defmodule Aprsme.PromEx.Plugins.Aprsme do
  @moduledoc """
  PromEx plugin exposing app-specific telemetry as Prometheus metrics.

  Mirrors the metrics already defined for LiveDashboard in
  `AprsmeWeb.Telemetry.metrics/0`, grouping them by subsystem:

    * GenStage packet pipeline (`[:aprsme, :packet_pipeline, :batch]`)
    * Producer backpressure (`[:aprsme, :packet_producer, :backpressure]`)
    * Spatial PubSub (`[:aprsme, :spatial_pubsub, ...]`)
    * Database connection pool (`[:aprsme, :repo, :pool]`)
    * Postgres database stats (`[:aprsme, :postgres, ...]`)
    * Insert optimizer (`[:aprsme, :insert_optimizer, ...]`)
  """

  use PromEx.Plugin

  @duration_buckets [10, 25, 50, 100, 250, 500, 1000, 2500, 5000, 10_000]

  @impl true
  def event_metrics(_opts) do
    [
      packet_pipeline_metrics(),
      producer_backpressure_metrics(),
      spatial_pubsub_metrics(),
      repo_pool_metrics(),
      postgres_metrics(),
      insert_optimizer_metrics(),
      api_metrics()
    ]
  end

  defp packet_pipeline_metrics do
    Event.build(
      :aprsme_packet_pipeline_event_metrics,
      [
        counter(
          [:aprsme, :packet_pipeline, :batch, :count],
          event_name: [:aprsme, :packet_pipeline, :batch],
          measurement: :count,
          description: "Total number of packets processed in batches"
        ),
        counter(
          [:aprsme, :packet_pipeline, :batch, :success],
          event_name: [:aprsme, :packet_pipeline, :batch],
          measurement: :success,
          description: "Total number of successful inserts"
        ),
        counter(
          [:aprsme, :packet_pipeline, :batch, :error],
          event_name: [:aprsme, :packet_pipeline, :batch],
          measurement: :error,
          description: "Total number of insert errors"
        ),
        distribution(
          [:aprsme, :packet_pipeline, :batch, :duration_milliseconds],
          event_name: [:aprsme, :packet_pipeline, :batch],
          measurement: :duration_ms,
          description: "Batch insert duration",
          unit: :millisecond,
          reporter_options: [buckets: @duration_buckets]
        )
      ]
    )
  end

  defp producer_backpressure_metrics do
    Event.build(
      :aprsme_packet_producer_event_metrics,
      [
        counter(
          [:aprsme, :packet_producer, :backpressure, :count],
          event_name: [:aprsme, :packet_producer, :backpressure],
          measurement: :count,
          description: "Backpressure state changes in the packet producer"
        )
      ]
    )
  end

  defp spatial_pubsub_metrics do
    Event.build(
      :aprsme_spatial_pubsub_event_metrics,
      [
        last_value(
          [:aprsme, :spatial_pubsub, :clients, :count],
          event_name: [:aprsme, :spatial_pubsub, :clients],
          measurement: :count,
          description: "Number of connected spatial PubSub clients"
        ),
        last_value(
          [:aprsme, :spatial_pubsub, :clients, :grid_cells],
          event_name: [:aprsme, :spatial_pubsub, :clients],
          measurement: :grid_cells,
          description: "Number of active grid cells"
        ),
        last_value(
          [:aprsme, :spatial_pubsub, :clients, :avg_clients_per_cell],
          event_name: [:aprsme, :spatial_pubsub, :clients],
          measurement: :avg_clients_per_cell,
          description: "Average clients per grid cell"
        ),
        counter(
          [:aprsme, :spatial_pubsub, :broadcasts, :total],
          event_name: [:aprsme, :spatial_pubsub, :broadcasts],
          measurement: :total,
          description: "Total spatial broadcasts sent"
        ),
        counter(
          [:aprsme, :spatial_pubsub, :broadcasts, :filtered],
          event_name: [:aprsme, :spatial_pubsub, :broadcasts],
          measurement: :filtered,
          description: "Broadcasts filtered out by viewport"
        ),
        counter(
          [:aprsme, :spatial_pubsub, :broadcasts, :packets],
          event_name: [:aprsme, :spatial_pubsub, :broadcasts],
          measurement: :packets,
          description: "Total packets processed by spatial PubSub"
        ),
        last_value(
          [:aprsme, :spatial_pubsub, :efficiency, :ratio],
          event_name: [:aprsme, :spatial_pubsub, :efficiency],
          measurement: :ratio,
          description: "Broadcast efficiency ratio (0-1)"
        ),
        counter(
          [:aprsme, :spatial_pubsub, :efficiency, :saved_broadcasts],
          event_name: [:aprsme, :spatial_pubsub, :efficiency],
          measurement: :saved_broadcasts,
          description: "Number of broadcasts saved by viewport filtering"
        )
      ]
    )
  end

  defp repo_pool_metrics do
    Event.build(
      :aprsme_repo_pool_event_metrics,
      [
        last_value(
          [:aprsme, :repo, :pool, :size],
          event_name: [:aprsme, :repo, :pool],
          measurement: :size,
          description: "Configured DB connection pool size"
        ),
        last_value(
          [:aprsme, :repo, :pool, :idle],
          event_name: [:aprsme, :repo, :pool],
          measurement: :idle,
          description: "Idle DB connections"
        ),
        last_value(
          [:aprsme, :repo, :pool, :busy],
          event_name: [:aprsme, :repo, :pool],
          measurement: :busy,
          description: "Busy DB connections"
        ),
        last_value(
          [:aprsme, :repo, :pool, :available],
          event_name: [:aprsme, :repo, :pool],
          measurement: :available,
          description: "Available DB connections"
        ),
        last_value(
          [:aprsme, :repo, :pool, :queue_length],
          event_name: [:aprsme, :repo, :pool],
          measurement: :queue_length,
          description: "Processes waiting on a DB connection"
        ),
        last_value(
          [:aprsme, :repo, :pool, :total],
          event_name: [:aprsme, :repo, :pool],
          measurement: :total,
          description: "Total connections in the DB pool"
        )
      ]
    )
  end

  defp postgres_metrics do
    Event.build(
      :aprsme_postgres_event_metrics,
      [
        last_value(
          [:aprsme, :postgres, :database, :size_bytes],
          event_name: [:aprsme, :postgres, :database],
          measurement: :size_bytes,
          description: "Total Postgres database size in bytes",
          unit: :byte
        ),
        last_value(
          [:aprsme, :postgres, :connections, :total],
          event_name: [:aprsme, :postgres, :connections],
          measurement: :total,
          description: "Total Postgres connections"
        ),
        last_value(
          [:aprsme, :postgres, :connections, :active],
          event_name: [:aprsme, :postgres, :connections],
          measurement: :active,
          description: "Active Postgres connections"
        ),
        last_value(
          [:aprsme, :postgres, :connections, :idle],
          event_name: [:aprsme, :postgres, :connections],
          measurement: :idle,
          description: "Idle Postgres connections"
        ),
        last_value(
          [:aprsme, :postgres, :connections, :idle_in_transaction],
          event_name: [:aprsme, :postgres, :connections],
          measurement: :idle_in_transaction,
          description: "Connections idle in transaction"
        ),
        last_value(
          [:aprsme, :postgres, :connections, :waiting],
          event_name: [:aprsme, :postgres, :connections],
          measurement: :waiting,
          description: "Postgres connections waiting on locks"
        ),
        last_value(
          [:aprsme, :postgres, :packets_table, :live_tuples],
          event_name: [:aprsme, :postgres, :packets_table],
          measurement: :live_tuples,
          description: "Live rows in the packets table"
        ),
        last_value(
          [:aprsme, :postgres, :packets_table, :dead_tuples],
          event_name: [:aprsme, :postgres, :packets_table],
          measurement: :dead_tuples,
          description: "Dead rows in the packets table"
        ),
        counter(
          [:aprsme, :postgres, :packets_table, :total_inserts],
          event_name: [:aprsme, :postgres, :packets_table],
          measurement: :total_inserts,
          description: "Total inserts into the packets table"
        ),
        counter(
          [:aprsme, :postgres, :packets_table, :total_updates],
          event_name: [:aprsme, :postgres, :packets_table],
          measurement: :total_updates,
          description: "Total updates on the packets table"
        ),
        counter(
          [:aprsme, :postgres, :packets_table, :total_deletes],
          event_name: [:aprsme, :postgres, :packets_table],
          measurement: :total_deletes,
          description: "Total deletes from the packets table"
        ),
        last_value(
          [:aprsme, :postgres, :packets_table, :table_size_bytes],
          event_name: [:aprsme, :postgres, :packets_table],
          measurement: :table_size_bytes,
          description: "Packets table size in bytes",
          unit: :byte
        ),
        last_value(
          [:aprsme, :postgres, :packets_table, :indexes_size_bytes],
          event_name: [:aprsme, :postgres, :packets_table],
          measurement: :indexes_size_bytes,
          description: "Packets indexes size in bytes",
          unit: :byte
        ),
        counter(
          [:aprsme, :postgres, :query_stats, :total_calls],
          event_name: [:aprsme, :postgres, :query_stats],
          measurement: :total_calls,
          description: "Total Postgres queries executed (pg_stat_statements)"
        ),
        last_value(
          [:aprsme, :postgres, :query_stats, :total_time_ms],
          event_name: [:aprsme, :postgres, :query_stats],
          measurement: :total_time_ms,
          description: "Total Postgres query execution time",
          unit: :millisecond
        ),
        last_value(
          [:aprsme, :postgres, :query_stats, :avg_time_ms],
          event_name: [:aprsme, :postgres, :query_stats],
          measurement: :avg_time_ms,
          description: "Average Postgres query execution time",
          unit: :millisecond
        ),
        last_value(
          [:aprsme, :postgres, :query_stats, :max_time_ms],
          event_name: [:aprsme, :postgres, :query_stats],
          measurement: :max_time_ms,
          description: "Maximum Postgres query execution time",
          unit: :millisecond
        ),
        last_value(
          [:aprsme, :postgres, :replication, :lag_seconds],
          event_name: [:aprsme, :postgres, :replication],
          measurement: :lag_seconds,
          description: "Postgres replication lag in seconds",
          unit: :second
        )
      ]
    )
  end

  defp insert_optimizer_metrics do
    Event.build(
      :aprsme_insert_optimizer_event_metrics,
      [
        last_value(
          [:aprsme, :insert_optimizer, :batch_size],
          event_name: [:aprsme, :insert_optimizer, :batch_size],
          measurement: :value,
          description: "Current batch size chosen by the insert optimizer"
        ),
        last_value(
          [:aprsme, :insert_optimizer, :throughput],
          event_name: [:aprsme, :insert_optimizer, :throughput],
          measurement: :value,
          description: "Average insert throughput observed by the optimizer"
        ),
        last_value(
          [:aprsme, :insert_optimizer, :duration],
          event_name: [:aprsme, :insert_optimizer, :duration],
          measurement: :value,
          description: "Average insert duration observed by the optimizer"
        ),
        counter(
          [:aprsme, :insert_optimizer, :optimizations],
          event_name: [:aprsme, :insert_optimizer, :optimizations],
          measurement: :count,
          description: "Number of times the optimizer adjusted batch parameters"
        )
      ]
    )
  end

  defp api_metrics do
    Event.build(
      :aprsme_api_request_event_metrics,
      [
        counter(
          [:aprsme, :api, :request, :total],
          event_name: [:aprsme, :api, :request],
          measurement: :count,
          description: "Total API and WebSocket requests",
          tags: [:event]
        )
      ]
    )
  end
end