/*
 * Copyright 2014-2020 the original author or authors.
 *
 * 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
 *
 *      https://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.
 */
package org.springframework.data.spel.spi;

import java.util.Collections;
import java.util.Map;

import org.springframework.data.repository.query.ExtensionAwareQueryMethodEvaluationContextProvider;
import org.springframework.expression.EvaluationContext;
import org.springframework.lang.Nullable;

SPI to allow adding a set of properties and function definitions accessible via the root of an EvaluationContext provided by a ExtensionAwareQueryMethodEvaluationContextProvider. 
Author:
Thomas Darimont, Oliver Gierke
Since:
1.9/**
 * SPI to allow adding a set of properties and function definitions accessible via the root of an
 * {@link EvaluationContext} provided by a {@link ExtensionAwareQueryMethodEvaluationContextProvider}.
 *
 * @author Thomas Darimont
 * @author Oliver Gierke
 * @since 1.9
 */
public interface EvaluationContextExtension {

	
Returns the identifier of the extension. The id can be leveraged by users to fully qualify property lookups and
thus overcome ambiguities in case multiple extensions expose properties with the same name.
Returns:
the extension id, must not be null./**
	 * Returns the identifier of the extension. The id can be leveraged by users to fully qualify property lookups and
	 * thus overcome ambiguities in case multiple extensions expose properties with the same name.
	 *
	 * @return the extension id, must not be {@literal null}.
	 */
	String getExtensionId();

	
Returns the properties exposed by the extension.
Returns:
the properties/**
	 * Returns the properties exposed by the extension.
	 *
	 * @return the properties
	 */
	default Map<String, Object> getProperties() {
		return Collections.emptyMap();
	}

	
Returns the functions exposed by the extension.
Returns:
the functions/**
	 * Returns the functions exposed by the extension.
	 *
	 * @return the functions
	 */
	default Map<String, Function> getFunctions() {
		return Collections.emptyMap();
	}

	
Returns the root object to be exposed by the extension. It's strongly recommended to declare the most concrete type
possible as return type of the implementation method. This will allow us to obtain the necessary metadata once and
not for every evaluation.
Returns:
/**
	 * Returns the root object to be exposed by the extension. It's strongly recommended to declare the most concrete type
	 * possible as return type of the implementation method. This will allow us to obtain the necessary metadata once and
	 * not for every evaluation.
	 *
	 * @return
	 */
	@Nullable
	default Object getRootObject() {
		return null;
	}
}