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/*
 * Copyright (C) 2013-2023 by XDEV Software, All Rights Reserved.
 *
 * This file is part of the RapidClipse Application Platform (RAP).
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see .
 *
 * SPDX-License-Identifier: AGPL-3.0-or-later
 *
 * Contributors:
 *     XDEV Software - initial API and implementation
 */
package com.rapidclipse.framework.security.authorization;

import static java.util.Objects.requireNonNull;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

import com.rapidclipse.framework.security.util.LockedMap;


/**
 * A registry type that provides a means for centralized lookup and iteration of known {@link Subject} instances.
 * Note that a registry conceptually only provides reading access, not modifying access to its contents. For
 * modifying operations, see {@link SubjectManager}.
 *
 * @author XDEV Software (TM)
 */
public interface SubjectRegistry
{
	/**
	 * Returns the {@link Subject} instance identified by the passed subject name.
	 *
	 * @param subjectName
	 *            the name identifying the desired {@link Subject} instance.
	 * @return the {@link Subject} instance identified by the passed name.
	 */
	public Subject subject(String subjectName);

	/**
	 * Returns a read-only map of all known {@link Subject} instances (values), identified by their names (keys).
	 *
	 * @return a read-only map containing all known subjects.
	 */
	public Map subjects();

	/**
	 * Returns the lock instance that is internally used by this registry instance.
	 *
	 * @return the lock.
	 */
	public Object lockSubjectRegistry();

	/**
	 * Creates a new {@link SubjectRegistry} instance using the passed map instance as its internal datastructure
	 * and the passed registryLock instance as the synchronization lock for accessing the registry.
	 *
	 * @param registry
	 *            the map instance to be used as the internal datastructure.
	 * @param registryLock
	 *            the locking instance to be used to synchronize on for accessing the registry.
	 * @return a new {@link SubjectRegistry} instance using the passed instances.
	 */
	public static SubjectRegistry New(final Map registry, final Object registryLock)
	{
		return new Default(
			requireNonNull(registry),
			requireNonNull(registryLock));
	}

	/**
	 * Creates a new {@link SubjectRegistry} instance using the passed map instance and a newly instantiated object
	 * to be used a synchronization lock.
	 *
	 * @param registry
	 *            the map instance to be used as the internal datastructure.
	 * @return a new {@link SubjectRegistry} instance using the passed instance.
	 */
	public static SubjectRegistry New(final Map registry)
	{
		return New(registry, new Object());
	}

	/**
	 * Creates a new {@link SubjectRegistry} instance using the passed {@link Subject} instances to derive its
	 * internal datastructure from and the passed registryLock instance as the synchronization lock for
	 * accessing the registry.
	 *
	 * @param subjects
	 *            the {@link Subject} instances to derive the internal datastructure from.
	 * @param registryLock
	 *            the locking instance to be used to synchronize on for accessing the registry.
	 * @return a new {@link SubjectRegistry} instance using the passed instances.
	 */
	public static SubjectRegistry New(final Collection subjects, final Object registryLock)
	{
		return New(
			Default.buildRegistry(requireNonNull(subjects)),
			requireNonNull(registryLock));
	}

	/**
	 * Creates a new {@link SubjectRegistry} instance using the passed {@link Subject} instance to derive its
	 * internal datastructure from and a newly instantiated object to be used as the synchronization lock.
	 *
	 * @param subjects
	 *            the {@link Subject} instance to be used as the internal datastructure.
	 * @return a new {@link SubjectRegistry} instance using the passed instance.
	 */
	public static SubjectRegistry New(final Collection subjects)
	{
		return New(subjects, new Object());
	}

	/**
	 * A simple {@link SubjectRegistry} default implementation that synchronizes on a provided lock instance for
	 * accessing the internal registry in order to avoid concurrency issues while the internal datastructure is
	 * rebuilt.
	 *
	 * @author XDEV Software (TM)
	 */
	public final class Default implements SubjectRegistry
	{
		///////////////////////////////////////////////////////////////////////////
		// static methods //
		///////////////////

		static final Map buildRegistry(final Collection subjects)
		{
			final HashMap registry = new HashMap<>();

			subjects.forEach(subject -> registry.put(subject.name(), subject));

			return registry;
		}

		///////////////////////////////////////////////////////////////////////////
		// instance fields //
		////////////////////

		/**
		 * The read-only subject-name-to-subject map used as an internal datastructure
		 */
		private final Map registry;

		/**
		 * The instance used to synchronize on. This may be any instance, even the map or registry instance itself.
		 */
		private final Object registryLock;

		/**
		 * A map wrapper implementation wrapping the actual registry map and using the registryLock instance to
		 * perform synchronization. Through this technique, the map can be accessed directly without losing the
		 * consistent concurrency protection achieve via the locking instance.
		 */
		private final LockedMap lockedRegistry;

		///////////////////////////////////////////////////////////////////////////
		// constructors //
		/////////////////

		/**
		 * Implementation-detail constructor that might change in the future.
		 *
		 * @param registry
		 *            the map instance to be used as the internal datastructure.
		 * @param registryLock
		 *            the locking instance to be used to synchronize on for accessing the registry.
		 */
		protected Default(final Map registry, final Object registryLock)
		{
			super();
			this.registry       = registry;
			this.registryLock   = registryLock;
			this.lockedRegistry = LockedMap.New(this.registry, registryLock);
		}

		///////////////////////////////////////////////////////////////////////////
		// override methods //
		/////////////////////

		/**
		 * {@inheritDoc}
		 */
		@Override
		public final Subject subject(final String subjectName)
		{
			// must lock registry instead of this as a supervising manager instance might modify registry
			synchronized(this.registryLock)
			{
				return this.registry.get(subjectName);
			}
		}

		/**
		 * {@inheritDoc}
		 */
		@Override
		public final Map subjects()
		{
			return this.lockedRegistry;
		}

		/**
		 * {@inheritDoc}
		 */
		@Override
		public final Object lockSubjectRegistry()
		{
			return this.registryLock;
		}

	}

}