Added permission app

apps/permission/models.py

@@ -0,0 +1,112 @@
+import json
+
+from django.contrib.contenttypes.models import ContentType
+from django.core.exceptions import ValidationError
+from django.db import models
+from django.db.models import Q
+from django.utils.translation import gettext_lazy as _
+
+
+class InstancedPermission:
+
+    def __init__(self, model, permission, type, field):
+        self.model = model
+        self.permission = permission
+        self.type = type
+        self.field = field
+
+    def applies(self, obj, permission_type, field_name=None):
+        if ContentType.objects.get_for_model(obj) != self.model:
+            # The permission does not apply to the object
+            return False
+        if self.permission is None:
+            if permission_type == self.type:
+                if field_name is not None:
+                    return field_name == self.field
+                else:
+                    return True
+            else:
+                return False
+        elif isinstance(self.permission, dict):
+            for field in self.permission:
+                value = getattr(obj, field)
+                if isinstance(value, models.Model):
+                    value = value.pk
+                if value != self.permission[field]:
+                    return False
+        elif isinstance(self.permission, type(obj.pk)):
+            if obj.pk != self.permission:
+                return False
+        if permission_type == self.type:
+            if field_name:
+                return field_name == self.field
+            else:
+                return True
+        return False
+
+    def __repr__(self):
+        if self.field:
+            return _("Can {type} {model}.{field} in {permission}").format(type=self.type, model=self.model, field=self.field, permission=self.permission)
+        else:
+            return _("Can {type} {model} in {permission}").format(type=self.type, model=self.model, permission=self.permission)
+
+
+class Permission(models.Model):
+
+    PERMISSION_TYPES = [
+        ('C', 'add'),
+        ('R', 'view'),
+        ('U', 'change'),
+        ('D', 'delete')
+    ]
+
+    model = models.ForeignKey(ContentType, on_delete=models.CASCADE, related_name='+')
+
+    permission = models.TextField()
+
+    type = models.CharField(max_length=15, choices=PERMISSION_TYPES)
+
+    field = models.CharField(max_length=255, blank=True)
+
+    class Meta:
+        unique_together = ('model', 'permission', 'type', 'field')
+
+    def clean(self):
+        if self.field and self.type not in {'R', 'U'}:
+            raise ValidationError(_("Specifying field applies only to view and change permission types."))
+
+    def save(self):
+        self.full_clean()
+        super().save()
+
+    def _about(_self, _permission, **kwargs):
+        if _permission[0] == 'all':
+            return None
+        elif _permission[0] == 'pk':
+            if _permission[1] in kwargs:
+                return kwargs[_permission[1]].pk
+            else:
+                return None
+        elif _permission[0] == 'filter':
+            return {field: _self._about(_permission[1][field], **kwargs) for field in _permission[1]}
+        else:
+            return _permission
+
+    def about(self, **kwargs):
+        permission = json.loads(self.permission)
+        permission = self._about(permission, **kwargs)
+        return InstancedPermission(self.model, permission, self.type, self.field)
+
+    def __str__(self):
+        if self.field:
+            return _("Can {type} {model}.{field} in {permission}").format(type=self.type, model=self.model, field=self.field, permission=self.permission)
+        else:
+            return _("Can {type} {model} in {permission}").format(type=self.type, model=self.model, permission=self.permission)
+
+
+class UserPermission(models.Model):
+
+    user = models.ForeignKey('auth.User', on_delete=models.CASCADE)
+
+    permission = models.ForeignKey(Permission, on_delete=models.CASCADE)
+