/*

 * Copyright (c) 2016, 2018, 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 jdk.jfr.internal;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.security.AccessControlContext;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Collections;

import java.util.HashSet;

import java.util.Objects;

import java.util.Set;

// User must never be able to subclass directly.

//

// Never put Control or Setting Control in a collections

// so overridable versions of hashCode or equals are

// executed in the wrong context. TODO: wrap this class

// in SsecureControl directly when it is instantiated and

// forward calls using AccessControlContext

abstract public class Control {

    private final AccessControlContext context;

    private final static int CACHE_SIZE = 5;

    private final Set<?>[] cachedUnions = new HashSet<?>[CACHE_SIZE];

    private final String[] cachedValues = new String[CACHE_SIZE];

    private String defaultValue;

    private String lastValue;

    // called by exposed subclass in external API

    public Control(AccessControlContext acc) {

        Objects.requireNonNull(acc);

        this.context = acc;

    }

    // only to be called by trusted VM code

    public Control(String defaultValue) {

        this.defaultValue = defaultValue;

        this.context = null;

    }

    // For user code to override, must never be called from jdk.jfr.internal

    // for user defined settings

    public abstract String combine(Set<String> values);

    // For user code to override, must never be called from jdk.jfr.internal

    // for user defined settings

    public abstract void setValue(String value);

    // For user code to override, must never be called from jdk.jfr.internal

    // for user defined settings

    public abstract String getValue();

      // Package private, user code should not have access to this method

    final void apply(Set<String> values) {

        setValueSafe(findCombineSafe(values));

    }

    // Package private, user code should not have access to this method.

    // Only called during event registration

    final void setDefault() {

        if (defaultValue == null) {

            defaultValue = getValueSafe();

        }

        apply(defaultValue);

    }

    final String getValueSafe() {

        if (context == null) {

            // VM events requires no access control context

            return getValue();

        } else {

            return AccessController.doPrivileged(new PrivilegedAction<String>() {

                @Override

                public String run() {

                    try {

                        return getValue();

                    } catch (Throwable t) {

                        // Prevent malicious user to propagate exception callback in the wrong context

                        Logger.log(LogTag.JFR_SETTING, LogLevel.WARN, "Exception occured when trying to get value for " + getClass());

                    }

                    return defaultValue != null ? defaultValue : ""; // Need to return something

                }

            }, context);

        }

    }

    private void apply(String value) {

        if (lastValue != null && Objects.equals(value, lastValue)) {

            return;

        }

        setValueSafe(value);

    }

    final void setValueSafe(String value) {

        if (context == null) {

            // VM events requires no access control context

            try {

                setValue(value);

            } catch (Throwable t) {

                Logger.log(LogTag.JFR_SETTING, LogLevel.WARN, "Exception occured when setting value \"" + value + "\" for " + getClass());

            }

        } else {

            AccessController.doPrivileged(new PrivilegedAction<Void>() {

                @Override

                public Void run() {

                    try {

                        setValue(value);

                    } catch (Throwable t) {

                        // Prevent malicious user to propagate exception callback in the wrong context

                        Logger.log(LogTag.JFR_SETTING, LogLevel.WARN, "Exception occured when setting value \"" + value + "\" for " + getClass());

                    }

                    return null;

                }

            }, context);

        }

        lastValue = value;

    }

    private String combineSafe(Set<String> values) {

        if (context == null) {

            // VM events requires no access control context

            return combine(values);

        }

        return AccessController.doPrivileged(new PrivilegedAction<String>() {

            @Override

            public String run() {

                try {

                    combine(Collections.unmodifiableSet(values));

                } catch (Throwable t) {

                    // Prevent malicious user to propagate exception callback in the wrong context

                    Logger.log(LogTag.JFR_SETTING, LogLevel.WARN, "Exception occured when combining " + values + " for " + getClass());

                }

                return null;

            }

        }, context);

    }

    private final String findCombineSafe(Set<String> values) {

        if (values.size() == 1) {

            return values.iterator().next();

        }

        for (int i = 0; i < CACHE_SIZE; i++) {

            if (Objects.equals(cachedUnions[i], values)) {

                return cachedValues[i];

            }

        }

        String result = combineSafe(values);

        for (int i = 0; i < CACHE_SIZE - 1; i++) {

            cachedUnions[i + 1] = cachedUnions[i];

            cachedValues[i + 1] = cachedValues[i];

        }

        cachedValues[0] = result;

        cachedUnions[0] = values;

        return result;

    }

    // package private, user code should not have access to this method

    final String getDefaultValue() {

        return defaultValue;

    }

    // package private, user code should not have access to this method

    final String getLastValue() {

        return lastValue;

    }

    // Precaution to prevent a malicious user from instantiating instances

    // of a control where the context has not been set up.

    @Override

    public final Object clone() throws java.lang.CloneNotSupportedException {

        throw new CloneNotSupportedException();

    }

    private final void writeObject(ObjectOutputStream out) throws IOException {

        throw new IOException("Object cannot be serialized");

    }

    private final void readObject(ObjectInputStream in) throws IOException {

        throw new IOException("Class cannot be deserialized");

    }

}