/*
 * Copyright 2012-present 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
 *
 *      https://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.boot.build.bom.bomr;

import java.net.URI;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.stream.Collectors;

import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;

import org.gradle.api.artifacts.repositories.MavenArtifactRepository;
import org.gradle.api.artifacts.repositories.PasswordCredentials;
import org.gradle.api.credentials.Credentials;
import org.gradle.internal.artifacts.repositories.AuthenticationSupportedInternal;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;

import org.springframework.boot.build.bom.bomr.version.DependencyVersion;
import org.springframework.boot.build.xml.XmlDocument;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.web.client.HttpClientErrorException;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.util.UriComponentsBuilder;

/**
 * A {@link VersionResolver} that examines {@code maven-metadata.xml} to determine the
 * available versions.
 *
 * @author Andy Wilkinson
 */
final class MavenMetadataVersionResolver implements VersionResolver {

	private final RestTemplate rest;

	private final Collection<MavenArtifactRepository> repositories;

	MavenMetadataVersionResolver(Collection<MavenArtifactRepository> repositories) {
		this(new RestTemplate(Collections.singletonList(new StringHttpMessageConverter())), repositories);
	}

	MavenMetadataVersionResolver(RestTemplate restTemplate, Collection<MavenArtifactRepository> repositories) {
		this.rest = restTemplate;
		this.repositories = repositories;
	}

	@Override
	public SortedSet<DependencyVersion> resolveVersions(String groupId, String artifactId) {
		Set<String> versions = new HashSet<>();
		for (MavenArtifactRepository repository : this.repositories) {
			versions.addAll(resolveVersions(groupId, artifactId, repository));
		}
		return versions.stream().map(DependencyVersion::parse).collect(Collectors.toCollection(TreeSet::new));
	}

	private Set<String> resolveVersions(String groupId, String artifactId, MavenArtifactRepository repository) {
		Set<String> versions = new HashSet<>();
		URI url = UriComponentsBuilder.fromUri(repository.getUrl())
			.pathSegment(groupId.replace('.', '/'), artifactId, "maven-metadata.xml")
			.build()
			.toUri();
		try {
			HttpHeaders headers = new HttpHeaders();
			PasswordCredentials credentials = credentialsOf(repository);
			String username = (credentials != null) ? credentials.getUsername() : null;
			if (username != null) {
				headers.setBasicAuth(username, credentials.getPassword());
			}
			HttpEntity<Void> request = new HttpEntity<>(headers);
			String metadata = this.rest.exchange(url, HttpMethod.GET, request, String.class).getBody();
			Document metadataDocument = XmlDocument.parseContent(metadata);
			NodeList versionNodes = (NodeList) XPathFactory.newInstance()
				.newXPath()
				.evaluate("/metadata/versioning/versions/version", metadataDocument, XPathConstants.NODESET);
			for (int i = 0; i < versionNodes.getLength(); i++) {
				versions.add(versionNodes.item(i).getTextContent());
			}
		}
		catch (HttpClientErrorException ex) {
			if (ex.getStatusCode() != HttpStatus.NOT_FOUND) {
				System.err.println("Failed to download maven-metadata.xml for " + groupId + ":" + artifactId + " from "
						+ url + ": " + ex.getMessage());
			}
		}
		catch (Exception ex) {
			System.err.println("Failed to resolve versions for module " + groupId + ":" + artifactId + " in repository "
					+ repository + ": " + ex.getMessage());
		}
		return versions;
	}

	/**
	 * Retrieves the configured credentials of the given {@code repository}. We cannot use
	 * {@link MavenArtifactRepository#getCredentials()} as, if the repository has no
	 * credentials, it has the unwanted side-effect of assigning an empty set of username
	 * and password credentials to the repository which may cause subsequent "Username
	 * must not be null!" failures.
	 * @param repository the repository that is the source of the credentials
	 * @return the configured password credentials or {@code null}
	 */
	private PasswordCredentials credentialsOf(MavenArtifactRepository repository) {
		Credentials credentials = ((AuthenticationSupportedInternal) repository).getConfiguredCredentials().getOrNull();
		if (credentials != null) {
			if (credentials instanceof PasswordCredentials passwordCredentials) {
				return passwordCredentials;
			}
			throw new IllegalStateException("Repository '%s (%s)' has credentials '%s' that are not PasswordCredentials"
				.formatted(repository.getName(), repository.getUrl(), credentials));
		}
		return null;
	}

}
