/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.shiro.web.filter;

import org.apache.shiro.SecurityUtils;
import org.apache.shiro.subject.Subject;
import org.apache.shiro.web.util.WebUtils;

import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import java.io.IOException;

/**
 * Superclass for any filter that controls access to a resource and may redirect the user to the login page
 * if they are not authenticated.  This superclass provides the method
 * {@link #saveRequestAndRedirectToLogin(javax.servlet.ServletRequest, javax.servlet.ServletResponse)}
 * which is used by many subclasses as the behavior when a user is unauthenticated.
 *
 * @since 0.9
 */
public abstract class AccessControlFilter extends PathMatchingFilter {

    /**
     * Simple default login URL equal to <code>/login.jsp</code>, which can be overridden by calling the
     * {@link #setLoginUrl(String) setLoginUrl} method.
     */
    public static final String DEFAULT_LOGIN_URL = "/login.jsp";

    /**
     * Constant representing the HTTP 'GET' request method, equal to <code>GET</code>.
     */
    public static final String GET_METHOD = "GET";

    /**
     * Constant representing the HTTP 'POST' request method, equal to <code>POST</code>.
     */
    public static final String POST_METHOD = "POST";

    /**
     * The login url to used to authenticate a user, used when redirecting users if authentication is required.
     */
    private String loginUrl = DEFAULT_LOGIN_URL;

    /**
     * Returns the login URL used to authenticate a user.
     * <p/>
     * Most Shiro filters use this url
     * as the location to redirect a user when the filter requires authentication.  Unless overridden, the
     * {@link #DEFAULT_LOGIN_URL DEFAULT_LOGIN_URL} is assumed, which can be overridden via
     * {@link #setLoginUrl(String) setLoginUrl}.
     *
     * @return the login URL used to authenticate a user, used when redirecting users if authentication is required.
     */
    public String getLoginUrl() {
        return loginUrl;
    }

    /**
     * Sets the login URL used to authenticate a user.
     * <p/>
     * Most Shiro filters use this url as the location to redirect a user when the filter requires
     * authentication.  Unless overridden, the {@link #DEFAULT_LOGIN_URL DEFAULT_LOGIN_URL} is assumed.
     *
     * @param loginUrl the login URL used to authenticate a user, used when redirecting users if authentication is required.
     */
    public void setLoginUrl(String loginUrl) {
        this.loginUrl = loginUrl;
    }

    /**
     * Convenience method that acquires the Subject associated with the request.
     * <p/>
     * The default implementation simply returns
     * {@link org.apache.shiro.SecurityUtils#getSubject() SecurityUtils.getSubject()}.
     *
     * @param request  the incoming <code>ServletRequest</code>
     * @param response the outgoing <code>ServletResponse</code>
     * @return the Subject associated with the request.
     */
    protected Subject getSubject(ServletRequest request, ServletResponse response) {
        return SecurityUtils.getSubject();
    }

    /**
     * Returns <code>true</code> if the request is allowed to proceed through the filter normally, or <code>false</code>
     * if the request should be handled by the
     * {@link #onAccessDenied(ServletRequest, ServletResponse, Object) onAccessDenied(request,response,mappedValue)}
     * method instead.
     *
     * @param request     the incoming <code>ServletRequest</code>
     * @param response    the outgoing <code>ServletResponse</code>
     * @param mappedValue the filter-specific config value mapped to this filter in the URL rules mappings.
     * @return <code>true</code> if the request should proceed through the filter normally, <code>false</code> if the
     * request should be processed by this filter's
     * {@link #onAccessDenied(ServletRequest, ServletResponse, Object)} method instead.
     * @throws Exception if an error occurs during processing.
     */
    protected abstract boolean isAccessAllowed(ServletRequest request, ServletResponse response,
                                               Object mappedValue) throws Exception;

    /**
     * Processes requests where the subject was denied access as determined by the
     * {@link #isAccessAllowed(javax.servlet.ServletRequest, javax.servlet.ServletResponse, Object) isAccessAllowed}
     * method, retaining the {@code mappedValue} that was used during configuration.
     * <p/>
     * This method immediately delegates to {@link #onAccessDenied(ServletRequest, ServletResponse)} as a
     * convenience in that most post-denial behavior does not need the mapped config again.
     *
     * @param request     the incoming <code>ServletRequest</code>
     * @param response    the outgoing <code>ServletResponse</code>
     * @param mappedValue the config specified for the filter in the matching request's filter chain.
     * @return <code>true</code> if the request should continue to be processed; false if the subclass will
     * handle/render the response directly.
     * @throws Exception if there is an error processing the request.
     * @since 1.0
     */
    protected boolean onAccessDenied(ServletRequest request, ServletResponse response, Object mappedValue) throws Exception {
        return onAccessDenied(request, response);
    }

    /**
     * Processes requests where the subject was denied access as determined by the
     * {@link #isAccessAllowed(javax.servlet.ServletRequest, javax.servlet.ServletResponse, Object) isAccessAllowed}
     * method.
     *
     * @param request  the incoming <code>ServletRequest</code>
     * @param response the outgoing <code>ServletResponse</code>
     * @return <code>true</code> if the request should continue to be processed; false if the subclass will
     * handle/render the response directly.
     * @throws Exception if there is an error processing the request.
     */
    protected abstract boolean onAccessDenied(ServletRequest request, ServletResponse response) throws Exception;

    /**
     * Returns <code>true</code> if
     * {@link #isAccessAllowed(ServletRequest, ServletResponse, Object) isAccessAllowed(Request,Response,Object)},
     * otherwise returns the result of
     * {@link #onAccessDenied(ServletRequest, ServletResponse, Object) onAccessDenied(Request,Response,Object)}.
     *
     * @return <code>true</code> if
     * {@link #isAccessAllowed(javax.servlet.ServletRequest, javax.servlet.ServletResponse, Object) isAccessAllowed},
     * otherwise returns the result of
     * {@link #onAccessDenied(javax.servlet.ServletRequest, javax.servlet.ServletResponse) onAccessDenied}.
     * @throws Exception if an error occurs.
     */
    public boolean onPreHandle(ServletRequest request, ServletResponse response, Object mappedValue) throws Exception {
        return isAccessAllowed(request, response, mappedValue) || onAccessDenied(request, response, mappedValue);
    }

    /**
     * Returns <code>true</code> if the incoming request is a login request, <code>false</code> otherwise.
     * <p/>
     * The default implementation merely returns <code>true</code> if the incoming request matches the configured
     * {@link #getLoginUrl() loginUrl} by calling
     * <code>{@link #pathsMatch(String, String) pathsMatch(loginUrl, request)}</code>.
     *
     * @param request  the incoming <code>ServletRequest</code>
     * @param response the outgoing <code>ServletResponse</code>
     * @return <code>true</code> if the incoming request is a login request, <code>false</code> otherwise.
     */
    protected boolean isLoginRequest(ServletRequest request, ServletResponse response) {
        return pathsMatch(getLoginUrl(), request);
    }


    /**
     * Convenience method for subclasses to use when a login redirect is required.
     * <p/>
     * This implementation simply calls {@link #saveRequest(javax.servlet.ServletRequest) saveRequest(request)}
     * and then {@link #redirectToLogin(ServletRequest, ServletResponse) redirectToLogin(request,response)}.
     *
     * @param request  the incoming <code>ServletRequest</code>
     * @param response the outgoing <code>ServletResponse</code>
     * @throws IOException if an error occurs.
     */
    protected void saveRequestAndRedirectToLogin(ServletRequest request, ServletResponse response) throws IOException {
        saveRequest(request);
        redirectToLogin(request, response);
    }

    /**
     * Convenience method merely delegates to
     * {@link WebUtils#saveRequest(javax.servlet.ServletRequest) WebUtils.saveRequest(request)} to save the request
     * state for reuse later.  This is mostly used to retain user request state when a redirect is issued to
     * return the user to their originally requested url/resource.
     * <p/>
     * If you need to save and then immediately redirect the user to login, consider using
     * {@link #saveRequestAndRedirectToLogin(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
     * saveRequestAndRedirectToLogin(request,response)} directly.
     *
     * @param request the incoming ServletRequest to save for re-use later (for example, after a redirect).
     */
    protected void saveRequest(ServletRequest request) {
        WebUtils.saveRequest(request);
    }

    /**
     * Convenience method for subclasses that merely acquires the {@link #getLoginUrl() getLoginUrl} and redirects
     * the request to that url.
     * <p/>
     * <b>N.B.</b>  If you want to issue a redirect with the intention of allowing the user to then return to their
     * originally requested URL, don't use this method directly.  Instead you should call
     * {@link #saveRequestAndRedirectToLogin(javax.servlet.ServletRequest, javax.servlet.ServletResponse)
     * saveRequestAndRedirectToLogin(request,response)}, which will save the current request state so that it can
     * be reconstructed and reused after a successful login.
     *
     * @param request  the incoming <code>ServletRequest</code>
     * @param response the outgoing <code>ServletResponse</code>
     * @throws IOException if an error occurs.
     */
    protected void redirectToLogin(ServletRequest request, ServletResponse response) throws IOException {
        String loginUrl = getLoginUrl();
        WebUtils.issueRedirect(request, response, loginUrl);
    }

}
