add django backend in /core

ported from laravel in c3lf/lfbackend repo

core/files/models.py

@@ -0,0 +1,57 @@
+from django.core.files.base import ContentFile
+from django.db import models, IntegrityError
+from django_softdelete.models import SoftDeleteModel
+
+from inventory.models import Item
+
+
+def hash_upload(instance, filename):
+    return f"{instance.hash[:2]}/{instance.hash[2:4]}/{instance.hash[4:6]}/{instance.hash[6:]}"
+
+
+class FileManager(models.Manager):
+    def get_or_create(self, **kwargs):
+        if 'data' in kwargs and type(kwargs['data']) == str:
+            import base64
+            from hashlib import sha256
+            content = base64.b64decode(kwargs['data'], validate=True)
+            kwargs.pop('data')
+            content_hash = sha256(content).hexdigest()
+            kwargs['file'] = ContentFile(content, content_hash)
+            kwargs['hash'] = content_hash
+        else:
+            raise ValueError('data must be a base64 encoded string or file and hash must be provided')
+        try:
+            return self.get(hash=kwargs['hash']), False
+        except self.model.DoesNotExist:
+            return self.create(**kwargs), True
+
+    def create(self, **kwargs):
+        if 'data' in kwargs and type(kwargs['data']) == str:
+            import base64
+            from hashlib import sha256
+            content = base64.b64decode(kwargs['data'], validate=True)
+            kwargs.pop('data')
+            content_hash = sha256(content).hexdigest()
+            kwargs['file'] = ContentFile(content, content_hash)
+            kwargs['hash'] = content_hash
+        elif 'file' in kwargs and 'hash' in kwargs and type(kwargs['file']) == ContentFile:
+            pass
+        else:
+            raise ValueError('data must be a base64 encoded string or file and hash must be provided')
+        if not self.filter(hash=kwargs['hash']).exists():
+            return super().create(**kwargs)
+        else:
+            raise IntegrityError('File with this hash already exists')
+
+
+class File(models.Model):
+    item = models.ForeignKey(Item, models.CASCADE, db_column='iid', null=True, blank=True, related_name='files')
+    created_at = models.DateTimeField(blank=True, null=True)
+    updated_at = models.DateTimeField(blank=True, null=True)
+    deleted_at = models.DateTimeField(blank=True, null=True)
+    file = models.ImageField(upload_to=hash_upload)
+    mime_type = models.CharField(max_length=255, null=False, blank=False)
+    hash = models.CharField(max_length=64, null=False, blank=False, unique=True)
+
+    objects = FileManager()