from Gaudi.Configuration import *                                          
from GaudiKernel.SystemOfUnits import MeV, GeV
from Configurables import CombineParticles
from PhysSelPython.Wrappers import Selection, SelectionSequence, DataOnDemand

# prepare input data
_muons = DataOnDemand('_stdLooseMuons', Location = 'StdLooseMuons')

# create algorithm
myalg = CombineParticles("myalg")

# define decay and cuts
myalg.DecayDescriptor = "J/psi(1S) -> mu+ mu-"
myalg.CombinationCut = "ADAMASS('J/psi(1S)')<30*MeV"
myalg.MotherCut = "(VFASPF(VCHI2/VDOF)<10)"

# add plots to algorithm
from Configurables import LoKi__Hybrid__PlotTool as PlotTool
myalg.HistoProduce = True
myalg.addTool ( PlotTool ( 'DaughtersPlots' ) )
myalg.DaughtersPlots.Histos = {
   'P'  : ('momentum' , 0*GeV ,30*GeV) ,
   'M'  : ('mass'     ,0*GeV,1*GeV)
   }
myalg.addTool( PlotTool ( "MotherPlots" ) )
myalg.MotherPlots.Histos = {
   "P"  : ('momentum',0*GeV,100*GeV) ,
   "M"  : ('mass',0*GeV,4*GeV)
   }

# create selection
# Selection needs to be defined after all changes to the Algorithm
LooseJpsi2MuMu = Selection("seqLooseJPsi2MuMu", Algorithm = myalg, RequiredSelections =[ _muons ])

# start selection sequence
mySeq = SelectionSequence("mySeq", TopSelection = LooseJpsi2MuMu)

# configure the application.
from Configurables import DaVinci
DaVinci().UserAlgorithms = [ mySeq.sequence() ]
DaVinci().HistogramFile  = "histograms.root"    # Histogram file
DaVinci().EvtMax         = 1000                  # Number of events to loop over
DaVinci().DataType       = "MC09"               # Default anyway
DaVinci().Simulation     = True                 # It's MC