/*
 * Copyright (c) 2005, 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 javax.lang.model;

import java.util.Collections;
import java.util.Set;
import java.util.HashSet;

/**
 * Source versions of the Java programming language.
 *
 * See the appropriate edition of
 * <cite>The Java Language Specification</cite>
 * for information about a particular source version.
 *
 * <p>Note that additional source version constants will be added to
 * model future releases of the language.
 *
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @since 1.6
 */
public enum SourceVersion {
    /*
     * Summary of language evolution
     * 1.1: nested classes
     * 1.2: strictfp
     * 1.3: no changes
     * 1.4: assert
     * 1.5: annotations, generics, autoboxing, var-args...
     * 1.6: no changes
     * 1.7: diamond syntax, try-with-resources, etc.
     * 1.8: lambda expressions and default methods
     *   9: modules, small cleanups to 1.7 and 1.8 changes
     *  10: local-variable type inference (var)
     *  11: local-variable syntax for lambda parameters
     *  12: no changes (switch expressions in preview)
     *  13: no changes (switch expressions and text blocks in preview)
     *  14: switch expressions (pattern matching and records in
     *      preview, text blocks in preview again)
     *  15: text blocks (records and pattern matching in preview again)
     */

    /**
     * The original version.
     *
     * The language described in
     * <cite>The Java Language Specification, First Edition</cite>.
     */
    RELEASE_0,

    /**
     * The version recognized by the Java Platform 1.1.
     *
     * The language is {@code RELEASE_0} augmented with nested classes as described in the 1.1 update to
     * <cite>The Java Language Specification, First Edition</cite>.
     */
    RELEASE_1,

    /**
     * The version recognized by the Java 2 Platform, Standard Edition,
     * v 1.2.
     *
     * The language described in
     * <cite>The Java Language Specification,
     * Second Edition</cite>, which includes the {@code
     * strictfp} modifier.
     */
    RELEASE_2,

    /**
     * The version recognized by the Java 2 Platform, Standard Edition,
     * v 1.3.
     *
     * No major changes from {@code RELEASE_2}.
     */
    RELEASE_3,

    /**
     * The version recognized by the Java 2 Platform, Standard Edition,
     * v 1.4.
     *
     * Added a simple assertion facility.
     */
    RELEASE_4,

    /**
     * The version recognized by the Java 2 Platform, Standard
     * Edition 5.0.
     *
     * The language described in
     * <cite>The Java Language Specification,
     * Third Edition</cite>.  First release to support
     * generics, annotations, autoboxing, var-args, enhanced {@code
     * for} loop, and hexadecimal floating-point literals.
     */
    RELEASE_5,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 6.
     *
     * No major changes from {@code RELEASE_5}.
     */
    RELEASE_6,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 7.
     *
     * Additions in this release include, diamond syntax for
     * constructors, {@code try}-with-resources, strings in switch,
     * binary literals, and multi-catch.
     * @since 1.7
     */
    RELEASE_7,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 8.
     *
     * Additions in this release include lambda expressions and default methods.
     * @since 1.8
     */
    RELEASE_8,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 9.
     *
     * Additions in this release include modules and removal of a
     * single underscore from the set of legal identifier names.
     *
     * @since 9
     */
     RELEASE_9,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 10.
     *
     * Additions in this release include local-variable type inference
     * ({@code var}).
     *
     * @since 10
     */
    RELEASE_10,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 11.
     *
     * Additions in this release include local-variable syntax for
     * lambda parameters.
     *
     * @since 11
     */
    RELEASE_11,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 12.
     *
     * @since 12
     */
    RELEASE_12,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 13.
     *
     * @since 13
     */
    RELEASE_13,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 14.
     *
     * Additions in this release include switch expressions.
     *
     * @since 14
     */
    RELEASE_14,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 15.
     *
     * Additions in this release include text blocks.
     *
     * @since 15
     */
    RELEASE_15,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 16.
     *
     * @since 16
     */
    RELEASE_16;

    // Note that when adding constants for newer releases, the
    // behavior of latest() and latestSupported() must be updated too.

    /**
     * Returns the latest source version that can be modeled.
     *
     * @return the latest source version that can be modeled
     */
    public static SourceVersion latest() {
        return RELEASE_16;
    }

    private static final SourceVersion latestSupported = getLatestSupported();

    /*
     * The integer version to enum constant mapping implemented by
     * this method assumes the JEP 322: "Time-Based Release
     * Versioning" scheme is in effect. This scheme began in JDK
     * 10. If the JDK versioning scheme is revised, this method may
     * need to be updated accordingly.
     */
    private static SourceVersion getLatestSupported() {
        int intVersion = Runtime.version().feature();
        return (intVersion >= 11) ?
            valueOf("RELEASE_" + Math.min(16, intVersion)):
            RELEASE_10;
    }

    /**
     * Returns the latest source version fully supported by the
     * current execution environment.  {@code RELEASE_9} or later must
     * be returned.
     *
     * @apiNote This method is included alongside {@link latest} to
     * allow identification of situations where the language model API
     * is running on a platform version different than the latest
     * version modeled by the API. One way that sort of situation can
     * occur is if an IDE or similar tool is using the API to model
     * source version <i>N</i> while running on platform version
     * (<i>N</i>&nbsp;-&nbsp;1). Running in this configuration is
     * supported by the API. Running an API on platform versions
     * earlier than (<i>N</i>&nbsp;-&nbsp;1) or later than <i>N</i>
     * may or may not work as an implementation detail. If an
     * annotation processor was generating code to run under the
     * current execution environment, the processor should only use
     * platform features up to the {@code latestSupported} release,
     * which may be earlier than the {@code latest} release.
     *
     * @return the latest source version that is fully supported
     */
    public static SourceVersion latestSupported() {
        return latestSupported;
    }

    /**
     * Returns whether or not {@code name} is a syntactically valid
     * identifier (simple name) or keyword in the latest source
     * version.  The method returns {@code true} if the name consists
     * of an initial character for which {@link
     * Character#isJavaIdentifierStart(int)} returns {@code true},
     * followed only by characters for which {@link
     * Character#isJavaIdentifierPart(int)} returns {@code true}.
     * This pattern matches regular identifiers, keywords, restricted
     * keywords, restricted identifiers and the literals {@code "true"},
     * {@code "false"}, {@code "null"}.
     *
     * The method returns {@code false} for all other strings.
     *
     * @param name the string to check
     * @return {@code true} if this string is a
     * syntactically valid identifier or keyword, {@code false}
     * otherwise.
     *
     * @jls 3.8 Identifiers
     */
    public static boolean isIdentifier(CharSequence name) {
        String id = name.toString();

        if (id.length() == 0) {
            return false;
        }
        int cp = id.codePointAt(0);
        if (!Character.isJavaIdentifierStart(cp)) {
            return false;
        }
        for (int i = Character.charCount(cp);
                i < id.length();
                i += Character.charCount(cp)) {
            cp = id.codePointAt(i);
            if (!Character.isJavaIdentifierPart(cp)) {
                return false;
            }
        }
        return true;
    }

    /**
     * Returns whether or not {@code name} is a syntactically valid
     * qualified name in the latest source version.
     *
     * Syntactically, a qualified name is a sequence of identifiers
     * separated by period characters ("{@code .}"). This method
     * splits the input string into period-separated segments and
     * applies checks to each segment in turn.
     *
     * Unlike {@link #isIdentifier isIdentifier}, this method returns
     * {@code false} for keywords, boolean literals, and the null
     * literal in any segment.
     *
     * This method returns {@code true} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>.
     *
     * @param name the string to check
     * @return {@code true} if this string is a
     * syntactically valid name, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 6.2 Names and Identifiers
     */
    public static boolean isName(CharSequence name) {
        return isName(name, latest());
    }

    /**
     * Returns whether or not {@code name} is a syntactically valid
     * qualified name in the given source version.
     *
     * Syntactically, a qualified name is a sequence of identifiers
     * separated by period characters ("{@code .}"). This method
     * splits the input string into period-separated segments and
     * applies checks to each segment in turn.
     *
     * Unlike {@link #isIdentifier isIdentifier}, this method returns
     * {@code false} for keywords, boolean literals, and the null
     * literal in any segment.
     *
     * This method returns {@code true} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>.
     *
     * @param name the string to check
     * @param version the version to use
     * @return {@code true} if this string is a
     * syntactically valid name, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 6.2 Names and Identifiers
     * @since 9
     */
    public static boolean isName(CharSequence name, SourceVersion version) {
        String id = name.toString();

        for(String s : id.split("\\.", -1)) {
            if (!isIdentifier(s) || isKeyword(s, version))
                return false;
        }
        return true;
    }

    /**
     * Returns whether or not {@code s} is a keyword, boolean literal,
     * or null literal in the latest source version.
     * This method returns {@code false} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>.
     *
     * @param s the string to check
     * @return {@code true} if {@code s} is a keyword, or boolean
     * literal, or null literal, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 3.10.3 Boolean Literals
     * @jls 3.10.7 The Null Literal
     */
    public static boolean isKeyword(CharSequence s) {
        return isKeyword(s, latest());
    }

    /**
     * Returns whether or not {@code s} is a keyword, boolean literal,
     * or null literal in the given source version.
     * This method returns {@code false} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>.
     *
     * @param s the string to check
     * @param version the version to use
     * @return {@code true} if {@code s} is a keyword, or boolean
     * literal, or null literal, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 3.10.3 Boolean Literals
     * @jls 3.10.7 The Null Literal
     * @since 9
     */
    public static boolean isKeyword(CharSequence s, SourceVersion version) {
        String id = s.toString();
        switch(id) {
            // A trip through history
        case "strictfp":
            return version.compareTo(RELEASE_2) >= 0;

        case "assert":
            return version.compareTo(RELEASE_4) >= 0;

        case "enum":
            return version.compareTo(RELEASE_5) >= 0;

        case "_":
            return version.compareTo(RELEASE_9) >= 0;

     // case "non-sealed": can be added once it is a keyword only
     // dependent on release and not also preview features being
     // enabled.

            // Keywords common across versions

            // Modifiers
        case "public":    case "protected": case "private":
        case "abstract":  case "static":    case "final":
        case "transient": case "volatile":  case "synchronized":
        case "native":

            // Declarations
        case "class":     case "interface": case "extends":
        case "package":   case "throws":    case "implements":

            // Primitive types and void
        case "boolean":   case "byte":      case "char":
        case "short":     case "int":       case "long":
        case "float":     case "double":
        case "void":

            // Control flow
        case "if":      case "else":
        case "try":     case "catch":    case "finally":
        case "do":      case "while":
        case "for":     case "continue":
        case "switch":  case "case":     case "default":
        case "break":   case "throw":    case "return":

            // Other keywords
        case  "this":   case "new":      case "super":
        case "import":  case "instanceof":

            // Forbidden!
        case "goto":        case "const":

            // literals
        case "null":         case "true":       case "false":
            return true;

        default:
            return false;
        }
    }
}