defmodule PromEx.TelemetryMetricsPrometheus.Core.Aggregator do
  @moduledoc false

  require Logger

  alias Telemetry.Metrics
  alias PromEx.TelemetryMetricsPrometheus.Core

  @typep bucket :: {upper_bound :: String.t(), count :: non_neg_integer()}
  @typep sample :: {name :: :telemetry.event_name(), {labels :: map(), measurement :: number()}}
  @typep key :: {name :: :telemetry.event_name(), map()}
  @typep aggregation :: {[bucket()], non_neg_integer(), number()}

  @spec aggregate(Core.metrics(), atom(), atom()) :: :ok
  def aggregate(definitions, table_id, dist_table_id) do
    for %Metrics.Distribution{} = metric <- definitions do
      :ets.take(dist_table_id, metric.name)
      |> aggregate_and_store(metric, table_id)
    end

    :ok
  end

  @spec aggregate_and_store(samples :: [sample()], Metrics.Distribution.t(), atom()) :: :ok
  defp aggregate_and_store(samples, metric, tid) do
    samples
    |> group_samples()
    |> Enum.map(fn {name, measurements} ->
      Enum.map(measurements, fn {labels, samples} ->
        key = {name, labels}
        prev_agg = get_aggregation(key, tid)

        Enum.sort(samples)
        |> bucket_measurements(metric.reporter_options[:buckets])
        |> merge(prev_agg)
        |> put_aggregation(key, tid)
      end)
    end)

    :ok
  end

  @spec get_time_series(atom()) :: %{:telemetry.event_name() => [sample()]}
  def get_time_series(table_id) do
    :ets.tab2list(table_id)
    |> Stream.filter(&filter_and_drop_time_series_with_bad_tag_values(&1, table_id))
    |> Enum.group_by(fn row -> row |> elem(0) |> elem(0) end)
  end

  defp filter_and_drop_time_series_with_bad_tag_values({[_, %{}], _}, _), do: true

  defp filter_and_drop_time_series_with_bad_tag_values({key, _}, table_id) do
    key
    |> elem(1)
    |> Enum.map(fn {label_key, value} ->
      case String.Chars.impl_for(value) do
        nil ->
          Logger.warn(
            "Dropping aggregation for bad tag value. metric:=#{inspect(elem(key, 0))} tag: #{inspect(label_key)}"
          )

          delete_aggregation(table_id, key)
          false

        _ ->
          true
      end
    end)
    |> Enum.all?()
  end

  defp delete_aggregation(table_id, key) do
    :ets.delete(table_id, key)
  end

  defp merge(new, {}), do: new

  defp merge({l_b, l_c, l_s}, {r_b, r_c, r_s}) do
    buckets =
      Enum.zip(l_b, r_b)
      |> Enum.map(fn {{bucket, a}, {bucket, b}} -> {bucket, a + b} end)

    {buckets, l_c + r_c, l_s + r_s}
  end

  @spec get_aggregation(key :: key(), table :: atom()) :: {} | aggregation()
  defp get_aggregation(key, table) do
    case :ets.lookup(table, key) do
      [] -> {}
      [agg] -> agg |> elem(1)
    end
  end

  @spec put_aggregation(aggregation :: nil | aggregation(), key :: key(), table :: atom()) :: true
  def put_aggregation(nil, _, _), do: true

  def put_aggregation(aggregation, key, tid) do
    :ets.insert(tid, {key, aggregation})
  end

  @spec group_samples(samples :: [sample()]) :: map()
  def group_samples(samples) do
    Enum.reduce(samples, %{}, fn {name, {labels, measurement}}, acc ->
      metric = Map.get(acc, name, %{})
      values = Map.get(metric, labels, [])
      new_values = [measurement | values]
      new_metric = Map.put(metric, labels, new_values)
      Map.put(acc, name, new_metric)
    end)
  end

  @spec bucket_measurements(measurements :: [number()], buckets :: Core.Distribution.buckets()) ::
          {[bucket()], non_neg_integer(), number()}
  def bucket_measurements(measurements, [b | buckets]),
    do: bucket(measurements, buckets, b, 0, 0, [])

  defp bucket([], [], _, count, sum, result), do: {Enum.reverse(result), count, sum}

  defp bucket(measurements, [], "+Inf", count, sum, result) do
    {new_count, new_sum} =
      Enum.reduce(measurements, {count, sum}, fn m, {c, s} ->
        {c + 1, s + m}
      end)

    bucket([], [], "+Inf", new_count, new_sum, [{"+Inf", new_count} | result])
  end

  defp bucket([], buckets, cur_bucket, count, sum, result) do
    rest = Enum.reverse([cur_bucket | buckets]) |> Enum.map(&{"#{&1}", count})
    bucket([], [], nil, count, sum, rest ++ result)
  end

  defp bucket([m | r_m] = measurements, [b | r_b] = buckets, cur_bucket, count, sum, result) do
    if m <= cur_bucket do
      bucket(r_m, buckets, cur_bucket, count + 1, sum + m, result)
    else
      bucket(measurements, r_b, b, count, sum, [{"#{cur_bucket}", count} | result])
    end
  end
end