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Spring Data REST - WebMVC
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/*
 * Copyright 2016-2021 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.data.rest.webmvc;

import java.util.List;
import java.util.function.Supplier;

import org.springframework.data.mapping.PersistentEntity;
import org.springframework.data.rest.webmvc.support.ETag;
import org.springframework.hateoas.EntityModel;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.util.Assert;

/**
 * Simple abstraction to capture the status of a resource to determine whether it has been modified or not and produce
 * {@link ResponseEntity} via its {@link StatusAndHeaders} sub component.
 *
 * @author Oliver Gierke
 * @since 2.6
 * @soundtrack Blumentopf - Dass ich nicht lache (Kein Zufall)
 */
class ResourceStatus {

	private static final String INVALID_DOMAIN_OBJECT = "Domain object %s is not an instance of the given PersistentEntity of type %s!";

	private final HttpHeadersPreparer preparer;

	private ResourceStatus(HttpHeadersPreparer preparer) {

		Assert.notNull(preparer, "HttpHeadersPreparer must not be null!");

		this.preparer = preparer;
	}

	public static ResourceStatus of(HttpHeadersPreparer preparer) {
		return new ResourceStatus(preparer);
	}

	/**
	 * Returns the {@link StatusAndHeaders} calculated from the given {@link HttpHeaders}, domain object and
	 * {@link RootResourceInformation.
	 *
	 * @param requestHeaders must not be {@literal null}.
	 * @param domainObject must not be {@literal null}.
	 * @param entity must not be {@literal null}.
	 * @return
	 */
	public StatusAndHeaders getStatusAndHeaders(HttpHeaders requestHeaders, Object domainObject,
			PersistentEntity entity) {

		Assert.notNull(requestHeaders, "Request headers must not be null!");
		Assert.notNull(domainObject, "Domain object must not be null!");
		Assert.notNull(entity, "PersistentEntity must not be null!");
		Assert.isTrue(entity.getType().isInstance(domainObject),
				() -> String.format(INVALID_DOMAIN_OBJECT, domainObject, entity.getType()));

		// Check ETag for If-Non-Match

		List ifNoneMatch = requestHeaders.getIfNoneMatch();
		ETag eTag = ifNoneMatch.isEmpty() ? ETag.NO_ETAG : ETag.from(ifNoneMatch.get(0));
		HttpHeaders responseHeaders = preparer.prepareHeaders(entity, domainObject);

		// Check last modification for If-Modified-Since

		return eTag.matches(entity, domainObject) || preparer.isObjectStillValid(domainObject, requestHeaders)
				? StatusAndHeaders.notModified(responseHeaders)
				: StatusAndHeaders.modified(responseHeaders);
	}

	public static class StatusAndHeaders {

		private final HttpHeaders headers;
		private final boolean modified;

		private StatusAndHeaders(HttpHeaders headers, boolean modified) {

			Assert.notNull(headers, "HttpHeaders must not be null!");

			this.headers = headers;
			this.modified = modified;
		}

		boolean isModified() {
			return this.modified;
		}

		private static StatusAndHeaders notModified(HttpHeaders headers) {
			return new StatusAndHeaders(headers, false);
		}

		private static StatusAndHeaders modified(HttpHeaders headers) {
			return new StatusAndHeaders(headers, true);
		}

		/**
		 * Creates a {@link ResponseEntity} based on the given {@link PersistentEntityResource}.
		 *
		 * @param supplier a {@link Supplier} to provide a {@link PersistentEntityResource} eventually, must not be
		 *          {@literal null}.
		 * @return
		 */
		public ResponseEntity> toResponseEntity(Supplier supplier) {

			return modified //
					? new ResponseEntity>(supplier.get(), headers, HttpStatus.OK) //
					: new ResponseEntity>(headers, HttpStatus.NOT_MODIFIED);
		}
	}
}