#!/opt/local/bin/ipython
#2019.02.05 Frayer
#Python 3.7.2
#IPython 7.2.0
#
#
#Flip Beam-2/3 positions for an ARGUS SDFITS file where the input file
#contains both beam 2 and beam 3 data and the data are in the same
#scan and integration order for both beams.  
#
#SDFITS files for the GBT are large tables stored in extension=1 where
#each row represents a specific interation number, scan number,
#spectral window, beam number, frequency-state, subreflector-state,
#and other states/parameters that are used by other instruments (83
#columns)
#
#
#Usage: %swap23.py SDFITSfile.fits
#Warning: Replaces data in original input file  
#
#
from astropy.io import fits 
import sys
import numpy as np

FILEIN = sys.argv[1]

#Python notes 
#How to view FITS info:
#fits.info(FILEIN)
#Alternative FITS access method:
#f=fits.open(FILEIN)
#tab=f[1].data
##Uses np.where command:
#x=np.array([2,4,5,2,6])
#idx=np.where(x == 2) 
#print(idx[0])
#type(idx)
##Careful with list vs np.array types
##Careful to work with copies 

tab=fits.getdata(FILEIN,ext=1)
h=fits.getheader(FILEIN,ext=1)
ra = tab["CRVAL2"]
dec = tab["CRVAL3"]
feed = tab["FEED"]

nra=np.copy(ra)
ndec=np.copy(dec)

id2=np.where(feed==2)
id3=np.where(feed==3)
idx2=id2[0]
idx3=id3[0]
#swap idexes
nra[idx2]=ra[idx3]
nra[idx3]=ra[idx2]
ndec[idx2]=dec[idx3]
ndec[idx3]=dec[idx2]
#replace values
tab["CRVAL2"]=nra
tab["CRVAL3"]=ndec

#update input file
fits.update(FILEIN,tab,h,ext=1)