/*
 * 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.maven.surefire.providerapi;

import javax.annotation.Nonnull;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;

import org.codehaus.plexus.component.annotations.Component;

import static java.lang.Character.isJavaIdentifierPart;
import static java.lang.Character.isJavaIdentifierStart;
import static java.util.Collections.emptySet;
import static org.apache.maven.surefire.api.util.ReflectionUtils.getConstructor;

/**
 * SPI loader for Surefire/Failsafe should use {@link Thread#getContextClassLoader() current ClassLoader}.
 * <br>
 * The {@link java.util.ServiceLoader} embedded in JVM uses
 * {@link ClassLoader#getSystemClassLoader() System ClassLoader} and cannot be used in Surefire/Failsafe.
 *
 * @since 2.20
 */
@Component(role = ServiceLoader.class)
public class ServiceLoader {

    @Nonnull
    @SuppressWarnings("unchecked")
    public <T> Set<T> load(Class<T> clazz, ClassLoader classLoader) {
        try {
            Set<T> implementations = new HashSet<>();
            for (String fullyQualifiedClassName : lookup(clazz, classLoader)) {
                Class<?> implClass = classLoader.loadClass(fullyQualifiedClassName);
                implementations.add((T) getConstructor(implClass).newInstance());
            }
            return implementations;
        } catch (IOException | ReflectiveOperationException e) {
            throw new IllegalStateException(e.getLocalizedMessage(), e);
        }
    }

    @Nonnull
    public Set<String> lookup(Class<?> clazz, ClassLoader classLoader) throws IOException {
        final String resourceName = "META-INF/services/" + clazz.getName();

        if (classLoader == null) {
            return emptySet();
        }
        final Enumeration<URL> urls = classLoader.getResources(resourceName);
        return lookupSpiImplementations(urls);
    }

    /**
     * Method loadServices loads the services of a class that are
     * defined using the SPI mechanism.
     *
     * @param urlEnumeration The urls from the resource
     * @return The set of service provider names
     * @throws IOException When reading the streams fails
     */
    @Nonnull
    @SuppressWarnings("checkstyle:innerassignment")
    private static Set<String> lookupSpiImplementations(final Enumeration<URL> urlEnumeration) throws IOException {
        final Set<String> names = new HashSet<>();
        nextUrl:
        while (urlEnumeration.hasMoreElements()) {
            final URL url = urlEnumeration.nextElement();
            try (BufferedReader reader = getReader(url)) {
                for (String line; (line = reader.readLine()) != null; ) {
                    int ci = line.indexOf('#');
                    if (ci >= 0) {
                        line = line.substring(0, ci);
                    }
                    line = line.trim();
                    int n = line.length();
                    if (n == 0) {
                        continue; // next line
                    }

                    if (line.indexOf(' ') >= 0 || line.indexOf('\t') >= 0) {
                        continue nextUrl; // next url
                    }
                    char cp = line.charAt(0); // should use codePointAt but this was JDK1.3
                    if (!isJavaIdentifierStart(cp)) {
                        continue nextUrl; // next url
                    }
                    for (int i = 1; i < n; i++) {
                        cp = line.charAt(i); // should use codePointAt but this was JDK1.3
                        if (!isJavaIdentifierPart(cp) && cp != '.') {
                            continue nextUrl; // next url
                        }
                    }
                    if (!names.contains(line)) {
                        names.add(line);
                    }
                }
            }
        }

        return names;
    }

    @Nonnull
    private static BufferedReader getReader(@Nonnull URL url) throws IOException {
        final InputStream inputStream = url.openStream();
        final InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
        return new BufferedReader(inputStreamReader);
    }
}
