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* Copyright 2010, Red Hat, Inc. and/or its affiliates, and individual contributors
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* 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 org.hibernate.validator.constraints;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import javax.script.ScriptContext;
import javax.script.ScriptEngineManager;
import javax.validation.Constraint;
import javax.validation.ConstraintDeclarationException;
import javax.validation.Payload;

import org.hibernate.validator.constraints.impl.ScriptAssertValidator;

import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * 
 * A class-level constraint, that evaluates a script expression against the
 * annotated element. This constraint can be used to implement validation
 * routines, that depend on multiple attributes of the annotated element.
 * 
 * 
 * For evaluation of expressions the Java Scripting API as defined by JSR 223
 * ("Scripting for the Java^TM Platform") is used. Therefore an
 * implementation of that API must part of the class path. This is automatically
 * the case when running on Java 6. For older Java versions, the JSR 223 RI can
 * be added manually to the class path.
 * 
 * The expressions to be evaluated can be written in any scripting or expression
 * language, for which a JSR 223 compatible engine can be found in the class
 * path. The following listing shows an example using the JavaScript engine,
 * which comes with Java 6: 
 * 
 * 
 * @ScriptAssert(lang = "javascript", script = "_this.startDate.before(_this.endDate)")
 * public class CalendarEvent {
 * 
 * 	private Date startDate;
 * 

 * 	private Date endDate;
 * 

 * 	//...
 * 

 * }
 * 
 * 
 * Using a real expression language in conjunction with a shorter object alias allows
 * for very compact expressions:
 * 
 *  * @ScriptAssert(lang = "jexl", script = "_.startDate < _.endDate", alias = "_")
 * public class CalendarEvent {
 * 
 * 	private Date startDate;
 * 

 * 	private Date endDate;
 * 

 * 	//...
 * 

 * }
 * 
 * 
 * Accepts any type.
 * 
 *
 * @author Gunnar Morling
 */
@Target({ TYPE })
@Retention(RUNTIME)
@Constraint(validatedBy = ScriptAssertValidator.class)
@Documented
public @interface ScriptAssert {

	String message() default "{org.hibernate.validator.constraints.ScriptAssert.message}";

	Class[] groups() default { };

	Class[] payload() default { };

	/**
	 * @return The name of the script language used by this constraint as
	 *         expected by the JSR 223 {@link ScriptEngineManager}. A
	 *         {@link ConstraintDeclarationException} will be thrown upon script
	 *         evaluation, if no engine for the given language could be found.
	 */
	String lang();

	/**
	 * @return The script to be executed. The script must return
	 *         Boolean.TRUE, if the annotated element could
	 *         successfully be validated, otherwise Boolean.FALSE.
	 *         Returning null or any type other than Boolean will cause a
	 *         {@link ConstraintDeclarationException} upon validation. Any
	 *         exception occurring during script evaluation will be wrapped into
	 *         a ConstraintDeclarationException, too. Within the script, the
	 *         validated object can be accessed from the {@link ScriptContext
	 *         script context} using the name specified in the
	 *         alias attribute.
	 */
	String script();

	/**
	 * @return The name, under which the annotated element shall be registered
	 *         within the script context. Defaults to "_this".
	 */
	String alias() default "_this";

	/**
	 * Defines several {@code @ScriptAssert} annotations on the same element.
	 */
	@Target({ TYPE })
	@Retention(RUNTIME)
	@Documented
	public @interface List {
		ScriptAssert[] value();
	}
}