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 * Copyright (c) 2014, 2016, 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

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 */

package java.lang.module;

import java.io.File;

import java.io.FilePermission;

import java.nio.file.Files;

import java.nio.file.Path;

import java.nio.file.Paths;

import java.security.AccessController;

import java.security.Permission;

import java.security.PrivilegedAction;

import java.util.Collections;

import java.util.Objects;

import java.util.Optional;

import java.util.Set;

import java.util.stream.Collectors;

import java.util.stream.Stream;

/**

 * A finder of modules. A {@code ModuleFinder} is used to find modules during

 * <a href="Configuration.html#resolution">resolution</a> or

 * <a href="Configuration.html#servicebinding">service binding</a>.

 *

 * <p> A {@code ModuleFinder} can only find one module with a given name. A

 * {@code ModuleFinder} that finds modules in a sequence of directories, for

 * example, will locate the first occurrence of a module of a given name and

 * will ignore other modules of that name that appear in directories later in

 * the sequence. </p>

 *

 * <p> Example usage: </p>

 *

 * <pre>{@code

 *     Path dir1, dir2, dir3;

 *

 *     ModuleFinder finder = ModuleFinder.of(dir1, dir2, dir3);

 *

 *     Optional<ModuleReference> omref = finder.find("jdk.foo");

 *     if (omref.isPresent()) { ... }

 *

 * }</pre>

 *

 * <p> The {@link #find(String) find} and {@link #findAll() findAll} methods

 * defined here can fail for several reasons. These include include I/O errors,

 * errors detected parsing a module descriptor ({@code module-info.class}), or

 * in the case of {@code ModuleFinder} returned by {@link #of ModuleFinder.of},

 * that two or more modules with the same name are found in a directory.

 * When an error is detected then these methods throw {@link FindException

 * FindException} with an appropriate {@link Throwable#getCause cause}.

 * The behavior of a {@code ModuleFinder} after a {@code FindException} is

 * thrown is undefined. For example, invoking {@code find} after an exception

 * is thrown may or may not scan the same modules that lead to the exception.

 * It is recommended that a module finder be discarded after an exception is

 * thrown. </p>

 *

 * <p> A {@code ModuleFinder} is not required to be thread safe. </p>

 *

 * @since 9

 */

public interface ModuleFinder {

    /**

     * Finds a reference to a module of a given name.

     *

     * <p> A {@code ModuleFinder} provides a consistent view of the

     * modules that it locates. If {@code find} is invoked several times to

     * locate the same module (by name) then it will return the same result

     * each time. If a module is located then it is guaranteed to be a member

     * of the set of modules returned by the {@link #findAll() findAll}

     * method. </p>

     *

     * @param  name

     *         The name of the module to find

     *

     * @return A reference to a module with the given name or an empty

     *         {@code Optional} if not found

     *

     * @throws FindException

     *         If an error occurs finding the module

     *

     * @throws SecurityException

     *         If denied by the security manager

     */

    Optional<ModuleReference> find(String name);

    /**

     * Returns the set of all module references that this finder can locate.

     *

     * <p> A {@code ModuleFinder} provides a consistent view of the modules

     * that it locates. If {@link #findAll() findAll} is invoked several times

     * then it will return the same (equals) result each time. For each {@code

     * ModuleReference} element in the returned set then it is guaranteed that

     * {@link #find find} will locate the {@code ModuleReference} if invoked

     * to find that module. </p>

     *

     * @apiNote This is important to have for methods such as {@link

     * Configuration#resolveRequiresAndUses resolveRequiresAndUses} that need

     * to scan the module path to find modules that provide a specific service.

     *

     * @return The set of all module references that this finder locates

     *

     * @throws FindException

     *         If an error occurs finding all modules

     *

     * @throws SecurityException

     *         If denied by the security manager

     */

    Set<ModuleReference> findAll();

    /**

     * Returns a module finder that locates the <em>system modules</em>. The

     * system modules are typically linked into the Java run-time image.

     * The module finder will always find {@code java.base}.

     *

     * <p> If there is a security manager set then its {@link

     * SecurityManager#checkPermission(Permission) checkPermission} method is

     * invoked to check that the caller has been granted {@link FilePermission}

     * to recursively read the directory that is the value of the system

     * property {@code java.home}. </p>

     *

     * @return A {@code ModuleFinder} that locates the system modules

     *

     * @throws SecurityException

     *         If denied by the security manager

     */

    static ModuleFinder ofSystem() {

        String home;

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            home = AccessController.doPrivileged(pa);

            Permission p = new FilePermission(home + File.separator + "-", "read");

            sm.checkPermission(p);

        } else {

            home = System.getProperty("java.home");

        }

        Path modules = Paths.get(home, "lib", "modules");

        if (Files.isRegularFile(modules)) {

            return new SystemModuleFinder();

        } else {

            Path mlib = Paths.get(home, "modules");

            if (Files.isDirectory(mlib)) {

                return of(mlib);

            } else {

                throw new InternalError("Unable to detect the run-time image");

            }

        }

    }

    /**

     * Returns a module finder that locates modules on the file system by

     * searching a sequence of directories and/or packaged modules.

     *

     * Each element in the given array is one of:

     * <ol>

     *     <li><p> A path to a directory of modules.</p></li>

     *     <li><p> A path to the <em>top-level</em> directory of an

     *         <em>exploded module</em>. </p></li>

     *     <li><p> A path to a <em>packaged module</em>. </p></li>

     * </ol>

     *

     * The module finder locates modules by searching each directory, exploded

     * module, or packaged module in array index order. It finds the first

     * occurrence of a module with a given name and ignores other modules of

     * that name that appear later in the sequence.

     *

     * <p> If an element is a path to a directory of modules then each entry in

     * the directory is a packaged module or the top-level directory of an

     * exploded module. The module finder's {@link #find(String) find} or

     * {@link #findAll() findAll} methods throw {@link FindException} if a

     * directory containing more than one module with the same name is

     * encountered. </p>

     *

     * <p> If an element in the array is a path to a directory, and that

     * directory contains a file named {@code module-info.class}, then the

     * directory is treated as an exploded module rather than a directory of

     * modules. </p>

     *

     * <p> The module finder returned by this method supports modules that are

     * packaged as JAR files. A JAR file with a {@code module-info.class} in

     * the top-level directory of the JAR file is a modular JAR and is an

     * <em>explicit module</em>. A JAR file that does not have a {@code

     * module-info.class} in the top-level directory is an {@link

     * ModuleDescriptor#isAutomatic automatic} module. The {@link

     * ModuleDescriptor} for an automatic module is created as follows:

     *

     * <ul>

     *

     *     <li><p> The module {@link ModuleDescriptor#name() name}, and {@link

     *     ModuleDescriptor#version() version} if applicable, is derived from

     *     the file name of the JAR file as follows: </p>

     *

     *     <ul>

     *

     *         <li><p> The {@code .jar} suffix is removed. </p></li>

     *

     *         <li><p> If the name matches the regular expression {@code

     *         "-(\\d+(\\.|$))"} then the module name will be derived from the

     *         subsequence proceeding the hyphen of the first occurrence. The

     *         subsequence after the hyphen is parsed as a {@link

     *         ModuleDescriptor.Version} and ignored if it cannot be parsed as

     *         a {@code Version}. </p></li>

     *

     *         <li><p> For the module name, then all non-alphanumeric

     *         characters ({@code [^A-Za-z0-9])} are replaced with a dot

     *         ({@code "."}), all repeating dots are replaced with one dot,

     *         and all leading and trailing dots are removed. </p></li>

     *

     *         <li><p> As an example, a JAR file named {@code foo-bar.jar} will

     *         derive a module name {@code foo.bar} and no version. A JAR file

     *         named {@code foo-1.2.3-SNAPSHOT.jar} will derive a module name

     *         {@code foo} and {@code 1.2.3-SNAPSHOT} as the version. </p></li>

     *

     *     </ul></li>

     *

     *     <li><p> It {@link ModuleDescriptor#requires() requires} {@code

     *     java.base}. </p></li>

     *

     *     <li><p> All entries in the JAR file with names ending with {@code

     *     .class} are assumed to be class files where the name corresponds

     *     to the fully qualified name of the class. The packages of all

     *     classes are {@link ModuleDescriptor#exports() exported}. </p></li>

     *

     *     <li><p> The contents of all entries starting with {@code

     *     META-INF/services/} are assumed to be service configuration files

     *     (see {@link java.util.ServiceLoader}). The name of the file

     *     (that follows {@code META-INF/services/}) is assumed to be the

     *     fully-qualified binary name of a service type. The entries in the

     *     file are assumed to be the fully-qualified binary names of

     *     provider classes. </p></li>

     *

     *     <li><p> If the JAR file has a {@code Main-Class} attribute in its

     *     main manifest then its value is the {@link

     *     ModuleDescriptor#mainClass() main class}. </p></li>

     *

     * </ul>

     *

     * <p> In addition to JAR files, an implementation may also support modules

     * that are packaged in other implementation specific module formats. As

     * with automatic modules, the contents of a packaged or exploded module

     * may need to be <em>scanned</em> in order to determine the packages in

     * the module. If a {@code .class} file that corresponds to a class in an

     * unnamed package is encountered then {@code FindException} is thrown. </p>

     *

     * <p> Finders created by this method are lazy and do not eagerly check

     * that the given file paths are directories or packaged modules.

     * Consequently, the {@code find} or {@code findAll} methods will only

     * fail if invoking these methods results in searching a directory or

     * packaged module and an error is encountered. Paths to files that do not

     * exist are ignored. </p>

     *

     * @param entries

     *        A possibly-empty array of paths to directories of modules

     *        or paths to packaged or exploded modules

     *

     * @return A {@code ModuleFinder} that locates modules on the file system

     */

    static ModuleFinder of(Path... entries) {

        return new ModulePath(entries);

    }

    /**

     * Returns a module finder that is the equivalent to composing two

     * module finders. The resulting finder will locate modules references

     * using {@code first}; if not found then it will attempt to locate module

     * references using {@code second}.

     *

     * <p> The {@link #findAll() findAll} method of the resulting module finder

     * will locate all modules located by the first module finder. It will

     * also locate all modules located by the second module finder that are not

     * located by the first module finder. </p>

     *

     * @apiNote This method will eventually be changed to take a sequence of

     *          module finders.

     *

     * @param first

     *        The first module finder

     * @param second

     *        The second module finder

     *

     * @return A {@code ModuleFinder} that composes two module finders

     */

    static ModuleFinder compose(ModuleFinder first, ModuleFinder second) {

        Objects.requireNonNull(first);

        Objects.requireNonNull(second);

        return new ModuleFinder() {

            Set<ModuleReference> allModules;

            @Override

            public Optional<ModuleReference> find(String name) {

                Optional<ModuleReference> om = first.find(name);

                if (!om.isPresent())

                    om = second.find(name);

                return om;

            }

            @Override

            public Set<ModuleReference> findAll() {

                if (allModules == null) {

                    allModules = Stream.concat(first.findAll().stream(),

                                               second.findAll().stream())

                                       .map(a -> a.descriptor().name())

                                       .distinct()

                                       .map(this::find)

                                       .map(Optional::get)

                                       .collect(Collectors.toSet());

                }

                return allModules;

            }

        };

    }

    /**

     * Returns an empty module finder.  The empty finder does not find any

     * modules.

     *

     * @apiNote This is useful when using methods such as {@link

     * Configuration#resolveRequires resolveRequires} where two finders are

     * specified. An alternative is {@code ModuleFinder.of()}.

     *

     * @return A {@code ModuleFinder} that does not find any modules

     */

    static ModuleFinder empty() {

        // an alternative implementation of ModuleFinder.of()

        return new ModuleFinder() {

            @Override public Optional<ModuleReference> find(String name) {

                Objects.requireNonNull(name);

                return Optional.empty();

            }

            @Override public Set<ModuleReference> findAll() {

                return Collections.emptySet();

            }

        };

    }

}