// $Id$
//
// Copyright (C) 2007
// Fraunhofer Institute for Open Communication Systems (FOKUS)
//
// The contents of this file are subject to the Fraunhofer FOKUS Public License
// Version 1.0 (the "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at 
// http://senf.berlios.de/license.html
//
// The Fraunhofer FOKUS Public License Version 1.0 is based on, 
// but modifies the Mozilla Public License Version 1.1.
// See the full license text for the amendments.
//
// Software distributed under the License is distributed on an "AS IS" basis, 
// WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License 
// for the specific language governing rights and limitations under the License.
//
// The Original Code is Fraunhofer FOKUS code.
//
// The Initial Developer of the Original Code is Fraunhofer-Gesellschaft e.V. 
// (registered association), Hansastraße 27 c, 80686 Munich, Germany.
//
// Contributor(s):
//   Stefan Bund <g0dil@berlios.de>


/** \mainpage The SENF Logging library

    The Loggger infrastructure implements a highly flexible compile- and run-time configurable
    logging infrastructure supporting multiple streams, user definable log areas and fine grained
    log levels. Logging can be configured at compile and runtime on any combination of above
    parameters. The library supports a host of log targets and messages can be routed into multiple
    targets at the same time. To allow concise usage of the library, a utility to define logging
    defaults for any scope is provided.

    \see
        \ref logging \n
        \ref config \n
        \ref targets \n
        \ref loglevels

    \section logging_concepts Concepts

    Log messages are arbitrarily created throughout the code using simple log statements (which are
    macros). Besides the log message itself, every log message is labeled with additional
    information: The \e stream, the \e area and a log \e level. If the message is not compile-time
    disabled, the message is then directed to one or several log \e targets.

    A \e stream combines log messages with a single purpose: Debug messages, access logging and so
    on. Any number of streams may be defined. There is one predefined default stream called \c
    senf::log::Debug. (see: \ref SENF_LOG_DEFINE_STREAM)

    The \e area gives information about the source location of the message. Areas may be defined and
    assigned arbitrarily but should be used to label messages from a single class or subsystem. It
    is possible to reuse a class as it's own area tag, which is often desireable.  There is a
    default area \c senf::log::DefaultArea which is used, when no other area is assigned. (see: \ref
    SENF_LOG_DEFINE_AREA, \ref SENF_LOG_CLASS_AREA)

    The log \e level gives information on the importance of the message. The list of log-levels is
    fixed. (see: \ref loglevels)

    Depending on their the \e stream, \e area and \e level information, log messages can be enabled
    or disabled at \e compile time. Messages disabled at compile time should not generate any
    code. (see: \ref SENF_LOG_CONF)

    \attention The default log stream senf::log::Debug has senf::log::VERBOSE messages
        <em>disabled</em> at compile time. senf::log::VERBOSE message will therefore only appear,
        if you explictly enable the messages for the area in question using (here for the area
        <code>some::Area</code>)
        <pre>
        g++ ... -DSENF_LOG_CONF="(( (senf)(log)(Debug), (some)(Area), VERBOSE ))"
        </pre>
        in addition to routing the messages at runtime. For more, see \ref config.

    To be of any use, the log messages have to be written somewhere. This is the responsibility of
    any number of \e targets. A \e target receives messages and using it's routing information
    decides, wether the message is output or not. A message may be routed to multiple targets
    simultaneously or may not be output by any target at all. (see: \ref targets)

    \section logging_tutorial Tutorial introduction

    Using the logging library mostly concerns using \ref SENF_LOG statements in your code. There are
    some other helpers used to simplify specifying parameters.

    \code
    namespace foo {

        // Define a new log stream with default level, runtime limit and compile time limit
        // set to senf::log::MESSAGE
        SENF_LOG_DEFINE_STREAM( UserLog, senf::log::MESSAGE, senf::log::MESSAGE, senf::log::MESSAGE );

        class Froblizer
        {
            // Define a log area which will automatically be used by all members of this class.
            // This is a combination of SENF_LOG_DEFINE_AREA and SENF_LOG_DEFAULT_AREA.
            SENF_LOG_CLASS_AREA();

            // Set default log parameters for this scope.
            SENF_LOG_DEFAULT_STREAM(foo::UserLog);
            SENF_LOG_DEFAULT_LEVEL(senf::log::NOTICE);

            // Define an alias for emergency debug messages
            // The log area is inherited from the default at the place, where this
            // alias is used *not* where it is defined
            SENF_LOG_DEFINE_ALIAS(LogEmerg, (senf::log::Debug)(senf::log::CRITICAL));

            void test();

        public:
            void froblize();
        };
    }

    void foo::Froblizer::froblize()
    {
        SENF_LOG(("This is the UserLog at level NOTICE in the FroblizeArea"));
        SENF_LOG((senf::log::IMPORTANT) ("Same stream and area but at important level"));
        SENF_LOG((LogEmerg) ("This goes to the DebugLog at level CRITICAL in the FroblizerArea"));
    }

    void foo::Froblizer::test()
    {
        // Change the default log level for this method. stream and area are taken
        // from the next scope up
        SENF_LOG_DEFAULT_LEVEL(senf::log::VERBOSE);

        SENF_LOG(("Log to UserLog stream in Froblizer area however at VERBOSE level"));
    }

    int main(int, char **)
    {
        // Set up the routing targets
        senf::log::ConsoleTarget & console (senf::log::ConsoleTarget::instance());
        senf::log::FileTarget logfile ("my.log");

        // Debug messages go to the console
        console.route<senf::log::Debug>();
        // Important user message are written to the log file
        logfile.route<foo::UserLog, senf::log::IMPORTANT>();
    }
    \endcode

    \implementation I would have much preferred a more C++ like implementation. However given the
        design goals
        \li Flexible configuration at compile and runtime
        \li Concise usage and simple interface
        \li Zero overhead for compile-time disabled log messages

        I did not find any non-mcaro implementation which was not either completely convoluted,
        unusable or slow. So I turned to a macro based implementation which can provide all the
        design goals stated above.
 */


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