fix: fix bug in directory selection for proof image

Solves #615

When the proof image folder reached the limit of 1000, we created
a new image dir and stored the image in it, but without the 0 padding.
This directory was never used again.
That's why we had directories named `1`, `2`,... `10` in the image dir.

open_prices/proofs/tests.py

@@ -20,7 +20,7 @@
     run_and_save_proof_prediction,
 )
 from open_prices.proofs.models import Proof
-from open_prices.proofs.utils import fetch_and_save_ocr_data
+from open_prices.proofs.utils import fetch_and_save_ocr_data, select_proof_image_dir
 
 LOCATION_OSM_NODE_652825274 = {
     "type": location_constants.TYPE_OSM,
@@ -473,3 +473,38 @@ def test_run_and_save_proof_prediction_proof(self):
                 proof_type_prediction.delete()
                 price_tag_prediction.delete()
                 proof.delete()
+
+
+class TestSelectProofImageDir(TestCase):
+    def test_select_proof_image_dir_no_dir(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            images_dir = Path(tmpdir) / "images"
+            images_dir.mkdir()
+            selected_dir = select_proof_image_dir(images_dir)
+            self.assertEqual(selected_dir, images_dir / "0001")
+
+    def test_select_proof_image_dir_existing_dir(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            images_dir = Path(tmpdir) / "images"
+            images_dir.mkdir()
+            (images_dir / "0001").mkdir()
+            selected_dir = select_proof_image_dir(images_dir)
+            self.assertEqual(selected_dir, images_dir / "0001")
+
+    def test_select_proof_image_dir_existing_dir_second_dir(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            images_dir = Path(tmpdir) / "images"
+            images_dir.mkdir()
+            (images_dir / "0001").mkdir()
+            (images_dir / "0002").mkdir()
+            selected_dir = select_proof_image_dir(images_dir)
+            self.assertEqual(selected_dir, images_dir / "0002")
+
+    def test_select_proof_image_dir_existing_dir_create_new_dir(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            images_dir = Path(tmpdir) / "images"
+            images_dir.mkdir()
+            (images_dir / "0001").mkdir()
+            (images_dir / "0001" / "0001.jpg").touch()
+            selected_dir = select_proof_image_dir(images_dir, max_images_per_dir=1)
+            self.assertEqual(selected_dir, images_dir / "0002")

open_prices/proofs/utils.py

@@ -110,31 +110,45 @@ def store_file(
     # We store the images in directories containing up to 1000 images
     # Once we reach 1000 images, we create a new directory by increasing the directory ID  # noqa
     # This is used to prevent the base image directory from containing too many files  # noqa
-    images_dir = settings.IMAGES_DIR
-    current_dir_id = max(
-        (int(p.name) for p in images_dir.iterdir() if p.is_dir() and p.name.isdigit()),
-        default=1,
-    )
-    current_dir_id_str = f"{current_dir_id:04d}"
-    current_dir = images_dir / current_dir_id_str
-    if current_dir.exists() and len(list(current_dir.iterdir())) >= 1_000:
-        # if the current directory contains 1000 images, we create a new one
-        current_dir_id += 1
-        current_dir = images_dir / str(current_dir_id)
+    current_dir = select_proof_image_dir(settings.IMAGES_DIR)
     current_dir.mkdir(exist_ok=True, parents=True)
     file_full_path = generate_full_path(current_dir, file_stem, extension)
     # write the content of the file to the new file
     with file_full_path.open("wb") as f:
         f.write(file.file.read())
     # create a thumbnail
     image_thumb_path = generate_thumbnail(
-        current_dir, current_dir_id_str, file_stem, extension, mimetype
+        current_dir, current_dir.name, file_stem, extension, mimetype
     )
     # Build file_path
-    file_path = generate_relative_path(current_dir_id_str, file_stem, extension)
+    file_path = generate_relative_path(current_dir.name, file_stem, extension)
     return (file_path, mimetype, image_thumb_path)
 
 
+def select_proof_image_dir(images_dir: Path, max_images_per_dir: int = 1_000) -> Path:
+    """ "Select the directory where to store the image.
+
+    We create a new directory when the current one contains more than 1000
+    images. The directories are named with a 4-digit number, starting at 0001.
+
+    :param images_dir: the directory where the images are stored
+    :param max_images_per_dir: the maximum number of images per directory
+    :return: the selected directory
+    """
+    current_dir_id = max(
+        (int(p.name) for p in images_dir.iterdir() if p.is_dir() and p.name.isdigit()),
+        default=1,
+    )
+    current_dir_id_str = f"{current_dir_id:04d}"
+    current_dir = images_dir / current_dir_id_str
+    if current_dir.exists() and len(list(current_dir.iterdir())) >= max_images_per_dir:
+        # if the current directory contains 1000 images, we create a new one
+        current_dir_id += 1
+        current_dir_id_str = f"{current_dir_id:04d}"
+        current_dir = images_dir / current_dir_id_str
+    return current_dir
+
+
 def run_ocr_on_image(image_path: Path | str, api_key: str) -> dict[str, Any] | None:
     """Run Google Cloud Vision OCR on the image stored at the given path.