/*
 * 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.Collections;
import javax.servlet.http.HttpServletRequest;

import org.springframework.core.io.Resource;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

A base class for a ResourceTransformer with an optional helper method for resolving public links within a transformed resource. 
Author:
Brian Clozel, Rossen Stoyanchev, Juergen Hoeller
Since:
4.1/**
 * A base class for a {@code ResourceTransformer} with an optional helper method
 * for resolving public links within a transformed resource.
 *
 * @author Brian Clozel
 * @author Rossen Stoyanchev
 * @author Juergen Hoeller
 * @since 4.1
 */
public abstract class ResourceTransformerSupport implements ResourceTransformer {

	@Nullable
	private ResourceUrlProvider resourceUrlProvider;


	
Configure a ResourceUrlProvider to use when resolving the public URL of links in a transformed resource (e.g. import links in a CSS file). This is required only for links expressed as full paths and not for relative links. /**
	 * Configure a {@link ResourceUrlProvider} to use when resolving the public
	 * URL of links in a transformed resource (e.g. import links in a CSS file).
	 * This is required only for links expressed as full paths and not for
	 * relative links.
	 */
	public void setResourceUrlProvider(@Nullable ResourceUrlProvider resourceUrlProvider) {
		this.resourceUrlProvider = resourceUrlProvider;
	}

	
Return the configured ResourceUrlProvider. /**
	 * Return the configured {@code ResourceUrlProvider}.
	 */
	@Nullable
	public ResourceUrlProvider getResourceUrlProvider() {
		return this.resourceUrlProvider;
	}


	
A transformer can use this method when a resource being transformed
contains links to other resources. Such links need to be replaced with the
public facing link as determined by the resource resolver chain (e.g. the
public URL may have a version inserted).
Params:
resourcePath – the path to a resource that needs to be re-written
request – the current request
resource – the resource being transformed
transformerChain – the transformer chain
Returns:
the resolved URL, or  if not resolvable/**
	 * A transformer can use this method when a resource being transformed
	 * contains links to other resources. Such links need to be replaced with the
	 * public facing link as determined by the resource resolver chain (e.g. the
	 * public URL may have a version inserted).
	 * @param resourcePath the path to a resource that needs to be re-written
	 * @param request the current request
	 * @param resource the resource being transformed
	 * @param transformerChain the transformer chain
	 * @return the resolved URL, or {@code} if not resolvable
	 */
	@Nullable
	protected String resolveUrlPath(String resourcePath, HttpServletRequest request,
			Resource resource, ResourceTransformerChain transformerChain) {

		if (resourcePath.startsWith("/")) {
			// full resource path
			ResourceUrlProvider urlProvider = findResourceUrlProvider(request);
			return (urlProvider != null ? urlProvider.getForRequestUrl(request, resourcePath) : null);
		}
		else {
			// try resolving as relative path
			return transformerChain.getResolverChain().resolveUrlPath(
					resourcePath, Collections.singletonList(resource));
		}
	}

	
Transform the given relative request path to an absolute path,
taking the path of the given request as a point of reference.
The resulting path is also cleaned from sequences like "path/..".
Params:
path – the relative path to transform
request – the referer request
Returns:
the absolute request path for the given resource path/**
	 * Transform the given relative request path to an absolute path,
	 * taking the path of the given request as a point of reference.
	 * The resulting path is also cleaned from sequences like "path/..".
	 * @param path the relative path to transform
	 * @param request the referer request
	 * @return the absolute request path for the given resource path
	 */
	protected String toAbsolutePath(String path, HttpServletRequest request) {
		String absolutePath = path;
		if (!path.startsWith("/")) {
			ResourceUrlProvider urlProvider = findResourceUrlProvider(request);
			Assert.state(urlProvider != null, "No ResourceUrlProvider");
			String requestPath = urlProvider.getUrlPathHelper().getRequestUri(request);
			absolutePath = StringUtils.applyRelativePath(requestPath, path);
		}
		return StringUtils.cleanPath(absolutePath);
	}

	@Nullable
	private ResourceUrlProvider findResourceUrlProvider(HttpServletRequest request) {
		if (this.resourceUrlProvider != null) {
			return this.resourceUrlProvider;
		}
		return (ResourceUrlProvider) request.getAttribute(
				ResourceUrlProviderExposingInterceptor.RESOURCE_URL_PROVIDER_ATTR);
	}

}