[automation] Add script extension to allow scripts to track their disposal (#1264)

* Added script extension to allow scripts to track their disposal

Signed-off-by: Jonathan Gilbert <jpg@trillica.com>

bundles/org.openhab.core.automation.module.script/src/main/java/org/openhab/core/automation/module/script/internal/defaultscope/LifecycleScriptExtensionProvider.java

@@ -0,0 +1,94 @@
+/**
+ * Copyright (c) 2010-2020 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.core.automation.module.script.internal.defaultscope;
+
+import org.openhab.core.automation.module.script.ScriptExtensionProvider;
+import org.osgi.service.component.annotations.Component;
+
+import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * ScriptExtensionProvider which providers a 'lifecycleTracker' object allowing scripts to register for disposal events.
+ *
+ * @author Jonathan Gilbert - Initial contribution
+ */
+@Component(immediate = true)
+public class LifecycleScriptExtensionProvider implements ScriptExtensionProvider {
+
+    private static final String LIFECYCLE_PRESET_NAME = "lifecycle";
+    private static final String LIFECYCLE_TRACKER_NAME = "lifecycleTracker";
+
+    private Map<String, LifecycleTracker> idToTracker= new ConcurrentHashMap<>();
+
+    @Override
+    public Collection<String> getDefaultPresets() {
+        return Collections.singleton(LIFECYCLE_PRESET_NAME);
+    }
+
+    @Override
+    public Collection<String> getPresets() {
+        return Collections.singleton(LIFECYCLE_PRESET_NAME);
+    }
+
+    @Override
+    public Collection<String> getTypes() {
+        return Collections.singleton(LIFECYCLE_TRACKER_NAME);
+    }
+
+    @Override
+    public Object get(String scriptIdentifier, String type) throws IllegalArgumentException {
+        if(LIFECYCLE_TRACKER_NAME.equals(type)) {
+            return idToTracker.computeIfAbsent(scriptIdentifier, k -> new LifecycleTracker());
+        }
+
+        return null;
+    }
+
+    @Override
+    public Map<String, Object> importPreset(String scriptIdentifier, String preset) {
+        if(LIFECYCLE_PRESET_NAME.equals(preset)) {
+            return Collections.singletonMap(LIFECYCLE_TRACKER_NAME, get(scriptIdentifier, LIFECYCLE_TRACKER_NAME));
+        }
+
+        return Collections.emptyMap();
+    }
+
+    @Override
+    public void unload(String scriptIdentifier) {
+        LifecycleTracker tracker = idToTracker.remove(scriptIdentifier);
+
+        if(tracker != null) {
+            tracker.dispose();
+        }
+    }
+
+    public static class LifecycleTracker {
+        List<Disposable> disposables = new ArrayList<>();
+
+        public void addDisposeHook(Disposable disposable) {
+            disposables.add(disposable);
+        }
+
+        void dispose() {
+            for(Disposable disposable : disposables) {
+                disposable.dispose();
+            }
+        }
+    }
+
+    @FunctionalInterface
+    interface Disposable {
+        void dispose();
+    }
+}