/*

 * Copyright (c) 2016, 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.File;

import java.io.IOException;

import java.nio.file.FileSystem;

import java.nio.file.Files;

import java.nio.file.NoSuchFileException;

import java.nio.file.Path;

import java.nio.file.attribute.BasicFileAttributes;

/**

 * A helper class to support working with resources in modules. Also provides

 * support for translating resource names to file paths.

 */

public final class Resources {

    private Resources() { }

    /**

     * Return true if a resource can be encapsulated. Resource with names

     * ending in ".class" or "/" cannot be encapsulated. Resource names

     * that map to a legal package name can be encapsulated.

     */

    public static boolean canEncapsulate(String name) {

        int len = name.length();

        if (len > 6 && name.endsWith(".class")) {

            return false;

        } else {

            return Checks.isPackageName(toPackageName(name));

        }

    }

    /**

     * Derive a <em>package name</em> for a resource. The package name

     * returned by this method may not be a legal package name. This method

     * returns null if the resource name ends with a "/" (a directory)

     * or the resource name does not contain a "/".

     */

    public static String toPackageName(String name) {

        int index = name.lastIndexOf('/');

        if (index == -1 || index == name.length()-1) {

            return "";

        } else {

            return name.substring(0, index).replace('/', '.');

        }

    }

    /**

     * Returns a resource name corresponding to the relative file path

     * between {@code dir} and {@code file}. If the file is a directory

     * then the name will end with a  "/", except the top-level directory

     * where the empty string is returned.

     */

    public static String toResourceName(Path dir, Path file) {

        String s = dir.relativize(file)

                      .toString()

                      .replace(File.separatorChar, '/');

        if (!s.isEmpty() && Files.isDirectory(file))

            s += "/";

        return s;

    }

    /**

     * Returns a file path to a resource in a file tree. If the resource

     * name has a trailing "/" then the file path will locate a directory.

     * Returns {@code null} if the resource does not map to a file in the

     * tree file.

     */

    public static Path toFilePath(Path dir, String name) throws IOException {

        boolean expectDirectory = name.endsWith("/");

        if (expectDirectory) {

            name = name.substring(0, name.length() - 1);  // drop trailing "/"

        }

        Path path = toSafeFilePath(dir.getFileSystem(), name);

        if (path != null) {

            Path file = dir.resolve(path);

            try {

                BasicFileAttributes attrs;

                attrs = Files.readAttributes(file, BasicFileAttributes.class);

                if (attrs.isDirectory()

                    || (!attrs.isDirectory() && !expectDirectory))

                    return file;

            } catch (NoSuchFileException ignore) { }

        }

        return null;

    }

    /**

     * Map a resource name to a "safe" file path. Returns {@code null} if

     * the resource name cannot be converted into a "safe" file path.

     *

     * Resource names with empty elements, or elements that are "." or ".."

     * are rejected, as are resource names that translates to a file path

     * with a root component.

     */

    private static Path toSafeFilePath(FileSystem fs, String name) {

        // scan elements of resource name

        int next;

        int off = 0;

        while ((next = name.indexOf('/', off)) != -1) {

            int len = next - off;

            if (!mayTranslate(name, off, len)) {

                return null;

            }

            off = next + 1;

        }

        int rem = name.length() - off;

        if (!mayTranslate(name, off, rem)) {

            return null;

        }

        // convert to file path

        Path path;

        if (File.separatorChar == '/') {

            path = fs.getPath(name);

        } else {

            // not allowed to embed file separators

            if (name.contains(File.separator))

                return null;

            path = fs.getPath(name.replace('/', File.separatorChar));

        }

        // file path not allowed to have root component

        return (path.getRoot() == null) ? path : null;

    }

    /**

     * Returns {@code true} if the element in a resource name is a candidate

     * to translate to the element of a file path.

     */

    private static boolean mayTranslate(String name, int off, int len) {

        if (len <= 2) {

            if (len == 0)

                return false;

            boolean starsWithDot = (name.charAt(off) == '.');

            if (len == 1 && starsWithDot)

                return false;

            if (len == 2 && starsWithDot && (name.charAt(off+1) == '.'))

                return false;

        }

        return true;

    }

}