ft: add Peep storage (#241)

* ft: implement pluggable storage

Preliminary work for supporting different storages beyond
`telemetry_metrics_prometheus_core`.

* ft: add Peep storage

---------

Co-authored-by: Alexander Koutmos <akoutmos@gmail.com>

lib/prom_ex/metric_types/event.ex

@@ -9,6 +9,8 @@ defmodule PromEx.MetricTypes.Event do
   - `metrics`: A list of Telemetry Metrics structs that define the metrics.
   """
 
+  alias Telemetry.Metrics.Distribution
+
   @type t :: %__MODULE__{
           group_name: atom(),
           metrics: list(PromEx.telemetry_metrics())
@@ -25,7 +27,43 @@ defmodule PromEx.MetricTypes.Event do
   def build(group_name, metrics) do
     %__MODULE__{
       group_name: group_name,
-      metrics: metrics
+      metrics: build_buckets(group_name, metrics)
     }
   end
+
+  defp build_buckets(name, metrics) do
+    if Code.ensure_loaded?(Peep.Buckets) do
+      build_buckets_modules(name, metrics)
+    else
+      metrics
+    end
+  end
+
+  defp build_buckets_modules(name, metrics) do
+    metrics
+    |> Enum.with_index()
+    |> Enum.map(&build_bucket(name, &1))
+  end
+
+  defp build_bucket(name, {%Distribution{} = dist, idx}) do
+    reporter_options =
+      Keyword.put_new_lazy(dist.reporter_options, :peep_bucket_calculator, fn ->
+        buckets = Keyword.fetch!(dist.reporter_options, :buckets)
+
+        {:module, name, _, _} =
+          Module.create(
+            Module.concat(name, "Bucket_#{idx}"),
+            quote do
+              use Peep.Buckets.Custom, buckets: unquote(buckets)
+            end,
+            __ENV__
+          )
+
+        name
+      end)
+
+    %Distribution{dist | reporter_options: reporter_options}
+  end
+
+  defp build_bucket(_name, {other, _}), do: other
 end

lib/prom_ex/storage/core.ex

@@ -1,3 +1,6 @@
+# TODO: For version 2.0.0 have all of the supported adapters be
+# optional deps.
+# if Code.ensure_loaded?(TelemetryMetricsPrometheus.Core) do
 defmodule PromEx.Storage.Core do
   @behaviour PromEx.Storage
 
@@ -22,4 +25,4 @@ defmodule PromEx.Storage.Core do
 
     Core.child_spec(opts)
   end
-end
+end

lib/prom_ex/storage/peep.ex

@@ -0,0 +1,22 @@
+if Code.ensure_loaded?(Peep) do
+  defmodule PromEx.Storage.Peep do
+    @behaviour PromEx.Storage
+
+    @impl true
+    def scrape(name) do
+      Peep.get_all_metrics(name)
+      |> Peep.Prometheus.export()
+      |> IO.iodata_to_binary()
+    end
+
+    @impl true
+    def child_spec(name, metrics) do
+      opts = [
+        name: name,
+        metrics: metrics
+      ]
+
+      Peep.child_spec(opts)
+    end
+  end
+end

mix.exs

@@ -60,6 +60,7 @@ defmodule PromEx.MixProject do
       {:telemetry_poller, "~> 1.1"},
       {:telemetry_metrics, "~> 1.0"},
       {:telemetry_metrics_prometheus_core, "~> 1.2"},
+      {:peep, "~> 2.0 or ~> 3.0", optional: true},
       {:plug_cowboy, ">= 2.6.0"},
       {:octo_fetch, "~> 0.4"},