Add generic paginator for API

1 files changed, 45 insertions, 0 deletions

diff --git a/api/pagination.py b/api/pagination.py
new file mode 100644
index 0000000..0539ae8
--- /dev/null
+++ b/api/pagination.py
@@ -0,0 +1,45 @@
+class MastodonPaginator:
+    """
+    Paginates in the Mastodon style (max_id, min_id, etc)
+    """
+
+    def __init__(
+        self,
+        anchor_model,
+        sort_attribute: str = "created",
+        default_limit: int = 20,
+        max_limit: int = 40,
+    ):
+        self.anchor_model = anchor_model
+        self.sort_attribute = sort_attribute
+        self.default_limit = default_limit
+        self.max_limit = max_limit
+
+    def paginate(
+        self,
+        queryset,
+        min_id: str | None,
+        max_id: str | None,
+        since_id: str | None,
+        limit: int | None,
+    ):
+        if max_id:
+            anchor = self.anchor_model.objects.get(pk=max_id)
+            queryset = queryset.filter(
+                **{self.sort_attribute + "__lt": getattr(anchor, self.sort_attribute)}
+            )
+        if since_id:
+            anchor = self.anchor_model.objects.get(pk=since_id)
+            queryset = queryset.filter(
+                **{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)}
+            )
+        if min_id:
+            # Min ID requires items _immediately_ newer than specified, so we
+            # invert the ordering to accomodate
+            anchor = self.anchor_model.objects.get(pk=min_id)
+            queryset = queryset.filter(
+                **{self.sort_attribute + "__gt": getattr(anchor, self.sort_attribute)}
+            ).order_by(self.sort_attribute)
+        else:
+            queryset = queryset.order_by("-" + self.sort_attribute)
+        return list(queryset[: min(limit or self.default_limit, self.max_limit)])