/*    Copyright 2013 10gen Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    This program 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 Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects
 *    for all of the code used other than as permitted herein. If you modify
 *    file(s) with this exception, you may extend this exception to your
 *    version of the file(s), but you are not obligated to do so. If you do not
 *    wish to do so, delete this exception statement from your version. If you
 *    delete this exception statement from all source files in the program,
 *    then also delete it in the license file.
 */

#pragma once

#include <boost/scoped_ptr.hpp>
#include <memory>
#include <string>
#include <vector>

#include "mongo/base/disallow_copying.h"
#include "mongo/logger/appender.h"
#include "mongo/logger/log_severity.h"

namespace mongo {
namespace logger {

    /**
     * Logging domain for events of type E.
     *
     * A logging domain consists of a set of Appenders and a minimum severity.
     *
     * TODO: The severity doesn't seem to apply for auditing, maybe it only belongs on the
     * MessageLogManager?  We don't really have multiple tunable logging domains, right now.  Other
     * than the global domain, shouldLog doesn't matter.
     *
     * Usage: Configure the log domain in a single threaded context, using attachAppender,
     * detachAppender and clearAppenders().  The domain takes ownership of any attached appender,
     * returning an AppenderHandle for each attached appender.  That handle may be used later to
     * detach the appender, causing the domain to release ownership of it.  Mostly, this
     * attach/detach behavior is useful in testing, since you do not want to change the appenders of
     * a domain that is currently receiving append() calls.
     *
     * Once you've configured the domain, call append() from potentially many threads, to add log
     * messages.
     */
    template <typename E>
    class LogDomain {
        MONGO_DISALLOW_COPYING(LogDomain);
    public:
        typedef E Event;
        typedef Appender<Event> EventAppender;

        /**
         * Opaque handle returned by attachAppender(), which can be subsequently passed to
         * detachAppender() to detach an appender from an instance of LogDomain.
         */
        class AppenderHandle {
            friend class LogDomain;
        public:
            AppenderHandle() {}

        private:
            explicit AppenderHandle(size_t index) : _index(index) {}

            size_t _index;
        };

        // TODO(schwerin): Replace with unique_ptr in C++11.
        typedef std::auto_ptr<EventAppender> AppenderAutoPtr;

        LogDomain();
        ~LogDomain();

        /**
         * Receives an event for logging, calling append(event) on all attached appenders.
         *
         * If any appender fails, the behavior is determined by the abortOnFailure flag:
         * *If abortOnFailure is set, ::abort() is immediately called.
         * *If abortOnFailure is not set, the error is returned and no further appenders are called.
         */
        Status append(const Event& event);

        /**
         * Predicate that answers the question, "Should I, the caller, append to you, the log
         * domain, messages of the given severity?"  True means yes.
         */
        bool shouldLog(LogSeverity severity) { return severity >= _minimumLoggedSeverity; }

        /**
         * Gets the minimum severity of messages that should be sent to this LogDomain.
         */
        LogSeverity getMinimumLogSeverity() { return _minimumLoggedSeverity; }

        /**
         * Sets the minimum severity of messages that should be sent to this LogDomain.
         */
        void setMinimumLoggedSeverity(LogSeverity severity) { _minimumLoggedSeverity = severity; }

        /**
         * Gets the state of the abortOnFailure flag.
         */
        bool getAbortOnFailure() const { return _abortOnFailure; }

        /**
         * Sets the state of the abortOnFailure flag.
         */
        void setAbortOnFailure(bool abortOnFailure) { _abortOnFailure = abortOnFailure; }

        //
        // Configuration methods.  Must be synchronized with each other and calls to "append" by the
        // caller.
        //

        /**
         * Attaches "appender" to this domain, taking ownership of it.  Returns a handle that may be
         * used later to detach this appender.
         */
        AppenderHandle attachAppender(AppenderAutoPtr appender);

        /**
         * Detaches the appender referenced by "handle" from this domain, releasing ownership of it.
         * Returns an auto_ptr to the handler to the caller, who is now responsible for its
         * deletion. Caller should consider "handle" is invalid after this call.
         */
        AppenderAutoPtr detachAppender(AppenderHandle handle);

        /**
         * Destroy all attached appenders, invalidating all handles.
         */
        void clearAppenders();

    private:
        typedef std::vector<EventAppender*> AppenderVector;

        LogSeverity _minimumLoggedSeverity;
        AppenderVector _appenders;
        bool _abortOnFailure;
    };

}  // namespace logger
}  // namespace mongo
