First pass at Nostr filters

lib/gc_index_relay/nostr/filter.ex

@@ -0,0 +1,56 @@
+defmodule GcIndexRelay.Nostr.Filter do
+  alias GcIndexRelay.Repo
+  import Ecto.Query
+
+  @derive [Jason.Encoder]
+  defstruct [:ids, :authors, :kinds, :tags, :since, :until, :limit]
+
+  # TODO: Implement tag filtering
+
+  @doc """
+  Applies a filter to an Ecto query of Nostr events.
+
+  ## Params
+
+  - `query` - An Ecto query. This MUST be a query over the `GcIndexRelay.Nostr.Event` schema.
+  - `filter` - A `GcIndexRelay.Nostr.Filter` struct.
+
+  ## Returns
+
+  A filtered list of events in descending order of creation time.
+  """
+  def apply(%Ecto.Query{} = query, %__MODULE__{} = filter) do
+    query
+    |> apply_ids(filter.ids)
+    |> apply_authors(filter.authors)
+    |> apply_kinds(filter.kinds)
+    |> apply_since(filter.since)
+    |> apply_until(filter.until)
+    |> preload(:tags)
+    # Always sort in descending order of creation time
+    |> order_by([e], desc: e.created_at)
+    |> apply_limit(filter.limit)
+    |> Repo.all()
+  end
+
+  defp apply_ids(query, nil), do: query
+  defp apply_ids(query, []), do: query
+  defp apply_ids(query, ids), do: where(query, [e], e.id in ^ids)
+
+  defp apply_authors(query, nil), do: query
+  defp apply_authors(query, []), do: query
+  defp apply_authors(query, authors), do: where(query, [e], e.author in ^authors)
+
+  defp apply_kinds(query, nil), do: query
+  defp apply_kinds(query, []), do: query
+  defp apply_kinds(query, kinds), do: where(query, [e], e.kind in ^kinds)
+
+  defp apply_since(query, nil), do: query
+  defp apply_since(query, since), do: where(query, [e], e.created_at >= ^since)
+
+  defp apply_until(query, nil), do: query
+  defp apply_until(query, until), do: where(query, [e], e.created_at <= ^until)
+
+  defp apply_limit(query, nil), do: query
+  defp apply_limit(query, limit), do: limit(query, ^limit)
+end