/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.wicket.resource;

import java.util.Collection;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import org.apache.wicket.WicketRuntimeException;
import org.apache.wicket.css.ICssCompressor;
import org.apache.wicket.request.Url;
import org.apache.wicket.request.cycle.RequestCycle;
import org.apache.wicket.request.resource.PackageResourceReference;
import org.apache.wicket.util.image.ImageUtil;

/**
 * This compressor is used to replace URLs within CSS files with URLs created from
 * PackageResourceReferences that belongs to their corresponding resources (e.g images).The scope of
 * the CSS file is used to create the PackageResourceReferences. The compress method is not
 * compressing any content, but replacing the URLs with Wicket representatives.<br>
 * <br>
 * Usage:
 * 
 * <pre>
 * this.getResourceSettings().setCssCompressor(new CssUrlReplacer());
 * </pre>
 * 
 * @since 6.20.0
 * @author Tobias Soloschenko
 */
public class CssUrlReplacer implements IScopeAwareTextResourceProcessor, ICssCompressor
{
	// The pattern to find URLs in CSS resources
	private static final Pattern URL_PATTERN = Pattern
		.compile("url\\([ ]*['|\"]?([^ ]*?)['|\"]?[ ]*\\)");

	/**
	 * Used to be append to CSS URLs (background-image: url('Beer.gif?embedBase64');). The
	 * CssUrlReplacer embeds the base64 content instead of using an URL.
	 */
	public static final String EMBED_BASE64 = "embedBase64";

	private final Set<String> excludes = new LinkedHashSet<>();

	/**
	 * Creates a css url replacer
	 */
	public CssUrlReplacer()
	{
	}

	/**
	 * Creates a css url replacer
	 * 
	 * @param excludes
	 *            css file names to be excluded
	 */
	public CssUrlReplacer(Collection<String> excludes)
	{
		this.excludes.addAll(excludes);
	}

	/**
	 * Replaces the URLs of CSS resources with Wicket representatives.
	 */
	@Override
	public String process(String input, Class<?> scope, String name)
	{
		// filter out the excluded css files
		for (String excludeName : excludes)
		{
			if(name.endsWith(excludeName)){
				return input;
			}
		}
		RequestCycle cycle = RequestCycle.get();
		Url cssUrl = Url.parse(name);
		Matcher matcher = URL_PATTERN.matcher(input);
		StringBuffer output = new StringBuffer();

		while (matcher.find())
		{
			Url imageCandidateUrl = Url.parse(matcher.group(1));
			CharSequence processedUrl;
			boolean embedded = false;

			if (imageCandidateUrl.isFull())
			{
				processedUrl = imageCandidateUrl.toString(Url.StringMode.FULL);
			}
			else if (imageCandidateUrl.isContextAbsolute())
			{
				processedUrl = imageCandidateUrl.toString();
			}
			else if (imageCandidateUrl.isDataUrl())
			{
				embedded = true;
				processedUrl = imageCandidateUrl.toString();
			}
			else
			{
				// relativize against the url for the containing CSS file
				Url cssUrlCopy = new Url(cssUrl);
				cssUrlCopy.resolveRelative(imageCandidateUrl);

				// if the image should be processed as URL or base64 embedded
				if (cssUrlCopy.getQueryString() != null
					&& cssUrlCopy.getQueryString().contains(EMBED_BASE64))
				{
					embedded = true;
					PackageResourceReference imageReference = new PackageResourceReference(scope,
						cssUrlCopy.toString().replace("?" + EMBED_BASE64, ""));
					try
					{
						processedUrl = ImageUtil.createBase64EncodedImage(imageReference, true);
					}
					catch (Exception e)
					{
						throw new WicketRuntimeException(
							"Error while embedding an image into the css: " + imageReference, e);
					}
				}
				else
				{
					PackageResourceReference imageReference = new PackageResourceReference(scope,
						cssUrlCopy.toString());
					processedUrl = cycle.urlFor(imageReference, null);
				}

			}

			// embedded data urls don't need single quotes, but regular urls do:
			matcher.appendReplacement(output,
				embedded ? "url(" + processedUrl + ")" : "url('" + processedUrl + "')");
		}
		matcher.appendTail(output);
		return output.toString();
	}

	@Override
	public String compress(String original)
	{
		throw new UnsupportedOperationException(
			CssUrlReplacer.class.getSimpleName() + ".process() should be used instead!");
	}

	/**
	 * Gets excluded css file names
	 * 
	 * @return a list with css file names to be excluded
	 */
	public Collection<String> getExcludes()
	{
		return excludes;
	}

	/**
	 * Sets a list of css file names to be excluded
	 * 
	 * @param excludes
	 *            a list with css file names to be excluded
	 */
	public void setExcludes(Collection<String> excludes)
	{
		this.excludes.clear();
		this.excludes.addAll(excludes);
	}
}