/*
 * Copyright 2004, 2005, 2006 Acegi Technology Pty Limited
 *
 * 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.security.acls.domain;

import java.util.Arrays;
import java.util.List;
import java.util.Set;

import org.springframework.security.access.AccessDeniedException;
import org.springframework.security.acls.model.Acl;
import org.springframework.security.acls.model.Sid;
import org.springframework.security.acls.model.SidRetrievalStrategy;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.authority.AuthorityUtils;
import org.springframework.security.core.context.SecurityContext;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.core.context.SecurityContextHolderStrategy;
import org.springframework.util.Assert;

/**
 * Default implementation of {@link AclAuthorizationStrategy}.
 * <p>
 * Permission will be granted if at least one of the following conditions is true for the
 * current principal.
 * <ul>
 * <li>is the owner (as defined by the ACL).</li>
 * <li>holds the relevant system-wide {@link GrantedAuthority} injected into the
 * constructor.</li>
 * <li>has {@link BasePermission#ADMINISTRATION} permission (as defined by the ACL).</li>
 * </ul>
 *
 * @author Ben Alex
 */
public class AclAuthorizationStrategyImpl implements AclAuthorizationStrategy {

	private SecurityContextHolderStrategy securityContextHolderStrategy = SecurityContextHolder
			.getContextHolderStrategy();

	private final GrantedAuthority gaGeneralChanges;

	private final GrantedAuthority gaModifyAuditing;

	private final GrantedAuthority gaTakeOwnership;

	private SidRetrievalStrategy sidRetrievalStrategy = new SidRetrievalStrategyImpl();

	/**
	 * Constructor. The only mandatory parameter relates to the system-wide
	 * {@link GrantedAuthority} instances that can be held to always permit ACL changes.
	 * @param auths the <code>GrantedAuthority</code>s that have special permissions
	 * (index 0 is the authority needed to change ownership, index 1 is the authority
	 * needed to modify auditing details, index 2 is the authority needed to change other
	 * ACL and ACE details) (required)
	 * <p>
	 * Alternatively, a single value can be supplied for all three permissions.
	 */
	public AclAuthorizationStrategyImpl(GrantedAuthority... auths) {
		Assert.isTrue(auths != null && (auths.length == 3 || auths.length == 1),
				"One or three GrantedAuthority instances required");
		if (auths.length == 3) {
			this.gaTakeOwnership = auths[0];
			this.gaModifyAuditing = auths[1];
			this.gaGeneralChanges = auths[2];
		}
		else {
			this.gaTakeOwnership = auths[0];
			this.gaModifyAuditing = auths[0];
			this.gaGeneralChanges = auths[0];
		}
	}

	@Override
	public void securityCheck(Acl acl, int changeType) {
		SecurityContext context = this.securityContextHolderStrategy.getContext();
		if ((context == null) || (context.getAuthentication() == null)
				|| !context.getAuthentication().isAuthenticated()) {
			throw new AccessDeniedException("Authenticated principal required to operate with ACLs");
		}
		Authentication authentication = context.getAuthentication();
		// Check if authorized by virtue of ACL ownership
		Sid currentUser = createCurrentUser(authentication);
		if (currentUser.equals(acl.getOwner())
				&& ((changeType == CHANGE_GENERAL) || (changeType == CHANGE_OWNERSHIP))) {
			return;
		}

		// Iterate this principal's authorities to determine right
		Set<String> authorities = AuthorityUtils.authorityListToSet(authentication.getAuthorities());
		if (acl.getOwner() instanceof GrantedAuthoritySid
				&& authorities.contains(((GrantedAuthoritySid) acl.getOwner()).getGrantedAuthority())) {
			return;
		}

		// Not authorized by ACL ownership; try via adminstrative permissions
		GrantedAuthority requiredAuthority = getRequiredAuthority(changeType);

		if (authorities.contains(requiredAuthority.getAuthority())) {
			return;
		}

		// Try to get permission via ACEs within the ACL
		List<Sid> sids = this.sidRetrievalStrategy.getSids(authentication);
		if (acl.isGranted(Arrays.asList(BasePermission.ADMINISTRATION), sids, false)) {
			return;
		}

		throw new AccessDeniedException(
				"Principal does not have required ACL permissions to perform requested operation");
	}

	private GrantedAuthority getRequiredAuthority(int changeType) {
		if (changeType == CHANGE_AUDITING) {
			return this.gaModifyAuditing;
		}
		if (changeType == CHANGE_GENERAL) {
			return this.gaGeneralChanges;
		}
		if (changeType == CHANGE_OWNERSHIP) {
			return this.gaTakeOwnership;
		}
		throw new IllegalArgumentException("Unknown change type");
	}

	/**
	 * Creates a principal-like sid from the authentication information.
	 * @param authentication the authentication information that can provide principal and
	 * thus the sid's id will be dependant on the value inside
	 * @return a sid with the ID taken from the authentication information
	 */
	protected Sid createCurrentUser(Authentication authentication) {
		return new PrincipalSid(authentication);
	}

	public void setSidRetrievalStrategy(SidRetrievalStrategy sidRetrievalStrategy) {
		Assert.notNull(sidRetrievalStrategy, "SidRetrievalStrategy required");
		this.sidRetrievalStrategy = sidRetrievalStrategy;
	}

	/**
	 * Sets the {@link SecurityContextHolderStrategy} to use. The default action is to use
	 * the {@link SecurityContextHolderStrategy} stored in {@link SecurityContextHolder}.
	 *
	 * @since 5.8
	 */
	public void setSecurityContextHolderStrategy(SecurityContextHolderStrategy securityContextHolderStrategy) {
		Assert.notNull(securityContextHolderStrategy, "securityContextHolderStrategy cannot be null");
		this.securityContextHolderStrategy = securityContextHolderStrategy;
	}

}
