# this program takes a root file that already contains histograms and makes an overlay plot in pdf format of those histograms

import ROOT
from ROOT import TFile, TH1F, TColor

ROOT.gROOT.SetBatch(True)

#import file
f = TFile.Open("FILE.root")

#get h1
h1 = f.Get("histogram_name_1")
print(h1.Integral()) # this is to check how many items are in the histogram

# get second histogram
h2 = f.Get("histogram_2_name")
print(h2.Integral())

# get third histogram

h3 = f.Get("histogram_3_name")
print(h3.Integral())

# 4th

h4 = f.Get("histogram_4_name")
print(h4.Integral())

# you can add or subtract as many histograms as you need to overlay


#set h1 preferences
h1.SetTitle("Name of overlay Plot") #define the name of the overlay plot here
h1.SetStats(0)
h1.SetLineColor(ROOT.kBlack) #choose some line color, options can be found by searching root color wheel

#set h2 preferences
h2.SetTitle("") # every other histogram title should be blank or else it will get messed up
h2.SetStats(0)
h2.SetLineColor(ROOT.kBlue+2) #make sure that it is a different color from above

#set h3 pref
h3.SetTitle("")
h3.SetStats(0)
h3.SetLineColor(ROOT.kRed+1)

#set h4 pref
h4.SetTitle("")
h4.SetStats(0)
h4.SetLineColor(ROOT.kCyan)



# draw canvas
c0 = ROOT.TCanvas("canvas_name")
c0.cd() # go onto the canvas you just created
h1.Draw() #draw your first histogram on the canvas

# draw other histogram on same canvas
c0.cd()
h2.Draw("SAME")
c0.cd()
h3.Draw("SAME")
c0.cd()
h4.Draw("SAME")
c0.cd()



#add legend for the overlay histograms

leg = ROOT.TLegend(.27, .75, .5, .90) # top right
leg.SetBorderSize(0) # no border
leg.SetFillColor(0) # no fill
leg.SetFillStyle(0) # no fill
leg.SetTextFont(42)
leg.SetTextSize(.02)
leg.AddEntry(h1, "entry_title" + ": "+str(h1.GetEntries()), "l") # "f" shows bin w color "l" shows line
leg.AddEntry(h2, "entry_title" + ": "+str(h2.GetEntries()), "l")
leg.AddEntry(h3, "entry_title" + ": "+str(h3.GetEntries()), "l")
leg.AddEntry(h4, "entry_title" + ": "+str(h4.GetEntries()), "l")
leg.Draw()

#create the overlay file
c0.Print("overlay_file.pdf")