/*
 * Copyright 2002-2018 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.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.StringTokenizer;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.BeanNameAware;
import org.springframework.http.MediaType;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.ContextExposingHttpServletRequest;
import org.springframework.web.context.support.WebApplicationObjectSupport;
import org.springframework.web.servlet.View;
import org.springframework.web.servlet.support.RequestContext;

/**
 * Abstract base class for {@link org.springframework.web.servlet.View}
 * implementations. Subclasses should be JavaBeans, to allow for
 * convenient configuration as Spring-managed bean instances.
 *
 * <p>Provides support for static attributes, to be made available to the view,
 * with a variety of ways to specify them. Static attributes will be merged
 * with the given dynamic attributes (the model that the controller returned)
 * for each render operation.
 *
 * <p>Extends {@link WebApplicationObjectSupport}, which will be helpful to
 * some views. Subclasses just need to implement the actual rendering.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see #setAttributes
 * @see #setAttributesMap
 * @see #renderMergedOutputModel
 */
public abstract class AbstractView extends WebApplicationObjectSupport implements View, BeanNameAware {

        /** Default content type. Overridable as bean property. */
        public static final String DEFAULT_CONTENT_TYPE = "text/html;charset=ISO-8859-1";

        /** Initial size for the temporary output byte array (if any). */
        private static final int OUTPUT_BYTE_ARRAY_INITIAL_SIZE = 4096;


        @Nullable
        private String contentType = DEFAULT_CONTENT_TYPE;

        @Nullable
        private String requestContextAttribute;

        private final Map<String, Object> staticAttributes = new LinkedHashMap<>();

        private boolean exposePathVariables = true;

        private boolean exposeContextBeansAsAttributes = false;

        @Nullable
        private Set<String> exposedContextBeanNames;

        @Nullable
        private String beanName;



        /**
         * Set the content type for this view.
         * Default is "text/html;charset=ISO-8859-1".
         * <p>May be ignored by subclasses 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 this view.
         */
        @Override
        @Nullable
        public String getContentType() {
                return this.contentType;
        }

        /**
         * Set the name of the RequestContext attribute for this view.
         * Default is none.
         */
        public void setRequestContextAttribute(@Nullable String requestContextAttribute) {
                this.requestContextAttribute = requestContextAttribute;
        }

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

        /**
         * Set static attributes as a CSV string.
         * Format is: attname0={value1},attname1={value1}
         * <p>"Static" attributes are fixed attributes that are specified in
         * the View instance configuration. "Dynamic" attributes, on the other hand,
         * are values passed in as part of the model.
         */
        public void setAttributesCSV(@Nullable String propString) throws IllegalArgumentException {
                if (propString != null) {
                        StringTokenizer st = new StringTokenizer(propString, ",");
                        while (st.hasMoreTokens()) {
                                String tok = st.nextToken();
                                int eqIdx = tok.indexOf('=');
                                if (eqIdx == -1) {
                                        throw new IllegalArgumentException(
                                                        "Expected '=' in attributes CSV string '" + propString + "'");
                                }
                                if (eqIdx >= tok.length() - 2) {
                                        throw new IllegalArgumentException(
                                                        "At least 2 characters ([]) required in attributes CSV string '" + propString + "'");
                                }
                                String name = tok.substring(0, eqIdx);
                                // Delete first and last characters of value: { and }
                                int beginIndex = eqIdx + 2;
                                int endIndex = tok.length() - 1;
                                String value = tok.substring(beginIndex, endIndex);

                                addStaticAttribute(name, value);
                        }
                }
        }

        /**
         * Set static attributes for this view from a
         * {@code java.util.Properties} object.
         * <p>"Static" attributes are fixed attributes that are specified in
         * the View instance configuration. "Dynamic" attributes, on the other hand,
         * are values passed in as part of the model.
         * <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
         */
        public void setAttributes(Properties attributes) {
                CollectionUtils.mergePropertiesIntoMap(attributes, this.staticAttributes);
        }

        /**
         * Set static attributes for this view from a Map. This allows to set
         * any kind of attribute values, for example bean references.
         * <p>"Static" attributes are fixed attributes that are specified in
         * the View instance configuration. "Dynamic" attributes, on the other hand,
         * are values passed in as part of the model.
         * <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
         */
        public void setAttributesMap(@Nullable Map<String, ?> attributes) {
                if (attributes != null) {
                        attributes.forEach(this::addStaticAttribute);
                }
        }

        /**
         * Allow Map access to the static attributes of this view,
         * 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;
        }

        /**
         * Add static data to this view, exposed in each view.
         * <p>"Static" attributes are fixed attributes that are specified in
         * the View instance configuration. "Dynamic" attributes, on the other hand,
         * are values passed in as part of the model.
         * <p>Must be invoked before any calls to {@code render}.
         * @param name the name of the attribute to expose
         * @param value the attribute value to expose
         * @see #render
         */
        public void addStaticAttribute(String name, Object value) {
                this.staticAttributes.put(name, value);
        }

        /**
         * Return the static attributes for this view. Handy for testing.
         * <p>Returns an unmodifiable Map, as this is not intended for
         * manipulating the Map but rather just for checking the contents.
         * @return the static attributes in this view
         */
        public Map<String, Object> getStaticAttributes() {
                return Collections.unmodifiableMap(this.staticAttributes);
        }

        /**
         * Specify whether to add path variables to the model or not.
         * <p>Path variables are commonly bound to URI template variables through the {@code @PathVariable}
         * annotation. They're are effectively URI template variables with type conversion applied to
         * them to derive typed Object values. Such values are frequently needed in views for
         * constructing links to the same and other URLs.
         * <p>Path variables added to the model override static attributes (see {@link #setAttributes(Properties)})
         * but not attributes already present in the model.
         * <p>By default this flag is set to {@code true}. Concrete view types can override this.
         * @param exposePathVariables {@code true} to expose path variables, and {@code false} otherwise
         */
        public void setExposePathVariables(boolean exposePathVariables) {
                this.exposePathVariables = exposePathVariables;
        }

        /**
         * Return whether to add path variables to the model or not.
         */
        public boolean isExposePathVariables() {
                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". Switch this flag on to transparently expose all
         * Spring beans in the request attribute namespace.
         * <p><b>NOTE:</b> Context beans will override any custom request or session
         * attributes of the same name that have been manually added. However, model
         * attributes (as explicitly exposed to this view) of the same name will
         * always override context beans.
         * @see #getRequestToExpose
         */
        public void setExposeContextBeansAsAttributes(boolean exposeContextBeansAsAttributes) {
                this.exposeContextBeansAsAttributes = 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.
         * <p>If you'd like to expose all Spring beans in the application context, switch
         * the {@link #setExposeContextBeansAsAttributes "exposeContextBeansAsAttributes"}
         * flag on but do not list specific bean names for this property.
         */
        public void setExposedContextBeanNames(String... exposedContextBeanNames) {
                this.exposedContextBeanNames = new HashSet<>(Arrays.asList(exposedContextBeanNames));
        }

        /**
         * Set the view's name. Helpful for traceability.
         * <p>Framework code must call this when constructing views.
         */
        @Override
        public void setBeanName(@Nullable String beanName) {
                this.beanName = beanName;
        }

        /**
         * Return the view's name. Should never be {@code null},
         * if the view was correctly configured.
         */
        @Nullable
        public String getBeanName() {
                return this.beanName;
        }


        /**
         * Prepares the view given the specified model, merging it with static
         * attributes and a RequestContext attribute, if necessary.
         * Delegates to renderMergedOutputModel for the actual rendering.
         * @see #renderMergedOutputModel
         */
        @Override
        public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
                        HttpServletResponse response) throws Exception {

                if (logger.isDebugEnabled()) {
                        logger.debug("View " + formatViewName() +
                                        ", model " + (model != null ? model : Collections.emptyMap()) +
                                        (this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
                }

                Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
                prepareResponse(request, response);
                renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
        }

        /**
         * Creates a combined output Map (never {@code null}) that includes dynamic values and static attributes.
         * Dynamic values take precedence over static attributes.
         */
        protected Map<String, Object> createMergedOutputModel(@Nullable Map<String, ?> model,
                        HttpServletRequest request, HttpServletResponse response) {

                @SuppressWarnings("unchecked")
                Map<String, Object> pathVars = (this.exposePathVariables ?
                                (Map<String, Object>) request.getAttribute(View.PATH_VARIABLES) : null);

                // Consolidate static and dynamic model attributes.
                int size = this.staticAttributes.size();
                size += (model != null ? model.size() : 0);
                size += (pathVars != null ? pathVars.size() : 0);

                Map<String, Object> mergedModel = new LinkedHashMap<>(size);
                mergedModel.putAll(this.staticAttributes);
                if (pathVars != null) {
                        mergedModel.putAll(pathVars);
                }
                if (model != null) {
                        mergedModel.putAll(model);
                }

                // Expose RequestContext?
                if (this.requestContextAttribute != null) {
                        mergedModel.put(this.requestContextAttribute, createRequestContext(request, response, mergedModel));
                }

                return mergedModel;
        }

        /**
         * Create a RequestContext to expose under the specified attribute name.
         * <p>The default implementation creates a standard RequestContext instance for the
         * given request and model. Can be overridden in subclasses for custom instances.
         * @param request current HTTP request
         * @param model combined output Map (never {@code null}),
         * with dynamic values taking precedence over static attributes
         * @return the RequestContext instance
         * @see #setRequestContextAttribute
         * @see org.springframework.web.servlet.support.RequestContext
         */
        protected RequestContext createRequestContext(
                        HttpServletRequest request, HttpServletResponse response, Map<String, Object> model) {

                return new RequestContext(request, response, getServletContext(), model);
        }

        /**
         * Prepare the given response for rendering.
         * <p>The default implementation applies a workaround for an IE bug
         * when sending download content via HTTPS.
         * @param request current HTTP request
         * @param response current HTTP response
         */
        protected void prepareResponse(HttpServletRequest request, HttpServletResponse response) {
                if (generatesDownloadContent()) {
                        response.setHeader("Pragma", "private");
                        response.setHeader("Cache-Control", "private, must-revalidate");
                }
        }

        /**
         * Return whether this view generates download content
         * (typically binary content like PDF or Excel files).
         * <p>The default implementation returns {@code false}. Subclasses are
         * encouraged to return {@code true} here if they know that they are
         * generating download content that requires temporary caching on the
         * client side, typically via the response OutputStream.
         * @see #prepareResponse
         * @see javax.servlet.http.HttpServletResponse#getOutputStream()
         */
        protected boolean generatesDownloadContent() {
                return false;
        }

        /**
         * Get the request handle to expose to {@link #renderMergedOutputModel}, i.e. to the view.
         * <p>The default implementation wraps the original request for exposure of Spring beans
         * as request attributes (if demanded).
         * @param originalRequest the original servlet request as provided by the engine
         * @return the wrapped request, or the original request if no wrapping is necessary
         * @see #setExposeContextBeansAsAttributes
         * @see #setExposedContextBeanNames
         * @see org.springframework.web.context.support.ContextExposingHttpServletRequest
         */
        protected HttpServletRequest getRequestToExpose(HttpServletRequest originalRequest) {
                if (this.exposeContextBeansAsAttributes || this.exposedContextBeanNames != null) {
                        WebApplicationContext wac = getWebApplicationContext();
                        Assert.state(wac != null, "No WebApplicationContext");
                        return new ContextExposingHttpServletRequest(originalRequest, wac, this.exposedContextBeanNames);
                }
                return originalRequest;
        }

        /**
         * Subclasses must implement this method to actually render the view.
         * <p>The first step will be preparing the request: In the JSP case,
         * this would mean setting model objects as request attributes.
         * The second step will be the actual rendering of the view,
         * for example including the JSP via a RequestDispatcher.
         * @param model combined output Map (never {@code null}),
         * with dynamic values taking precedence over static attributes
         * @param request current HTTP request
         * @param response current HTTP response
         * @throws Exception if rendering failed
         */
        protected abstract void renderMergedOutputModel(
                        Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception;


        /**
         * Expose the model objects in the given map as request attributes.
         * Names will be taken from the model Map.
         * This method is suitable for all resources reachable by {@link javax.servlet.RequestDispatcher}.
         * @param model a Map of model objects to expose
         * @param request current HTTP request
         */
        protected void exposeModelAsRequestAttributes(Map<String, Object> model,
                        HttpServletRequest request) throws Exception {

                model.forEach((name, value) -> {
                        if (value != null) {
                                request.setAttribute(name, value);
                        }
                        else {
                                request.removeAttribute(name);
                        }
                });
        }

        /**
         * Create a temporary OutputStream for this view.
         * <p>This is typically used as IE workaround, for setting the content length header
         * from the temporary stream before actually writing the content to the HTTP response.
         */
        protected ByteArrayOutputStream createTemporaryOutputStream() {
                return new ByteArrayOutputStream(OUTPUT_BYTE_ARRAY_INITIAL_SIZE);
        }

        /**
         * Write the given temporary OutputStream to the HTTP response.
         * @param response current HTTP response
         * @param baos the temporary OutputStream to write
         * @throws IOException if writing/flushing failed
         */
        protected void writeToResponse(HttpServletResponse response, ByteArrayOutputStream baos) throws IOException {
                // Write content type and also length (determined via byte array).
                response.setContentType(getContentType());
                response.setContentLength(baos.size());

                // Flush byte array to servlet output stream.
                ServletOutputStream out = response.getOutputStream();
                baos.writeTo(out);
                out.flush();
        }

        /**
         * Set the content type of the response to the configured
         * {@link #setContentType(String) content type} unless the
         * {@link View#SELECTED_CONTENT_TYPE} request attribute is present and set
         * to a concrete media type.
         */
        protected void setResponseContentType(HttpServletRequest request, HttpServletResponse response) {
                MediaType mediaType = (MediaType) request.getAttribute(View.SELECTED_CONTENT_TYPE);
                if (mediaType != null && mediaType.isConcrete()) {
                        response.setContentType(mediaType.toString());
                }
                else {
                        response.setContentType(getContentType());
                }
        }

        @Override
        public String toString() {
                return getClass().getName() + ": " + formatViewName();
        }

        protected String formatViewName() {
                return (getBeanName() != null ? "name '" + getBeanName() + "'" : "[" + getClass().getSimpleName() + "]");
        }

}