    // Copyright (C) 2006  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_LOGGER_KERNEl_ABSTRACT_
    #ifdef DLIB_LOGGER_KERNEl_ABSTRACT_

    #include "../threads.h"
    #include <limits>
    #include <string>
    #include <iostream>
    #include "../uintn.h"

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        class log_level
        {
            /*!
                WHAT THIS OBJECT REPRESENTS
                    This object is a simple named level to log at.  It contains a numeric
                    priority and a name to use in the logging messages.
            !*/
        public:
            log_level(
                int priority_,
                const char* name_
            );
            /*!
                ensures
                    - #priority = priority_
                    - the first 19 characters of name_ are copied into name and name
                      is null terminated.
            !*/

            int priority;
            char name[20];
        };

    // ----------------------------------------------------------------------------------------

        const log_level LALL  (std::numeric_limits<int>::min(),"ALL");
        const log_level LNONE (std::numeric_limits<int>::max(),"NONE");
        const log_level LTRACE(-100,"TRACE");
        const log_level LDEBUG(0   ,"DEBUG");
        const log_level LINFO (100 ,"INFO ");
        const log_level LWARN (200 ,"WARN ");
        const log_level LERROR(300 ,"ERROR");
        const log_level LFATAL(400 ,"FATAL");

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        void set_all_logging_output_streams (
            std::ostream& out
        );
        /*!
            ensures
                - for all loggers L:
                    - #L.output_streambuf() == out.rdbuf()
                    - Removes any previous output hook from L.  So now the logger
                      L will write all its messages to the given output stream.
            throws
                - std::bad_alloc
        !*/

    // ----------------------------------------------------------------------------------------

        template <
            typename T
            >
        void set_all_logging_output_hooks (
            T& object,
            void (T::*hook)(const std::string& logger_name,
                            const log_level& l,
                            const uint64 thread_id,
                            const char* message_to_log)
        );
        /*!
            ensures
                - for all loggers L:
                    - #L.output_streambuf() == 0
                    - performs the equivalent to calling L.set_output_hook(object, hook);
                      (i.e. sets all loggers so that they will use the given hook function)
            throws
                - std::bad_alloc
        !*/

    // ----------------------------------------------------------------------------------------

        void set_all_logging_levels (
            const log_level& new_level
        );
        /*!
            ensures
                - for all loggers L:
                    - #L.level() == new_level
            throws
                - std::bad_alloc
        !*/

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        void print_default_logger_header (
            std::ostream& out,
            const std::string& logger_name,
            const log_level& l,
            const uint64 thread_id
        );
        /*!
            requires
                - is not called more than once at a time (i.e. is not called from multiple
                  threads at the same time).
            ensures
                - let MS be the number of milliseconds since program start.
                - prints a string to out in the form:  "MS l.name [thread_id] logger_name:"
        !*/

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

        class logger
        {
            /*!
                INITIAL VALUE
                    - name() == a user supplied value given to the constructor
                    - The values of level(), output_streambuf(), logger_header(), and
                      auto_flush() are inherited from the parent of this logger.

                WHAT THIS OBJECT REPRESENTS
                    This object represents a logging output stream in the style of the log4j
                    logger available for Java.

                    Additionally, the logger doesn't perform any memory allocations during
                    each logging action.  It just writes directly into the user supplied output
                    stream.  Alternatively, if you use a logging output hook no memory allocations
                    are performed either.  Logging just goes straight into a memory buffer
                    which gets passed to the user supplied logging hook.

                DEFAULTS
                    If the user hasn't specified values for the four inherited values level(),
                    output_streambuf(), logger_header(), or auto_flush() then the default
                    values will be used.  The defaults are as follows:
                    - level() == LERROR
                    - output_streambuf() == std::cout.rdbuf() (i.e. the default is to log
                      to standard output).
                    - logger_header() == print_default_logger_header
                    - auto_flush() == true

                THREAD SAFETY
                    All methods of this class are thread safe.  Note that it is safe to
                    chain calls to operator << such as:
                        log << LINFO << "message " << variable << " more message";
                    The logger ensures that the entire statement executes atomically so the
                    message won't be broken up by other loggers in other threads.
            !*/

            class logger_stream
            {
            public:

                bool is_enabled (
                ) const;
                /*!
                    ensures
                        - returns true if this logger stream will print out items
                          given to it by the << operator.  returns false otherwise.
                !*/

                template <typename T>
                logger_stream& operator << (
                    const T& item
                );
                /*!
                    ensures
                        - if (is_enabled()) then
                            - writes item to this output stream
                        - returns *this
                !*/
            };

        public:

            logger (
                const char* name_
            );
            /*!
                requires
                    - name_ != ""
                ensures
                    - #*this is properly initialized
                    - #name() == name_
                throws
                    - std::bad_alloc
                    - dlib::thread_error
            !*/

            virtual ~logger (
            );
            /*!
                ensures
                    - any resources associated with *this have been released
            !*/

            const std::string& name (
            ) const;
            /*!
                ensures
                    - returns the name of this logger
            !*/

            logger_stream operator << (
                const log_level& l
            ) const;
            /*!
                ensures
                    - if (l.priority >= level().priority) then
                        - returns a logger_stream with is_enabled() == true.  I.e. this
                          returned stream will write its output to the I/O destination
                          used by this logger object.
                    - else
                        - returns a logger stream with is_enabled() == false
                throws
                    - std::bad_alloc
            !*/

            bool is_child_of (
                const logger& log
            ) const;
            /*!
                ensures
                    - if ( (name().find(log.name() + ".") == 0) || (log.name() == name()) ) then
                        - returns true
                          (i.e. if log.name() + "." is a prefix of name() or if both *this and log
                          have the same name then return true)
                    - else
                        - returns false
            !*/

            const log_level level (
            ) const;
            /*!
                ensures
                    - returns the current log level of this logger.
            !*/

            void set_level (
                const log_level& new_level
            );
            /*!
                ensures
                    - for all loggers L such that L.is_child_of(*this) == true:
                        - #L.level() == new_level
                throws
                    - std::bad_alloc
            !*/

            bool auto_flush (
            );
            /*!
                ensures
                    - returns true if the output stream is flushed after every logged message.
                      returns false otherwise.  (Note that flushing only does anything if
                      the logger is set to use an output stream rather than a hook)
            !*/

            void set_auto_flush (
                bool enabled
            );
            /*!
                ensures
                    - for all loggers L such that L.is_child_of(*this) == true:
                        - #L.auto_flush() == enabled
                throws
                    - std::bad_alloc
            !*/

            template <
                typename T
                >
            void set_output_hook (
                T& object,
                void (T::*hook)(const std::string& logger_name,
                                const log_level& l,
                                const uint64 thread_id,
                                const char* message_to_log)
            );
            /*!
                requires
                    - hook is a valid pointer to a member function in T
                ensures
                    - for all loggers L such that L.is_child_of(*this) == true:
                        - #L.output_streambuf() == 0
                        - #L will not send its log messages to an ostream object anymore.  Instead
                          it will call the given hook member function (i.e. (object.*hook)(name,l,id,msg) )
                          for each message that needs to be logged.
                        - The arguments to the hook function have the following meanings:
                            - logger_name == The name of the logger that is printing the log message.
                            - l == The level of the logger that is printing the log message.
                            - thread_id == A number that uniquely identifies the thread trying to log
                              the message.  Note that this number is unique among all threads, past and
                              present.  Also note that this id is not the same one returned by
                              get_thread_id().
                            - message_to_log == the actual text of the message the user is giving to
                              the logger object to log.
                        - All hook functions will also only be called one at a time. This means
                          that hook functions don't need to be thread safe.
            !*/

            std::streambuf* output_streambuf (
            );
            /*!
                ensures
                    - if (an output hook isn't set) then
                        - returns the output stream buffer that this logger writes all
                          messages to.
                    - else
                        - returns 0
            !*/

            void set_output_stream (
                std::ostream& out
            );
            /*!
                ensures
                    - for all loggers L such that L.is_child_of(*this) == true:
                        - #L.output_streambuf() == out.rdbuf()
                        - Removes any previous output hook from L.  So now the logger
                          L will write all its messages to the given output stream.
                throws
                    - std::bad_alloc
            !*/

            typedef void (*print_header_type)(
                    std::ostream& out,
                    const std::string& logger_name,
                    const log_level& l,
                    const uint64 thread_id
                    );

            print_header_type logger_header (
            ) const;
            /*!
                ensures
                    - returns the function that is called to print the header information
                      onto each logged message.  The arguments to the function have the following
                      meanings:
                        - out == The output stream this function writes the header to.
                        - logger_name == The name of the logger that is printing the log message.
                        - l == The level of the logger that is printing the log message.
                        - thread_id == A number that uniquely identifies the thread trying to log
                          the message.  Note that this number is unique among all threads, past and
                          present.  Also note that this id is not the same one returned by
                          get_thread_id().
                    - This logger_header function will also only be called once at a time. This means
                      the logger_header function doesn't need to be thread safe.
                    - the logger_header function is only used when output_streambuf() != 0
            !*/

            void set_logger_header (
                print_header_type print_header
            );
            /*!
                ensures
                    - for all loggers L such that L.is_child_of(*this) == true:
                        - #L.logger_header() == print_header
                throws
                    - std::bad_alloc
            !*/

        private:

            // restricted functions
            logger(const logger&);        // copy constructor
            logger& operator=(const logger&);    // assignment operator

        };

    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------
    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_LOGGER_KERNEl_ABSTRACT_