/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 com.actiontech.dble.memory.environment;


/**
 * An enumeration indicating the operating system that the JVM runs on.
 */

public enum OperatingSystem {

    LINUX,
    WINDOWS,
    MAC_OS,
    FREE_BSD,
    UNKNOWN;

    // ------------------------------------------------------------------------

    /**
     * Gets the operating system that the JVM runs on from the java system properties.
     * this method returns <tt>UNKNOWN</tt>, if the operating system was not successfully determined.
     *
     * @return The enum constant for the operating system, or <tt>UNKNOWN</tt>, if it was not possible to determine.
     */
    public static OperatingSystem getCurrentOperatingSystem() {
        return OS;
    }

    /**
     * Checks whether the operating system this JVM runs on is Windows.
     *
     * @return <code>true</code> if the operating system this JVM runs on is
     * Windows, <code>false</code> otherwise
     */
    public static boolean isWindows() {
        return getCurrentOperatingSystem() == WINDOWS;
    }

    /**
     * Checks whether the operating system this JVM runs on is Linux.
     *
     * @return <code>true</code> if the operating system this JVM runs on is
     * Linux, <code>false</code> otherwise
     */
    public static boolean isLinux() {
        return getCurrentOperatingSystem() == LINUX;
    }

    /**
     * Checks whether the operating system this JVM runs on is Windows.
     *
     * @return <code>true</code> if the operating system this JVM runs on is
     * Windows, <code>false</code> otherwise
     */
    public static boolean isMac() {
        return getCurrentOperatingSystem() == MAC_OS;
    }

    /**
     * Checks whether the operating system this JVM runs on is FreeBSD.
     *
     * @return <code>true</code> if the operating system this JVM runs on is
     * FreeBSD, <code>false</code> otherwise
     */
    public static boolean isFreeBSD() {
        return getCurrentOperatingSystem() == FREE_BSD;
    }

    /**
     * The enum constant for the operating system.
     */
    private static final OperatingSystem OS = readOSFromSystemProperties();

    /**
     * Parses the operating system that the JVM runs on from the java system properties.
     * If the operating system was not successfully determined, this method returns {@code UNKNOWN}.
     *
     * @return The enum constant for the operating system, or {@code UNKNOWN}, if it was not possible to determine.
     */
    private static OperatingSystem readOSFromSystemProperties() {
        String osName = System.getProperty(OS_KEY);

        if (osName.startsWith(LINUX_OS_PREFIX)) {
            return LINUX;
        }
        if (osName.startsWith(WINDOWS_OS_PREFIX)) {
            return WINDOWS;
        }
        if (osName.startsWith(MAC_OS_PREFIX)) {
            return MAC_OS;
        }
        if (osName.startsWith(FREEBSD_OS_PREFIX)) {
            return FREE_BSD;
        }

        return UNKNOWN;
    }

    // --------------------------------------------------------------------------------------------
    //  Constants to extract the OS type from the java environment
    // --------------------------------------------------------------------------------------------

    /**
     * The key to extract the operating system name from the system properties.
     */
    private static final String OS_KEY = "os.name";

    /**
     * The expected prefix for Linux operating systems.
     */
    private static final String LINUX_OS_PREFIX = "Linux";

    /**
     * The expected prefix for Windows operating systems.
     */
    private static final String WINDOWS_OS_PREFIX = "Windows";

    /**
     * The expected prefix for Mac OS operating systems.
     */
    private static final String MAC_OS_PREFIX = "Mac";

    /**
     * The expected prefix for FreeBSD.
     */
    private static final String FREEBSD_OS_PREFIX = "FreeBSD";
}
