/*
 * 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
 *
 *      http://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.accept;

import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Optional;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.http.MediaType;
import org.springframework.http.MediaTypeFactory;
import org.springframework.lang.Nullable;
import org.springframework.util.StringUtils;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.context.request.NativeWebRequest;

Base class for ContentNegotiationStrategy implementations with the steps to resolve a request to media types. 
First a key (e.g. "json", "pdf") must be extracted from the request (e.g. file extension, query param). The key must then be resolved to media type(s) through the base class MappingMediaTypeFileExtensionResolver which stores such mappings. 
The method handleNoMatch allow sub-classes to plug in additional ways of looking up media types (e.g. through the Java Activation framework, or ServletContext.getMimeType. Media types resolved via base classes are then added to the base class MappingMediaTypeFileExtensionResolver, i.e. cached for new lookups. 
Author:
Rossen Stoyanchev
Since:
3.2/**
 * Base class for {@code ContentNegotiationStrategy} implementations with the
 * steps to resolve a request to media types.
 *
 * <p>First a key (e.g. "json", "pdf") must be extracted from the request (e.g.
 * file extension, query param). The key must then be resolved to media type(s)
 * through the base class {@link MappingMediaTypeFileExtensionResolver} which
 * stores such mappings.
 *
 * <p>The method {@link #handleNoMatch} allow sub-classes to plug in additional
 * ways of looking up media types (e.g. through the Java Activation framework,
 * or {@link javax.servlet.ServletContext#getMimeType}. Media types resolved
 * via base classes are then added to the base class
 * {@link MappingMediaTypeFileExtensionResolver}, i.e. cached for new lookups.
 *
 * @author Rossen Stoyanchev
 * @since 3.2
 */
public abstract class AbstractMappingContentNegotiationStrategy extends MappingMediaTypeFileExtensionResolver
		implements ContentNegotiationStrategy {

	protected final Log logger = LogFactory.getLog(getClass());

	private boolean useRegisteredExtensionsOnly = false;

	private boolean ignoreUnknownExtensions = false;


	
Create an instance with the given map of file extensions and media types.
/**
	 * Create an instance with the given map of file extensions and media types.
	 */
	public AbstractMappingContentNegotiationStrategy(@Nullable Map<String, MediaType> mediaTypes) {
		super(mediaTypes);
	}


	
Whether to only use the registered mappings to look up file extensions, or also to use dynamic resolution (e.g. via MediaTypeFactory. 
By default this is set to false. /**
	 * Whether to only use the registered mappings to look up file extensions,
	 * or also to use dynamic resolution (e.g. via {@link MediaTypeFactory}.
	 * <p>By default this is set to {@code false}.
	 */
	public void setUseRegisteredExtensionsOnly(boolean useRegisteredExtensionsOnly) {
		this.useRegisteredExtensionsOnly = useRegisteredExtensionsOnly;
	}

	public boolean isUseRegisteredExtensionsOnly() {
		return this.useRegisteredExtensionsOnly;
	}

	
Whether to ignore requests with unknown file extension. Setting this to false results in HttpMediaTypeNotAcceptableException. 
By default this is set to false but is overridden in PathExtensionContentNegotiationStrategy to true. /**
	 * Whether to ignore requests with unknown file extension. Setting this to
	 * {@code false} results in {@code HttpMediaTypeNotAcceptableException}.
	 * <p>By default this is set to {@literal false} but is overridden in
	 * {@link PathExtensionContentNegotiationStrategy} to {@literal true}.
	 */
	public void setIgnoreUnknownExtensions(boolean ignoreUnknownExtensions) {
		this.ignoreUnknownExtensions = ignoreUnknownExtensions;
	}

	public boolean isIgnoreUnknownExtensions() {
		return this.ignoreUnknownExtensions;
	}


	@Override
	public List<MediaType> resolveMediaTypes(NativeWebRequest webRequest)
			throws HttpMediaTypeNotAcceptableException {

		return resolveMediaTypeKey(webRequest, getMediaTypeKey(webRequest));
	}

	
An alternative to resolveMediaTypes(NativeWebRequest) that accepts an already extracted key. 
Since:
3.2.16/**
	 * An alternative to {@link #resolveMediaTypes(NativeWebRequest)} that accepts
	 * an already extracted key.
	 * @since 3.2.16
	 */
	public List<MediaType> resolveMediaTypeKey(NativeWebRequest webRequest, @Nullable String key)
			throws HttpMediaTypeNotAcceptableException {

		if (StringUtils.hasText(key)) {
			MediaType mediaType = lookupMediaType(key);
			if (mediaType != null) {
				handleMatch(key, mediaType);
				return Collections.singletonList(mediaType);
			}
			mediaType = handleNoMatch(webRequest, key);
			if (mediaType != null) {
				addMapping(key, mediaType);
				return Collections.singletonList(mediaType);
			}
		}
		return MEDIA_TYPE_ALL_LIST;
	}


	
Extract a key from the request to use to look up media types.
Returns:
the lookup key, or null if none/**
	 * Extract a key from the request to use to look up media types.
	 * @return the lookup key, or {@code null} if none
	 */
	@Nullable
	protected abstract String getMediaTypeKey(NativeWebRequest request);

	
Override to provide handling when a key is successfully resolved via MappingMediaTypeFileExtensionResolver.lookupMediaType. /**
	 * Override to provide handling when a key is successfully resolved via
	 * {@link #lookupMediaType}.
	 */
	protected void handleMatch(String key, MediaType mediaType) {
	}

	
Override to provide handling when a key is not resolved via. MappingMediaTypeFileExtensionResolver.lookupMediaType. Sub-classes can take further steps to determine the media type(s). If a MediaType is returned from this method it will be added to the cache in the base class. /**
	 * Override to provide handling when a key is not resolved via.
	 * {@link #lookupMediaType}. Sub-classes can take further steps to
	 * determine the media type(s). If a MediaType is returned from
	 * this method it will be added to the cache in the base class.
	 */
	@Nullable
	protected MediaType handleNoMatch(NativeWebRequest request, String key)
			throws HttpMediaTypeNotAcceptableException {

		if (!isUseRegisteredExtensionsOnly()) {
			Optional<MediaType> mediaType = MediaTypeFactory.getMediaType("file." + key);
			if (mediaType.isPresent()) {
				return mediaType.get();
			}
		}
		if (isIgnoreUnknownExtensions()) {
			return null;
		}
		throw new HttpMediaTypeNotAcceptableException(getAllMediaTypes());
	}

}