/*
 * 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
 *
 *      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.springframework.security.taglibs.authz;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.Tag;
import javax.servlet.jsp.tagext.TagSupport;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.security.access.PermissionEvaluator;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.security.taglibs.TagLibConfig;
import org.springframework.security.web.context.support.SecurityWebApplicationContextUtils;


/**
 * An implementation of {@link Tag} that allows its body through if all authorizations are
 * granted to the request's principal.
 * <p>
 * One or more comma separate numeric are specified via the {@code hasPermission}
 * attribute. The tag delegates to the configured {@link PermissionEvaluator} which it
 * obtains from the {@code ApplicationContext}.
 * <p>
 * For this class to operate it must be able to access the application context via the
 * {@code WebApplicationContextUtils} and attempt to locate the
 * {@code PermissionEvaluator} instance. There cannot be more than one of these present
 * for the tag to function.
 *
 * @author Ben Alex
 * @author Luke Taylor
 * @author Rob Winch
 */
public class AccessControlListTag extends TagSupport {
	// ~ Static fields/initializers
	// =====================================================================================

	protected static final Log logger = LogFactory.getLog(AccessControlListTag.class);

	// ~ Instance fields
	// ================================================================================================

	private ApplicationContext applicationContext;
	private Object domainObject;
	private PermissionEvaluator permissionEvaluator;
	private String hasPermission = "";
	private String var;

	// ~ Methods
	// ========================================================================================================

	public int doStartTag() throws JspException {
		if ((null == hasPermission) || "".equals(hasPermission)) {
			return skipBody();
		}

		initializeIfRequired();

		if (domainObject == null) {
			if (logger.isDebugEnabled()) {
				logger.debug("domainObject resolved to null, so including tag body");
			}

			// Of course they have access to a null object!
			return evalBody();
		}

		Authentication authentication = SecurityContextHolder.getContext()
				.getAuthentication();
		if (authentication == null) {
			if (logger.isDebugEnabled()) {
				logger.debug("SecurityContextHolder did not return a non-null Authentication object, so skipping tag body");
			}

			return skipBody();
		}

		List<Object> requiredPermissions = parseHasPermission(hasPermission);
		for (Object requiredPermission : requiredPermissions) {
			if (!permissionEvaluator.hasPermission(authentication, domainObject,
					requiredPermission)) {
				return skipBody();
			}
		}

		return evalBody();
	}

	private List<Object> parseHasPermission(String hasPermission) {
		String[] requiredPermissions = hasPermission.split(",");
		List<Object> parsedPermissions = new ArrayList<Object>(requiredPermissions.length);
		for (String permissionToParse : requiredPermissions) {
			Object parsedPermission = permissionToParse;
			try {
				parsedPermission = Integer.parseInt(permissionToParse);
			}
			catch (NumberFormatException notBitMask) {
			}
			parsedPermissions.add(parsedPermission);
		}
		return parsedPermissions;
	}

	private int skipBody() {
		if (var != null) {
			pageContext.setAttribute(var, Boolean.FALSE, PageContext.PAGE_SCOPE);
		}
		return TagLibConfig.evalOrSkip(false);
	}

	private int evalBody() {
		if (var != null) {
			pageContext.setAttribute(var, Boolean.TRUE, PageContext.PAGE_SCOPE);
		}
		return TagLibConfig.evalOrSkip(true);
	}

	/**
	 * Allows test cases to override where application context obtained from.
	 *
	 * @param pageContext so the <code>ServletContext</code> can be accessed as required
	 * by Spring's <code>WebApplicationContextUtils</code>
	 *
	 * @return the Spring application context (never <code>null</code>)
	 */
	protected ApplicationContext getContext(PageContext pageContext) {
		ServletContext servletContext = pageContext.getServletContext();

		return SecurityWebApplicationContextUtils.findRequiredWebApplicationContext(servletContext);
	}

	public Object getDomainObject() {
		return domainObject;
	}

	public String getHasPermission() {
		return hasPermission;
	}

	private void initializeIfRequired() throws JspException {
		if (applicationContext != null) {
			return;
		}

		this.applicationContext = getContext(pageContext);

		permissionEvaluator = getBeanOfType(PermissionEvaluator.class);
	}

	private <T> T getBeanOfType(Class<T> type) throws JspException {
		Map<String, T> map = applicationContext.getBeansOfType(type);

		for (ApplicationContext context = applicationContext.getParent(); context != null; context = context
				.getParent()) {
			map.putAll(context.getBeansOfType(type));
		}

		if (map.size() == 0) {
			return null;
		}
		else if (map.size() == 1) {
			return map.values().iterator().next();
		}

		throw new JspException("Found incorrect number of " + type.getSimpleName()
				+ " instances in " + "application context - you must have only have one!");
	}

	public void setDomainObject(Object domainObject) {
		this.domainObject = domainObject;
	}

	public void setHasPermission(String hasPermission) {
		this.hasPermission = hasPermission;
	}

	public void setVar(String var) {
		this.var = var;
	}
}
