ToStringBuilder;
+import org.lamsfoundation.lams.learningdesign.strategy.ScheduleGateActivityStrategy;
 
 
 /**
@@ -110,10 +111,12 @@
                 waitingLearners);
         this.gateStartTimeOffset = gateStartTimeOffset;
         this.gateEndTimeOffset = gateEndTimeOffset;
+        this.simpleActivityStrategy = new ScheduleGateActivityStrategy();
     }
 
     /** default constructor */
     public ScheduleGateActivity() {
+        this.simpleActivityStrategy = new ScheduleGateActivityStrategy();
     }
 
     /** minimal constructor */
@@ -145,6 +148,7 @@
                 waitingLearners);
       this.gateStartTimeOffset = gateStartTimeOffset;
       this.gateEndTimeOffset = gateEndTimeOffset;
+      this.simpleActivityStrategy = new ScheduleGateActivityStrategy();
     }
     /**
      * Makes a copy of the ScheduleGateActivity for authoring, preview and monitoring enviornment 
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/SynchGateActivity.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/src/java/org/lamsfoundation/lams/learningdesign/SynchGateActivity.java,v
diff -u -r1.10 -r1.11
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/SynchGateActivity.java	6 Apr 2005 05:02:57 -0000	1.10
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/SynchGateActivity.java	6 Apr 2005 07:34:45 -0000	1.11
@@ -5,6 +5,7 @@
 import java.util.Set;
 
 import org.apache.commons.lang.builder.ToStringBuilder;
+import org.lamsfoundation.lams.learningdesign.strategy.SynchGateActivityStrategy;
 
 
 /** 
@@ -55,10 +56,12 @@
 				transitionFrom,
                 gateActivityLevelId,
                 waitingLearners);
+        super.simpleActivityStrategy = new SynchGateActivityStrategy();
     }
 
     /** default constructor */
     public SynchGateActivity() {
+        super.simpleActivityStrategy = new SynchGateActivityStrategy();
     }
 
     /** minimal constructor */
@@ -87,6 +90,7 @@
 			  transitionFrom,
               gateActivityLevelId,
               waitingLearners);
+      super.simpleActivityStrategy = new SynchGateActivityStrategy();
     }
     
     /**
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/GateActivityStrategy.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/GateActivityStrategy.java,v
diff -u -r1.1 -r1.2
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/GateActivityStrategy.java	5 Apr 2005 23:59:22 -0000	1.1
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/GateActivityStrategy.java	6 Apr 2005 07:34:45 -0000	1.2
@@ -23,8 +23,11 @@
 package org.lamsfoundation.lams.learningdesign.strategy;
 
 import java.util.ArrayList;
+import java.util.List;
 
 import org.lamsfoundation.lams.learningdesign.Activity;
+import org.lamsfoundation.lams.learningdesign.GateActivity;
+import org.lamsfoundation.lams.usermanagement.User;
 
 
 /**
@@ -38,9 +41,48 @@
  */
 public abstract class GateActivityStrategy extends SimpleActivityStrategy
 {
+    //---------------------------------------------------------------------
+    // Template methods
+    //---------------------------------------------------------------------
+    /**
+     * Returns wether we should open the gate or close the gate. It's 
+     * implementation depends on the type of the gate we are dealing with. 
+     * Generally, it needs the check up the current gate status. If the gate
+     * is already opened, we will keep it open for current learner. Otherwise,
+     * we need to validate the open condition for this learner.
+     * 
+     * @param learner the learner who just arrived at the gate.
+     * @param activity the gate activity.
+     * @param lessonLearners all learners who are currently in the lesson.
+     * @return whether we should open it or not.
+     */
+    public boolean shouldOpenGateFor(User learner,List lessonLearners,GateActivity activity)
+    {
+        activity.addWaitingLeaner(learner);
+        
+        if(!activity.getGateOpen().booleanValue())
+        {
+            if( isOpenConditionMet(activity, lessonLearners))
+            {
+            	activity.setGateOpen(new Boolean(true));
+            	activity.getWaitingLearners().clear();
+            }
+
+        }
+
+        return activity.getGateOpen().booleanValue();
+    }
     
-    
     //---------------------------------------------------------------------
+    // Abstract methods
+    //---------------------------------------------------------------------
+    /**
+     * Check up the open condition according the gate type.
+     * @return return true if the condition is met.
+     */
+    protected abstract boolean isOpenConditionMet(GateActivity activity,
+                                                  List lessonLearners);
+    //---------------------------------------------------------------------
     // Overidden methods
     //---------------------------------------------------------------------
     /**
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/PermissionGateActivityStrategy.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/PermissionGateActivityStrategy.java,v
diff -u -r1.2 -r1.3
--- lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/PermissionGateActivityStrategy.java	5 Apr 2005 23:59:22 -0000	1.2
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/PermissionGateActivityStrategy.java	6 Apr 2005 07:34:45 -0000	1.3
@@ -21,8 +21,10 @@
 package org.lamsfoundation.lams.learningdesign.strategy;
 
 import java.util.ArrayList;
+import java.util.List;
 
 import org.lamsfoundation.lams.learningdesign.Activity;
+import org.lamsfoundation.lams.learningdesign.GateActivity;
 
 /**
  * Activity strategy that deals with the calculation specific to gate activity.
@@ -46,4 +48,16 @@
         contributionTypes.add(PERMISSION_GATE);
     }
 
+    /**
+     * Regarding permission gate, we don't validate the open condition for the 
+     * learner because the decision of opening the gate or not comes from the 
+     * teacher. The teacher may open or close the gate at monitoring interface.
+     * 
+     * @see org.lamsfoundation.lams.learningdesign.strategy.GateActivityStrategy#isOpenConditionMet()
+     */
+    protected boolean isOpenConditionMet(GateActivity activity,List lessonLearners)
+    {
+        return activity.getGateOpen().booleanValue();
+    }
+
 }
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/ScheduleGateActivityStrategy.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/ScheduleGateActivityStrategy.java,v
diff -u
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/ScheduleGateActivityStrategy.java	6 Apr 2005 07:34:45 -0000	1.1
@@ -0,0 +1,72 @@
+/***************************************************************************
+ * Copyright (C) 2005 LAMS Foundation (http://lamsfoundation.org)
+ * =============================================================
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
+ * USA
+ * 
+ * http://www.gnu.org/licenses/gpl.txt
+ * ***********************************************************************/
+
+package org.lamsfoundation.lams.learningdesign.strategy;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.lamsfoundation.lams.learningdesign.Activity;
+import org.lamsfoundation.lams.learningdesign.GateActivity;
+
+
+/**
+ * Activity strategy that deals with the calculation specific to schedule gate 
+ * activity. The major part of this strategy will be overiding the methods that 
+ * defined in the abstract level.
+ * 
+ * @author Jacky Fang
+ * @since  2005-4-6
+ * @version 1.1
+ * 
+ */
+public class ScheduleGateActivityStrategy extends GateActivityStrategy
+{
+    //---------------------------------------------------------------------
+    // Overriden methods
+    //---------------------------------------------------------------------
+
+    /**
+     * @see org.lamsfoundation.lams.learningdesign.strategy.GateActivityStrategy#setUpContributionType(org.lamsfoundation.lams.learningdesign.Activity, java.util.ArrayList)
+     */
+    protected void setUpContributionType(Activity activity, 
+                                         ArrayList contributionTypes)
+    {
+        contributionTypes.add(SCHEDULE_GATE);        
+    }
+
+    /**
+     * Regarding schedule gate, we don't validate the open condition for the 
+     * learner because the decision of opening the gate or not comes from the 
+     * system scheduler. Lams open the gate when the start time is reached and 
+     * closed the gate when the end time is reached.
+     * 
+     * @see org.lamsfoundation.lams.learningdesign.strategy.GateActivityStrategy#isOpenConditionMet()
+     */
+    protected boolean isOpenConditionMet(GateActivity activity,
+                                         List lessonLearners)
+    {
+        return activity.getGateOpen().booleanValue();
+    }
+
+
+}
Index: lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/SynchGateActivityStrategy.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/SynchGateActivityStrategy.java,v
diff -u
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ lams_common/src/java/org/lamsfoundation/lams/learningdesign/strategy/SynchGateActivityStrategy.java	6 Apr 2005 07:34:45 -0000	1.1
@@ -0,0 +1,85 @@
+/***************************************************************************
+ * Copyright (C) 2005 LAMS Foundation (http://lamsfoundation.org)
+ * =============================================================
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
+ * USA
+ * 
+ * http://www.gnu.org/licenses/gpl.txt
+ * ***********************************************************************/
+
+package org.lamsfoundation.lams.learningdesign.strategy;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+import org.lamsfoundation.lams.learningdesign.Activity;
+import org.lamsfoundation.lams.learningdesign.GateActivity;
+import org.lamsfoundation.lams.usermanagement.User;
+
+
+/**
+ * Activity strategy that deals with the calculation specific to schedule gate 
+ * activity. The major part of this strategy will be overiding the methods that 
+ * defined in the abstract level.
+ * 
+ * @author Jacky Fang
+ * @since  2005-4-6
+ * @version 1.1
+ * 
+ */
+public class SynchGateActivityStrategy extends GateActivityStrategy
+{
+    //---------------------------------------------------------------------
+    // Overriden methods
+    //---------------------------------------------------------------------
+    /**
+     * <p>Check up the waiting learners list and lesson learner list. If all 
+     * lesson learner appears in the waiting list, we assume the open condition
+     * for the sync gate is met. </p>
+     * 
+     * <p>Note, simply compares the size of two list might be proper. Waiting
+     * learners might not want to wait any more and exit the lesson, who will
+     * be removed from current lesson learner list. Therefore, it is possible
+     * that the waiting learner list is larger than the current lesson learner
+     * list. </p>
+     * 
+     * @see org.lamsfoundation.lams.learningdesign.strategy.GateActivityStrategy#isOpenConditionMet()
+     */
+    protected boolean isOpenConditionMet(GateActivity activity,
+                                         List lessonLearners)
+    {
+        for(Iterator i = lessonLearners.iterator();i.hasNext();)
+        {
+            User learner = (User)i.next();
+            if (!activity.getWaitingLearners().contains(learner))
+                return false;
+        }
+        return true;
+    }
+    
+    /**
+     * @see org.lamsfoundation.lams.learningdesign.strategy.SimpleActivityStrategy#setUpContributionType(org.lamsfoundation.lams.learningdesign.Activity, java.util.ArrayList)
+     */
+    protected void setUpContributionType(Activity activity,
+                                         ArrayList contributionTypes)
+    {
+        contributionTypes.add(SYNC_GATE);   
+    }
+
+
+
+}
Index: lams_common/test/java/org/lamsfoundation/lams/learningdesign/TestGateActivityStrategy.java
===================================================================
RCS file: /usr/local/cvsroot/lams_common/test/java/org/lamsfoundation/lams/learningdesign/Attic/TestGateActivityStrategy.java,v
diff -u
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ lams_common/test/java/org/lamsfoundation/lams/learningdesign/TestGateActivityStrategy.java	6 Apr 2005 07:34:45 -0000	1.1
@@ -0,0 +1,116 @@
+/***************************************************************************
+ * Copyright (C) 2005 LAMS Foundation (http://lamsfoundation.org)
+ * =============================================================
+ * 
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
+ * USA
+ * 
+ * http://www.gnu.org/licenses/gpl.txt
+ * ***********************************************************************/
+
+package org.lamsfoundation.lams.learningdesign;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.lamsfoundation.lams.usermanagement.User;
+
+import junit.framework.TestCase;
+
+
+/**
+ * 
+ * @author Jacky Fang
+ * @since  2005-4-6
+ * @version
+ * 
+ */
+public class TestGateActivityStrategy extends TestCase
+{
+    private GateActivity schduleGate = new ScheduleGateActivity();
+    private GateActivity permissionGate = new PermissionGateActivity();
+    private GateActivity synchGate = new SynchGateActivity();
+    
+    private static List testLessonUsers = new ArrayList();
+    private static final int NUM_OF_TEST_USERS = 5;
+    private static final int TEST_USER_ID = 1;
+    
+    /*
+     * @see AbstractLamsTestCase#setUp()
+     */
+    protected void setUp() throws Exception
+    {
+
+        //initialize lesson users
+        for(int i =0; i<NUM_OF_TEST_USERS;i++)
+            testLessonUsers.add(createUser(new Integer(i+1),"tester"+i));
+    }
+    /*
+     * @see AbstractLamsTestCase#tearDown()
+     */
+    protected void tearDown() throws Exception
+    {
+        super.tearDown();
+    }
+    
+    public void testShouldCloseSynchGateForTestLearner()
+    {
+        User testLearner = createUser(new Integer(TEST_USER_ID),"tester"+TEST_USER_ID);;
+        boolean gateOpen = synchGate.shouldOpenGateFor(testLearner,testLessonUsers);
+        
+        assertTrue("gate should be closed",!gateOpen);
+        assertEquals("there should be one learner",1,synchGate.getWaitingLearners().size());
+    }
+    
+    public void testShouldOpenSynchGateForTestLearner()
+    {
+        //create the number of learner that is the same as the number of all 
+        //lesson learners.
+        List testLearners = new ArrayList();
+        //initialize test learners
+        for(int i =0; i<NUM_OF_TEST_USERS;i++)
+            testLearners.add(createUser(new Integer(i+1),"tester"+i));
+        
+        boolean gateOpen = false;
+        //learners arrived at synch gate one by one.
+        for(int i =0; i<testLearners.size();i++)
+        {
+            User learner = (User)testLearners.get(i);
+            gateOpen = synchGate.shouldOpenGateFor(learner,testLessonUsers);
+            if((i+1)!=testLearners.size())
+                assertEquals("verify the number of learners",i+1,synchGate.getWaitingLearners().size());
+
+        }
+        
+        assertTrue("gate should be closed",gateOpen);
+        assertEquals("there should be one learner",0,synchGate.getWaitingLearners().size());
+
+        
+    }
+    //---------------------------------------------------------------------
+    // Helpers
+    //---------------------------------------------------------------------
+    /**
+     * @param userId
+     * @param userName
+     */
+    private User createUser(Integer userId, String userName)
+    {
+        User user = new User();
+        user.setUserId(userId);
+        user.setLogin(userName);
+        return user;
+    }
+}