Added simple Shared Cache into scope (openhab#11693)

Signed-off-by: Jonathan Gilbert <jpg@trillica.com>
Signed-off-by: Nick Waterton <n.waterton@outlook.com>

bundles/org.openhab.automation.jsscripting/src/main/java/org/openhab/automation/jsscripting/internal/scope/SharedCache.java

@@ -0,0 +1,101 @@
+/**
+ * Copyright (c) 2010-2021 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.automation.jsscripting.internal.scope;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Supplier;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+import org.openhab.core.automation.module.script.ScriptExtensionProvider;
+import org.osgi.service.component.annotations.Component;
+
+/**
+ * Shared Cache implementation for JS scripting.
+ *
+ * @author Jonathan Gilbert - Initial contribution
+ */
+@Component(immediate = true)
+@NonNullByDefault
+public class SharedCache implements ScriptExtensionProvider {
+
+    private static final String PRESET_NAME = "cache";
+    private static final String OBJECT_NAME = "sharedcache";
+
+    private JSCache cache = new JSCache();
+
+    @Override
+    public Collection<String> getDefaultPresets() {
+        return Set.of(PRESET_NAME);
+    }
+
+    @Override
+    public Collection<String> getPresets() {
+        return Set.of(PRESET_NAME);
+    }
+
+    @Override
+    public Collection<String> getTypes() {
+        return Set.of(OBJECT_NAME);
+    }
+
+    @Override
+    public @Nullable Object get(String scriptIdentifier, String type) throws IllegalArgumentException {
+        if (OBJECT_NAME.equals(type)) {
+            return cache;
+        }
+
+        return null;
+    }
+
+    @Override
+    public Map<String, Object> importPreset(String scriptIdentifier, String preset) {
+        if (PRESET_NAME.equals(preset)) {
+            final Object requestedType = get(scriptIdentifier, OBJECT_NAME);
+            if (requestedType != null) {
+                return Map.of(OBJECT_NAME, requestedType);
+            }
+        }
+
+        return Collections.emptyMap();
+    }
+
+    @Override
+    public void unload(String scriptIdentifier) {
+        // ignore for now
+    }
+
+    public static class JSCache {
+        private Map<String, Object> backingMap = new HashMap<>();
+
+        public void put(String k, Object v) {
+            backingMap.put(k, v);
+        }
+
+        public @Nullable Object remove(String k) {
+            return backingMap.remove(k);
+        }
+
+        public @Nullable Object get(String k) {
+            return backingMap.get(k);
+        }
+
+        public @Nullable Object get(String k, Supplier<Object> supplier) {
+            return backingMap.computeIfAbsent(k, (unused_key) -> supplier.get());
+        }
+    }
+}