filter design and wip implementation

filter-design.md

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+# Django
+
+Session.objects.filter(timestamp_start__year=2024)
+
+# JSON
+```json
+{
+    "type": "session_start",
+    "operator": "equals",
+    "value": "2024"
+}
+```
+
+# HTML
+```html
+<select name="filters">
+    <option value='[{"type": "session_start", "operator": "equals", "value": "2024"}]'>2024</option>
+    <option value='[{"type": "session_start", "operator": "equals", "value": "2023"}]'>2023</option>
+</select>
+```
+
+# Python: Python -> HTML
+```python
+filters = [
+    {
+        "type": "session_start",
+        "operator": "equals",
+        "value": "2024"
+    }
+]
+
+# predefined values
+session_start_select = Select(name="filters", children=session_start_options)
+session_start_options = [
+    Option(value=create_filter("session_start", "equals", value=year))
+    for year in range(2000, 2024)
+]
+
+# user-selected values
+
+
+```
+
+# Python: JSON -> Django
+```python
+filter_types = {
+    "session_start": {
+        "equals": "timestamp_start__exact=",
+        "isnull": "timestamp_start__exact=None",
+        "greater_than": "timestamp_start__gt=",
+        "less_than": "timestamp_start__lt=",
+    },
+}
+# filter_string = request.GET.get("filters")
+filter_string = """
+{
+    "type": "session_start",
+    "operator": "equals",
+    "value": "2024"
+}
+"""
+def string_to_django_filter_dict(s: str):
+    if s[-1] == "=":
+        s + value
+    key, value = s.split("=")
+    return {key: value}
+    
+filter_obj = json.loads(filter_string)[0]
+field, operator, value = filter_obj
+
+if type in filter_types:
+    if operator in filter_types[type]:
+        queryset.filter(Q(**string_to_django_filter_dict(filter_types[type][operator])}))
+    else:
+        return False
+```
+
+# Python: Django -> JSON -> URI param
+```python
+filters = [
+    {
+        "type": "session_start",
+        "operator": "equals",
+        "value": "2024"
+    }
+]
+context = {
+    "filters": json.dumps(filters)
+}
+return render("filter.html", context)
+```
+
+# Python: Django -> JSON (function)
+```python
+create_filter("session_start", "operator": "equals", "value": "2024")
+```

games/filters.py

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+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