/*
 * 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.util.ArrayList;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;

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

import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.lang.Nullable;
import org.springframework.util.AntPathMatcher;
import org.springframework.util.PathMatcher;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.handler.SimpleUrlHandlerMapping;
import org.springframework.web.util.UrlPathHelper;

A central component to use to obtain the public URL path that clients should
use to access a static resource.
This class is aware of Spring MVC handler mappings used to serve static resources and uses the ResourceResolver chains of the configured ResourceHttpRequestHandlers to make its decisions. 
Author:
Rossen Stoyanchev
Since:
4.1/**
 * A central component to use to obtain the public URL path that clients should
 * use to access a static resource.
 *
 * <p>This class is aware of Spring MVC handler mappings used to serve static
 * resources and uses the {@code ResourceResolver} chains of the configured
 * {@code ResourceHttpRequestHandler}s to make its decisions.
 *
 * @author Rossen Stoyanchev
 * @since 4.1
 */
public class ResourceUrlProvider implements ApplicationListener<ContextRefreshedEvent> {

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

	private UrlPathHelper urlPathHelper = new UrlPathHelper();

	private PathMatcher pathMatcher = new AntPathMatcher();

	private final Map<String, ResourceHttpRequestHandler> handlerMap = new LinkedHashMap<>();

	private boolean autodetect = true;


	
Configure a UrlPathHelper to use in getForRequestUrl(HttpServletRequest, String) in order to derive the lookup path for a target request URL path. /**
	 * Configure a {@code UrlPathHelper} to use in
	 * {@link #getForRequestUrl(javax.servlet.http.HttpServletRequest, String)}
	 * in order to derive the lookup path for a target request URL path.
	 */
	public void setUrlPathHelper(UrlPathHelper urlPathHelper) {
		this.urlPathHelper = urlPathHelper;
	}

	
Return the configured UrlPathHelper. 
Since:
4.2.8/**
	 * Return the configured {@code UrlPathHelper}.
	 * @since 4.2.8
	 */
	public UrlPathHelper getUrlPathHelper() {
		return this.urlPathHelper;
	}

	
Configure a PathMatcher to use when comparing target lookup path against resource mappings. /**
	 * Configure a {@code PathMatcher} to use when comparing target lookup path
	 * against resource mappings.
	 */
	public void setPathMatcher(PathMatcher pathMatcher) {
		this.pathMatcher = pathMatcher;
	}

	
Return the configured PathMatcher. /**
	 * Return the configured {@code PathMatcher}.
	 */
	public PathMatcher getPathMatcher() {
		return this.pathMatcher;
	}

	
Manually configure the resource mappings.
Note: by default resource mappings are auto-detected from the Spring ApplicationContext. However if this property is used, the auto-detection is turned off. /**
	 * Manually configure the resource mappings.
	 * <p><strong>Note:</strong> by default resource mappings are auto-detected
	 * from the Spring {@code ApplicationContext}. However if this property is
	 * used, the auto-detection is turned off.
	 */
	public void setHandlerMap(@Nullable Map<String, ResourceHttpRequestHandler> handlerMap) {
		if (handlerMap != null) {
			this.handlerMap.clear();
			this.handlerMap.putAll(handlerMap);
			this.autodetect = false;
		}
	}

	
Return the resource mappings, either manually configured or auto-detected when the Spring ApplicationContext is refreshed. /**
	 * Return the resource mappings, either manually configured or auto-detected
	 * when the Spring {@code ApplicationContext} is refreshed.
	 */
	public Map<String, ResourceHttpRequestHandler> getHandlerMap() {
		return this.handlerMap;
	}

	
Return false if resource mappings were manually configured, true otherwise. /**
	 * Return {@code false} if resource mappings were manually configured,
	 * {@code true} otherwise.
	 */
	public boolean isAutodetect() {
		return this.autodetect;
	}

	@Override
	public void onApplicationEvent(ContextRefreshedEvent event) {
		if (isAutodetect()) {
			this.handlerMap.clear();
			detectResourceHandlers(event.getApplicationContext());
			if (!this.handlerMap.isEmpty()) {
				this.autodetect = false;
			}
		}
	}


	protected void detectResourceHandlers(ApplicationContext appContext) {
		Map<String, SimpleUrlHandlerMapping> beans = appContext.getBeansOfType(SimpleUrlHandlerMapping.class);
		List<SimpleUrlHandlerMapping> mappings = new ArrayList<>(beans.values());
		AnnotationAwareOrderComparator.sort(mappings);

		for (SimpleUrlHandlerMapping mapping : mappings) {
			for (String pattern : mapping.getHandlerMap().keySet()) {
				Object handler = mapping.getHandlerMap().get(pattern);
				if (handler instanceof ResourceHttpRequestHandler) {
					ResourceHttpRequestHandler resourceHandler = (ResourceHttpRequestHandler) handler;
					this.handlerMap.put(pattern, resourceHandler);
				}
			}
		}

		if (this.handlerMap.isEmpty()) {
			logger.trace("No resource handling mappings found");
		}
	}

	
A variation on getForLookupPath(String) that accepts a full request URL path (i.e. including context and servlet path) and returns the full request URL path to expose for public use. 
Params:
request – the current request
requestUrl – the request URL path to resolve
Returns:
the resolved public URL path, or null if unresolved/**
	 * A variation on {@link #getForLookupPath(String)} that accepts a full request
	 * URL path (i.e. including context and servlet path) and returns the full request
	 * URL path to expose for public use.
	 * @param request the current request
	 * @param requestUrl the request URL path to resolve
	 * @return the resolved public URL path, or {@code null} if unresolved
	 */
	@Nullable
	public final String getForRequestUrl(HttpServletRequest request, String requestUrl) {
		int prefixIndex = getLookupPathIndex(request);
		int suffixIndex = getEndPathIndex(requestUrl);
		if (prefixIndex >= suffixIndex) {
			return null;
		}
		String prefix = requestUrl.substring(0, prefixIndex);
		String suffix = requestUrl.substring(suffixIndex);
		String lookupPath = requestUrl.substring(prefixIndex, suffixIndex);
		String resolvedLookupPath = getForLookupPath(lookupPath);
		return (resolvedLookupPath != null ? prefix + resolvedLookupPath + suffix : null);
	}

	private int getLookupPathIndex(HttpServletRequest request) {
		UrlPathHelper pathHelper = getUrlPathHelper();
		String requestUri = pathHelper.getRequestUri(request);
		String lookupPath = pathHelper.getLookupPathForRequest(request);
		return requestUri.indexOf(lookupPath);
	}

	private int getEndPathIndex(String lookupPath) {
		int suffixIndex = lookupPath.length();
		int queryIndex = lookupPath.indexOf('?');
		if (queryIndex > 0) {
			suffixIndex = queryIndex;
		}
		int hashIndex = lookupPath.indexOf('#');
		if (hashIndex > 0) {
			suffixIndex = Math.min(suffixIndex, hashIndex);
		}
		return suffixIndex;
	}

	
Compare the given path against configured resource handler mappings and if a match is found use the ResourceResolver chain of the matched ResourceHttpRequestHandler to resolve the URL path to expose for public use. 
It is expected that the given path is what Spring MVC would use for
request mapping purposes, i.e. excluding context and servlet path portions.
If several handler mappings match, the handler used will be the one
configured with the most specific pattern.
Params:
lookupPath – the lookup path to check
Returns:
the resolved public URL path, or null if unresolved/**
	 * Compare the given path against configured resource handler mappings and
	 * if a match is found use the {@code ResourceResolver} chain of the matched
	 * {@code ResourceHttpRequestHandler} to resolve the URL path to expose for
	 * public use.
	 * <p>It is expected that the given path is what Spring MVC would use for
	 * request mapping purposes, i.e. excluding context and servlet path portions.
	 * <p>If several handler mappings match, the handler used will be the one
	 * configured with the most specific pattern.
	 * @param lookupPath the lookup path to check
	 * @return the resolved public URL path, or {@code null} if unresolved
	 */
	@Nullable
	public final String getForLookupPath(String lookupPath) {

		// Clean duplicate slashes or pathWithinPattern won't match lookupPath
		String previous;
		do {
			previous = lookupPath;
			lookupPath = StringUtils.replace(lookupPath, "//", "/");
		} while (!lookupPath.equals(previous));

		List<String> matchingPatterns = new ArrayList<>();
		for (String pattern : this.handlerMap.keySet()) {
			if (getPathMatcher().match(pattern, lookupPath)) {
				matchingPatterns.add(pattern);
			}
		}

		if (!matchingPatterns.isEmpty()) {
			Comparator<String> patternComparator = getPathMatcher().getPatternComparator(lookupPath);
			matchingPatterns.sort(patternComparator);
			for (String pattern : matchingPatterns) {
				String pathWithinMapping = getPathMatcher().extractPathWithinPattern(pattern, lookupPath);
				String pathMapping = lookupPath.substring(0, lookupPath.indexOf(pathWithinMapping));
				ResourceHttpRequestHandler handler = this.handlerMap.get(pattern);
				ResourceResolverChain chain = new DefaultResourceResolverChain(handler.getResourceResolvers());
				String resolved = chain.resolveUrlPath(pathWithinMapping, handler.getLocations());
				if (resolved == null) {
					continue;
				}
				return pathMapping + resolved;
			}
		}

		if (logger.isTraceEnabled()) {
			logger.trace("No match for \"" + lookupPath + "\"");
		}

		return null;
	}

}