auto-derive alternate tiles extension

bin/desi_create_tiletable

@@ -109,10 +109,10 @@ def main():
     import argparse
     p = argparse.ArgumentParser()
     p.add_argument('-o', '--outfile', required=True, help="output filename")
-    p.add_argument('--outfile2', required=False, help="Additional output filename (e.g. csv instead of fits)")
     p.add_argument('--specprod', required=False, help="specprod to use")
     p.add_argument('--nproc', type=int, default=32, help="number of processes to use")
     p.add_argument('--debug', action="store_true", help="start ipython at the end")
+    p.epilog = 'Note: in addition to --outfile, also writes .csv or .fits equivalent'
     args = p.parse_args()
 
     log = get_logger()
@@ -145,11 +145,20 @@ def main():
     os.rename(tmpfile, args.outfile)
     log.info(f'Wrote {args.outfile}')
 
-    if args.outfile2 is not None:
-        tmpfile = get_tempfilename(args.outfile2)
+    prefix, extension = os.path.splitext(args.outfile)
+    if extension == '.csv':
+        altoutfile = prefix+'.fits'
+    elif extension == '.fits' or extension == '.fits.gz':
+        altoutfile = prefix+'.csv'
+    else:
+        log.info('Unrecognized outfile extension %s; not writing alternate .csv/.fits file')
+        altoutfile = None
+
+    if altoutfile is not None:
+        tmpfile = get_tempfilename(altoutfile)
         results.write(tmpfile)
-        os.rename(tmpfile, args.outfile2)
-        log.info(f'Wrote {args.outfile2}')
+        os.rename(tmpfile, altoutfile)
+        log.info(f'Wrote {altoutfile}')
 
     if args.debug:
         import IPython; IPython.embed()