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import java.nio.file.*;

import java.nio.file.attribute.*;

import static java.nio.file.attribute.PosixFilePermission.*;

import static java.nio.file.FileVisitResult.*;

import java.io.IOException;

import java.util.*;

/**

 * Sample code that changes the permissions of files in a similar manner to the

 * chmod(1) program.

 */

public class Chmod {

    /**

     * Compiles a list of one or more <em>symbolic mode expressions</em> that

     * may be used to change a set of file permissions. This method is

     * intended for use where file permissions are required to be changed in

     * a manner similar to the UNIX <i>chmod</i> program.

     *

     * <p> The {@code exprs} parameter is a comma separated list of expressions

     * where each takes the form:

     * <blockquote>

     * <i>who operator</i> [<i>permissions</i>]

     * </blockquote>

     * where <i>who</i> is one or more of the characters {@code 'u'}, {@code 'g'},

     * {@code 'o'}, or {@code 'a'} meaning the owner (user), group, others, or

     * all (owner, group, and others) respectively.

     *

     * <p> <i>operator</i> is the character {@code '+'}, {@code '-'}, or {@code

     * '='} signifying how permissions are to be changed. {@code '+'} means the

     * permissions are added, {@code '-'} means the permissions are removed, and

     * {@code '='} means the permissions are assigned absolutely.

     *

     * <p> <i>permissions</i> is a sequence of zero or more of the following:

     * {@code 'r'} for read permission, {@code 'w'} for write permission, and

     * {@code 'x'} for execute permission. If <i>permissions</i> is omitted

     * when assigned absolutely, then the permissions are cleared for

     * the owner, group, or others as identified by <i>who</i>. When omitted

     * when adding or removing then the expression is ignored.

     *

     * <p> The following examples demonstrate possible values for the {@code

     * exprs} parameter:

     *

     * <table border="0">

     * <tr>

     *   <td> {@code u=rw} </td>

     *   <td> Sets the owner permissions to be read and write. </td>

     * </tr>

     * <tr>

     *   <td> {@code ug+w} </td>

     *   <td> Sets the owner write and group write permissions. </td>

     * </tr>

     * <tr>

     *   <td> {@code u+w,o-rwx} </td>

     *   <td> Sets the owner write, and removes the others read, others write

     *     and others execute permissions. </td>

     * </tr>

     * <tr>

     *   <td> {@code o=} </td>

     *   <td> Sets the others permission to none (others read, others write and

     *     others execute permissions are removed if set) </td>

     * </tr>

     * </table>

     *

     * @param   exprs

     *          List of one or more <em>symbolic mode expressions</em>

     *

     * @return  A {@code Changer} that may be used to changer a set of

     *          file permissions

     *

     * @throws  IllegalArgumentException

     *          If the value of the {@code exprs} parameter is invalid

     */

    public static Changer compile(String exprs) {

        // minimum is who and operator (u= for example)

        if (exprs.length() < 2)

            throw new IllegalArgumentException("Invalid mode");

        // permissions that the changer will add or remove

        final Set<PosixFilePermission> toAdd = new HashSet<PosixFilePermission>();

        final Set<PosixFilePermission> toRemove = new HashSet<PosixFilePermission>();

        // iterate over each of expression modes

        for (String expr: exprs.split(",")) {

            // minimum of who and operator

            if (expr.length() < 2)

                throw new IllegalArgumentException("Invalid mode");

            int pos = 0;

            // who

            boolean u = false;

            boolean g = false;

            boolean o = false;

            boolean done = false;

            for (;;) {

                switch (expr.charAt(pos)) {

                    case 'u' : u = true; break;

                    case 'g' : g = true; break;

                    case 'o' : o = true; break;

                    case 'a' : u = true; g = true; o = true; break;

                    default : done = true;

                }

                if (done)

                    break;

                pos++;

            }

            if (!u && !g && !o)

                throw new IllegalArgumentException("Invalid mode");

            // get operator and permissions

            char op = expr.charAt(pos++);

            String mask = (expr.length() == pos) ? "" : expr.substring(pos);

            // operator

            boolean add = (op == '+');

            boolean remove = (op == '-');

            boolean assign = (op == '=');

            if (!add && !remove && !assign)

                throw new IllegalArgumentException("Invalid mode");

            // who= means remove all

            if (assign && mask.length() == 0) {

                assign = false;

                remove = true;

                mask = "rwx";

            }

            // permissions

            boolean r = false;

            boolean w = false;

            boolean x = false;

            for (int i=0; i<mask.length(); i++) {

                switch (mask.charAt(i)) {

                    case 'r' : r = true; break;

                    case 'w' : w = true; break;

                    case 'x' : x = true; break;

                    default:

                        throw new IllegalArgumentException("Invalid mode");

                }

            }

            // update permissions set

            if (add) {

                if (u) {

                    if (r) toAdd.add(OWNER_READ);

                    if (w) toAdd.add(OWNER_WRITE);

                    if (x) toAdd.add(OWNER_EXECUTE);

                }

                if (g) {

                    if (r) toAdd.add(GROUP_READ);

                    if (w) toAdd.add(GROUP_WRITE);

                    if (x) toAdd.add(GROUP_EXECUTE);

                }

                if (o) {

                    if (r) toAdd.add(OTHERS_READ);

                    if (w) toAdd.add(OTHERS_WRITE);

                    if (x) toAdd.add(OTHERS_EXECUTE);

                }

            }

            if (remove) {

                if (u) {

                    if (r) toRemove.add(OWNER_READ);

                    if (w) toRemove.add(OWNER_WRITE);

                    if (x) toRemove.add(OWNER_EXECUTE);

                }

                if (g) {

                    if (r) toRemove.add(GROUP_READ);

                    if (w) toRemove.add(GROUP_WRITE);

                    if (x) toRemove.add(GROUP_EXECUTE);

                }

                if (o) {

                    if (r) toRemove.add(OTHERS_READ);

                    if (w) toRemove.add(OTHERS_WRITE);

                    if (x) toRemove.add(OTHERS_EXECUTE);

                }

            }

            if (assign) {

                if (u) {

                    if (r) toAdd.add(OWNER_READ);

                      else toRemove.add(OWNER_READ);

                    if (w) toAdd.add(OWNER_WRITE);

                      else toRemove.add(OWNER_WRITE);

                    if (x) toAdd.add(OWNER_EXECUTE);

                      else toRemove.add(OWNER_EXECUTE);

                }

                if (g) {

                    if (r) toAdd.add(GROUP_READ);

                      else toRemove.add(GROUP_READ);

                    if (w) toAdd.add(GROUP_WRITE);

                      else toRemove.add(GROUP_WRITE);

                    if (x) toAdd.add(GROUP_EXECUTE);

                      else toRemove.add(GROUP_EXECUTE);

                }

                if (o) {

                    if (r) toAdd.add(OTHERS_READ);

                      else toRemove.add(OTHERS_READ);

                    if (w) toAdd.add(OTHERS_WRITE);

                      else toRemove.add(OTHERS_WRITE);

                    if (x) toAdd.add(OTHERS_EXECUTE);

                      else toRemove.add(OTHERS_EXECUTE);

                }

            }

        }

        // return changer

        return new Changer() {

            @Override

            public Set<PosixFilePermission> change(Set<PosixFilePermission> perms) {

                perms.addAll(toAdd);

                perms.removeAll(toRemove);

                return perms;

            }

        };

    }

    /**

     * A task that <i>changes</i> a set of {@link PosixFilePermission} elements.

     */

    public interface Changer {

        /**

         * Applies the changes to the given set of permissions.

         *

         * @param   perms

         *          The set of permissions to change

         *

         * @return  The {@code perms} parameter

         */

        Set<PosixFilePermission> change(Set<PosixFilePermission> perms);

    }

    /**

     * Changes the permissions of the file using the given Changer.

     */

    static void chmod(Path file, Changer changer) {

        try {

            Set<PosixFilePermission> perms = Files.getPosixFilePermissions(file);

            Files.setPosixFilePermissions(file, changer.change(perms));

        } catch (IOException x) {

            System.err.println(x);

        }

    }

    /**

     * Changes the permission of each file and directory visited

     */

    static class TreeVisitor implements FileVisitor<Path> {

        private final Changer changer;

        TreeVisitor(Changer changer) {

            this.changer = changer;

        }

        @Override

        public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) {

            chmod(dir, changer);

            return CONTINUE;

        }

        @Override

        public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) {

            chmod(file, changer);

            return CONTINUE;

        }

        @Override

        public FileVisitResult postVisitDirectory(Path dir, IOException exc) {

            if (exc != null)

                System.err.println("WARNING: " + exc);

            return CONTINUE;

        }

        @Override

        public FileVisitResult visitFileFailed(Path file, IOException exc) {

            System.err.println("WARNING: " + exc);

            return CONTINUE;

        }

    }

    static void usage() {

        System.err.println("java Chmod [-R] symbolic-mode-list file...");

        System.exit(-1);

    }

    public static void main(String[] args) throws IOException {

        if (args.length < 2)

            usage();

        int argi = 0;

        int maxDepth = 0;

        if (args[argi].equals("-R")) {

            if (args.length < 3)

                usage();

            argi++;

            maxDepth = Integer.MAX_VALUE;

        }

        // compile the symbolic mode expressions

        Changer changer = compile(args[argi++]);

        TreeVisitor visitor = new TreeVisitor(changer);

        Set<FileVisitOption> opts = Collections.emptySet();

        while (argi < args.length) {

            Path file = Paths.get(args[argi]);

            Files.walkFileTree(file, opts, maxDepth, visitor);

            argi++;

        }

    }

}