/*
 * 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;

import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.lang.Nullable;
import org.springframework.ui.ModelMap;
import org.springframework.util.CollectionUtils;

/**
 * Holder for both Model and View in the web MVC framework.
 * Note that these are entirely distinct. This class merely holds
 * both to make it possible for a controller to return both model
 * and view in a single return value.
 *
 * <p>Represents a model and view returned by a handler, to be resolved
 * by a DispatcherServlet. The view can take the form of a String
 * view name which will need to be resolved by a ViewResolver object;
 * alternatively a View object can be specified directly. The model
 * is a Map, allowing the use of multiple objects keyed by name.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Rossen Stoyanchev
 * @see DispatcherServlet
 * @see ViewResolver
 * @see HandlerAdapter#handle
 * @see org.springframework.web.servlet.mvc.Controller#handleRequest
 */
public class ModelAndView {

        /** View instance or view name String. */
        @Nullable
        private Object view;

        /** Model Map. */
        @Nullable
        private ModelMap model;

        /** Optional HTTP status for the response. */
        @Nullable
        private HttpStatus status;

        /** Indicates whether or not this instance has been cleared with a call to {@link #clear()}. */
        private boolean cleared = false;


        /**
         * Default constructor for bean-style usage: populating bean
         * properties instead of passing in constructor arguments.
         * @see #setView(View)
         * @see #setViewName(String)
         */
        public ModelAndView() {
        }

        /**
         * Convenient constructor when there is no model data to expose.
         * Can also be used in conjunction with {@code addObject}.
         * @param viewName name of the View to render, to be resolved
         * by the DispatcherServlet's ViewResolver
         * @see #addObject
         */
        public ModelAndView(String viewName) {
                this.view = viewName;
        }

        /**
         * Convenient constructor when there is no model data to expose.
         * Can also be used in conjunction with {@code addObject}.
         * @param view the View object to render
         * @see #addObject
         */
        public ModelAndView(View view) {
                this.view = view;
        }

        /**
         * Create a new ModelAndView given a view name and a model.
         * @param viewName name of the View to render, to be resolved
         * by the DispatcherServlet's ViewResolver
         * @param model a Map of model names (Strings) to model objects
         * (Objects). Model entries may not be {@code null}, but the
         * model Map may be {@code null} if there is no model data.
         */
        public ModelAndView(String viewName, @Nullable Map<String, ?> model) {
                this.view = viewName;
                if (model != null) {
                        getModelMap().addAllAttributes(model);
                }
        }

        /**
         * Create a new ModelAndView given a View object and a model.
         * <em>Note: the supplied model data is copied into the internal
         * storage of this class. You should not consider to modify the supplied
         * Map after supplying it to this class</em>
         * @param view the View object to render
         * @param model a Map of model names (Strings) to model objects
         * (Objects). Model entries may not be {@code null}, but the
         * model Map may be {@code null} if there is no model data.
         */
        public ModelAndView(View view, @Nullable Map<String, ?> model) {
                this.view = view;
                if (model != null) {
                        getModelMap().addAllAttributes(model);
                }
        }

        /**
         * Create a new ModelAndView given a view name and HTTP status.
         * @param viewName name of the View to render, to be resolved
         * by the DispatcherServlet's ViewResolver
         * @param status an HTTP status code to use for the response
         * (to be set just prior to View rendering)
         * @since 4.3.8
         */
        public ModelAndView(String viewName, HttpStatus status) {
                this.view = viewName;
                this.status = status;
        }

        /**
         * Create a new ModelAndView given a view name, model, and HTTP status.
         * @param viewName name of the View to render, to be resolved
         * by the DispatcherServlet's ViewResolver
         * @param model a Map of model names (Strings) to model objects
         * (Objects). Model entries may not be {@code null}, but the
         * model Map may be {@code null} if there is no model data.
         * @param status an HTTP status code to use for the response
         * (to be set just prior to View rendering)
         * @since 4.3
         */
        public ModelAndView(@Nullable String viewName, @Nullable Map<String, ?> model, @Nullable HttpStatus status) {
                this.view = viewName;
                if (model != null) {
                        getModelMap().addAllAttributes(model);
                }
                this.status = status;
        }

        /**
         * Convenient constructor to take a single model object.
         * @param viewName name of the View to render, to be resolved
         * by the DispatcherServlet's ViewResolver
         * @param modelName name of the single entry in the model
         * @param modelObject the single model object
         */
        public ModelAndView(String viewName, String modelName, Object modelObject) {
                this.view = viewName;
                addObject(modelName, modelObject);
        }

        /**
         * Convenient constructor to take a single model object.
         * @param view the View object to render
         * @param modelName name of the single entry in the model
         * @param modelObject the single model object
         */
        public ModelAndView(View view, String modelName, Object modelObject) {
                this.view = view;
                addObject(modelName, modelObject);
        }


        /**
         * Set a view name for this ModelAndView, to be resolved by the
         * DispatcherServlet via a ViewResolver. Will override any
         * pre-existing view name or View.
         */
        public void setViewName(@Nullable String viewName) {
                this.view = viewName;
        }

        /**
         * Return the view name to be resolved by the DispatcherServlet
         * via a ViewResolver, or {@code null} if we are using a View object.
         */
        @Nullable
        public String getViewName() {
                return (this.view instanceof String ? (String) this.view : null);
        }

        /**
         * Set a View object for this ModelAndView. Will override any
         * pre-existing view name or View.
         */
        public void setView(@Nullable View view) {
                this.view = view;
        }

        /**
         * Return the View object, or {@code null} if we are using a view name
         * to be resolved by the DispatcherServlet via a ViewResolver.
         */
        @Nullable
        public View getView() {
                return (this.view instanceof View ? (View) this.view : null);
        }

        /**
         * Indicate whether or not this {@code ModelAndView} has a view, either
         * as a view name or as a direct {@link View} instance.
         */
        public boolean hasView() {
                return (this.view != null);
        }

        /**
         * Return whether we use a view reference, i.e. {@code true}
         * if the view has been specified via a name to be resolved by the
         * DispatcherServlet via a ViewResolver.
         */
        public boolean isReference() {
                return (this.view instanceof String);
        }

        /**
         * Return the model map. May return {@code null}.
         * Called by DispatcherServlet for evaluation of the model.
         */
        @Nullable
        protected Map<String, Object> getModelInternal() {
                return this.model;
        }

        /**
         * Return the underlying {@code ModelMap} instance (never {@code null}).
         */
        public ModelMap getModelMap() {
                if (this.model == null) {
                        this.model = new ModelMap();
                }
                return this.model;
        }

        /**
         * Return the model map. Never returns {@code null}.
         * To be called by application code for modifying the model.
         */
        public Map<String, Object> getModel() {
                return getModelMap();
        }

        /**
         * Set the HTTP status to use for the response.
         * <p>The response status is set just prior to View rendering.
         * @since 4.3
         */
        public void setStatus(@Nullable HttpStatus status) {
                this.status = status;
        }

        /**
         * Return the configured HTTP status for the response, if any.
         * @since 4.3
         */
        @Nullable
        public HttpStatus getStatus() {
                return this.status;
        }


        /**
         * Add an attribute to the model.
         * @param attributeName name of the object to add to the model (never {@code null})
         * @param attributeValue object to add to the model (can be {@code null})
         * @see ModelMap#addAttribute(String, Object)
         * @see #getModelMap()
         */
        public ModelAndView addObject(String attributeName, @Nullable Object attributeValue) {
                getModelMap().addAttribute(attributeName, attributeValue);
                return this;
        }

        /**
         * Add an attribute to the model using parameter name generation.
         * @param attributeValue the object to add to the model (never {@code null})
         * @see ModelMap#addAttribute(Object)
         * @see #getModelMap()
         */
        public ModelAndView addObject(Object attributeValue) {
                getModelMap().addAttribute(attributeValue);
                return this;
        }

        /**
         * Add all attributes contained in the provided Map to the model.
         * @param modelMap a Map of attributeName -> attributeValue pairs
         * @see ModelMap#addAllAttributes(Map)
         * @see #getModelMap()
         */
        public ModelAndView addAllObjects(@Nullable Map<String, ?> modelMap) {
                getModelMap().addAllAttributes(modelMap);
                return this;
        }


        /**
         * Clear the state of this ModelAndView object.
         * The object will be empty afterwards.
         * <p>Can be used to suppress rendering of a given ModelAndView object
         * in the {@code postHandle} method of a HandlerInterceptor.
         * @see #isEmpty()
         * @see HandlerInterceptor#postHandle
         */
        public void clear() {
                this.view = null;
                this.model = null;
                this.cleared = true;
        }

        /**
         * Return whether this ModelAndView object is empty,
         * i.e. whether it does not hold any view and does not contain a model.
         */
        public boolean isEmpty() {
                return (this.view == null && CollectionUtils.isEmpty(this.model));
        }

        /**
         * Return whether this ModelAndView object is empty as a result of a call to {@link #clear}
         * i.e. whether it does not hold any view and does not contain a model.
         * <p>Returns {@code false} if any additional state was added to the instance
         * <strong>after</strong> the call to {@link #clear}.
         * @see #clear()
         */
        public boolean wasCleared() {
                return (this.cleared && isEmpty());
        }


        /**
         * Return diagnostic information about this model and view.
         */
        @Override
        public String toString() {
                return "ModelAndView [view=" + formatView() + "; model=" + this.model + "]";
        }

        private String formatView() {
                return isReference() ? "\"" + this.view + "\"" : "[" + this.view + "]";
        }

}