// This module contains (or will contain) various routines for
// timing. It is also home of the ubiquitous "sleep" idle function.

module monster.modules.timer;

import std.stdio;
import std.date;

// For some utterly idiotic reason, DMD's public imports will suddenly
// stop working from time to time.
import monster.vm.mclass;
import monster.vm.mobject;
import monster.vm.stack;
import monster.vm.thread;
import monster.vm.idlefunction;

import monster.monster;

const char[] moduleDef =
"singleton timer;
idle sleep(float secs);
"; //"

// Sleep a given amount of time. This implementation uses the system
// clock and is the default.
class IdleSleep_SystemClock : IdleFunction
{
 override:
  IS initiate(Thread* cn)
    {
      // Get the parameter
      float secs = stack.popFloat;

      // Get current time
      cn.idleData.l = getUTCtime();

      // Calculate when we should return
      cn.idleData.l += secs*TicksPerSecond;

      // Schedule us
      return IS.Poll;
    }

  bool hasFinished(Thread* cn)
    {
      // Is it time?
      return getUTCtime() >= cn.idleData.l;
    }
}

// This implementation uses a user-driven timer instead of the system
// clock. It's more efficient, but requires the user to update the
// given timer manuall each frame. The default sleep (timer.sleep) is
// bound to the default timer, but it's possible to create multiple
// independent timers.
class IdleSleep_Timer : IdleFunction
{
 override:
  IS initiate(Thread* cn)
    {
      // The timer is stored in the object's 'extra' pointer
      auto t = cast(SleepManager)cn.extraData.obj;
      assert(t !is null);

      // Calculate the return time
      cn.idleData.l = t.current + cast(long)(t.tickSize*stack.popFloat);

      // Schedule us
      return IS.Poll;
    }

  bool hasFinished(Thread* cn)
    {
      // Get the timer
      auto t = cast(SleepManager)cn.extraData.obj;
      assert(t !is null);

      // Is it time?
      return t.current >= cn.idleData.l;
    }
}

// A manually updated timer. This can be improved quite a lot: Most
// sleep operations (depending on application of course) will skip
// many frames before they return. For example, for sleep(0.5) at 100
// fps, hasFinished will return false approximately 50 times before
// returning true. For bigger sleep values and a large number of
// objects, the impact of this is significant. A good solution would
// be to pool scheduled objects together and only perform one check on
// the entire pool. If the pool is due, all the nodes within it are
// inserted into the scheduler for detailed checking. We could have a
// series of such pools, ordered by expiration time, so that we only
// ever need to check the first pool in the list. The optimal pool
// interval, number of pools etc depends on the application and the
// fps - but it should be possible to find some reasonable defaults. A
// more generalized priority queue implementation is also possible.
class SleepManager
{
 private:
  // Instance of the timer class that is associated with this timer
  MonsterObject *tobj;

  // Current tick count
  long current;

 public:

  // Specify a Monster object to associate with this timer. Use 'null'
  // if you don't need an object.
  this(MonsterObject *obj)
    {
      if(obj is null) return;

      tobj = obj;
      tobj.getExtra(_timerClass).obj = this;
    }

  // By default, create a new object
  this()
    { this(_timerClass.createObject); }

  // Number of 'ticks' per second
  static const long tickSize = 1000;

  // Reset the timer to zero
  void reset() { current = 0; }

  // Return the total number of elapsed seconds since start (or last
  // reset)
  double read() { return current/cast(double)tickSize; }

  // Add time to the timer.
  void add(double d) { current += cast(long)(tickSize*d); }
  void addl(long l) { current += l; }

  MonsterObject *getObj() { return tobj; }
}

SleepManager idleTime;

MonsterClass _timerClass;

void initTimerModule()
{
  if(_timerClass !is null)
    {
      assert(idleTime !is null);
      return;
    }

  _timerClass = new MonsterClass(MC.String, moduleDef, "timer");

  assert(idleTime is null);
  idleTime = new SleepManager(_timerClass.getSing());

  setSleepMethod(SleepMethod.Clock);
}

enum SleepMethod
  { Clock, Timer }

void setSleepMethod(SleepMethod meth)
{
  initTimerModule();

  if(meth == SleepMethod.Clock)
    _timerClass.bind("sleep", new IdleSleep_SystemClock);
  else if(meth == SleepMethod.Timer)
    _timerClass.bind("sleep", new IdleSleep_Timer);
  else assert(0, "unknown timer method");
}