Adding JSON Schema support in APEX-PDP

More details can be found here:
https://wiki.onap.org/display/DW/JSON+Schema+support+in+APEX-PDP

A separate review will be raised as part of POLICY-4292 with a reference
example on how to use the JSON Schema.

Change-Id: I903d48969c6c5a24c63b8465b2412ed0b75b9351
Issue-ID: POLICY-4291
Signed-off-by: a.sreekumar <ajith.sreekumar@bell.ca>

2 files changed, 152 insertions, 0 deletions

diff --git a/plugins/plugins-context/plugins-context-schema/plugins-context-schema-json/src/main/java/org/onap/policy/apex/plugins/context/schema/json/JsonSchemaHelper.java b/plugins/plugins-context/plugins-context-schema/plugins-context-schema-json/src/main/java/org/onap/policy/apex/plugins/context/schema/json/JsonSchemaHelper.java
new file mode 100644
index 000000000..4896e5d4a
--- /dev/null
+++ b/plugins/plugins-context/plugins-context-schema/plugins-context-schema-json/src/main/java/org/onap/policy/apex/plugins/context/schema/json/JsonSchemaHelper.java
@@ -0,0 +1,122 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2022 Bell Canada. All rights reserved.
+ * ================================================================================
+ * Licensed 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.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.apex.plugins.context.schema.json;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import com.worldturner.medeia.api.SchemaSource;
+import com.worldturner.medeia.api.StringInputSource;
+import com.worldturner.medeia.api.StringSchemaSource;
+import com.worldturner.medeia.api.gson.MedeiaGsonApi;
+import com.worldturner.medeia.schema.validation.SchemaValidator;
+import java.io.StringWriter;
+import java.util.List;
+import java.util.Map;
+import org.onap.policy.apex.context.ContextRuntimeException;
+import org.onap.policy.apex.context.impl.schema.AbstractSchemaHelper;
+import org.onap.policy.apex.model.basicmodel.concepts.AxKey;
+import org.onap.policy.apex.model.contextmodel.concepts.AxContextSchema;
+
+/**
+ * This class is the implementation of the {@link org.onap.policy.apex.context.SchemaHelper} interface for JSON schema.
+ */
+public class JsonSchemaHelper extends AbstractSchemaHelper {
+
+    private static final Gson gson = new Gson();
+
+    private MedeiaGsonApi api = new MedeiaGsonApi();
+    private SchemaValidator validator;
+
+    @Override
+    public void init(final AxKey userKey, final AxContextSchema schema) {
+        super.init(userKey, schema);
+
+        try {
+            SchemaSource source = new StringSchemaSource(schema.getSchema());
+            validator = api.loadSchema(source);
+        } catch (final Exception e) {
+            final String resultSting = userKey.getId() + ": json context schema \"" + schema.getId()
+                + "\" schema is invalid, schema: " + schema.getSchema();
+            throw new ContextRuntimeException(resultSting, e);
+        }
+    }
+
+    @Override
+    public Object createNewInstance(final String stringValue) {
+        return unmarshal(stringValue);
+    }
+
+    @Override
+    public Object createNewInstance(final Object incomingObject) {
+        if (incomingObject instanceof JsonElement) {
+            final var elementJsonString = gson.toJson((JsonElement) incomingObject);
+
+            return createNewInstance(elementJsonString);
+        } else {
+            final var returnString =
+                getUserKey().getId() + ": the object \"" + incomingObject + "\" is not an instance of JsonObject";
+            throw new ContextRuntimeException(returnString);
+        }
+    }
+
+    @Override
+    public Object unmarshal(Object object) {
+        // If an object is already in the correct format, just carry on
+        if (passThroughObject(object)) {
+            return object;
+        }
+        var objectString = (String) object;
+        JsonReader reader = api.createJsonReader(validator, new StringInputSource(objectString));
+        return gson.fromJson(reader, Object.class);
+    }
+
+    @Override
+    public String marshal2String(Object schemaObject) {
+        StringWriter stringWriter = new StringWriter();
+        validateAndDecode(schemaObject, stringWriter);
+        return stringWriter.toString();
+    }
+
+    @Override
+    public Object marshal2Object(Object schemaObject) {
+        return validateAndDecode(schemaObject, new StringWriter());
+    }
+
+    private JsonElement validateAndDecode(Object schemaObject, StringWriter stringWriter) {
+        JsonWriter jsonWriter = api.createJsonWriter(validator, stringWriter);
+        jsonWriter.setIndent("  "); // to enable pretty print
+        JsonElement jsonObj = gson.toJsonTree(schemaObject);
+        gson.toJson(jsonObj, jsonWriter);
+        return jsonObj;
+    }
+
+    /**
+     * Check if we can pass this object straight through encoding or decoding.
+     *
+     * @param object the object to check
+     * @return true if it's a straight pass through
+     */
+    private boolean passThroughObject(final Object object) {
+        return (object instanceof JsonElement || object instanceof Map || object instanceof List);
+    }
+}
diff --git a/plugins/plugins-context/plugins-context-schema/plugins-context-schema-json/src/main/java/org/onap/policy/apex/plugins/context/schema/json/JsonSchemaHelperParameters.java b/plugins/plugins-context/plugins-context-schema/plugins-context-schema-json/src/main/java/org/onap/policy/apex/plugins/context/schema/json/JsonSchemaHelperParameters.java
new file mode 100644
index 000000000..0e275130d
--- /dev/null
+++ b/plugins/plugins-context/plugins-context-schema/plugins-context-schema-json/src/main/java/org/onap/policy/apex/plugins/context/schema/json/JsonSchemaHelperParameters.java
@@ -0,0 +1,30 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2022 Bell Canada. All rights reserved.
+ * ================================================================================
+ * Licensed 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.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.apex.plugins.context.schema.json;
+
+import org.onap.policy.apex.context.parameters.SchemaHelperParameters;
+
+public class JsonSchemaHelperParameters extends SchemaHelperParameters {
+
+    public JsonSchemaHelperParameters() {
+        this.setSchemaHelperPluginClass(JsonSchemaHelper.class.getName());
+    }
+}