perf: add persistent ETS weather cache for N+1 prevention

Ultraworked with Sisyphus

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

lib/aprsme/application.ex

@@ -197,6 +197,7 @@ defmodule Aprsme.Application do
     _ = :ets.new(:query_cache, [:set, :public, :named_table, read_concurrency: true, write_concurrency: true])
     _ = :ets.new(:device_cache, [:set, :public, :named_table, read_concurrency: true, write_concurrency: true])
     _ = :ets.new(:symbol_cache, [:set, :public, :named_table, read_concurrency: true, write_concurrency: true])
+    _ = :ets.new(:weather_cache, [:set, :public, :named_table, read_concurrency: true, write_concurrency: true])
     _ = :ets.new(:aprsme, [:set, :public, :named_table, read_concurrency: true, write_concurrency: true])
     _ = :ets.insert(:aprsme, {:message_number, 0})
 

lib/aprsme/weather_cache.ex

@@ -0,0 +1,93 @@
+defmodule Aprsme.WeatherCache do
+  @moduledoc """
+  Persistent ETS-based cache for weather callsign lookups.
+
+  Eliminates N+1 queries for `has_weather_packets?` checks during map
+  marker rendering. Entries expire after `@ttl_ms` to stay reasonably
+  current without per-callsign DB queries.
+  """
+  @cache_name :weather_cache
+  @ttl_ms to_timeout(minute: 5)
+
+  @doc """
+  Create the ETS table if it doesn't exist yet.
+  The table is typically created in application.ex alongside other ETS tables.
+  """
+  def setup do
+    _ =
+      case :ets.info(@cache_name) do
+        :undefined ->
+          :ets.new(@cache_name, [
+            :named_table,
+            :public,
+            :set,
+            :protected,
+            read_concurrency: true,
+            write_concurrency: true
+          ])
+
+        _ ->
+          :ok
+      end
+
+    :ok
+  end
+
+  @doc """
+  Batch-populate the cache for the given list of callsigns.
+  """
+  def cache_weather_callsigns(callsigns) when is_list(callsigns) do
+    weather_set = Aprsme.Packets.weather_callsigns(callsigns)
+    expires_at = System.monotonic_time(:millisecond) + @ttl_ms
+
+    Enum.each(callsigns, fn cs ->
+      key = String.upcase(String.trim(cs))
+      has_weather = MapSet.member?(weather_set, key)
+      :ets.insert(@cache_name, {key, has_weather, expires_at})
+    end)
+
+    :ok
+  rescue
+    _ -> :ok
+  end
+
+  @doc """
+  Check if a callsign has weather packets.
+  Returns `:unknown` if not cached, `true`/`false` if cached.
+  """
+  def weather_callsign?(callsign) when is_binary(callsign) do
+    key = String.upcase(String.trim(callsign))
+
+    case :ets.lookup(@cache_name, key) do
+      [{^key, value, expires_at}] ->
+        if System.monotonic_time(:millisecond) < expires_at do
+          value
+        else
+          :ets.delete(@cache_name, key)
+          :unknown
+        end
+
+      _ ->
+        :unknown
+    end
+  end
+
+  @doc """
+  Evict expired entries.
+  """
+  def evict_expired do
+    now = System.monotonic_time(:millisecond)
+
+    @cache_name
+    |> :ets.tab2list()
+    |> Enum.each(fn
+      {key, _value, expires_at} when expires_at < now ->
+        :ets.delete(@cache_name, key)
+
+      _ ->
+        :ok
+    end)
+
+    :ok
+  end
+end