NEW - bug 370620: [api] extend ExtensionPointReader to support filtering

and priority 
https://bugs.eclipse.org/bugs/show_bug.cgi?id=370620

Change-Id: Ib277af565a58a14844bd06eb7194925137636146

4 files changed, 120 insertions, 5 deletions

diff --git a/org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/commons/core/ExtensionPointReader.java b/org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/commons/core/ExtensionPointReader.java
index 578e8605..68d88e48 100644
--- a/org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/commons/core/ExtensionPointReader.java
+++ b/org.eclipse.mylyn.commons.core/src/org/eclipse/mylyn/commons/core/ExtensionPointReader.java
@@ -1,5 +1,3 @@
-package org.eclipse.mylyn.commons.core;
-
 /*******************************************************************************
  * Copyright (c) 2011 Tasktop Technologies.
  * All rights reserved. This program and the accompanying materials
@@ -10,8 +8,11 @@ package org.eclipse.mylyn.commons.core;
  * Contributors:
  *     Tasktop Technologies - initial API and implementation
  *******************************************************************************/
+package org.eclipse.mylyn.commons.core;
 
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Comparator;
 import java.util.List;
 
 import org.eclipse.core.runtime.Assert;
@@ -27,10 +28,43 @@ import org.eclipse.osgi.util.NLS;
 
 /**
  * @author Steffen Pingel
+ * @author Sam Davis
  * @since 3.7
  */
 public class ExtensionPointReader<T> {
 
+	private static final String ATTRIBUTE_EXTENSION_PRIORITY = "extensionPriority"; //$NON-NLS-1$
+
+	private static final class PriorityComparator implements Comparator<IConfigurationElement> {
+
+		public int compare(IConfigurationElement arg0, IConfigurationElement arg1) {
+			double p0 = 0;
+			double p1 = 0;
+			try {
+				String priorityAttribute = arg0.getAttribute(ATTRIBUTE_EXTENSION_PRIORITY);
+				if (priorityAttribute != null) {
+					p0 = Double.parseDouble(priorityAttribute);
+				}
+			} catch (NumberFormatException e) {
+			}
+			try {
+				String priorityAttribute = arg1.getAttribute(ATTRIBUTE_EXTENSION_PRIORITY);
+				if (priorityAttribute != null) {
+					p1 = Double.parseDouble(priorityAttribute);
+				}
+			} catch (NumberFormatException e) {
+			}
+			if (p1 > p0) {
+				return 1;
+			} else if (p1 < -p0) {
+				return -1;
+			}
+			return 0;
+		}
+	}
+
+	private static final PriorityComparator PRIORITY_COMPARATOR = new PriorityComparator();
+
 	private final String extensionId;
 
 	private final String elementId;
@@ -43,6 +77,17 @@ public class ExtensionPointReader<T> {
 
 	private final List<T> items;
 
+	private String filterAttributeId;
+
+	private String filterAttributeValue;
+
+	public ExtensionPointReader(String pluginId, String extensionId, String elementId, Class<T> clazz,
+			String filterAttributeId, String filterAttributeValue) {
+		this(pluginId, extensionId, elementId, clazz);
+		this.filterAttributeId = filterAttributeId;
+		this.filterAttributeValue = filterAttributeValue;
+	}
+
 	public ExtensionPointReader(String pluginId, String extensionId, String elementId, Class<T> clazz) {
 		Assert.isNotNull(pluginId);
 		Assert.isNotNull(extensionId);
@@ -88,8 +133,9 @@ public class ExtensionPointReader<T> {
 			IExtension[] extensions = extensionPoint.getExtensions();
 			for (IExtension extension : extensions) {
 				IConfigurationElement[] elements = extension.getConfigurationElements();
+				Arrays.sort(elements, PRIORITY_COMPARATOR);
 				for (IConfigurationElement element : elements) {
-					if (element.getName().equals(elementId)) {
+					if (element.getName().equals(elementId) && shouldRead(element)) {
 						T item = readElement(element, result);
 						if (item != null) {
 							items.add(item);
@@ -104,6 +150,20 @@ public class ExtensionPointReader<T> {
 		return result;
 	}
 
+	/**
+	 * Determines whether the element should be instantiated by this ExtensionPointReader. This implementation checks
+	 * whether the element defines an attribute with id and value matching filterAttributeId and filterAttributeValue.
+	 * If filterAttributeValue is the empty string, an element is also considered to match if it does not define the
+	 * attribute.
+	 * <p>
+	 * Subclasses may override.
+	 */
+	protected boolean shouldRead(IConfigurationElement element) {
+		return filterAttributeId == null || filterAttributeValue == null
+				|| filterAttributeValue.equals(element.getAttribute(filterAttributeId))
+				|| (filterAttributeValue.length() == 0 && element.getAttribute(filterAttributeId) == null);
+	}
+
 	protected void handleResult(IStatus result) {
 		if (!result.isOK()) {
 			StatusHandler.log(result);
diff --git a/org.eclipse.mylyn.commons.tests/plugin.xml b/org.eclipse.mylyn.commons.tests/plugin.xml
index 26fc4537..714a8cf5 100644
--- a/org.eclipse.mylyn.commons.tests/plugin.xml
+++ b/org.eclipse.mylyn.commons.tests/plugin.xml
@@ -26,6 +26,20 @@
          point="org.eclipse.mylyn.commons.tests.extensionPointReaderTest">
       <extensionElement
             class="org.eclipse.mylyn.commons.tests.core.ExtensionPointReaderTest$ExtensionPointReaderExtensionImplementation"></extensionElement>
+      <extensionElement
+            class="org.eclipse.mylyn.commons.tests.core.ExtensionPointReaderTest$P5ExtensionPointReaderExtensionImplementation"
+            extensionPriority="5"
+            testFilterAttribute="value1">
+      </extensionElement>
+      <extensionElement
+            class="org.eclipse.mylyn.commons.tests.core.ExtensionPointReaderTest$PNegative5ExtensionPointReaderExtensionImplementation"
+            extensionPriority="-5"
+            testFilterAttribute="value2">
+      </extensionElement>
+      <extensionElement
+            class="org.eclipse.mylyn.commons.tests.core.ExtensionPointReaderTest$P10ExtensionPointReaderExtensionImplementation"
+            extensionPriority="10">
+      </extensionElement>
    </extension>
 
 </plugin>
diff --git a/org.eclipse.mylyn.commons.tests/schema/extensionPointReaderTest.exsd b/org.eclipse.mylyn.commons.tests/schema/extensionPointReaderTest.exsd
index 06a40f79..3929cf58 100644
--- a/org.eclipse.mylyn.commons.tests/schema/extensionPointReaderTest.exsd
+++ b/org.eclipse.mylyn.commons.tests/schema/extensionPointReaderTest.exsd
@@ -66,6 +66,20 @@
                </documentation>
             </annotation>
          </attribute>
+         <attribute name="testFilterAttribute" type="string">
+            <annotation>
+               <documentation>
+                  
+               </documentation>
+            </annotation>
+         </attribute>
+         <attribute name="extensionPriority" type="string">
+            <annotation>
+               <documentation>
+                  
+               </documentation>
+            </annotation>
+         </attribute>
       </complexType>
    </element>
 
@@ -91,7 +105,6 @@ All rights reserved. This program and the accompanying materials
 are made available under the terms of the Eclipse Public License v1.0
 which accompanies this distribution, and is available at
 http://www.eclipse.org/legal/epl-v10.html
-
       </documentation>
    </annotation>
 
diff --git a/org.eclipse.mylyn.commons.tests/src/org/eclipse/mylyn/commons/tests/core/ExtensionPointReaderTest.java b/org.eclipse.mylyn.commons.tests/src/org/eclipse/mylyn/commons/tests/core/ExtensionPointReaderTest.java
index 63ef09d0..93585b84 100644
--- a/org.eclipse.mylyn.commons.tests/src/org/eclipse/mylyn/commons/tests/core/ExtensionPointReaderTest.java
+++ b/org.eclipse.mylyn.commons.tests/src/org/eclipse/mylyn/commons/tests/core/ExtensionPointReaderTest.java
@@ -11,6 +11,7 @@
 
 package org.eclipse.mylyn.commons.tests.core;
 
+import java.util.Arrays;
 import java.util.Collections;
 
 import junit.framework.TestCase;
@@ -20,6 +21,7 @@ import org.eclipse.mylyn.commons.core.ExtensionPointReader;
 
 /**
  * @author Steffen Pingel
+ * @author Sam Davis
  */
 public class ExtensionPointReaderTest extends TestCase {
 
@@ -62,6 +64,18 @@ public class ExtensionPointReaderTest extends TestCase {
 		}
 	}
 
+	public static class P5ExtensionPointReaderExtensionImplementation extends
+			ExtensionPointReaderExtensionImplementation {
+	}
+
+	public static class PNegative5ExtensionPointReaderExtensionImplementation extends
+			ExtensionPointReaderExtensionImplementation {
+	}
+
+	public static class P10ExtensionPointReaderExtensionImplementation extends
+			ExtensionPointReaderExtensionImplementation {
+	}
+
 	private static final String ID_PLUGIN = "org.eclipse.mylyn.commons.tests";
 
 	public void testRead() {
@@ -69,7 +83,21 @@ public class ExtensionPointReaderTest extends TestCase {
 				ID_PLUGIN, "extensionPointReaderTest", "extensionElement", ExtensionPointReaderExtension.class);
 		IStatus status = reader.read();
 		assertEquals(IStatus.OK, status.getSeverity());
-		assertEquals(Collections.singletonList(new ExtensionPointReaderExtensionImplementation()), reader.getItems());
+		assertEquals(
+				Arrays.asList(new ExtensionPointReaderExtension[] {
+						new P10ExtensionPointReaderExtensionImplementation(),
+						new P5ExtensionPointReaderExtensionImplementation(),
+						new ExtensionPointReaderExtensionImplementation(),
+						new PNegative5ExtensionPointReaderExtensionImplementation() }), reader.getItems());
+	}
+
+	public void testReadWithFiltering() {
+		ExtensionPointReader<ExtensionPointReaderExtension> reader = new ExtensionPointReader<ExtensionPointReaderExtension>(
+				ID_PLUGIN, "extensionPointReaderTest", "extensionElement", ExtensionPointReaderExtension.class,
+				"testFilterAttribute", "value1");
+		IStatus status = reader.read();
+		assertEquals(IStatus.OK, status.getSeverity());
+		assertEquals(Collections.singletonList(new P5ExtensionPointReaderExtensionImplementation()), reader.getItems());
 	}
 
 }