defmodule Microwaveprop.RoverPlanning do
  @moduledoc """
  Context for the `/rover-planning` feature: planned rover missions
  with stationary endpoints and per-rover-location terrain path
  profiles. Mutations are scoped to a user (or admin); reads are
  global.

  After a successful `create_mission/2` or
  `replace_mission_paths/1`, the context enqueues one
  `RoverPathProfileWorker` job per (rover-location, station) pair
  so the show page can render results as they land.
  """

  import Ecto.Query

  alias Ecto.Multi
  alias Microwaveprop.Accounts.User
  alias Microwaveprop.Repo
  alias Microwaveprop.Rover.Location
  alias Microwaveprop.RoverPlanning.Mission
  alias Microwaveprop.RoverPlanning.Path
  alias Microwaveprop.RoverPlanning.Station
  alias Microwaveprop.Workers.RoverPathProfileWorker

  @spec list_missions() :: [Mission.t()]
  def list_missions do
    Mission
    |> order_by([m], desc: m.inserted_at)
    |> preload([:user, :stations])
    |> Repo.all()
  end

  @spec get_mission(Ecto.UUID.t()) :: Mission.t() | nil
  def get_mission(id) when is_binary(id) do
    case Ecto.UUID.cast(id) do
      {:ok, uuid} ->
        Mission
        |> Repo.get(uuid)
        |> Repo.preload([:user, stations: from(s in Station, order_by: s.position)])

      :error ->
        nil
    end
  end

  @spec get_mission_with_paths(Ecto.UUID.t()) :: Mission.t() | nil
  def get_mission_with_paths(id) do
    case get_mission(id) do
      nil -> nil
      mission -> Repo.preload(mission, paths: [:rover_location, :station])
    end
  end

  @spec create_mission(User.t(), map()) ::
          {:ok, Mission.t()} | {:error, Ecto.Changeset.t()}
  def create_mission(%User{} = user, attrs) do
    changeset = Mission.changeset(%Mission{user_id: user.id}, attrs)

    case Repo.insert(changeset) do
      {:ok, mission} ->
        mission = Repo.preload(mission, [:user, :stations])
        :ok = enqueue_paths_for(mission)
        {:ok, mission}

      {:error, _} = error ->
        error
    end
  end

  @spec update_mission(User.t(), Ecto.UUID.t(), map()) ::
          {:ok, Mission.t()} | {:error, :not_found | Ecto.Changeset.t()}
  def update_mission(%User{} = user, id, attrs) do
    case fetch_owned(user, id) do
      {:ok, mission} ->
        mission
        |> Repo.preload(stations: from(s in Station, order_by: s.position))
        |> Mission.changeset(attrs)
        |> Repo.update()
        |> case do
          {:ok, updated} ->
            updated = Repo.preload(updated, [:user, :stations], force: true)
            :ok = replace_mission_paths(updated)
            {:ok, updated}

          other ->
            other
        end

      {:error, :not_found} ->
        {:error, :not_found}
    end
  end

  @spec delete_mission(User.t(), Ecto.UUID.t()) ::
          {:ok, Mission.t()} | {:error, :not_found}
  def delete_mission(%User{} = user, id) do
    case fetch_owned(user, id) do
      {:ok, mission} -> Repo.delete(mission)
      {:error, :not_found} -> {:error, :not_found}
    end
  end

  @spec list_paths(Mission.t()) :: [Path.t()]
  def list_paths(%Mission{id: mission_id}) do
    Repo.all(
      from(p in Path,
        where: p.mission_id == ^mission_id,
        preload: [:rover_location, :station],
        order_by: [asc: p.station_id, asc: p.rover_location_id]
      )
    )
  end

  @doc """
  Wipes the existing path matrix for a mission and re-enqueues all
  pairings. Called after a mission edit when the station list or
  `only_known_good` toggle could have shifted the matrix.
  """
  @spec replace_mission_paths(Mission.t()) :: :ok
  def replace_mission_paths(%Mission{} = mission) do
    Repo.delete_all(from(p in Path, where: p.mission_id == ^mission.id))
    enqueue_paths_for(mission)
  end

  defp enqueue_paths_for(%Mission{} = mission) do
    rovers = candidate_rover_locations(mission)
    stations = mission.stations || []

    pairs =
      for rover <- rovers, station <- stations do
        %{rover: rover, station: station}
      end

    case pairs do
      [] -> :ok
      _ -> insert_pending_paths_and_jobs(mission, pairs)
    end
  end

  defp candidate_rover_locations(%Mission{only_known_good: true}) do
    Repo.all(from(l in Location, where: l.status == :good))
  end

  defp candidate_rover_locations(%Mission{only_known_good: false}) do
    Repo.all(Location)
  end

  defp insert_pending_paths_and_jobs(mission, pairs) do
    {:ok, _} =
      pairs
      |> Enum.reduce(Multi.new(), fn %{rover: r, station: s}, multi ->
        attrs = %{
          mission_id: mission.id,
          rover_location_id: r.id,
          station_id: s.id,
          status: :pending
        }

        Multi.insert(multi, {:path, r.id, s.id}, Path.changeset(%Path{}, attrs),
          on_conflict: :nothing,
          conflict_target: [:mission_id, :rover_location_id, :station_id]
        )
      end)
      |> Repo.transaction()

    enqueue_jobs(mission, pairs)
    :ok
  end

  defp enqueue_jobs(mission, pairs) do
    for %{rover: r, station: s} <- pairs do
      %{
        "mission_id" => mission.id,
        "rover_location_id" => r.id,
        "station_id" => s.id
      }
      |> RoverPathProfileWorker.new()
      |> Oban.insert()
    end

    :ok
  end

  defp fetch_owned(%User{is_admin: true}, id) do
    case get_mission(id) do
      nil -> {:error, :not_found}
      mission -> {:ok, mission}
    end
  end

  defp fetch_owned(%User{id: user_id}, id) do
    case get_mission(id) do
      %Mission{user_id: ^user_id} = mission -> {:ok, mission}
      _ -> {:error, :not_found}
    end
  end
end