//
// kernel.js
//
// run-loop manager for physics and tween updates
//
    
  var Kernel = function(pSystem){
    // in chrome, web workers aren't available to pages with file:// urls
    var chrome_local_file = window.location.protocol == "file:" &&
                            navigator.userAgent.toLowerCase().indexOf('chrome') > -1;
    var USE_WORKER = (window.Worker !== undefined && !chrome_local_file)    
    
    var _physics = null
    var _tween = null
    var _fpsWindow = [] // for keeping track of the actual frame rate
    _fpsWindow.last = new Date()
    var _screenInterval = null
    var _attached = null

    var _tickInterval = null
    var _lastTick = null
    var _paused = false
    
    var that = {
      system:pSystem,
      tween:null,
      nodes:{},

      init:function(){ 
        if (typeof(Tween)!='undefined') _tween = Tween()
        else if (typeof(arbor.Tween)!='undefined') _tween = arbor.Tween()
        else _tween = {busy:function(){return false},
                       tick:function(){return true},
                       to:function(){ trace('Please include arbor-tween.js to enable tweens'); _tween.to=function(){}; return} }
        that.tween = _tween
        var params = pSystem.parameters()
                
        if(USE_WORKER){
          trace('arbor.js/web-workers',params)
          _screenInterval = setInterval(that.screenUpdate, params.timeout)

          _physics = new Worker(arbor_path()+'physics/worker.js')
          _physics.onmessage = that.workerMsg
          _physics.onerror = function(e){ trace('physics:',e) }
          _physics.postMessage({type:"physics", 
                                physics:objmerge(params, 
                                                {timeout:Math.ceil(params.timeout)}) })
        }else{
          trace('arbor.js/single-threaded',params)
          _physics = Physics(params.dt, params.stiffness, params.repulsion, params.friction, that.system._updateGeometry, params.integrator)
          that.start()
        }

        return that
      },

      //
      // updates from the ParticleSystem
      graphChanged:function(changes){
        // a node or edge was added or deleted
        if (USE_WORKER) _physics.postMessage({type:"changes","changes":changes})
        else _physics._update(changes)
        that.start() // <- is this just to kick things off in the non-worker mode? (yes)
      },

      particleModified:function(id, mods){
        // a particle's position or mass is changed
        // trace('mod',objkeys(mods))
        if (USE_WORKER) _physics.postMessage({type:"modify", id:id, mods:mods})
        else _physics.modifyNode(id, mods)
        that.start() // <- is this just to kick things off in the non-worker mode? (yes)
      },

      physicsModified:function(param){

        // intercept changes to the framerate in case we're using a worker and
        // managing our own draw timer
        if (!isNaN(param.timeout)){
          if (USE_WORKER){
            clearInterval(_screenInterval)
            _screenInterval = setInterval(that.screenUpdate, param.timeout)
          }else{
            // clear the old interval then let the call to .start set the new one
            clearInterval(_tickInterval)
            _tickInterval=null
          }
        }

        // a change to the physics parameters 
        if (USE_WORKER) _physics.postMessage({type:'sys',param:param})
        else _physics.modifyPhysics(param)
        that.start() // <- is this just to kick things off in the non-worker mode? (yes)
      },
      
      workerMsg:function(e){
        var type = e.data.type
        if (type=='geometry'){
          that.workerUpdate(e.data)
        }else{
          trace('physics:',e.data)
        }
      },
      _lastPositions:null,
      workerUpdate:function(data){
        that._lastPositions = data
        that._lastBounds = data.bounds
      },
      

      // 
      // the main render loop when running in web worker mode
      _lastFrametime:new Date().valueOf(),
      _lastBounds:null,
      _currentRenderer:null,
      screenUpdate:function(){        
        var now = new Date().valueOf()
        
        var shouldRedraw = false
        if (that._lastPositions!==null){
          that.system._updateGeometry(that._lastPositions)
          that._lastPositions = null
          shouldRedraw = true
        }
        
        if (_tween && _tween.busy()) shouldRedraw = true

        if (that.system._updateBounds(that._lastBounds)) shouldRedraw=true
        

        if (shouldRedraw){
          var render = that.system.renderer
          if (render!==undefined){
            if (render !== _attached){
               render.init(that.system)
               _attached = render
            }          
            
            if (_tween) _tween.tick()
            render.redraw()

            var prevFrame = _fpsWindow.last
            _fpsWindow.last = new Date()
            _fpsWindow.push(_fpsWindow.last-prevFrame)
            if (_fpsWindow.length>50) _fpsWindow.shift()
          }
        }
      },

      // 
      // the main render loop when running in non-worker mode
      physicsUpdate:function(){
        if (_tween) _tween.tick()
        _physics.tick()

        var stillActive = that.system._updateBounds()
        if (_tween && _tween.busy()) stillActive = true

        var render = that.system.renderer
        var now = new Date()        
        var render = that.system.renderer
        if (render!==undefined){
          if (render !== _attached){
            render.init(that.system)
            _attached = render
          }          
          render.redraw({timestamp:now})
        }

        var prevFrame = _fpsWindow.last
        _fpsWindow.last = now
        _fpsWindow.push(_fpsWindow.last-prevFrame)
        if (_fpsWindow.length>50) _fpsWindow.shift()

        // but stop the simulation when energy of the system goes below a threshold
        var sysEnergy = _physics.systemEnergy()
        if ((sysEnergy.mean + sysEnergy.max)/2 < 0.05){
          if (_lastTick===null) _lastTick=new Date().valueOf()
          if (new Date().valueOf()-_lastTick>1000){
            // trace('stopping')
            clearInterval(_tickInterval)
            _tickInterval = null
          }else{
            // trace('pausing')
          }
        }else{
          // trace('continuing')
          _lastTick = null
        }
      },


      fps:function(newTargetFPS){
        if (newTargetFPS!==undefined){
          var timeout = 1000/Math.max(1,targetFps)
          that.physicsModified({timeout:timeout})
        }
        
        var totInterv = 0
        for (var i=0, j=_fpsWindow.length; i<j; i++) totInterv+=_fpsWindow[i]
        var meanIntev = totInterv/Math.max(1,_fpsWindow.length)
        if (!isNaN(meanIntev)) return Math.round(1000/meanIntev)
        else return 0
      },

      // 
      // start/stop simulation
      // 
      start:function(unpause){
      	if (_tickInterval !== null) return; // already running
        if (_paused && !unpause) return; // we've been .stopped before, wait for unpause
        _paused = false
        
        if (USE_WORKER){
           _physics.postMessage({type:"start"})
        }else{
          _lastTick = null
          _tickInterval = setInterval(that.physicsUpdate, 
                                      that.system.parameters().timeout)
        }
      },
      stop:function(){
        _paused = true
        if (USE_WORKER){
           _physics.postMessage({type:"stop"})
        }else{
          if (_tickInterval!==null){
            clearInterval(_tickInterval)
            _tickInterval = null
          }
        }
      
      }
    }
    
    return that.init()    
  }