/*
 * Copyright 2014-2020 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 de.codecentric.boot.admin.server.ui.extensions;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.Stream;

import javax.annotation.Nullable;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.ResourcePatternResolver;

public class UiExtensionsScanner {

	private static final Logger log = LoggerFactory.getLogger(UiExtensionsScanner.class);

	private final ResourcePatternResolver resolver;

	public UiExtensionsScanner(ResourcePatternResolver resolver) {
		this.resolver = resolver;
	}

	public UiExtensions scan(String... locations) throws IOException {
		List<UiExtension> extensions = new ArrayList<>();
		for (String location : locations) {
			for (Resource resource : resolveAssets(location)) {
				String resourcePath = this.getResourcePath(location, resource);
				if (resourcePath != null && resource.isReadable()) {
					UiExtension extension = new UiExtension(resourcePath, location + resourcePath);
					log.debug("Found UiExtension {}", extension);
					extensions.add(extension);
				}
			}
		}
		return new UiExtensions(extensions);
	}

	private List<Resource> resolveAssets(String location) throws IOException {
		String widerLocation = toPattern(location);
		return Stream
				.concat(Arrays.stream(this.resolver.getResources(widerLocation + "**/*.js")),
						Arrays.stream(this.resolver.getResources(widerLocation + "**/*.css")))
				.collect(Collectors.toList());
	}

	private String toPattern(String location) {
		// replace the classpath pattern to search all locations and not just the first
		return location.replace("classpath:", "classpath*:");
	}

	@Nullable
	private String getResourcePath(String location, Resource resource) throws IOException {
		String locationWithoutPrefix = location.replaceFirst("^[^:]+:", "");
		Matcher m = Pattern.compile(Pattern.quote(locationWithoutPrefix) + "(.+)$")
				.matcher(resource.getURI().toString());
		if (m.find()) {
			return m.group(1);
		}
		else {
			return null;
		}
	}

}
