/*
 * 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.method.annotation;

import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.bind.annotation.SessionAttributes;
import org.springframework.web.bind.support.SessionAttributeStore;
import org.springframework.web.bind.support.SessionStatus;
import org.springframework.web.context.request.WebRequest;

Manages controller-specific session attributes declared via @SessionAttributes. Actual storage is delegated to a SessionAttributeStore instance. 
When a controller annotated with @SessionAttributes adds attributes to its model, those attributes are checked against names and types specified via @SessionAttributes. Matching model attributes are saved in the HTTP session and remain there until the controller calls SessionStatus.setComplete(). 
Author:
Rossen Stoyanchev, Juergen Hoeller
Since:
3.1/**
 * Manages controller-specific session attributes declared via
 * {@link SessionAttributes @SessionAttributes}. Actual storage is
 * delegated to a {@link SessionAttributeStore} instance.
 *
 * <p>When a controller annotated with {@code @SessionAttributes} adds
 * attributes to its model, those attributes are checked against names and
 * types specified via {@code @SessionAttributes}. Matching model attributes
 * are saved in the HTTP session and remain there until the controller calls
 * {@link SessionStatus#setComplete()}.
 *
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 3.1
 */
public class SessionAttributesHandler {

	private final Set<String> attributeNames = new HashSet<>();

	private final Set<Class<?>> attributeTypes = new HashSet<>();

	private final Set<String> knownAttributeNames = Collections.newSetFromMap(new ConcurrentHashMap<>(4));

	private final SessionAttributeStore sessionAttributeStore;


	
Create a new session attributes handler. Session attribute names and types are extracted from the @SessionAttributes annotation, if present, on the given type. 
Params:
handlerType – the controller type
sessionAttributeStore – used for session access/**
	 * Create a new session attributes handler. Session attribute names and types
	 * are extracted from the {@code @SessionAttributes} annotation, if present,
	 * on the given type.
	 * @param handlerType the controller type
	 * @param sessionAttributeStore used for session access
	 */
	public SessionAttributesHandler(Class<?> handlerType, SessionAttributeStore sessionAttributeStore) {
		Assert.notNull(sessionAttributeStore, "SessionAttributeStore may not be null");
		this.sessionAttributeStore = sessionAttributeStore;

		SessionAttributes ann = AnnotatedElementUtils.findMergedAnnotation(handlerType, SessionAttributes.class);
		if (ann != null) {
			Collections.addAll(this.attributeNames, ann.names());
			Collections.addAll(this.attributeTypes, ann.types());
		}
		this.knownAttributeNames.addAll(this.attributeNames);
	}


	
Whether the controller represented by this instance has declared any session attributes through an SessionAttributes annotation. /**
	 * Whether the controller represented by this instance has declared any
	 * session attributes through an {@link SessionAttributes} annotation.
	 */
	public boolean hasSessionAttributes() {
		return (!this.attributeNames.isEmpty() || !this.attributeTypes.isEmpty());
	}

	
Whether the attribute name or type match the names and types specified via @SessionAttributes on the underlying controller. 
Attributes successfully resolved through this method are "remembered" and subsequently used in retrieveAttributes(WebRequest) and cleanupAttributes(WebRequest). 
Params:
attributeName – the attribute name to check
attributeType – the type for the attribute/**
	 * Whether the attribute name or type match the names and types specified
	 * via {@code @SessionAttributes} on the underlying controller.
	 * <p>Attributes successfully resolved through this method are "remembered"
	 * and subsequently used in {@link #retrieveAttributes(WebRequest)} and
	 * {@link #cleanupAttributes(WebRequest)}.
	 * @param attributeName the attribute name to check
	 * @param attributeType the type for the attribute
	 */
	public boolean isHandlerSessionAttribute(String attributeName, Class<?> attributeType) {
		Assert.notNull(attributeName, "Attribute name must not be null");
		if (this.attributeNames.contains(attributeName) || this.attributeTypes.contains(attributeType)) {
			this.knownAttributeNames.add(attributeName);
			return true;
		}
		else {
			return false;
		}
	}

	
Store a subset of the given attributes in the session. Attributes not declared as session attributes via @SessionAttributes are ignored. 
Params:
request – the current request
attributes – candidate attributes for session storage/**
	 * Store a subset of the given attributes in the session. Attributes not
	 * declared as session attributes via {@code @SessionAttributes} are ignored.
	 * @param request the current request
	 * @param attributes candidate attributes for session storage
	 */
	public void storeAttributes(WebRequest request, Map<String, ?> attributes) {
		attributes.forEach((name, value) -> {
			if (value != null && isHandlerSessionAttribute(name, value.getClass())) {
				this.sessionAttributeStore.storeAttribute(request, name, value);
			}
		});
	}

	
Retrieve "known" attributes from the session, i.e. attributes listed by name in @SessionAttributes or attributes previously stored in the model that matched by type. 
Params:
request – the current request
Returns:
a map with handler session attributes, possibly empty/**
	 * Retrieve "known" attributes from the session, i.e. attributes listed
	 * by name in {@code @SessionAttributes} or attributes previously stored
	 * in the model that matched by type.
	 * @param request the current request
	 * @return a map with handler session attributes, possibly empty
	 */
	public Map<String, Object> retrieveAttributes(WebRequest request) {
		Map<String, Object> attributes = new HashMap<>();
		for (String name : this.knownAttributeNames) {
			Object value = this.sessionAttributeStore.retrieveAttribute(request, name);
			if (value != null) {
				attributes.put(name, value);
			}
		}
		return attributes;
	}

	
Remove "known" attributes from the session, i.e. attributes listed by name in @SessionAttributes or attributes previously stored in the model that matched by type. 
Params:
request – the current request/**
	 * Remove "known" attributes from the session, i.e. attributes listed
	 * by name in {@code @SessionAttributes} or attributes previously stored
	 * in the model that matched by type.
	 * @param request the current request
	 */
	public void cleanupAttributes(WebRequest request) {
		for (String attributeName : this.knownAttributeNames) {
			this.sessionAttributeStore.cleanupAttribute(request, attributeName);
		}
	}

	
A pass-through call to the underlying SessionAttributeStore. 
Params:
request – the current request
attributeName – the name of the attribute of interest
Returns:
the attribute value, or null if none/**
	 * A pass-through call to the underlying {@link SessionAttributeStore}.
	 * @param request the current request
	 * @param attributeName the name of the attribute of interest
	 * @return the attribute value, or {@code null} if none
	 */
	@Nullable
	Object retrieveAttribute(WebRequest request, String attributeName) {
		return this.sessionAttributeStore.retrieveAttribute(request, attributeName);
	}

}