/*
 * 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.servlet.resource;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;

import org.springframework.core.io.AbstractResource;
import org.springframework.core.io.Resource;
import org.springframework.http.HttpHeaders;
import org.springframework.lang.Nullable;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

Resolves request paths containing a version string that can be used as part
of an HTTP caching strategy in which a resource is cached with a date in the
distant future (e.g. 1 year) and cached until the version, and therefore the
URL, is changed.
Different versioning strategies exist, and this resolver must be configured
with one or more such strategies along with path mappings to indicate which
strategy applies to which resources.
ContentVersionStrategy is a good default choice except in cases where it cannot be used. Most notably the ContentVersionStrategy cannot be combined with JavaScript module loaders. For such cases the FixedVersionStrategy is a better choice. 
Note that using this resolver to serve CSS files means that the CssLinkResourceTransformer should also be used in order to modify links within CSS files to also contain the appropriate versions generated by this resolver. 
Author:
Brian Clozel, Rossen Stoyanchev
See Also:
VersionStrategy
Since:
4.1/**
 * Resolves request paths containing a version string that can be used as part
 * of an HTTP caching strategy in which a resource is cached with a date in the
 * distant future (e.g. 1 year) and cached until the version, and therefore the
 * URL, is changed.
 *
 * <p>Different versioning strategies exist, and this resolver must be configured
 * with one or more such strategies along with path mappings to indicate which
 * strategy applies to which resources.
 *
 * <p>{@code ContentVersionStrategy} is a good default choice except in cases
 * where it cannot be used. Most notably the {@code ContentVersionStrategy}
 * cannot be combined with JavaScript module loaders. For such cases the
 * {@code FixedVersionStrategy} is a better choice.
 *
 * <p>Note that using this resolver to serve CSS files means that the
 * {@link CssLinkResourceTransformer} should also be used in order to modify
 * links within CSS files to also contain the appropriate versions generated
 * by this resolver.
 *
 * @author Brian Clozel
 * @author Rossen Stoyanchev
 * @since 4.1
 * @see VersionStrategy
 */
public class VersionResourceResolver extends AbstractResourceResolver {

	private AntPathMatcher pathMatcher = new AntPathMatcher();

	
Map from path pattern -> VersionStrategy. /** Map from path pattern -> VersionStrategy. */
	private final Map<String, VersionStrategy> versionStrategyMap = new LinkedHashMap<>();


	
Set a Map with URL paths as keys and VersionStrategy as values. 
Supports direct URL matches and Ant-style pattern matches. For syntax details, see the AntPathMatcher javadoc. 
Params:
map – map with URLs as keys and version strategies as values/**
	 * Set a Map with URL paths as keys and {@code VersionStrategy} as values.
	 * <p>Supports direct URL matches and Ant-style pattern matches. For syntax
	 * details, see the {@link org.springframework.util.AntPathMatcher} javadoc.
	 * @param map map with URLs as keys and version strategies as values
	 */
	public void setStrategyMap(Map<String, VersionStrategy> map) {
		this.versionStrategyMap.clear();
		this.versionStrategyMap.putAll(map);
	}

	
Return the map with version strategies keyed by path pattern.
/**
	 * Return the map with version strategies keyed by path pattern.
	 */
	public Map<String, VersionStrategy> getStrategyMap() {
		return this.versionStrategyMap;
	}

	
Insert a content-based version in resource URLs that match the given path patterns. The version is computed from the content of the file, e.g. "css/main-e36d2e05253c6c7085a91522ce43a0b4.css". This is a good default strategy to use except when it cannot be, for example when using JavaScript module loaders, use addFixedVersionStrategy instead for serving JavaScript files. 
Params:
pathPatterns – one or more resource URL path patterns,
relative to the pattern configured with the resource handler
See Also:
ContentVersionStrategy
Returns:
the current instance for chained method invocation/**
	 * Insert a content-based version in resource URLs that match the given path
	 * patterns. The version is computed from the content of the file, e.g.
	 * {@code "css/main-e36d2e05253c6c7085a91522ce43a0b4.css"}. This is a good
	 * default strategy to use except when it cannot be, for example when using
	 * JavaScript module loaders, use {@link #addFixedVersionStrategy} instead
	 * for serving JavaScript files.
	 * @param pathPatterns one or more resource URL path patterns,
	 * relative to the pattern configured with the resource handler
	 * @return the current instance for chained method invocation
	 * @see ContentVersionStrategy
	 */
	public VersionResourceResolver addContentVersionStrategy(String... pathPatterns) {
		addVersionStrategy(new ContentVersionStrategy(), pathPatterns);
		return this;
	}

	
Insert a fixed, prefix-based version in resource URLs that match the given
path patterns, for example: "{version}/js/main.js". This is useful (vs.
content-based versions) when using JavaScript module loaders.
The version may be a random number, the current date, or a value fetched from a git commit sha, a property file, or environment variable and set with SpEL expressions in the configuration (e.g. see @Value in Java config). 
If not done already, variants of the given pathPatterns, prefixed with the version will be also configured. For example, adding a "/js/**" path pattern will also cofigure automatically a "/v1.0.0/js/**" with "v1.0.0" the version String given as an argument. 
Params:
version – a version string
pathPatterns – one or more resource URL path patterns,
relative to the pattern configured with the resource handler
See Also:
FixedVersionStrategy
Returns:
the current instance for chained method invocation/**
	 * Insert a fixed, prefix-based version in resource URLs that match the given
	 * path patterns, for example: <code>"{version}/js/main.js"</code>. This is useful (vs.
	 * content-based versions) when using JavaScript module loaders.
	 * <p>The version may be a random number, the current date, or a value
	 * fetched from a git commit sha, a property file, or environment variable
	 * and set with SpEL expressions in the configuration (e.g. see {@code @Value}
	 * in Java config).
	 * <p>If not done already, variants of the given {@code pathPatterns}, prefixed with
	 * the {@code version} will be also configured. For example, adding a {@code "/js/**"} path pattern
	 * will also cofigure automatically a {@code "/v1.0.0/js/**"} with {@code "v1.0.0"} the
	 * {@code version} String given as an argument.
	 * @param version a version string
	 * @param pathPatterns one or more resource URL path patterns,
	 * relative to the pattern configured with the resource handler
	 * @return the current instance for chained method invocation
	 * @see FixedVersionStrategy
	 */
	public VersionResourceResolver addFixedVersionStrategy(String version, String... pathPatterns) {
		List<String> patternsList = Arrays.asList(pathPatterns);
		List<String> prefixedPatterns = new ArrayList<>(pathPatterns.length);
		String versionPrefix = "/" + version;
		for (String pattern : patternsList) {
			prefixedPatterns.add(pattern);
			if (!pattern.startsWith(versionPrefix) && !patternsList.contains(versionPrefix + pattern)) {
				prefixedPatterns.add(versionPrefix + pattern);
			}
		}
		return addVersionStrategy(new FixedVersionStrategy(version), StringUtils.toStringArray(prefixedPatterns));
	}

	
Register a custom VersionStrategy to apply to resource URLs that match the
given path patterns.
Params:
strategy – the custom strategy
pathPatterns – one or more resource URL path patterns,
relative to the pattern configured with the resource handler
See Also:
VersionStrategy
Returns:
the current instance for chained method invocation/**
	 * Register a custom VersionStrategy to apply to resource URLs that match the
	 * given path patterns.
	 * @param strategy the custom strategy
	 * @param pathPatterns one or more resource URL path patterns,
	 * relative to the pattern configured with the resource handler
	 * @return the current instance for chained method invocation
	 * @see VersionStrategy
	 */
	public VersionResourceResolver addVersionStrategy(VersionStrategy strategy, String... pathPatterns) {
		for (String pattern : pathPatterns) {
			getStrategyMap().put(pattern, strategy);
		}
		return this;
	}


	@Override
	protected Resource resolveResourceInternal(@Nullable HttpServletRequest request, String requestPath,
			List<? extends Resource> locations, ResourceResolverChain chain) {

		Resource resolved = chain.resolveResource(request, requestPath, locations);
		if (resolved != null) {
			return resolved;
		}

		VersionStrategy versionStrategy = getStrategyForPath(requestPath);
		if (versionStrategy == null) {
			return null;
		}

		String candidateVersion = versionStrategy.extractVersion(requestPath);
		if (StringUtils.isEmpty(candidateVersion)) {
			return null;
		}

		String simplePath = versionStrategy.removeVersion(requestPath, candidateVersion);
		Resource baseResource = chain.resolveResource(request, simplePath, locations);
		if (baseResource == null) {
			return null;
		}

		String actualVersion = versionStrategy.getResourceVersion(baseResource);
		if (candidateVersion.equals(actualVersion)) {
			return new FileNameVersionedResource(baseResource, candidateVersion);
		}
		else {
			if (logger.isTraceEnabled()) {
				logger.trace("Found resource for \"" + requestPath + "\", but version [" +
						candidateVersion + "] does not match");
			}
			return null;
		}
	}

	@Override
	protected String resolveUrlPathInternal(String resourceUrlPath,
			List<? extends Resource> locations, ResourceResolverChain chain) {

		String baseUrl = chain.resolveUrlPath(resourceUrlPath, locations);
		if (StringUtils.hasText(baseUrl)) {
			VersionStrategy versionStrategy = getStrategyForPath(resourceUrlPath);
			if (versionStrategy == null) {
				return baseUrl;
			}
			Resource resource = chain.resolveResource(null, baseUrl, locations);
			Assert.state(resource != null, "Unresolvable resource");
			String version = versionStrategy.getResourceVersion(resource);
			return versionStrategy.addVersion(baseUrl, version);
		}
		return baseUrl;
	}

	
Find a VersionStrategy for the request path of the requested resource. 
Returns:
an instance of a VersionStrategy or null if none matches that request path/**
	 * Find a {@code VersionStrategy} for the request path of the requested resource.
	 * @return an instance of a {@code VersionStrategy} or null if none matches that request path
	 */
	@Nullable
	protected VersionStrategy getStrategyForPath(String requestPath) {
		String path = "/".concat(requestPath);
		List<String> matchingPatterns = new ArrayList<>();
		for (String pattern : this.versionStrategyMap.keySet()) {
			if (this.pathMatcher.match(pattern, path)) {
				matchingPatterns.add(pattern);
			}
		}
		if (!matchingPatterns.isEmpty()) {
			Comparator<String> comparator = this.pathMatcher.getPatternComparator(path);
			matchingPatterns.sort(comparator);
			return this.versionStrategyMap.get(matchingPatterns.get(0));
		}
		return null;
	}


	private class FileNameVersionedResource extends AbstractResource implements HttpResource {

		private final Resource original;

		private final String version;

		public FileNameVersionedResource(Resource original, String version) {
			this.original = original;
			this.version = version;
		}

		@Override
		public boolean exists() {
			return this.original.exists();
		}

		@Override
		public boolean isReadable() {
			return this.original.isReadable();
		}

		@Override
		public boolean isOpen() {
			return this.original.isOpen();
		}

		@Override
		public boolean isFile() {
			return this.original.isFile();
		}

		@Override
		public URL getURL() throws IOException {
			return this.original.getURL();
		}

		@Override
		public URI getURI() throws IOException {
			return this.original.getURI();
		}

		@Override
		public File getFile() throws IOException {
			return this.original.getFile();
		}

		@Override
		@Nullable
		public String getFilename() {
			return this.original.getFilename();
		}

		@Override
		public long contentLength() throws IOException {
			return this.original.contentLength();
		}

		@Override
		public long lastModified() throws IOException {
			return this.original.lastModified();
		}

		@Override
		public Resource createRelative(String relativePath) throws IOException {
			return this.original.createRelative(relativePath);
		}

		@Override
		public String getDescription() {
			return this.original.getDescription();
		}

		@Override
		public InputStream getInputStream() throws IOException {
			return this.original.getInputStream();
		}

		@Override
		public HttpHeaders getResponseHeaders() {
			HttpHeaders headers = (this.original instanceof HttpResource ?
					((HttpResource) this.original).getResponseHeaders() : new HttpHeaders());
			headers.setETag("\"" + this.version + "\"");
			return headers;
		}
	}

}