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/*
 * Copyright (C) 2015-2024 Jason van Zyl
 *
 * Licensed 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 ca.vanzyl.provisio.perms;

import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.attribute.PosixFilePermission;
import java.util.EnumSet;
import java.util.Set;

public final class PosixModes {
    static final PosixFilePermission[] PERMISSIONS = PosixFilePermission.values();

    private static final int PERMISSIONS_LENGTH = PERMISSIONS.length;
    private static final int INT_MODE_MAX = (1 << PERMISSIONS_LENGTH) - 1;

    private PosixModes() {
        throw new Error("nice try!");
    }

    /**
     * Convert an integer into a set of {@link PosixFilePermission}s
     *
     * Note that this method will not try and read {@code 755} "in octal";
     * you must prefix your integer with {@code 0} so that the
     * constant be octal, as in {@code 0755}.
     *
     * @param intMode the mode
     * @return a set of POSIX permissions
     * @throws InvalidIntModeException invalid integer mode
     *
     * @see Files#setPosixFilePermissions(Path, Set)
     */
    public static Set intModeToPosix(int intMode) {
        if ((intMode & INT_MODE_MAX) != intMode) {
            throw new RuntimeException("Invalid intMode: " + intMode);
        }
        final Set set = EnumSet.noneOf(PosixFilePermission.class);

        for (int i = 0; i < PERMISSIONS_LENGTH; i++) {
            if ((intMode & 1) == 1) {
                set.add(PERMISSIONS[PERMISSIONS_LENGTH - i - 1]);
            }
            /*
             * We're OK with >> instead of >>>, the sign bit will never be set
             */
            intMode >>= 1;
        }
        return set;
    }
}