defmodule AbsintheMetrics.Backend.PrometheusHistogram do
  @behaviour AbsintheMetrics
  @query_metric_name :graphql_query_duration_milliseconds
  @field_metric_name :graphql_fields_duration_milliseconds
  use Prometheus

  def field(:query, _field, buckets: buckets) do
    _ = Histogram.declare([name: @query_metric_name,
                           labels: [:query, :status],
                           buckets: buckets,
                           help: "Resolution time for GraphQL queries"])
  end

  def field(object, field, buckets: buckets) do
    _ = Histogram.declare([name: @field_metric_name,
                           labels: [:object, :field, :status],
                           buckets: buckets,
                           help: "Metrics for GraphQL field resolvers"])
  end

  def instrument(:query, field, {status, _}, time) do
    Histogram.observe([name: @query_metric_name, labels: [field, status]], time)
  end

  def instrument(object, field, {status, _}, time) do
    Histogram.observe([name: @field_metric_name, labels: [object, field, status]], time)
  end
end