perf: avoid scanning entire dicom directory for header lookup

package/src/pyaslreport/main.py

@@ -46,24 +46,16 @@ def get_dicom_header(dicom_dir: str):
     # Get all files in the directory
     all_files = [f for f in os.listdir(dicom_dir) if os.path.isfile(os.path.join(dicom_dir, f))]
 
-    # Try to find DICOM files by attempting to read them with pydicom
-    dcm_files = []
+    # Return the first readable DICOM header instead of scanning the whole directory
+    # and reading the winning file a second time.
     for file in all_files:
         file_path = os.path.join(dicom_dir, file)
         try:
-            # Try to read the file as DICOM
-            pydicom.dcmread(file_path, stop_before_pixels=True)
-            dcm_files.append(file)
+            dcm_header = pydicom.dcmread(file_path, stop_before_pixels=True)
+            log.info(f"Found a readable DICOM file in {dicom_dir}: {file}")
+            return dcm_header
         except (InvalidDicomError, OSError, PermissionError):
             # File is not a valid DICOM file or cannot be read
             continue
 
-    log.info(f"Found {len(dcm_files)} DICOM files in {dicom_dir}")
-
-    if not dcm_files:
-        raise ValueError(f"No DICOM files found in directory: {dicom_dir}")
-
-    # Read the first valid DICOM file
-    dcm_header = pydicom.dcmread(os.path.join(dicom_dir, dcm_files[0]))
-
-    return dcm_header
+    raise ValueError(f"No DICOM files found in directory: {dicom_dir}")

package/src/pyaslreport/tests/test_get_dicom_header.py

@@ -0,0 +1,23 @@
+from pathlib import Path
+from unittest.mock import patch
+
+from pyaslreport.main import get_dicom_header
+
+
+def test_get_dicom_header_returns_first_valid_header_without_scanning_rest(tmp_path):
+    first_file = tmp_path / "first.dcm"
+    second_file = tmp_path / "second.dcm"
+    first_file.write_bytes(b"first")
+    second_file.write_bytes(b"second")
+
+    calls = []
+
+    def fake_dcmread(path, stop_before_pixels=True):
+        calls.append(Path(path).name)
+        return {"path": Path(path).name}
+
+    with patch("pyaslreport.main.pydicom.dcmread", side_effect=fake_dcmread):
+        header = get_dicom_header(str(tmp_path))
+
+    assert header == {"path": "first.dcm"}
+    assert calls == ["first.dcm"]