/*
 * Copyright (C) 2012 The Guava Authors
 * Copyright 2020-2022 Equinix, Inc
 * Copyright 2014-2022 The Billing Project, LLC
 *
 * The Billing Project 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 org.killbill.commons.utils;

import javax.annotation.CheckForNull;

public enum StandardSystemProperty {

    /** Java Runtime Environment version. */
    JAVA_VERSION("java.version"),

    /** Java Runtime Environment vendor. */
    JAVA_VENDOR("java.vendor"),

    /** Java vendor URL. */
    JAVA_VENDOR_URL("java.vendor.url"),

    /** Java installation directory. */
    JAVA_HOME("java.home"),

    /** Java Virtual Machine specification version. */
    JAVA_VM_SPECIFICATION_VERSION("java.vm.specification.version"),

    /** Java Virtual Machine specification vendor. */
    JAVA_VM_SPECIFICATION_VENDOR("java.vm.specification.vendor"),

    /** Java Virtual Machine specification name. */
    JAVA_VM_SPECIFICATION_NAME("java.vm.specification.name"),

    /** Java Virtual Machine implementation version. */
    JAVA_VM_VERSION("java.vm.version"),

    /** Java Virtual Machine implementation vendor. */
    JAVA_VM_VENDOR("java.vm.vendor"),

    /** Java Virtual Machine implementation name. */
    JAVA_VM_NAME("java.vm.name"),

    /** Java Runtime Environment specification version. */
    JAVA_SPECIFICATION_VERSION("java.specification.version"),

    /** Java Runtime Environment specification vendor. */
    JAVA_SPECIFICATION_VENDOR("java.specification.vendor"),

    /** Java Runtime Environment specification name. */
    JAVA_SPECIFICATION_NAME("java.specification.name"),

    /** Java class format version number. */
    JAVA_CLASS_VERSION("java.class.version"),

    /** Java class path. */
    JAVA_CLASS_PATH("java.class.path"),

    /** List of paths to search when loading libraries. */
    JAVA_LIBRARY_PATH("java.library.path"),

    /** Default temp file path. */
    JAVA_IO_TMPDIR("java.io.tmpdir"),

    /** Name of JIT compiler to use. */
    JAVA_COMPILER("java.compiler"),

    /**
     * Path of extension directory or directories.
     *
     * @deprecated This property was <a
     *     href="https://openjdk.java.net/jeps/220#Removed:-The-extension-mechanism">deprecated</a> in
     *     Java 8 and removed in Java 9. We do not plan to remove this API from Guava, but if you are
     *     using it, it is probably not doing what you want.
     */
    @Deprecated
    JAVA_EXT_DIRS("java.ext.dirs"),

    /** Operating system name. */
    OS_NAME("os.name"),

    /** Operating system architecture. */
    OS_ARCH("os.arch"),

    /** Operating system version. */
    OS_VERSION("os.version"),

    /** File separator ("/" on UNIX). */
    FILE_SEPARATOR("file.separator"),

    /** Path separator (":" on UNIX). */
    PATH_SEPARATOR("path.separator"),

    /** Line separator ("\n" on UNIX). */
    LINE_SEPARATOR("line.separator"),

    /** User's account name. */
    USER_NAME("user.name"),

    /** User's home directory. */
    USER_HOME("user.home"),

    /** User's current working directory. */
    USER_DIR("user.dir");

    private final String key;

    StandardSystemProperty(String key) {
        this.key = key;
    }

    /** Returns the key used to lookup this system property. */
    public String key() {
        return key;
    }

    /**
     * Returns the current value for this system property by delegating to {@link
     * System#getProperty(String)}.
     *
     * <p>The value returned by this method is non-null except in rare circumstances:
     *
     * <ul>
     *   <li>{@link #JAVA_EXT_DIRS} was deprecated in Java 8 and removed in Java 9. We have not
     *       confirmed whether it is available under older versions.
     *   <li>{@link #JAVA_COMPILER}, while still listed as required as of Java 15, is typically not
     *       available even under older version.
     *   <li>Any property may be cleared through APIs like {@link System#clearProperty}.
     *   <li>Unusual environments like GWT may have their own special handling of system properties.
     * </ul>
     *
     * <p>Note that {@code StandardSystemProperty} does not provide constants for more recently added
     * properties, including:
     *
     * <ul>
     *   <li>{@code java.vendor.version} (added in Java 11, listed as optional as of Java 13)
     *   <li>{@code jdk.module.*} (added in Java 9, optional)
     * </ul>
     */
    @CheckForNull
    public String value() {
        return System.getProperty(key);
    }

    /** Returns a string representation of this system property. */
    @Override
    public String toString() {
        return key() + "=" + value();
    }
}
