From d8fa3db01a58f73db44283aa953527ef1cbcfcaf Mon Sep 17 00:00:00 2001
From: James Chiang <jchiang87@gmail.com>
Date: Thu, 28 May 2026 17:32:19 -0700
Subject: [PATCH] use a temp dir to do an atomic write for the raw file output;
 update test code to actually do the write

---
 imsim/readout.py               |  9 ++++++++-
 tests/test_raw_file_writing.py | 12 +++++++++---
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/imsim/readout.py b/imsim/readout.py
index fea757e1..444418d3 100644
--- a/imsim/readout.py
+++ b/imsim/readout.py
@@ -1,4 +1,5 @@
 import os
+import tempfile
 import numpy as np
 import subprocess
 import scipy
@@ -529,7 +530,13 @@ def prepare_hdus(self, rng):
     def write_raw_file(hdus, file_name):
         """Write the raw data file."""
         hdus[0].header['OUTFILE'] = os.path.basename(file_name)
-        hdus.writeto(file_name, overwrite=True)
+
+        # Use a temporary directory to do an atomic write.
+        dir_name = os.path.dirname(os.path.abspath(file_name))
+        with tempfile.TemporaryDirectory(dir=dir_name) as tmp_dir:
+            tmp_path = os.path.join(tmp_dir, "raw_file.fits.fz")
+            hdus.writeto(tmp_path)
+            os.replace(tmp_path, file_name)
 
 
 class CameraReadout(ExtraOutputBuilder):
diff --git a/tests/test_raw_file_writing.py b/tests/test_raw_file_writing.py
index ebd79e2f..95dc6fc3 100644
--- a/tests/test_raw_file_writing.py
+++ b/tests/test_raw_file_writing.py
@@ -3,6 +3,7 @@
 """
 import os
 from pathlib import Path
+import logging
 import unittest
 from astropy.io import fits
 import galsim
@@ -40,9 +41,11 @@ def test_raw_file_writing(self):
         added_keywords = {'GAUSFWHM': 0.4,
                           'FOOBAR': 'hello, world'}
 
-        hdu = imsim.get_primary_hdu(eimage, "E2V-CCD250-382",
-                                    added_keywords=added_keywords)
-        hdr = hdu.header
+        logger = logging.getLogger()
+        ccd_readout = imsim.CcdReadout(eimage, logger, added_keywords=added_keywords)
+        rng = galsim.BaseDeviate()
+        hdus = ccd_readout.prepare_hdus(rng)
+        hdr = hdus[0].header
 
         # Test some keywords.
         self.assertAlmostEqual(hdr['RA'], eimage.header['RATEL'])
@@ -66,6 +69,9 @@ def test_raw_file_writing(self):
         for key, value in added_keywords.items():
             self.assertEqual(hdr[key], value)
 
+        # Write the file.
+        ccd_readout.write_raw_file(hdus, self.outfile)
+
 
 if __name__ == '__main__':
     unittest.main()