/*
 * Copyright 2002-2004 the original author or authors.
 * 
 * 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.web.util;

import java.io.File;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.ServletRequest;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import org.springframework.util.StringUtils;

/**
 * Miscellaneous utilities for web applications.
 * Used by various framework classes.
 * @author Rod Johnson
 * @author Juergen Hoeller
 */
public abstract class WebUtils {

	/**
	 * Default character encoding to use when request.getCharacterEncoding
	 * returns null, according to the Servlet spec.
	 * @see ServletRequest#getCharacterEncoding
	 */
	public static final String DEFAULT_CHARACTER_ENCODING = "ISO-8859-1";

	/**
	 * Standard Servlet spec context attribute that specifies a temporary
	 * directory for the current web application, of type java.io.File
	 */
	public static final String TEMP_DIR_CONTEXT_ATTRIBUTE = "javax.servlet.context.tempdir";

	/**
	 * HTML escape parameter at the servlet context level
	 * (i.e. a context-param in web.xml): "defaultHtmlEscape".
	 */
	public static final String HTML_ESCAPE_CONTEXT_PARAM = "defaultHtmlEscape";

	/**
	 * Web app root key parameter at the servlet context level
	 * (i.e. a context-param in web.xml): "webAppRootKey".
	 */
	public static final String WEB_APP_ROOT_KEY_PARAM = "webAppRootKey";

	/** Default web app root key: "webapp.root" */
	public static final String DEFAULT_WEB_APP_ROOT_KEY = "webapp.root";

	/** Name suffixes in case of image buttons */
	public static final String[] SUBMIT_IMAGE_SUFFIXES = {".x", ".y"};


	/**
	 * Set a system property to the web application root directory.
	 * The key of the system property can be defined with the "webAppRootKey"
	 * context-param in web.xml. Default is "webapp.root".
	 * <p>Can be used for toolkits that support substition with System.getProperty
	 * values, like Log4J's "${key}" syntax within log file locations.
	 * @param servletContext the servlet context of the web application
	 * @throws IllegalStateException if the system property is already set,
	 * or if the WAR file is not expanded
	 * @see #WEB_APP_ROOT_KEY_PARAM
	 * @see #DEFAULT_WEB_APP_ROOT_KEY
	 * @see WebAppRootListener
	 * @see Log4jWebConfigurer
	 */
	public static void setWebAppRootSystemProperty(ServletContext servletContext) throws IllegalStateException {
		String root = servletContext.getRealPath("/");
		if (root == null) {
			throw new IllegalStateException(
			    "Cannot set web app root system property when WAR file is not expanded");
		}
		String param = servletContext.getInitParameter(WEB_APP_ROOT_KEY_PARAM);
		String key = (param != null ? param : DEFAULT_WEB_APP_ROOT_KEY);
		String oldValue = System.getProperty(key);
		if (oldValue != null && !StringUtils.pathEquals(oldValue, root)) {
			throw new IllegalStateException(
			    "Web app root system property already set to different value: '" +
			    key + "' = [" + oldValue + "] instead of [" + root + "] - " +
			    "Choose unique values for the 'webAppRootKey' context-param in your web.xml files!");
		}
		System.setProperty(key, root);
		servletContext.log("Set web app root system property: '" + key + "' = [" + root + "]");
	}

	/**
	 * Return whether default HTML escaping is enabled for the web application,
	 * i.e. the value of the "defaultHtmlEscape" context-param in web.xml (if any).
	 * @param servletContext the servlet context of the web application
	 * @return whether default HTML escaping is enabled (default is false)
	 */
	public static boolean isDefaultHtmlEscape(ServletContext servletContext) {
		String param = servletContext.getInitParameter(HTML_ESCAPE_CONTEXT_PARAM);
		return Boolean.valueOf(param).booleanValue();
	}

	/**
	 * Return the temporary directory for the current web application,
	 * as provided by the servlet container.
	 * @param servletContext the servlet context of the web application
	 * @return the File representing the temporary directory
	 */
	public static File getTempDir(ServletContext servletContext) {
		return (File) servletContext.getAttribute(TEMP_DIR_CONTEXT_ATTRIBUTE);
	}


	/**
	 * Determine the session id of the given request, if any.
	 * @param request current HTTP request
	 * @return the session id, or null if none
	 */
	public static String getSessionId(HttpServletRequest request) {
		HttpSession session = request.getSession(false);
		return (session != null ? session.getId() : null);
	}

	/**
	 * Check the given request for a session attribute of the given name.
	 * Returns null if there is no session or if the session has no such attribute.
	 * Does not create a new session if none has existed before!
	 * @param request current HTTP request
	 * @param name the name of the session attribute
	 * @return the value of the session attribute, or null if not found
	 */
	public static Object getSessionAttribute(HttpServletRequest request, String name) {
		HttpSession session = request.getSession(false);
		return (session != null ? session.getAttribute(name) : null);
	}

	/**
	 * Check the given request for a session attribute of the given name.
	 * Throws an exception if there is no session or if the session has no such
	 * attribute. Does not create a new session if none has existed before!
	 * @param request current HTTP request
	 * @param name the name of the session attribute
	 * @return the value of the session attribute, or null if not found
	 * @throws IllegalStateException if the session attribute could not be found
	 */
	public static Object getRequiredSessionAttribute(HttpServletRequest request, String name)
	    throws IllegalStateException {
		Object attr = getSessionAttribute(request, name);
		if (attr == null) {
			throw new IllegalStateException("No session attribute '" + name + "' found");
		}
		return attr;
	}

	/**
	 * Set the session attribute with the given name to the given value.
	 * Removes the session attribute if value is null, if a session existed at all.
	 * Does not create a new session if not necessary!
	 * @param request current HTTP request
	 * @param name the name of the session attribute
	 */
	public static void setSessionAttribute(HttpServletRequest request, String name, Object value) {
		if (value != null) {
			request.getSession().setAttribute(name, value);
		}
		else {
			HttpSession session = request.getSession(false);
			if (session != null) {
				session.removeAttribute(name);
			}
		}
	}

	/**
	 * Get the specified session attribute, creating and setting a new attribute if
	 * no existing found. The given class needs to have a public no-arg constructor.
	 * Useful for on-demand state objects in a web tier, like shopping carts.
	 * @param session current HTTP session
	 * @param name the name of the session attribute
	 * @param clazz the class to instantiate for a new attribute
	 * @return the value of the session attribute, newly created if not found
	 * @throws IllegalArgumentException if the session attribute could not be instantiated
	 */
	public static Object getOrCreateSessionAttribute(HttpSession session, String name, Class clazz)
			throws IllegalArgumentException {
		Object sessionObject = session.getAttribute(name);
		if (sessionObject == null) {
			try {
				sessionObject = clazz.newInstance();
			}
			catch (InstantiationException ex) {
				throw new IllegalArgumentException(
				    "Could not instantiate class [" + clazz.getName() +
				    "] for session attribute '" + name + "': " + ex.getMessage());
			}
			catch (IllegalAccessException ex) {
				throw new IllegalArgumentException(
				    "Could not access default constructor of class [" + clazz.getName() +
				    "] for session attribute '" + name + "': " + ex.getMessage());
			}
			session.setAttribute(name, sessionObject);
		}
		return sessionObject;
	}


	/**
	 * Retrieve the first cookie with the given name. Note that multiple
	 * cookies can have the same name but different paths or domains.
	 * @param name cookie name
	 * @return the first cookie with the given name, or null if none is found
	 */
	public static Cookie getCookie(HttpServletRequest request, String name) {
		Cookie cookies[] = request.getCookies();
		if (cookies != null) {
			for (int i = 0; i < cookies.length; i++) {
				if (name.equals(cookies[i].getName()))
					return cookies[i];
			}
		}
		return null;
	}

	/**
	 * Return a map containing all parameters with the given prefix.
	 * Maps single values to String and multiple values to String array.
	 * <p>For example, with a prefix of "spring_", "spring_param1" and
	 * "spring_param2" result in a Map with "param1" and "param2" as keys.
	 * <p>Similar to Servlet 2.3's <code>ServletRequest.getParameterMap</code>,
	 * but more flexible and compatible with Servlet 2.2.
	 * @param request HTTP request in which to look for parameters
	 * @param prefix the beginning of parameter names
	 * (if this is null or the empty string, all parameters will match)
	 * @return map containing request parameters <b>without the prefix</b>,
	 * containing either a String or a String array as values
	 * @see javax.servlet.ServletRequest#getParameterNames
	 * @see javax.servlet.ServletRequest#getParameterValues
	 * @see javax.servlet.ServletRequest#getParameterMap
	 */
	public static Map getParametersStartingWith(ServletRequest request, String prefix) {
		Enumeration en = request.getParameterNames();
		Map params = new HashMap();
		if (prefix == null) {
			prefix = "";
		}
		while (en != null && en.hasMoreElements()) {
			String paramName = (String) en.nextElement();
			if ("".equals(prefix) || paramName.startsWith(prefix)) {
				String unprefixed = paramName.substring(prefix.length());
				String[] values = request.getParameterValues(paramName);
				if (values == null) {
					// do nothing, no values found at all
				}
				else if (values.length > 1) {
					params.put(unprefixed, values);
				}
				else {
					params.put(unprefixed, values[0]);
				}
			}
		}
		return params;
	}

	/**
	 * Check if a specific input type="submit" parameter was sent in the request,
	 * either via a button (directly with name) or via an image (name + ".x" or
	 * name + ".y").
	 * @param request current HTTP request
	 * @param name name of the parameter
	 * @return if the parameter was sent
	 * @see #SUBMIT_IMAGE_SUFFIXES
	 */
	public static boolean hasSubmitParameter(ServletRequest request, String name) {
		if (request.getParameter(name) != null) {
			return true;
		}
		for (int i = 0; i < SUBMIT_IMAGE_SUFFIXES.length; i++) {
			String suffix = SUBMIT_IMAGE_SUFFIXES[i];
			if (request.getParameter(name + suffix) != null) {
				return true;
			}
		}
		return false;
	}

}
