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Rhino is an open-source implementation of JavaScript written entirely in Java. It is typically embedded into Java applications to provide scripting to end users.
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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.javascript;

import java.util.HashMap;
import java.util.Map;

/**
 * This is an implementation of the standard "Symbol" type that implements all of its weird
 * properties. One of them is that some objects can have an "internal data slot" that makes them a
 * Symbol and others cannot.
 */
public class NativeSymbol extends IdScriptableObject implements Symbol {
    private static final long serialVersionUID = -589539749749830003L;

    public static final String CLASS_NAME = "Symbol";
    public static final String TYPE_NAME = "symbol";

    private static final Object GLOBAL_TABLE_KEY = new Object();
    private static final Object CONSTRUCTOR_SLOT = new Object();

    private final SymbolKey key;
    private final NativeSymbol symbolData;

    public static void init(Context cx, Scriptable scope, boolean sealed) {
        NativeSymbol obj = new NativeSymbol("");
        ScriptableObject ctor = obj.exportAsJSClass(MAX_PROTOTYPE_ID, scope, false);

        cx.putThreadLocal(CONSTRUCTOR_SLOT, Boolean.TRUE);
        try {
            createStandardSymbol(cx, scope, ctor, "iterator", SymbolKey.ITERATOR);
            createStandardSymbol(cx, scope, ctor, "species", SymbolKey.SPECIES);
            createStandardSymbol(cx, scope, ctor, "toStringTag", SymbolKey.TO_STRING_TAG);
            createStandardSymbol(cx, scope, ctor, "hasInstance", SymbolKey.HAS_INSTANCE);
            createStandardSymbol(
                    cx, scope, ctor, "isConcatSpreadable", SymbolKey.IS_CONCAT_SPREADABLE);
            createStandardSymbol(cx, scope, ctor, "isRegExp", SymbolKey.IS_REGEXP);
            createStandardSymbol(cx, scope, ctor, "toPrimitive", SymbolKey.TO_PRIMITIVE);
            createStandardSymbol(cx, scope, ctor, "match", SymbolKey.MATCH);
            createStandardSymbol(cx, scope, ctor, "replace", SymbolKey.REPLACE);
            createStandardSymbol(cx, scope, ctor, "search", SymbolKey.SEARCH);
            createStandardSymbol(cx, scope, ctor, "split", SymbolKey.SPLIT);
            createStandardSymbol(cx, scope, ctor, "unscopables", SymbolKey.UNSCOPABLES);

        } finally {
            cx.removeThreadLocal(CONSTRUCTOR_SLOT);
        }

        if (sealed) {
            // Can't seal until we have created all the stuff above!
            ctor.sealObject();
        }
    }

    /**
     * This has to be used only for constructing the prototype instance. This sets symbolData to
     * null (see isSymbol() for more).
     *
     * @param desc the description
     */
    private NativeSymbol(String desc) {
        this.key = new SymbolKey(desc);
        this.symbolData = null;
    }

    NativeSymbol(SymbolKey key) {
        this.key = key;
        this.symbolData = this;
    }

    public NativeSymbol(NativeSymbol s) {
        this.key = s.key;
        this.symbolData = s.symbolData;
    }

    /**
     * Use this when we need to create symbols internally because of the convoluted way we have to
     * construct them.
     */
    public static NativeSymbol construct(Context cx, Scriptable scope, Object[] args) {
        cx.putThreadLocal(CONSTRUCTOR_SLOT, Boolean.TRUE);
        try {
            return (NativeSymbol) cx.newObject(scope, CLASS_NAME, args);
        } finally {
            cx.removeThreadLocal(CONSTRUCTOR_SLOT);
        }
    }

    @Override
    public String getClassName() {
        return CLASS_NAME;
    }

    @Override
    protected void fillConstructorProperties(IdFunctionObject ctor) {
        super.fillConstructorProperties(ctor);
        addIdFunctionProperty(ctor, CLASS_NAME, ConstructorId_for, "for", 1);
        addIdFunctionProperty(ctor, CLASS_NAME, ConstructorId_keyFor, "keyFor", 1);
    }

    private static void createStandardSymbol(
            Context cx, Scriptable scope, ScriptableObject ctor, String name, SymbolKey key) {
        Scriptable sym = cx.newObject(scope, CLASS_NAME, new Object[] {name, key});
        ctor.defineProperty(name, sym, DONTENUM | READONLY | PERMANENT);
    }

    @Override
    protected int findPrototypeId(String s) {
        int id = 0;
        switch (s) {
            case "constructor":
                id = Id_constructor;
                break;
            case "toString":
                id = Id_toString;
                break;
            case "valueOf":
                id = Id_valueOf;
                break;
            default:
                id = 0;
                break;
        }
        return id;
    }

    @Override
    protected int findPrototypeId(Symbol key) {
        if (SymbolKey.TO_STRING_TAG.equals(key)) {
            return SymbolId_toStringTag;
        } else if (SymbolKey.TO_PRIMITIVE.equals(key)) {
            return SymbolId_toPrimitive;
        }
        return 0;
    }

    private static final int ConstructorId_keyFor = -2,
            ConstructorId_for = -1,
            Id_constructor = 1,
            Id_toString = 2,
            Id_valueOf = 4,
            SymbolId_toStringTag = 3,
            SymbolId_toPrimitive = 5,
            MAX_PROTOTYPE_ID = SymbolId_toPrimitive;

    @Override
    protected void initPrototypeId(int id) {
        switch (id) {
            case Id_constructor:
                initPrototypeMethod(CLASS_NAME, id, "constructor", 0);
                break;
            case Id_toString:
                initPrototypeMethod(CLASS_NAME, id, "toString", 0);
                break;
            case Id_valueOf:
                initPrototypeMethod(CLASS_NAME, id, "valueOf", 0);
                break;
            case SymbolId_toStringTag:
                initPrototypeValue(id, SymbolKey.TO_STRING_TAG, CLASS_NAME, DONTENUM | READONLY);
                break;
            case SymbolId_toPrimitive:
                initPrototypeMethod(
                        CLASS_NAME, id, SymbolKey.TO_PRIMITIVE, "Symbol.toPrimitive", 1);
                break;
            default:
                super.initPrototypeId(id);
                break;
        }
    }

    @Override
    public Object execIdCall(
            IdFunctionObject f, Context cx, Scriptable scope, Scriptable thisObj, Object[] args) {
        if (!f.hasTag(CLASS_NAME)) {
            return super.execIdCall(f, cx, scope, thisObj, args);
        }
        int id = f.methodId();
        switch (id) {
            case ConstructorId_for:
                return js_for(cx, scope, args);
            case ConstructorId_keyFor:
                return js_keyFor(cx, scope, args);

            case Id_constructor:
                if (thisObj == null) {
                    if (cx.getThreadLocal(CONSTRUCTOR_SLOT) == null) {
                        // We should never get to this via "new".
                        throw ScriptRuntime.typeErrorById("msg.no.symbol.new");
                    }
                    // Unless we are being called by our own internal "new"
                    return js_constructor(args);
                }
                return construct(cx, scope, args);

            case Id_toString:
                return getSelf(cx, scope, thisObj).toString();
            case Id_valueOf:
            case SymbolId_toPrimitive:
                return getSelf(cx, scope, thisObj).js_valueOf();
            default:
                return super.execIdCall(f, cx, scope, thisObj, args);
        }
    }

    private static NativeSymbol getSelf(Context cx, Scriptable scope, Object thisObj) {
        try {
            return (NativeSymbol) ScriptRuntime.toObject(cx, scope, thisObj);
        } catch (ClassCastException cce) {
            throw ScriptRuntime.typeErrorById("msg.invalid.type", thisObj.getClass().getName());
        }
    }

    private static NativeSymbol js_constructor(Object[] args) {
        String desc;
        if (args.length > 0) {
            if (Undefined.instance.equals(args[0])) {
                desc = "";
            } else {
                desc = ScriptRuntime.toString(args[0]);
            }
        } else {
            desc = "";
        }

        if (args.length > 1) {
            return new NativeSymbol((SymbolKey) args[1]);
        }

        return new NativeSymbol(new SymbolKey(desc));
    }

    private Object js_valueOf() {
        // In the case that "Object()" was called we actually have a different "internal slot"
        return symbolData;
    }

    private Object js_for(Context cx, Scriptable scope, Object[] args) {
        String name =
                (args.length > 0
                        ? ScriptRuntime.toString(args[0])
                        : ScriptRuntime.toString(Undefined.instance));

        Map table = getGlobalMap();
        NativeSymbol ret = table.get(name);

        if (ret == null) {
            ret = construct(cx, scope, new Object[] {name});
            table.put(name, ret);
        }
        return ret;
    }

    private Object js_keyFor(Context cx, Scriptable scope, Object[] args) {
        Object s = (args.length > 0 ? args[0] : Undefined.instance);
        if (!(s instanceof NativeSymbol)) {
            throw ScriptRuntime.throwCustomError(cx, scope, "TypeError", "Not a Symbol");
        }
        NativeSymbol sym = (NativeSymbol) s;

        Map table = getGlobalMap();
        for (Map.Entry e : table.entrySet()) {
            if (e.getValue().key == sym.key) {
                return e.getKey();
            }
        }
        return Undefined.instance;
    }

    @Override
    public String toString() {
        return key.toString();
    }

    // Symbol objects have a special property that one cannot add properties.

    private static boolean isStrictMode() {
        final Context cx = Context.getCurrentContext();
        return (cx != null) && cx.isStrictMode();
    }

    @Override
    public void put(String name, Scriptable start, Object value) {
        if (!isSymbol()) {
            super.put(name, start, value);
        } else if (isStrictMode()) {
            throw ScriptRuntime.typeErrorById("msg.no.assign.symbol.strict");
        }
    }

    @Override
    public void put(int index, Scriptable start, Object value) {
        if (!isSymbol()) {
            super.put(index, start, value);
        } else if (isStrictMode()) {
            throw ScriptRuntime.typeErrorById("msg.no.assign.symbol.strict");
        }
    }

    @Override
    public void put(Symbol key, Scriptable start, Object value) {
        if (!isSymbol()) {
            super.put(key, start, value);
        } else if (isStrictMode()) {
            throw ScriptRuntime.typeErrorById("msg.no.assign.symbol.strict");
        }
    }

    /**
     * Object() on a Symbol constructs an object which is NOT a symbol, but which has an "internal
     * data slot" that is. Furthermore, such an object has the Symbol prototype so this particular
     * object is still used. Account for that here: an "Object" that was created from a Symbol has a
     * different value of the slot.
     */
    public boolean isSymbol() {
        return (symbolData == this);
    }

    @Override
    public String getTypeOf() {
        return (isSymbol() ? TYPE_NAME : super.getTypeOf());
    }

    @Override
    public int hashCode() {
        return key.hashCode();
    }

    @Override
    public boolean equals(Object x) {
        return key.equals(x);
    }

    SymbolKey getKey() {
        return key;
    }

    @SuppressWarnings("unchecked")
    private Map getGlobalMap() {
        ScriptableObject top = (ScriptableObject) getTopLevelScope(this);
        Map map =
                (Map) top.getAssociatedValue(GLOBAL_TABLE_KEY);
        if (map == null) {
            map = new HashMap<>();
            top.associateValue(GLOBAL_TABLE_KEY, map);
        }
        return map;
    }
}