auto compress product icons

core/fields.py

@@ -0,0 +1,125 @@
+from pathlib import Path
+
+from django.core.exceptions import FieldError
+from django.db import models
+from django.db.models.fields.files import ImageFieldFile
+from PIL import Image
+
+from core.utils import resize_image_explicit
+
+
+class ResizedImageFieldFile(ImageFieldFile):
+    def get_resized_dimensions(self, image: Image.Image) -> tuple[int, int]:
+        """Get the dimensions of the resized image.
+
+        If the width and height are given, they are used.
+        If only one is given, the other is calculated to keep the same ratio.
+
+        Returns:
+            Tuple of width and height
+        """
+        width = self.field.width
+        height = self.field.height
+        if width is not None and height is not None:
+            return self.field.width, self.field.height
+        if width is None:
+            width = int(image.width * height / image.height)
+        elif height is None:
+            height = int(image.height * width / image.width)
+        return width, height
+
+    def get_name(self) -> str:
+        """Get the name of the resized image.
+
+        If the field has a force_format attribute,
+        the extension of the file will be changed to match it.
+        Otherwise, the name is left unchanged.
+
+        Raises:
+            ValueError: If the image format is unknown
+        """
+        if not self.field.force_format:
+            return self.name
+        formats = {val: key for key, val in Image.registered_extensions().items()}
+        new_format = self.field.force_format
+        if new_format in formats:
+            extension = formats[new_format]
+        else:
+            raise ValueError(f"Unknown format {new_format}")
+        return str(Path(self.file.name).with_suffix(f".{extension}"))
+
+    def save(self, name, content, save=True):  # noqa FBT002
+        content.file.seek(0)
+        img = Image.open(content.file)
+        width, height = self.get_resized_dimensions(img)
+        img_format = self.field.force_format or img.format
+        new_content = resize_image_explicit(img, (width, height), img_format)
+        name = self.get_name()
+        return super().save(name, new_content, save)
+
+
+class ResizedImageField(models.ImageField):
+    """A field that automatically resizes images to a given size.
+
+    This field is useful for profile pictures or product icons, for example.
+
+    The final size of the image is determined by the width and height parameters :
+
+    - If both are given, the image will be resized
+      to fit in a rectangle of width x height
+    - If only one is given, the other will be calculated to keep the same ratio
+
+    If the force_format parameter is given, the image will be converted to this format.
+
+    Examples:
+        To resize an image with a height of 100px, without changing the ratio,
+        and a format of WEBP :
+
+        ```python
+        class Product(models.Model):
+            icon = ResizedImageField(height=100, force_format="WEBP")
+        ```
+
+        To explicitly resize an image to 100x100px (but possibly change the ratio) :
+
+        ```python
+        class Product(models.Model):
+            icon = ResizedImageField(width=100, height=100)
+        ```
+
+    Raises:
+        FieldError: If neither width nor height is given
+
+    Args:
+        width: If given, the width of the resized image
+        height: If given, the height of the resized image
+        force_format: If given, the image will be converted to this format
+    """
+
+    attr_class = ResizedImageFieldFile
+
+    def __init__(
+        self,
+        width: int | None = None,
+        height: int | None = None,
+        force_format: str | None = None,
+        **kwargs,
+    ):
+        if width is None and height is None:
+            raise FieldError(
+                f"{self.__class__.__name__} requires "
+                "width, height or both, but got neither"
+            )
+        self.width = width
+        self.height = height
+        self.force_format = force_format
+        super().__init__(**kwargs)
+
+    def deconstruct(self):
+        name, path, args, kwargs = super().deconstruct()
+        if self.width is not None:
+            kwargs["width"] = self.width
+        if self.height is not None:
+            kwargs["height"] = self.height
+        kwargs["force_format"] = self.force_format
+        return name, path, args, kwargs

core/utils.py

@@ -25,7 +25,7 @@ from django.core.files.base import ContentFile
 from django.http import HttpRequest
 from django.utils import timezone
 from PIL import ExifTags
-from PIL.Image import Resampling
+from PIL.Image import Image, Resampling
 
 
 def get_start_of_semester(today: Optional[date] = None) -> date:
@@ -82,18 +82,20 @@ def get_semester_code(d: Optional[date] = None) -> str:
     return "P" + str(start.year)[-2:]
 
 
-def scale_dimension(width, height, long_edge):
-    ratio = long_edge / max(width, height)
-    return int(width * ratio), int(height * ratio)
-
-
-def resize_image(im, edge, img_format):
+def resize_image(im: Image, edge: int, img_format: str):
+    """Resize an image to fit the given edge length and format."""
     (w, h) = im.size
-    (width, height) = scale_dimension(w, h, long_edge=edge)
+    ratio = edge / max(w, h)
+    (width, height) = int(w * ratio), int(h * ratio)
+    return resize_image_explicit(im, (width, height), img_format)
+
+
+def resize_image_explicit(im: Image, size: tuple[int, int], img_format: str):
+    """Resize an image to the given size and format."""
     img_format = img_format.upper()
     content = BytesIO()
     # use the lanczos filter for antialiasing and discard the alpha channel
-    im = im.resize((width, height), Resampling.LANCZOS)
+    im = im.resize((size[0], size[1]), Resampling.LANCZOS)
     if img_format == "JPEG":
         # converting an image with an alpha channel to jpeg would cause a crash
         im = im.convert("RGB")