//
// fg_time.hxx -- data structures and routines for managing time related stuff.
//
// Written by Curtis Olson, started August 1997.
//
// Copyright (C) 1997  Curtis L. Olson  - curt@infoplane.com
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// 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
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
//
// $Id$
// (Log is kept at end of this file)


#ifndef _FG_TIME_HXX
#define _FG_TIME_HXX


#ifndef __cplusplus                                                          
# error This library requires C++
#endif                                   


#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#ifdef HAVE_WINDOWS_H
#  include <windows.h>
#endif

#include <GL/glut.h>
#include <time.h>

#include <Include/fg_types.h>
#include <Flight/flight.h>


// Define a structure containing global time parameters
typedef struct {
    // the date/time in various forms
    // Unix "calendar" time in seconds
    time_t cur_time;

    // Break down of GMT time
    struct tm *gmt;

    // Julian date
    double jd;

    // modified Julian date
    double mjd;

    // side real time at prime meridian
    double gst;

    // local side real time
    double lst;

    // the difference between the precise sidereal time algorithm
    // result and the course result.  
    // course + diff has good accuracy for the short term
    double gst_diff;

    // An offset in seconds from the true time.  Allows us to adjust
    // the effective time of day.
    long int warp;

    // How much to change the value of warp each iteration.  Allows us
    // to make time progress faster than normal.
    long int warp_delta; 

    // Paused (0 = no, 1 = yes)
    int pause;
} fgTIME;

extern fgTIME cur_time_params;


typedef struct {
    long seconds;
    long millis;
} fg_timestamp;


// Portability wrap to get current time.
void timestamp(fg_timestamp *timestamp);


// Return duration in millis from first to last
long timediff(fg_timestamp *first, fg_timestamp *last);


// Return new timestamp given a time stamp and an interval to add in
void timesum(fg_timestamp *res, fg_timestamp *start, long millis);


// Update time variables such as gmt, julian date, and sidereal time
void fgTimeInit(fgTIME *t);


// Update the time dependent variables
void fgTimeUpdate(fgFLIGHT *f, fgTIME *t);


#endif // _FG_TIME_HXX


// $Log$
// Revision 1.6  1998/07/27 18:42:22  curt
// Added a pause option.
//
// Revision 1.5  1998/05/22 21:14:54  curt
// Rewrote event.cxx in C++ as a class using STL for the internal event list
// and run queue this removes the arbitrary list sizes and makes things much
// more dynamic.  Because this is C++-classified we can now have multiple
// event_tables if we'd ever want them.
//
// Revision 1.4  1998/04/28 01:22:17  curt
// Type-ified fgTIME and fgVIEW.
//
// Revision 1.3  1998/04/25 22:06:34  curt
// Edited cvs log messages in source files ... bad bad bad!
//
// Revision 1.2  1998/04/25 20:24:03  curt
// Cleaned up initialization sequence to eliminate interdependencies
// between sun position, lighting, and view position.  This creates a
// valid single pass initialization path.
//
// Revision 1.1  1998/04/24 00:52:28  curt
// Wrapped "#include <config.h>" in "#ifdef HAVE_CONFIG_H"
// Fog color fixes.
// Separated out lighting calcs into their own file.
//
// Revision 1.20  1998/04/22 13:24:05  curt
// C++ - ifiing the code a bit.
// Starting to reorginize some of the lighting calcs to use a table lookup.
//
// Revision 1.19  1998/04/21 17:01:44  curt
// Fixed a problems where a pointer to a function was being passed around.  In
// one place this functions arguments were defined as ( void ) while in another
// place they were defined as ( int ).  The correct answer was ( int ).
//
// Prepairing for C++ integration.
//
// Revision 1.18  1998/04/08 23:35:40  curt
// Tweaks to Gnu automake/autoconf system.
//
// Revision 1.17  1998/04/03 22:12:56  curt
// Converting to Gnu autoconf system.
// Centralized time handling differences.
//
// Revision 1.16  1998/02/07 15:29:47  curt
// Incorporated HUD changes and struct/typedef changes from Charlie Hotchkiss
// <chotchkiss@namg.us.anritsu.com>
//
// Revision 1.15  1998/01/27 00:48:06  curt
// Incorporated Paul Bleisch's <pbleisch@acm.org> new debug message
// system and commandline/config file processing code.
//
// Revision 1.14  1998/01/22 02:59:43  curt
// Changed #ifdef FILE_H to #ifdef _FILE_H
//
// Revision 1.13  1998/01/19 19:27:20  curt
// Merged in make system changes from Bob Kuehne <rpk@sgi.com>
// This should simplify things tremendously.
//
// Revision 1.12  1998/01/05 18:44:37  curt
// Add an option to advance/decrease time from keyboard.
//
// Revision 1.11  1997/12/19 23:35:07  curt
// Lot's of tweaking with sky rendering and lighting.
//
// Revision 1.10  1997/12/15 23:55:07  curt
// Add xgl wrappers for debugging.
// Generate terrain normals on the fly.
//
// Revision 1.9  1997/12/10 22:37:55  curt
// Prepended "fg" on the name of all global structures that didn't have it yet.
// i.e. "struct WEATHER {}" became "struct fgWEATHER {}"
//
// Revision 1.8  1997/12/09 04:25:38  curt
// Working on adding a global lighting params structure.
//
// Revision 1.7  1997/11/25 19:25:41  curt
// Changes to integrate Durk's moon/sun code updates + clean up.
//
// Revision 1.6  1997/09/20 03:34:35  curt
// Still trying to get those durned stars aligned properly.
//
// Revision 1.5  1997/09/16 15:50:31  curt
// Working on star alignment and time issues.
//
// Revision 1.4  1997/09/13 02:00:08  curt
// Mostly working on stars and generating sidereal time for accurate star
// placement.
//
// Revision 1.3  1997/09/04 02:17:39  curt
// Shufflin' stuff.
//
// Revision 1.2  1997/08/27 03:30:36  curt
// Changed naming scheme of basic shared structures.
//
// Revision 1.1  1997/08/13 21:56:00  curt
// Initial revision.
//