/* LICENSE BLOCK
Part of mde: a Modular D game-oriented Engine
Copyright © 2007-2008 Diggory Hardy

This program is free software; you can redistribute it and/or modify it under the terms of
the GNU General Public License, version 2, 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 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.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. */

/** Scheduler
*/
module mde.scheduler.runTime;

import tango.time.Time;

debug {
    import tango.util.log.Log : Log, Logger;
    private Logger logger;
}
static this() {
    debug logger = Log.getLogger ("mde.scheduler.runTime");
}

/** Some enums used by per request functions. */
enum RF_KEYS : uint { DRAW };

// NOTE: Currently has no support for removing functions. To fix, assign ID and store fct pointers
// in an associative array, returning the ID [on adding fct pointer].
// NOTE: support delegates or not?
/// This class can run scheduled functions per frame or every t seconds (sim-time).
abstract class Scheduler
{
    /** The type of function pointer to be passed to the scheduler.
    *
    * The double $(I time) parameter gives the number of (sim) seconds since the function was last
    * called, or zero on the first run. */
    alias void function (double time) scheduleFct;
    
    /** Add a function to be called per frame. */
    static void perFrame (scheduleFct fct) {
        frameFcts ~= fct;
    }
    
    /** Add a function to be called per t secs or n 100-nano-sec intevals.
    *
    * Since the scheduler cannot guarantee a maximum time between calls, the interval at which
    * functions are called is always greater than or equal to the inverval specified here. Of
    * course, the actual inteval is given when the function is run.
    */
    static void perTime (double t, scheduleFct fct) {
        perTime (TimeSpan.interval(t), fct);
    }
    /** ditto */
    static void perTime (TimeSpan n, scheduleFct fct)
    in { assert (n > TimeSpan (0L)); }
    body {
        timeFcts ~= new TimeFct (fct, n);
    }
    
    /** Add a function to be called per requested update.
    *
    * A bool parameter is stored locally describing whether or not the function needs recalling,
    * and is set true upon creation and when requestUpdate is called with the same key. The
    * function is then called by scheduler's run() whenever this bool variable is true.
    */
    static void perRequest (uint key, void function() fct)
    in {
        debug if ((key in requestFcts) is null)
            logger.warn ("perRequest: replacing existing function with same key!");
    }
    body {
        requestFcts[key] = fct;
        requestFctsUpdate[key] = true;
    }
    
    /** Request an update to request function key. */
    static void requestUpdate (uint key) {
        // Note: check the value for this key actually exists
        bool* p = key in requestFctsUpdate;
        if (p) *p = true;
        else debug logger.warn ("requestUpdate called with invalid key");
    }
    
    /** This function should get called by the main loop, once per frame.
    *
    * The parameter time should be the current sim-time, using the tango.core.Types.Time enum; all
    * time evaluations will use this.
    */
    static void run (Time time) {
        double interval;
        
        // Call all per-frame functions:
        if (lastTime == Time (0L)) interval = 0.0;		// 0 interval for first loop
        else interval = (time-lastTime).interval();
        
        foreach (fct; frameFcts) fct(interval);
        
        // Call all per-interval functions:
        foreach (fct; timeFcts) if (time >= fct.nextCall) {
            if (fct.nextCall == Time (0L)) interval = 0.0;	// 0 interval for first call
            else interval = (time - (fct.nextCall - fct.interval)).interval();
            fct.nextCall = time + fct.interval;		// when to call next
            
            fct.fct (interval);				// call
        }
        
        // Call all per-request functions:
        foreach (key, fct; requestFcts) {
            if (requestFctsUpdate[key]) {
                fct();
                requestFctsUpdate[key] = false;
            }
        }
    }
    
    /* Holds details for functions called per time interval.
    * Needs to be a reference type, and using a class is easiest for this. */
    private static class TimeFct {
        scheduleFct fct;			// function to call
        
        TimeSpan interval;			// interval to call at
        // Storing nextCall is more efficient than storing lastCall since only this number has to
        // be compared to time every frame where fct is not called:
        Time nextCall = Time (0L);
        
        this (scheduleFct f, TimeSpan t) {
            fct = f;
            interval = t;
        }
    }
    
    private static Time lastTime = Time (0L);
    private static scheduleFct[] frameFcts;
    private static TimeFct[] timeFcts;
    private static void function()[uint] requestFcts;
    private static bool[uint] requestFctsUpdate;    // associated with requestFcts
}