/*
 * Copyright 2002-2019 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
 *
 *      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.web.servlet.view;

import java.util.HashMap;
import java.util.Locale;
import java.util.Map;
import java.util.Properties;

import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.BeanUtils;
import org.springframework.context.ApplicationContext;
import org.springframework.core.Ordered;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.PatternMatchUtils;
import org.springframework.web.servlet.View;

/**
 * Simple implementation of the {@link org.springframework.web.servlet.ViewResolver}
 * interface, allowing for direct resolution of symbolic view names to URLs,
 * without explicit mapping definitions. This is useful if your symbolic names
 * match the names of your view resources in a straightforward manner
 * (i.e. the symbolic name is the unique part of the resource's filename),
 * without the need for a dedicated mapping to be defined for each view.
 *
 * <p>Supports {@link AbstractUrlBasedView} subclasses like {@link InternalResourceView}
 * and {@link org.springframework.web.servlet.view.freemarker.FreeMarkerView}.
 * The view class for all views generated by this resolver can be specified
 * via the "viewClass" property.
 *
 * <p>View names can either be resource URLs themselves, or get augmented by a
 * specified prefix and/or suffix. Exporting an attribute that holds the
 * RequestContext to all views is explicitly supported.
 *
 * <p>Example: prefix="/WEB-INF/jsp/", suffix=".jsp", viewname="test" ->
 * "/WEB-INF/jsp/test.jsp"
 *
 * <p>As a special feature, redirect URLs can be specified via the "redirect:"
 * prefix. E.g.: "redirect:myAction" will trigger a redirect to the given
 * URL, rather than resolution as standard view name. This is typically used
 * for redirecting to a controller URL after finishing a form workflow.
 *
 * <p>Furthermore, forward URLs can be specified via the "forward:" prefix.
 * E.g.: "forward:myAction" will trigger a forward to the given URL, rather than
 * resolution as standard view name. This is typically used for controller URLs;
 * it is not supposed to be used for JSP URLs - use logical view names there.
 *
 * <p>Note: This class does not support localized resolution, i.e. resolving
 * a symbolic view name to different resources depending on the current locale.
 *
 * <p><b>Note:</b> When chaining ViewResolvers, a UrlBasedViewResolver will check whether
 * the {@linkplain AbstractUrlBasedView#checkResource specified resource actually exists}.
 * However, with {@link InternalResourceView}, it is not generally possible to
 * determine the existence of the target resource upfront. In such a scenario,
 * a UrlBasedViewResolver will always return a View for any given view name;
 * as a consequence, it should be configured as the last ViewResolver in the chain.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Sam Brannen
 * @since 13.12.2003
 * @see #setViewClass
 * @see #setPrefix
 * @see #setSuffix
 * @see #setRequestContextAttribute
 * @see #REDIRECT_URL_PREFIX
 * @see AbstractUrlBasedView
 * @see InternalResourceView
 * @see org.springframework.web.servlet.view.freemarker.FreeMarkerView
 */
public class UrlBasedViewResolver extends AbstractCachingViewResolver implements Ordered {

        /**
         * Prefix for special view names that specify a redirect URL (usually
         * to a controller after a form has been submitted and processed).
         * Such view names will not be resolved in the configured default
         * way but rather be treated as special shortcut.
         */
        public static final String REDIRECT_URL_PREFIX = "redirect:";

        /**
         * Prefix for special view names that specify a forward URL (usually
         * to a controller after a form has been submitted and processed).
         * Such view names will not be resolved in the configured default
         * way but rather be treated as special shortcut.
         */
        public static final String FORWARD_URL_PREFIX = "forward:";


        @Nullable
        private Class<?> viewClass;

        private String prefix = "";

        private String suffix = "";

        @Nullable
        private String contentType;

        private boolean redirectContextRelative = true;

        private boolean redirectHttp10Compatible = true;

        @Nullable
        private String[] redirectHosts;

        @Nullable
        private String requestContextAttribute;

        /** Map of static attributes, keyed by attribute name (String). */
        private final Map<String, Object> staticAttributes = new HashMap<>();

        @Nullable
        private Boolean exposePathVariables;

        @Nullable
        private Boolean exposeContextBeansAsAttributes;

        @Nullable
        private String[] exposedContextBeanNames;

        @Nullable
        private String[] viewNames;

        private int order = Ordered.LOWEST_PRECEDENCE;


        /**
         * Set the view class that should be used to create views.
         * @param viewClass class that is assignable to the required view class
         * (by default, AbstractUrlBasedView)
         * @see AbstractUrlBasedView
         */
        public void setViewClass(@Nullable Class<?> viewClass) {
                if (viewClass != null && !requiredViewClass().isAssignableFrom(viewClass)) {
                        throw new IllegalArgumentException("Given view class [" + viewClass.getName() +
                                        "] is not of type [" + requiredViewClass().getName() + "]");
                }
                this.viewClass = viewClass;
        }

        /**
         * Return the view class to be used to create views.
         */
        @Nullable
        protected Class<?> getViewClass() {
                return this.viewClass;
        }

        /**
         * Return the required type of view for this resolver.
         * This implementation returns AbstractUrlBasedView.
         * @see AbstractUrlBasedView
         */
        protected Class<?> requiredViewClass() {
                return AbstractUrlBasedView.class;
        }

        /**
         * Set the prefix that gets prepended to view names when building a URL.
         */
        public void setPrefix(@Nullable String prefix) {
                this.prefix = (prefix != null ? prefix : "");
        }

        /**
         * Return the prefix that gets prepended to view names when building a URL.
         */
        protected String getPrefix() {
                return this.prefix;
        }

        /**
         * Set the suffix that gets appended to view names when building a URL.
         */
        public void setSuffix(@Nullable String suffix) {
                this.suffix = (suffix != null ? suffix : "");
        }

        /**
         * Return the suffix that gets appended to view names when building a URL.
         */
        protected String getSuffix() {
                return this.suffix;
        }

        /**
         * Set the content type for all views.
         * <p>May be ignored by view classes if the view itself is assumed
         * to set the content type, e.g. in case of JSPs.
         */
        public void setContentType(@Nullable String contentType) {
                this.contentType = contentType;
        }

        /**
         * Return the content type for all views, if any.
         */
        @Nullable
        protected String getContentType() {
                return this.contentType;
        }

        /**
         * Set whether to interpret a given redirect URL that starts with a
         * slash ("/") as relative to the current ServletContext, i.e. as
         * relative to the web application root.
         * <p>Default is "true": A redirect URL that starts with a slash will be
         * interpreted as relative to the web application root, i.e. the context
         * path will be prepended to the URL.
         * <p><b>Redirect URLs can be specified via the "redirect:" prefix.</b>
         * E.g.: "redirect:myAction"
         * @see RedirectView#setContextRelative
         * @see #REDIRECT_URL_PREFIX
         */
        public void setRedirectContextRelative(boolean redirectContextRelative) {
                this.redirectContextRelative = redirectContextRelative;
        }

        /**
         * Return whether to interpret a given redirect URL that starts with a
         * slash ("/") as relative to the current ServletContext, i.e. as
         * relative to the web application root.
         */
        protected boolean isRedirectContextRelative() {
                return this.redirectContextRelative;
        }

        /**
         * Set whether redirects should stay compatible with HTTP 1.0 clients.
         * <p>In the default implementation, this will enforce HTTP status code 302
         * in any case, i.e. delegate to {@code HttpServletResponse.sendRedirect}.
         * Turning this off will send HTTP status code 303, which is the correct
         * code for HTTP 1.1 clients, but not understood by HTTP 1.0 clients.
         * <p>Many HTTP 1.1 clients treat 302 just like 303, not making any
         * difference. However, some clients depend on 303 when redirecting
         * after a POST request; turn this flag off in such a scenario.
         * <p><b>Redirect URLs can be specified via the "redirect:" prefix.</b>
         * E.g.: "redirect:myAction"
         * @see RedirectView#setHttp10Compatible
         * @see #REDIRECT_URL_PREFIX
         */
        public void setRedirectHttp10Compatible(boolean redirectHttp10Compatible) {
                this.redirectHttp10Compatible = redirectHttp10Compatible;
        }

        /**
         * Return whether redirects should stay compatible with HTTP 1.0 clients.
         */
        protected boolean isRedirectHttp10Compatible() {
                return this.redirectHttp10Compatible;
        }

        /**
         * Configure one or more hosts associated with the application.
         * All other hosts will be considered external hosts.
         * <p>In effect, this property provides a way turn off encoding on redirect
         * via {@link HttpServletResponse#encodeRedirectURL} for URLs that have a
         * host and that host is not listed as a known host.
         * <p>If not set (the default) all URLs are encoded through the response.
         * @param redirectHosts one or more application hosts
         * @since 4.3
         */
        public void setRedirectHosts(@Nullable String... redirectHosts) {
                this.redirectHosts = redirectHosts;
        }

        /**
         * Return the configured application hosts for redirect purposes.
         * @since 4.3
         */
        @Nullable
        public String[] getRedirectHosts() {
                return this.redirectHosts;
        }

        /**
         * Set the name of the RequestContext attribute for all views.
         * @param requestContextAttribute name of the RequestContext attribute
         * @see AbstractView#setRequestContextAttribute
         */
        public void setRequestContextAttribute(@Nullable String requestContextAttribute) {
                this.requestContextAttribute = requestContextAttribute;
        }

        /**
         * Return the name of the RequestContext attribute for all views, if any.
         */
        @Nullable
        protected String getRequestContextAttribute() {
                return this.requestContextAttribute;
        }

        /**
         * Set static attributes from a {@code java.util.Properties} object,
         * for all views returned by this resolver.
         * <p>This is the most convenient way to set static attributes. Note that
         * static attributes can be overridden by dynamic attributes, if a value
         * with the same name is included in the model.
         * <p>Can be populated with a String "value" (parsed via PropertiesEditor)
         * or a "props" element in XML bean definitions.
         * @see org.springframework.beans.propertyeditors.PropertiesEditor
         * @see AbstractView#setAttributes
         */
        public void setAttributes(Properties props) {
                CollectionUtils.mergePropertiesIntoMap(props, this.staticAttributes);
        }

        /**
         * Set static attributes from a Map, for all views returned by this resolver.
         * This allows to set any kind of attribute values, for example bean references.
         * <p>Can be populated with a "map" or "props" element in XML bean definitions.
         * @param attributes a Map with name Strings as keys and attribute objects as values
         * @see AbstractView#setAttributesMap
         */
        public void setAttributesMap(@Nullable Map<String, ?> attributes) {
                if (attributes != null) {
                        this.staticAttributes.putAll(attributes);
                }
        }

        /**
         * Allow Map access to the static attributes for views returned by
         * this resolver, with the option to add or override specific entries.
         * <p>Useful for specifying entries directly, for example via
         * "attributesMap[myKey]". This is particularly useful for
         * adding or overriding entries in child view definitions.
         */
        public Map<String, Object> getAttributesMap() {
                return this.staticAttributes;
        }

        /**
         * Specify whether views resolved by this resolver should add path variables to the model or not.
         * <p>>The default setting is to let each View decide (see {@link AbstractView#setExposePathVariables}.
         * However, you can use this property to override that.
         * @param exposePathVariables
         * <ul>
         * <li>{@code true} - all Views resolved by this resolver will expose path variables
         * <li>{@code false} - no Views resolved by this resolver will expose path variables
         * <li>{@code null} - individual Views can decide for themselves (this is used by the default)
         * </ul>
         * @see AbstractView#setExposePathVariables
         */
        public void setExposePathVariables(@Nullable Boolean exposePathVariables) {
                this.exposePathVariables = exposePathVariables;
        }

        /**
         * Return whether views resolved by this resolver should add path variables to the model or not.
         */
        @Nullable
        protected Boolean getExposePathVariables() {
                return this.exposePathVariables;
        }

        /**
         * Set whether to make all Spring beans in the application context accessible
         * as request attributes, through lazy checking once an attribute gets accessed.
         * <p>This will make all such beans accessible in plain {@code ${...}}
         * expressions in a JSP 2.0 page, as well as in JSTL's {@code c:out}
         * value expressions.
         * <p>Default is "false".
         * @see AbstractView#setExposeContextBeansAsAttributes
         */
        public void setExposeContextBeansAsAttributes(boolean exposeContextBeansAsAttributes) {
                this.exposeContextBeansAsAttributes = exposeContextBeansAsAttributes;
        }

        @Nullable
        protected Boolean getExposeContextBeansAsAttributes() {
                return this.exposeContextBeansAsAttributes;
        }

        /**
         * Specify the names of beans in the context which are supposed to be exposed.
         * If this is non-null, only the specified beans are eligible for exposure as
         * attributes.
         * @see AbstractView#setExposedContextBeanNames
         */
        public void setExposedContextBeanNames(@Nullable String... exposedContextBeanNames) {
                this.exposedContextBeanNames = exposedContextBeanNames;
        }

        @Nullable
        protected String[] getExposedContextBeanNames() {
                return this.exposedContextBeanNames;
        }

        /**
         * Set the view names (or name patterns) that can be handled by this
         * {@link org.springframework.web.servlet.ViewResolver}. View names can contain
         * simple wildcards such that 'my*', '*Report' and '*Repo*' will all match the
         * view name 'myReport'.
         * @see #canHandle
         */
        public void setViewNames(@Nullable String... viewNames) {
                this.viewNames = viewNames;
        }

        /**
         * Return the view names (or name patterns) that can be handled by this
         * {@link org.springframework.web.servlet.ViewResolver}.
         */
        @Nullable
        protected String[] getViewNames() {
                return this.viewNames;
        }

        /**
         * Specify the order value for this ViewResolver bean.
         * <p>The default value is {@code Ordered.LOWEST_PRECEDENCE}, meaning non-ordered.
         * @see org.springframework.core.Ordered#getOrder()
         */
        public void setOrder(int order) {
                this.order = order;
        }

        @Override
        public int getOrder() {
                return this.order;
        }

        @Override
        protected void initApplicationContext() {
                super.initApplicationContext();
                if (getViewClass() == null) {
                        throw new IllegalArgumentException("Property 'viewClass' is required");
                }
        }


        /**
         * This implementation returns just the view name,
         * as this ViewResolver doesn't support localized resolution.
         */
        @Override
        protected Object getCacheKey(String viewName, Locale locale) {
                return viewName;
        }

        /**
         * Overridden to implement check for "redirect:" prefix.
         * <p>Not possible in {@code loadView}, since overridden
         * {@code loadView} versions in subclasses might rely on the
         * superclass always creating instances of the required view class.
         * @see #loadView
         * @see #requiredViewClass
         */
        @Override
        protected View createView(String viewName, Locale locale) throws Exception {
                // If this resolver is not supposed to handle the given view,
                // return null to pass on to the next resolver in the chain.
                if (!canHandle(viewName, locale)) {
                        return null;
                }

                // Check for special "redirect:" prefix.
                if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
                        String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
                        RedirectView view = new RedirectView(redirectUrl,
                                        isRedirectContextRelative(), isRedirectHttp10Compatible());
                        String[] hosts = getRedirectHosts();
                        if (hosts != null) {
                                view.setHosts(hosts);
                        }
                        return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
                }

                // Check for special "forward:" prefix.
                if (viewName.startsWith(FORWARD_URL_PREFIX)) {
                        String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
                        InternalResourceView view = new InternalResourceView(forwardUrl);
                        return applyLifecycleMethods(FORWARD_URL_PREFIX, view);
                }

                // Else fall back to superclass implementation: calling loadView.
                return super.createView(viewName, locale);
        }

        /**
         * Indicates whether or not this {@link org.springframework.web.servlet.ViewResolver} can
         * handle the supplied view name. If not, {@link #createView(String, java.util.Locale)} will
         * return {@code null}. The default implementation checks against the configured
         * {@link #setViewNames view names}.
         * @param viewName the name of the view to retrieve
         * @param locale the Locale to retrieve the view for
         * @return whether this resolver applies to the specified view
         * @see org.springframework.util.PatternMatchUtils#simpleMatch(String, String)
         */
        protected boolean canHandle(String viewName, Locale locale) {
                String[] viewNames = getViewNames();
                return (viewNames == null || PatternMatchUtils.simpleMatch(viewNames, viewName));
        }

        /**
         * Delegates to {@code buildView} for creating a new instance of the
         * specified view class. Applies the following Spring lifecycle methods
         * (as supported by the generic Spring bean factory):
         * <ul>
         * <li>ApplicationContextAware's {@code setApplicationContext}
         * <li>InitializingBean's {@code afterPropertiesSet}
         * </ul>
         * @param viewName the name of the view to retrieve
         * @return the View instance
         * @throws Exception if the view couldn't be resolved
         * @see #buildView(String)
         * @see org.springframework.context.ApplicationContextAware#setApplicationContext
         * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
         */
        @Override
        protected View loadView(String viewName, Locale locale) throws Exception {
                AbstractUrlBasedView view = buildView(viewName);
                View result = applyLifecycleMethods(viewName, view);
                return (view.checkResource(locale) ? result : null);
        }

        /**
         * Creates a new View instance of the specified view class and configures it.
         * Does <i>not</i> perform any lookup for pre-defined View instances.
         * <p>Spring lifecycle methods as defined by the bean container do not have to
         * be called here; those will be applied by the {@code loadView} method
         * after this method returns.
         * <p>Subclasses will typically call {@code super.buildView(viewName)}
         * first, before setting further properties themselves. {@code loadView}
         * will then apply Spring lifecycle methods at the end of this process.
         * @param viewName the name of the view to build
         * @return the View instance
         * @throws Exception if the view couldn't be resolved
         * @see #loadView(String, java.util.Locale)
         */
        protected AbstractUrlBasedView buildView(String viewName) throws Exception {
                Class<?> viewClass = getViewClass();
                Assert.state(viewClass != null, "No view class");

                AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
                view.setUrl(getPrefix() + viewName + getSuffix());
                view.setAttributesMap(getAttributesMap());

                String contentType = getContentType();
                if (contentType != null) {
                        view.setContentType(contentType);
                }

                String requestContextAttribute = getRequestContextAttribute();
                if (requestContextAttribute != null) {
                        view.setRequestContextAttribute(requestContextAttribute);
                }

                Boolean exposePathVariables = getExposePathVariables();
                if (exposePathVariables != null) {
                        view.setExposePathVariables(exposePathVariables);
                }
                Boolean exposeContextBeansAsAttributes = getExposeContextBeansAsAttributes();
                if (exposeContextBeansAsAttributes != null) {
                        view.setExposeContextBeansAsAttributes(exposeContextBeansAsAttributes);
                }
                String[] exposedContextBeanNames = getExposedContextBeanNames();
                if (exposedContextBeanNames != null) {
                        view.setExposedContextBeanNames(exposedContextBeanNames);
                }

                return view;
        }

        /**
         * Apply the containing {@link ApplicationContext}'s lifecycle methods
         * to the given {@link View} instance, if such a context is available.
         * @param viewName the name of the view
         * @param view the freshly created View instance, pre-configured with
         * {@link AbstractUrlBasedView}'s properties
         * @return the {@link View} instance to use (either the original one
         * or a decorated variant)
         * @since 5.0
         * @see #getApplicationContext()
         * @see ApplicationContext#getAutowireCapableBeanFactory()
         * @see org.springframework.beans.factory.config.AutowireCapableBeanFactory#initializeBean
         */
        protected View applyLifecycleMethods(String viewName, AbstractUrlBasedView view) {
                ApplicationContext context = getApplicationContext();
                if (context != null) {
                        Object initialized = context.getAutowireCapableBeanFactory().initializeBean(view, viewName);
                        if (initialized instanceof View) {
                                return (View) initialized;
                        }
                }
                return view;
        }

}