/*

 * Copyright (c) 2017, 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.

 *

 * 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 org.graalvm.compiler.options;

import java.util.concurrent.atomic.AtomicReference;

/**

 * A context for obtaining values for {@link OptionKey}s that allows for key/value pairs to be

 * updated. Updates have atomic copy-on-write semantics which means a thread may see an old value

 * when reading but writers will never loose updates.

 */

public class ModifiableOptionValues extends OptionValues {

    private final AtomicReference<UnmodifiableEconomicMap<OptionKey<?>, Object>> v = new AtomicReference<>();

    private static final EconomicMap<OptionKey<?>, Object> EMPTY_MAP = newOptionMap();

    public ModifiableOptionValues(UnmodifiableEconomicMap<OptionKey<?>, Object> values) {

        super(EMPTY_MAP);

        EconomicMap<OptionKey<?>, Object> map = newOptionMap();

        initMap(map, values);

        v.set(map);

    }

    /**

     * Value that can be used in {@link #update(UnmodifiableEconomicMap)} and

     * {@link #update(OptionKey, Object)} to remove an explicitly set value for a key such that

     * {@link OptionKey#hasBeenSet(OptionValues)} will return {@code false} for the key.

     */

    public static final Object UNSET_KEY = new Object();

    /**

     * Updates this object with the given key/value pair.

     *

     * @see #UNSET_KEY

     */

    public void update(OptionKey<?> key, Object value) {

        UnmodifiableEconomicMap<OptionKey<?>, Object> expect;

        EconomicMap<OptionKey<?>, Object> newMap;

        do {

            expect = v.get();

            newMap = EconomicMap.create(Equivalence.IDENTITY, expect);

            if (value == UNSET_KEY) {

                newMap.removeKey(key);

            } else {

                key.update(newMap, value);

                // Need to do the null encoding here as `key.update()` doesn't do it

                newMap.put(key, encodeNull(value));

            }

        } while (!v.compareAndSet(expect, newMap));

    }

    /**

     * Updates this object with the key/value pairs in {@code values}.

     *

     * @see #UNSET_KEY

     */

    public void update(UnmodifiableEconomicMap<OptionKey<?>, Object> values) {

        if (values.isEmpty()) {

            return;

        }

        UnmodifiableEconomicMap<OptionKey<?>, Object> expect;

        EconomicMap<OptionKey<?>, Object> newMap;

        do {

            expect = v.get();

            newMap = EconomicMap.create(Equivalence.IDENTITY, expect);

            UnmodifiableMapCursor<OptionKey<?>, Object> cursor = values.getEntries();

            while (cursor.advance()) {

                OptionKey<?> key = cursor.getKey();

                Object value = cursor.getValue();

                if (value == UNSET_KEY) {

                    newMap.removeKey(key);

                } else {

                    key.update(newMap, value);

                    // Need to do the null encoding here as `key.update()` doesn't do it

                    newMap.put(key, encodeNull(value));

                }

            }

        } while (!v.compareAndSet(expect, newMap));

    }

    @Override

    protected <T> T get(OptionKey<T> key) {

        return OptionValues.get(v.get(), key);

    }

    @Override

    protected boolean containsKey(OptionKey<?> key) {

        return v.get().containsKey(key);

    }

    @Override

    public UnmodifiableEconomicMap<OptionKey<?>, Object> getMap() {

        return v.get();

    }

}