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 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.RoverMissionReconcileWorker
  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 | [%{atom() => any()}]
  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 | [%{atom() => any()}]
  def get_mission_with_paths(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), paths: [:rover_location, :station]])

      :error ->
        nil
    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])
        # Async: a brand-new mission can have hundreds of (rover x
        # station x band) tuples. Hand the matrix population off to
        # the reconcile worker so the form-submit request returns
        # immediately instead of blocking on N inserts + N Oban
        # enqueues per pair. The worker calls reconcile_mission_paths,
        # which is identical to enqueue_paths_for for an empty matrix.
        :ok = enqueue_reconcile(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 = enqueue_reconcile(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 "Fetches a single path by id or raises Ecto.NoResultsError."
  @spec get_path!(Ecto.UUID.t()) :: Path.t()
  def get_path!(id), do: Repo.get!(Path, id)

  @doc """
  Reconciles the path matrix for a mission against the current set of
  (rover_location × station × band) tuples. Deletes paths for tuples
  that no longer apply, leaves :complete paths in place when they're
  still relevant, and enqueues new pending paths for any tuple missing
  from the table. Called after a mission edit, or after the user
  adds/removes a rover site.

  Aliased as `replace_mission_paths/1` for backwards compatibility
  with callers that expected the previous destructive behaviour;
  internally both go through the same reconcile path.
  """
  @spec reconcile_mission_paths(Mission.t()) :: :ok
  def reconcile_mission_paths(%Mission{} = mission) do
    desired = MapSet.new(desired_tuples(mission))

    actual_paths =
      Repo.all(from(p in Path, where: p.mission_id == ^mission.id))

    actual = MapSet.new(actual_paths, &{&1.rover_location_id, &1.station_id, &1.band_mhz})

    stale_ids =
      actual_paths
      |> Enum.reject(&MapSet.member?(desired, {&1.rover_location_id, &1.station_id, &1.band_mhz}))
      |> Enum.map(& &1.id)

    Repo.transaction(fn ->
      if stale_ids != [] do
        Repo.delete_all(from(p in Path, where: p.id in ^stale_ids))
      end

      desired
      |> MapSet.difference(actual)
      |> Enum.to_list()
      |> insert_pending_paths_and_jobs(mission)
    end)

    :ok
  end

  @spec replace_mission_paths(Mission.t()) :: :ok
  defdelegate replace_mission_paths(mission), to: __MODULE__, as: :reconcile_mission_paths

  @doc """
  Async entry point for path-matrix reconciliation. Enqueues a
  `RoverMissionReconcileWorker` job and returns immediately so callers
  (form save, rover-site add/remove) don't pay the per-tuple insert
  cost on the request path. Oban inline mode in tests still runs
  this synchronously, so test expectations don't have to change.
  """
  @spec enqueue_reconcile(Mission.t()) :: :ok
  def enqueue_reconcile(%Mission{id: mission_id}) do
    _ =
      %{"mission_id" => mission_id}
      |> RoverMissionReconcileWorker.new()
      |> Oban.insert()

    :ok
  end

  @doc """
  Walks every mission and re-enqueues any (rover_location × station ×
  band) pair whose `Path` is missing, not `:complete`, OR whose
  cached `result` lacks the `"term"` blob (paths persisted before
  PathCompute extraction shipped — the row click on /rover-planning
  needs that blob to render `/path` from cache instead of recomputing).

  Idempotent: the path-profile worker short-circuits on `:complete`,
  and we only nudge :complete rows back to :pending when their term
  is missing. Safe to run on a cron.
  """
  @spec backfill_paths() :: :ok
  def backfill_paths do
    reset_paths_missing_term()

    Mission
    |> Repo.all()
    |> Repo.preload(stations: from(s in Station, order_by: s.position))
    |> Enum.each(&enqueue_paths_for/1)

    :ok
  end

  # Flip :complete paths whose result map has no "term" key back to
  # :pending so the next reconcile pass picks them up. JSONB
  # `key_exists` is `?` in pg, but Ecto's fragment uses `?` as a
  # placeholder — use the function form `jsonb_exists/2` instead.
  defp reset_paths_missing_term do
    Repo.update_all(
      from(p in Path,
        where: p.status == :complete,
        where: not fragment("jsonb_exists(?, 'term')", p.result)
      ),
      set: [status: :pending]
    )
  end

  defp enqueue_paths_for(%Mission{} = mission) do
    mission
    |> desired_tuples()
    |> insert_pending_paths_and_jobs(mission)
  end

  # Cross product of (rover_location_id, station_id, band_mhz) for the
  # mission's current scope. The reconcile + initial-create paths both
  # go through this same source of truth.
  @spec desired_tuples(Mission.t()) :: [{Ecto.UUID.t(), Ecto.UUID.t(), integer()}]
  defp desired_tuples(%Mission{} = mission) do
    rovers = candidate_rover_locations(mission)
    stations = mission.stations || []
    bands = Mission.bands(mission)

    for rover <- rovers, station <- stations, band <- bands do
      {rover.id, station.id, band}
    end
  end

  @doc """
  Rover-locations the matrix actually scores against, given the
  mission's `only_known_good` flag. Public so the show LiveView can
  render the same list the worker enqueues against.
  """
  @spec candidate_rover_locations(Mission.t()) :: [Location.t()]
  def candidate_rover_locations(%Mission{only_known_good: true}) do
    Repo.all(from(l in Location, where: l.status == :good, order_by: [desc: l.inserted_at], limit: 500))
  end

  def candidate_rover_locations(%Mission{only_known_good: false}) do
    Repo.all(from(l in Location, order_by: [desc: l.inserted_at], limit: 500))
  end

  defp insert_pending_paths_and_jobs([], _mission), do: :ok

  defp insert_pending_paths_and_jobs(tuples, mission) when is_list(tuples) do
    # Batch the path-row inserts and the Oban-job inserts into a
    # single SQL statement each. The previous Multi-of-N-inserts +
    # N x Oban.insert call took ~1.5s per pair × 900 pairs in the
    # worst-case mission — `insert_all` collapses both to one
    # roundtrip per kind regardless of pair count.
    now = DateTime.truncate(DateTime.utc_now(), :second)

    path_rows =
      Enum.map(tuples, fn {rover_id, station_id, band_mhz} ->
        %{
          id: Ecto.UUID.generate(),
          mission_id: mission.id,
          rover_location_id: rover_id,
          station_id: station_id,
          band_mhz: band_mhz,
          status: :pending,
          inserted_at: now,
          updated_at: now
        }
      end)

    _ =
      Repo.insert_all(Path, path_rows,
        on_conflict: :nothing,
        conflict_target: [:mission_id, :rover_location_id, :station_id, :band_mhz]
      )

    enqueue_jobs(tuples, mission)
    :ok
  end

  defp enqueue_jobs(tuples, mission) do
    changesets =
      Enum.map(tuples, fn {rover_id, station_id, band_mhz} ->
        RoverPathProfileWorker.new(%{
          "mission_id" => mission.id,
          "rover_location_id" => rover_id,
          "station_id" => station_id,
          "band_mhz" => band_mhz
        })
      end)

    _ = Oban.insert_all(changesets)
    :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