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Celerio Core Generation Engine

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/*
 * Copyright 2015 JAXIO http://www.jaxio.com
 *
 * 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.
 */

package com.jaxio.celerio.spi;

import com.jaxio.celerio.model.Relation;

import java.util.ServiceLoader;

/**
 * The RelationSpi interface allows Celerio template developers to plug new {@link Relation} helpers.
 * 
 * The implementations are loaded by the java's {@link ServiceLoader}.
 */
public interface RelationSpi {

    /**
     * Whether the SPI is compatible with the passed relation.
     *
     * @return true if this SPI must be binded on the passed relation, false otherwise.
     */
    boolean compatibleWith(Relation relation);

    /**
     * Invoked by Celerio, when this RelationSpi is binded on a {@link Relation} instance.
     */
    void init(Relation relation);

    /**
     * The var name under which the target is bound during template evaluation.

     * For example if velocityVar() methods returns myextension, the corresponding RelationSpi implementation instance is given by
     * $relation.myextension.
     */
    String velocityVar();

    /**
     * The bound target.
     */
    Object getTarget();
}