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Client Library for integrating Jakarta EE applications with SAP Authorization Management Service (AMS)

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/************************************************************************
 * © 2019-2023 SAP SE or an SAP affiliate company. All rights reserved. *
 ************************************************************************/
package com.sap.cloud.security.ams.api;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.*;

/**
 * Enhances the predefined
 * {@link com.sap.cloud.security.ams.dcl.client.pdp.Attributes} instance.
 */
public interface AttributesProcessor extends Comparable {
	Logger LOGGER = LoggerFactory.getLogger(AttributesProcessor.class);
	/**
	 * Instance is called first with lowest priority. 

	 * In case of multiple {@link AttributesProcessor} implementations, the
	 * {@link com.sap.cloud.security.ams.dcl.client.pdp.Attributes} might be
	 * overwritten by a {@link AttributesProcessor} that has specified a higher
	 * priority with {@link #getPriority()}.
	 */
	int LOWEST_PRECEDENCE = 0;

	/**
	 * Is called last, can be used to override the
	 * {@link com.sap.cloud.security.ams.dcl.client.pdp.Attributes} from other
	 * {@link AttributesProcessor} previously called.
	 */
	int HIGHEST_PRECEDENCE = 100;

	/**
	 * Allows ordering between multiple {@link AttributesProcessor}.
	 *
	 * @return by default {@link #LOWEST_PRECEDENCE}
	 */
	default int getPriority() {
		return LOWEST_PRECEDENCE;
	}

	/**
	 * Returns all services that implements {@code AttributesProcessor} interface.
	 *
	 * @return attribute processors
	 */
	static List getAll() {
		List services = new ArrayList<>();
		ServiceLoader loader = ServiceLoader.load(AttributesProcessor.class);
		loader.forEach(services::add);
		services.sort(Comparator.comparing(AttributesProcessor::getPriority));
		LOGGER.debug("found the following attribute processors: {}", services);
		return services;
	}

	/**
	 * Callback to enhance or modify the predefined attributes. You can get the
	 * actual {@link com.sap.cloud.security.ams.dcl.client.pdp.Attributes} with
	 * {@link Principal#getAttributes()}.
	 *
	 * @param principal
	 *            provides all principal information including the predefined
	 *            attributes.
	 *
	 */
	void processAttributes(Principal principal);

	@Override
	default int compareTo(AttributesProcessor other) {
		return Integer.compare(this.getPriority(), other.getPriority());
	}
}