Initial

backend/common/form/img_with_preview.py

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+from django import forms
+from django.conf import settings
+from django.contrib.admin.widgets import AdminFileWidget
+from django.core.validators import FileExtensionValidator
+from django.db import models
+from django.forms import FileInput, widgets
+
+from common.validators import MaxFilesizeValidator, readableToInt
+
+MAX_UPLOAD_SIZE = '312 KB'
+
+
+class ImageFileWidget(widgets.ClearableFileInput):
+    template_name = 'forms/img-with-preview.html'
+
+    def get_context(self, name, value, attrs):
+        context = super().get_context(name, value, attrs)
+        context['MEDIA_URL'] = settings.MEDIA_URL
+        return context
+
+
+class ImgField(forms.FileField):
+    widget = ImageFileWidget
+    default_validators = [
+        FileExtensionValidator(['jpg', 'jpeg', 'png']),
+        MaxFilesizeValidator(MAX_UPLOAD_SIZE),
+    ]
+
+    def widget_attrs(self, widget):
+        attrs = super().widget_attrs(widget)
+        if isinstance(widget, FileInput) and 'accept' not in widget.attrs:
+            attrs.setdefault('accept', 'image/png,image/jpeg')  # image/*
+        if isinstance(widget, ImageFileWidget):
+            attrs.update({
+                'data-upload-limit': readableToInt(MAX_UPLOAD_SIZE),
+                'data-upload-limit-str': MAX_UPLOAD_SIZE,
+                'onchange': 'validate_upload_limit(this)',
+            })
+        return attrs
+
+
+class FileWithImagePreview(models.FileField):  # use ImageField to omit Pillow
+    __del_image_on_save = False
+
+    def formfield(self, **kwargs):
+        if kwargs['widget'] is AdminFileWidget:
+            # Override admin widget. Defined by ImgField anyway
+            del kwargs['widget']
+        return super().formfield(**{'form_class': ImgField, **kwargs})
+
+    def save_form_data(self, instance, data):
+        if data is False:
+            self.__del_image_on_save = True
+        super().save_form_data(instance, data)
+
+    def pre_save(self, model_instance, add):
+        if self.__del_image_on_save:
+            self.__del_image_on_save = False
+            self.deletePreviousImage(model_instance)
+        return super().pre_save(model_instance, add)
+
+    def deletePreviousImage(self, instance: models.Model):
+        if not instance.pk:
+            return
+        prev = instance.__class__.objects.get(pk=instance.pk)
+        imgField = getattr(prev, self.attname)
+        imgField.delete(save=False)