defmodule Microwaveprop.Propagation.GridTaskEnqueuer do
  @moduledoc """
  Seeds `grid_tasks` rows for the Rust `prop-grid-rs` worker.

  Called from `PropagationGridWorker.seed_chain/0` alongside the existing
  Elixir f00..f18 Oban fan-out. Rust only claims rows with
  `forecast_hour > 0`; Elixir still owns the f00 analysis-hour chain
  because of native-duct + NEXRAD + commercial-link enrichment.

  Inserts are idempotent via the `(run_time, forecast_hour)` unique
  index — re-seeding the same cycle is a no-op.
  """

  alias Microwaveprop.Repo

  require Logger

  @max_forecast_hour 18

  @spec seed(DateTime.t()) :: {:ok, non_neg_integer()} | {:error, term()}
  def seed(%DateTime{} = run_time) do
    run_time = DateTime.truncate(run_time, :second)
    now = DateTime.truncate(DateTime.utc_now(), :microsecond)

    rows =
      for fh <- 1..@max_forecast_hour do
        %{
          id: Ecto.UUID.bingenerate(),
          run_time: run_time,
          forecast_hour: fh,
          valid_time: DateTime.add(run_time, fh * 3600, :second),
          status: "queued",
          attempt: 0,
          claimed_at: nil,
          completed_at: nil,
          error: nil,
          inserted_at: now,
          updated_at: now
        }
      end

    {count, _} =
      Repo.insert_all("grid_tasks", rows,
        on_conflict: :nothing,
        conflict_target: [:run_time, :forecast_hour]
      )

    if count > 0 do
      Logger.info("GridTaskEnqueuer: seeded #{count} grid_tasks for run_time=#{run_time}")
    else
      Logger.info("GridTaskEnqueuer: run_time=#{run_time} already seeded")
    end

    {:ok, count}
  rescue
    e ->
      Logger.error("GridTaskEnqueuer: seed failed: #{inspect(e)}")
      {:error, e}
  end
end