filter design and wip implementation

games/filters.py

@@ -0,0 +1,61 @@
+import json
+from typing import TypeAlias, TypedDict, TypeVar
+
+from django.db.models import Model, Q
+from django.db.models.query import QuerySet
+
+filter_types = {
+    "session_start": {
+        "equals": "timestamp_start__year__exact=",
+        "isnull": "timestamp_start__exact=None",
+        "greater_than": "timestamp_start__gt=",
+        "less_than": "timestamp_start__lt=",
+    },
+}
+
+
+class Filter(TypedDict):
+    name: str
+    operator: str
+    value: str
+
+
+FilterList: TypeAlias = list[Filter]
+
+
+def string_to_django_filter_dict(s: str, value: str = "") -> dict[str, str | int]:
+    if s[-1] == "=":
+        s += value
+    key, value = s.split("=")
+    return {key: value}
+
+
+T = TypeVar("T", bound=Model)
+
+
+def apply_json_filter[T](s: str, queryset: QuerySet[T]) -> QuerySet[T]:
+    filter_obj = urlsafe_json_decode(s)
+    name, operator, value = (filter_obj[k] for k in ["name", "operator", "value"])
+    if name in filter_types:
+        if operator in filter_types[name]:
+            filtered = queryset.filter(
+                Q(**string_to_django_filter_dict(filter_types[name][operator], value))
+            )
+            return filtered
+    return queryset
+
+
+urlsafe_encode_table = str.maketrans({",": "^", ":": "-", " ": ""})
+urlsafe_decode_table = str.maketrans({"^": ",", "-": ":"})
+
+
+def urlsafe_json_encode[T](obj: T) -> str:
+    json_string = json.dumps(obj)
+    safe_string = json_string.translate(urlsafe_encode_table)
+    return safe_string
+
+
+def urlsafe_json_decode[T](s: str) -> T:
+    unsafe_string = s.translate(urlsafe_decode_table)
+    obj = json.loads(unsafe_string)
+    return obj