/*
 * Copyright (c) 2014, 2020, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package jdk.internal.module;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UncheckedIOException;
import java.lang.module.FindException;
import java.lang.module.InvalidModuleDescriptorException;
import java.lang.module.ModuleDescriptor;
import java.lang.module.ModuleDescriptor.Builder;
import java.lang.module.ModuleFinder;
import java.lang.module.ModuleReference;
import java.net.URI;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.NoSuchFileException;
import java.nio.file.Path;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.jar.Attributes;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.jar.Manifest;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.zip.ZipException;
import java.util.zip.ZipFile;

import sun.nio.cs.UTF_8;

import jdk.internal.jmod.JmodFile;
import jdk.internal.jmod.JmodFile.Section;
import jdk.internal.perf.PerfCounter;

A ModuleFinder that locates modules on the file system by searching a sequence of directories or packaged modules. The ModuleFinder can be created to work in either the run-time or link-time phases. In both cases it locates modular JAR and exploded modules. When created for link-time then it additionally locates modules in JMOD files. The ModuleFinder can also optionally patch any modules that it locates with a ModulePatcher. /**
 * A {@code ModuleFinder} that locates modules on the file system by searching
 * a sequence of directories or packaged modules. The ModuleFinder can be
 * created to work in either the run-time or link-time phases. In both cases it
 * locates modular JAR and exploded modules. When created for link-time then it
 * additionally locates modules in JMOD files. The ModuleFinder can also
 * optionally patch any modules that it locates with a ModulePatcher.
 */

public class ModulePath implements ModuleFinder {
    private static final String MODULE_INFO = "module-info.class";

    // the version to use for multi-release modular JARs
    private final Runtime.Version releaseVersion;

    // true for the link phase (supports modules packaged in JMOD format)
    private final boolean isLinkPhase;

    // for patching modules, can be null
    private final ModulePatcher patcher;

    // the entries on this module path
    private final Path[] entries;
    private int next;

    // map of module name to module reference map for modules already located
    private final Map<String, ModuleReference> cachedModules = new HashMap<>();


    private ModulePath(Runtime.Version version,
                       boolean isLinkPhase,
                       ModulePatcher patcher,
                       Path... entries) {
        this.releaseVersion = version;
        this.isLinkPhase = isLinkPhase;
        this.patcher = patcher;
        this.entries = entries.clone();
        for (Path entry : this.entries) {
            Objects.requireNonNull(entry);
        }
    }

    
Returns a ModuleFinder that locates modules on the file system by
searching a sequence of directories and/or packaged modules. The modules
may be patched by the given ModulePatcher.
/**
     * Returns a ModuleFinder that locates modules on the file system by
     * searching a sequence of directories and/or packaged modules. The modules
     * may be patched by the given ModulePatcher.
     */
    public static ModuleFinder of(ModulePatcher patcher, Path... entries) {
        return new ModulePath(JarFile.runtimeVersion(), false, patcher, entries);
    }

    
Returns a ModuleFinder that locates modules on the file system by
searching a sequence of directories and/or packaged modules.
/**
     * Returns a ModuleFinder that locates modules on the file system by
     * searching a sequence of directories and/or packaged modules.
     */
    public static ModuleFinder of(Path... entries) {
        return of((ModulePatcher)null, entries);
    }

    
Returns a ModuleFinder that locates modules on the file system by
searching a sequence of directories and/or packaged modules.
Params:
version – The release version to use for multi-release JAR files
isLinkPhase – true if the link phase to locate JMOD files/**
     * Returns a ModuleFinder that locates modules on the file system by
     * searching a sequence of directories and/or packaged modules.
     *
     * @param version The release version to use for multi-release JAR files
     * @param isLinkPhase {@code true} if the link phase to locate JMOD files
     */
    public static ModuleFinder of(Runtime.Version version,
                                  boolean isLinkPhase,
                                  Path... entries) {
        return new ModulePath(version, isLinkPhase, null, entries);
    }


    @Override
    public Optional<ModuleReference> find(String name) {
        Objects.requireNonNull(name);

        // try cached modules
        ModuleReference m = cachedModules.get(name);
        if (m != null)
            return Optional.of(m);

        // the module may not have been encountered yet
        while (hasNextEntry()) {
            scanNextEntry();
            m = cachedModules.get(name);
            if (m != null)
                return Optional.of(m);
        }
        return Optional.empty();
    }

    @Override
    public Set<ModuleReference> findAll() {
        // need to ensure that all entries have been scanned
        while (hasNextEntry()) {
            scanNextEntry();
        }
        return cachedModules.values().stream().collect(Collectors.toSet());
    }

    
Returns true if there are additional entries to scan /**
     * Returns {@code true} if there are additional entries to scan
     */
    private boolean hasNextEntry() {
        return next < entries.length;
    }

    
Scans the next entry on the module path. A no-op if all entries have
already been scanned.
Throws:
FindException – if an error occurs scanning the next entry/**
     * Scans the next entry on the module path. A no-op if all entries have
     * already been scanned.
     *
     * @throws FindException if an error occurs scanning the next entry
     */
    private void scanNextEntry() {
        if (hasNextEntry()) {

            long t0 = System.nanoTime();

            Path entry = entries[next];
            Map<String, ModuleReference> modules = scan(entry);
            next++;

            // update cache, ignoring duplicates
            int initialSize = cachedModules.size();
            for (Map.Entry<String, ModuleReference> e : modules.entrySet()) {
                cachedModules.putIfAbsent(e.getKey(), e.getValue());
            }

            // update counters
            int added = cachedModules.size() - initialSize;
            moduleCount.add(added);

            scanTime.addElapsedTimeFrom(t0);
        }
    }


    
Scan the given module path entry. If the entry is a directory then it is
a directory of modules or an exploded module. If the entry is a regular
file then it is assumed to be a packaged module.
Throws:
FindException – if an error occurs scanning the entry/**
     * Scan the given module path entry. If the entry is a directory then it is
     * a directory of modules or an exploded module. If the entry is a regular
     * file then it is assumed to be a packaged module.
     *
     * @throws FindException if an error occurs scanning the entry
     */
    private Map<String, ModuleReference> scan(Path entry) {

        BasicFileAttributes attrs;
        try {
            attrs = Files.readAttributes(entry, BasicFileAttributes.class);
        } catch (NoSuchFileException e) {
            return Map.of();
        } catch (IOException ioe) {
            throw new FindException(ioe);
        }

        try {

            if (attrs.isDirectory()) {
                Path mi = entry.resolve(MODULE_INFO);
                if (!Files.exists(mi)) {
                    // assume a directory of modules
                    return scanDirectory(entry);
                }
            }

            // packaged or exploded module
            ModuleReference mref = readModule(entry, attrs);
            if (mref != null) {
                String name = mref.descriptor().name();
                return Map.of(name, mref);
            }

            // not recognized
            String msg;
            if (!isLinkPhase && entry.toString().endsWith(".jmod")) {
                msg = "JMOD format not supported at execution time";
            } else {
                msg = "Module format not recognized";
            }
            throw new FindException(msg + ": " + entry);

        } catch (IOException ioe) {
            throw new FindException(ioe);
        }
    }


    
Scans the given directory for packaged or exploded modules.
Throws:
IOException – if an I/O error occurs
FindException – if an error occurs scanning the entry or the
        directory contains two or more modules with the same name
Returns:
a map of module name to ModuleReference for the modules found
        in the directory/**
     * Scans the given directory for packaged or exploded modules.
     *
     * @return a map of module name to ModuleReference for the modules found
     *         in the directory
     *
     * @throws IOException if an I/O error occurs
     * @throws FindException if an error occurs scanning the entry or the
     *         directory contains two or more modules with the same name
     */
    private Map<String, ModuleReference> scanDirectory(Path dir)
        throws IOException
    {
        // The map of name -> mref of modules found in this directory.
        Map<String, ModuleReference> nameToReference = new HashMap<>();

        try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
            for (Path entry : stream) {
                BasicFileAttributes attrs;
                try {
                    attrs = Files.readAttributes(entry, BasicFileAttributes.class);
                } catch (NoSuchFileException ignore) {
                    // file has been removed or moved, ignore for now
                    continue;
                }

                ModuleReference mref = readModule(entry, attrs);

                // module found
                if (mref != null) {
                    // can have at most one version of a module in the directory
                    String name = mref.descriptor().name();
                    ModuleReference previous = nameToReference.put(name, mref);
                    if (previous != null) {
                        String fn1 = fileName(mref);
                        String fn2 = fileName(previous);
                        throw new FindException("Two versions of module "
                                                 + name + " found in " + dir
                                                 + " (" + fn1 + " and " + fn2 + ")");
                    }
                }
            }
        }

        return nameToReference;
    }


    
Reads a packaged or exploded module, returning a ModuleReference to the module. Returns null if the entry is not recognized. 
Throws:
IOException – if an I/O error occurs
FindException – if an error occurs parsing its module descriptor/**
     * Reads a packaged or exploded module, returning a {@code ModuleReference}
     * to the module. Returns {@code null} if the entry is not recognized.
     *
     * @throws IOException if an I/O error occurs
     * @throws FindException if an error occurs parsing its module descriptor
     */
    private ModuleReference readModule(Path entry, BasicFileAttributes attrs)
        throws IOException
    {
        try {

            // exploded module
            if (attrs.isDirectory()) {
                return readExplodedModule(entry); // may return null
            }

            // JAR or JMOD file
            if (attrs.isRegularFile()) {
                String fn = entry.getFileName().toString();
                boolean isDefaultFileSystem = isDefaultFileSystem(entry);

                // JAR file
                if (fn.endsWith(".jar")) {
                    if (isDefaultFileSystem) {
                        return readJar(entry);
                    } else {
                        // the JAR file is in a custom file system so
                        // need to copy it to the local file system
                        Path tmpdir = Files.createTempDirectory("mlib");
                        Path target = Files.copy(entry, tmpdir.resolve(fn));
                        return readJar(target);
                    }
                }

                // JMOD file
                if (isDefaultFileSystem && isLinkPhase && fn.endsWith(".jmod")) {
                    return readJMod(entry);
                }
            }

            return null;

        } catch (InvalidModuleDescriptorException e) {
            throw new FindException("Error reading module: " + entry, e);
        }
    }

    
Returns a string with the file name of the module if possible.
If the module location is not a file URI then return the URI
as a string.
/**
     * Returns a string with the file name of the module if possible.
     * If the module location is not a file URI then return the URI
     * as a string.
     */
    private String fileName(ModuleReference mref) {
        URI uri = mref.location().orElse(null);
        if (uri != null) {
            if (uri.getScheme().equalsIgnoreCase("file")) {
                Path file = Path.of(uri);
                return file.getFileName().toString();
            } else {
                return uri.toString();
            }
        } else {
            return "<unknown>";
        }
    }

    // -- JMOD files --

    private Set<String> jmodPackages(JmodFile jf) {
        return jf.stream()
            .filter(e -> e.section() == Section.CLASSES)
            .map(JmodFile.Entry::name)
            .map(this::toPackageName)
            .flatMap(Optional::stream)
            .collect(Collectors.toSet());
    }

    
Returns a ModuleReference to a module in JMOD file on the file system. 
Throws:
IOException – 
InvalidModuleDescriptorException – /**
     * Returns a {@code ModuleReference} to a module in JMOD file on the
     * file system.
     *
     * @throws IOException
     * @throws InvalidModuleDescriptorException
     */
    private ModuleReference readJMod(Path file) throws IOException {
        try (JmodFile jf = new JmodFile(file)) {
            ModuleInfo.Attributes attrs;
            try (InputStream in = jf.getInputStream(Section.CLASSES, MODULE_INFO)) {
                attrs  = ModuleInfo.read(in, () -> jmodPackages(jf));
            }
            return ModuleReferences.newJModModule(attrs, file);
        }
    }


    // -- JAR files --

    private static final String SERVICES_PREFIX = "META-INF/services/";

    private static final Attributes.Name AUTOMATIC_MODULE_NAME
        = new Attributes.Name("Automatic-Module-Name");

    
Returns the service type corresponding to the name of a services
configuration file if it is a legal type name.
For example, if called with "META-INF/services/p.S" then this method
returns a container with the value "p.S".
/**
     * Returns the service type corresponding to the name of a services
     * configuration file if it is a legal type name.
     *
     * For example, if called with "META-INF/services/p.S" then this method
     * returns a container with the value "p.S".
     */
    private Optional<String> toServiceName(String cf) {
        assert cf.startsWith(SERVICES_PREFIX);
        int index = cf.lastIndexOf("/") + 1;
        if (index < cf.length()) {
            String prefix = cf.substring(0, index);
            if (prefix.equals(SERVICES_PREFIX)) {
                String sn = cf.substring(index);
                if (Checks.isClassName(sn))
                    return Optional.of(sn);
            }
        }
        return Optional.empty();
    }

    
Reads the next line from the given reader and trims it of comments and
leading/trailing white space.
Returns null if the reader is at EOF.
/**
     * Reads the next line from the given reader and trims it of comments and
     * leading/trailing white space.
     *
     * Returns null if the reader is at EOF.
     */
    private String nextLine(BufferedReader reader) throws IOException {
        String ln = reader.readLine();
        if (ln != null) {
            int ci = ln.indexOf('#');
            if (ci >= 0)
                ln = ln.substring(0, ci);
            ln = ln.trim();
        }
        return ln;
    }

    
Treat the given JAR file as a module as follows:
1. The value of the Automatic-Module-Name attribute is the module name
2. The version, and the module name when the  Automatic-Module-Name
   attribute is not present, is derived from the file ame of the JAR file
3. All packages are derived from the .class files in the JAR file
4. The contents of any META-INF/services configuration files are mapped
   to "provides" declarations
5. The Main-Class attribute in the main attributes of the JAR manifest
   is mapped to the module descriptor mainClass if possible
/**
     * Treat the given JAR file as a module as follows:
     *
     * 1. The value of the Automatic-Module-Name attribute is the module name
     * 2. The version, and the module name when the  Automatic-Module-Name
     *    attribute is not present, is derived from the file ame of the JAR file
     * 3. All packages are derived from the .class files in the JAR file
     * 4. The contents of any META-INF/services configuration files are mapped
     *    to "provides" declarations
     * 5. The Main-Class attribute in the main attributes of the JAR manifest
     *    is mapped to the module descriptor mainClass if possible
     */
    private ModuleDescriptor deriveModuleDescriptor(JarFile jf)
        throws IOException
    {
        // Read Automatic-Module-Name attribute if present
        Manifest man = jf.getManifest();
        Attributes attrs = null;
        String moduleName = null;
        if (man != null) {
            attrs = man.getMainAttributes();
            if (attrs != null) {
                moduleName = attrs.getValue(AUTOMATIC_MODULE_NAME);
            }
        }

        // Derive the version, and the module name if needed, from JAR file name
        String fn = jf.getName();
        int i = fn.lastIndexOf(File.separator);
        if (i != -1)
            fn = fn.substring(i + 1);

        // drop ".jar"
        String name = fn.substring(0, fn.length() - 4);
        String vs = null;

        // find first occurrence of -${NUMBER}. or -${NUMBER}$
        Matcher matcher = Patterns.DASH_VERSION.matcher(name);
        if (matcher.find()) {
            int start = matcher.start();

            // attempt to parse the tail as a version string
            try {
                String tail = name.substring(start + 1);
                ModuleDescriptor.Version.parse(tail);
                vs = tail;
            } catch (IllegalArgumentException ignore) { }

            name = name.substring(0, start);
        }

        // Create builder, using the name derived from file name when
        // Automatic-Module-Name not present
        Builder builder;
        if (moduleName != null) {
            try {
                builder = ModuleDescriptor.newAutomaticModule(moduleName);
            } catch (IllegalArgumentException e) {
                throw new FindException(AUTOMATIC_MODULE_NAME + ": " + e.getMessage());
            }
        } else {
            builder = ModuleDescriptor.newAutomaticModule(cleanModuleName(name));
        }

        // module version if present
        if (vs != null)
            builder.version(vs);

        // scan the names of the entries in the JAR file
        Map<Boolean, Set<String>> map = jf.versionedStream()
                .filter(e -> !e.isDirectory())
                .map(JarEntry::getName)
                .filter(e -> (e.endsWith(".class") ^ e.startsWith(SERVICES_PREFIX)))
                .collect(Collectors.partitioningBy(e -> e.startsWith(SERVICES_PREFIX),
                                                   Collectors.toSet()));

        Set<String> classFiles = map.get(Boolean.FALSE);
        Set<String> configFiles = map.get(Boolean.TRUE);

        // the packages containing class files
        Set<String> packages = classFiles.stream()
                .map(this::toPackageName)
                .flatMap(Optional::stream)
                .distinct()
                .collect(Collectors.toSet());

        // all packages are exported and open
        builder.packages(packages);

        // map names of service configuration files to service names
        Set<String> serviceNames = configFiles.stream()
                .map(this::toServiceName)
                .flatMap(Optional::stream)
                .collect(Collectors.toSet());

        // parse each service configuration file
        for (String sn : serviceNames) {
            JarEntry entry = jf.getJarEntry(SERVICES_PREFIX + sn);
            List<String> providerClasses = new ArrayList<>();
            try (InputStream in = jf.getInputStream(entry)) {
                BufferedReader reader
                    = new BufferedReader(new InputStreamReader(in, UTF_8.INSTANCE));
                String cn;
                while ((cn = nextLine(reader)) != null) {
                    if (!cn.isEmpty()) {
                        String pn = packageName(cn);
                        if (!packages.contains(pn)) {
                            String msg = "Provider class " + cn + " not in module";
                            throw new InvalidModuleDescriptorException(msg);
                        }
                        providerClasses.add(cn);
                    }
                }
            }
            if (!providerClasses.isEmpty())
                builder.provides(sn, providerClasses);
        }

        // Main-Class attribute if it exists
        if (attrs != null) {
            String mainClass = attrs.getValue(Attributes.Name.MAIN_CLASS);
            if (mainClass != null) {
                mainClass = mainClass.replace('/', '.');
                if (Checks.isClassName(mainClass)) {
                    String pn = packageName(mainClass);
                    if (packages.contains(pn)) {
                        builder.mainClass(mainClass);
                    }
                }
            }
        }

        return builder.build();
    }

    
Patterns used to derive the module name from a JAR file name.
/**
     * Patterns used to derive the module name from a JAR file name.
     */
    private static class Patterns {
        static final Pattern DASH_VERSION = Pattern.compile("-(\\d+(\\.|$))");
        static final Pattern NON_ALPHANUM = Pattern.compile("[^A-Za-z0-9]");
        static final Pattern REPEATING_DOTS = Pattern.compile("(\\.)(\\1)+");
        static final Pattern LEADING_DOTS = Pattern.compile("^\\.");
        static final Pattern TRAILING_DOTS = Pattern.compile("\\.$");
    }

    
Clean up candidate module name derived from a JAR file name.
/**
     * Clean up candidate module name derived from a JAR file name.
     */
    private static String cleanModuleName(String mn) {
        // replace non-alphanumeric
        mn = Patterns.NON_ALPHANUM.matcher(mn).replaceAll(".");

        // collapse repeating dots
        mn = Patterns.REPEATING_DOTS.matcher(mn).replaceAll(".");

        // drop leading dots
        if (!mn.isEmpty() && mn.charAt(0) == '.')
            mn = Patterns.LEADING_DOTS.matcher(mn).replaceAll("");

        // drop trailing dots
        int len = mn.length();
        if (len > 0 && mn.charAt(len-1) == '.')
            mn = Patterns.TRAILING_DOTS.matcher(mn).replaceAll("");

        return mn;
    }

    private Set<String> jarPackages(JarFile jf) {
        return jf.versionedStream()
                .filter(e -> !e.isDirectory())
                .map(JarEntry::getName)
                .map(this::toPackageName)
                .flatMap(Optional::stream)
                .collect(Collectors.toSet());
    }

    
Returns a ModuleReference to a module in modular JAR file on the file system. 
Throws:
IOException – 
FindException – 
InvalidModuleDescriptorException – /**
     * Returns a {@code ModuleReference} to a module in modular JAR file on
     * the file system.
     *
     * @throws IOException
     * @throws FindException
     * @throws InvalidModuleDescriptorException
     */
    private ModuleReference readJar(Path file) throws IOException {
        try (JarFile jf = new JarFile(file.toFile(),
                                      true,               // verify
                                      ZipFile.OPEN_READ,
                                      releaseVersion))
        {
            ModuleInfo.Attributes attrs;
            JarEntry entry = jf.getJarEntry(MODULE_INFO);
            if (entry == null) {

                // no module-info.class so treat it as automatic module
                try {
                    ModuleDescriptor md = deriveModuleDescriptor(jf);
                    attrs = new ModuleInfo.Attributes(md, null, null, null);
                } catch (RuntimeException e) {
                    throw new FindException("Unable to derive module descriptor for "
                                            + jf.getName(), e);
                }

            } else {
                attrs = ModuleInfo.read(jf.getInputStream(entry),
                                        () -> jarPackages(jf));
            }

            return ModuleReferences.newJarModule(attrs, patcher, file);
        } catch (ZipException e) {
            throw new FindException("Error reading " + file, e);
        }
    }


    // -- exploded directories --

    private Set<String> explodedPackages(Path dir) {
        try {
            return Files.find(dir, Integer.MAX_VALUE,
                    ((path, attrs) -> attrs.isRegularFile() && !isHidden(path)))
                    .map(path -> dir.relativize(path))
                    .map(this::toPackageName)
                    .flatMap(Optional::stream)
                    .collect(Collectors.toSet());
        } catch (IOException x) {
            throw new UncheckedIOException(x);
        }
    }

    
Returns a ModuleReference to an exploded module on the file system or null if module-info.class not found. 
Throws:
IOException – 
InvalidModuleDescriptorException – /**
     * Returns a {@code ModuleReference} to an exploded module on the file
     * system or {@code null} if {@code module-info.class} not found.
     *
     * @throws IOException
     * @throws InvalidModuleDescriptorException
     */
    private ModuleReference readExplodedModule(Path dir) throws IOException {
        Path mi = dir.resolve(MODULE_INFO);
        ModuleInfo.Attributes attrs;
        try (InputStream in = Files.newInputStream(mi)) {
            attrs = ModuleInfo.read(new BufferedInputStream(in),
                                    () -> explodedPackages(dir));
        } catch (NoSuchFileException e) {
            // for now
            return null;
        }
        return ModuleReferences.newExplodedModule(attrs, patcher, dir);
    }

    
Maps a type name to its package name.
/**
     * Maps a type name to its package name.
     */
    private static String packageName(String cn) {
        int index = cn.lastIndexOf('.');
        return (index == -1) ? "" : cn.substring(0, index);
    }

    
Maps the name of an entry in a JAR or ZIP file to a package name.
Throws:
InvalidModuleDescriptorException – if the name is a class file in
        the top-level directory of the JAR/ZIP file (and it's not
        module-info.class)/**
     * Maps the name of an entry in a JAR or ZIP file to a package name.
     *
     * @throws InvalidModuleDescriptorException if the name is a class file in
     *         the top-level directory of the JAR/ZIP file (and it's not
     *         module-info.class)
     */
    private Optional<String> toPackageName(String name) {
        assert !name.endsWith("/");
        int index = name.lastIndexOf("/");
        if (index == -1) {
            if (name.endsWith(".class") && !name.equals(MODULE_INFO)) {
                String msg = name + " found in top-level directory"
                             + " (unnamed package not allowed in module)";
                throw new InvalidModuleDescriptorException(msg);
            }
            return Optional.empty();
        }

        String pn = name.substring(0, index).replace('/', '.');
        if (Checks.isPackageName(pn)) {
            return Optional.of(pn);
        } else {
            // not a valid package name
            return Optional.empty();
        }
    }

    
Maps the relative path of an entry in an exploded module to a package
name.
Throws:
InvalidModuleDescriptorException – if the name is a class file in
        the top-level directory (and it's not module-info.class)/**
     * Maps the relative path of an entry in an exploded module to a package
     * name.
     *
     * @throws InvalidModuleDescriptorException if the name is a class file in
     *         the top-level directory (and it's not module-info.class)
     */
    private Optional<String> toPackageName(Path file) {
        assert file.getRoot() == null;

        Path parent = file.getParent();
        if (parent == null) {
            String name = file.toString();
            if (name.endsWith(".class") && !name.equals(MODULE_INFO)) {
                String msg = name + " found in top-level directory"
                             + " (unnamed package not allowed in module)";
                throw new InvalidModuleDescriptorException(msg);
            }
            return Optional.empty();
        }

        String pn = parent.toString().replace(File.separatorChar, '.');
        if (Checks.isPackageName(pn)) {
            return Optional.of(pn);
        } else {
            // not a valid package name
            return Optional.empty();
        }
    }

    
Returns true if the given file exists and is a hidden file
/**
     * Returns true if the given file exists and is a hidden file
     */
    private boolean isHidden(Path file) {
        try {
            return Files.isHidden(file);
        } catch (IOException ioe) {
            return false;
        }
    }


    
Return true if a path locates a path in the default file system
/**
     * Return true if a path locates a path in the default file system
     */
    private boolean isDefaultFileSystem(Path path) {
        return path.getFileSystem().provider()
                .getScheme().equalsIgnoreCase("file");
    }


    private static final PerfCounter scanTime
        = PerfCounter.newPerfCounter("jdk.module.finder.modulepath.scanTime");
    private static final PerfCounter moduleCount
        = PerfCounter.newPerfCounter("jdk.module.finder.modulepath.modules");
}