defmodule Microwaveprop.BeaconMonitors do
  @moduledoc """
  The BeaconMonitors context: manages the physical SDR-based monitor
  hardware assigned to users.

  Each monitor has a unique random token the `propmonitor` client uses
  to authenticate its measurement uploads.
  """

  import Ecto.Query

  alias Ecto.Query.CastError
  alias Microwaveprop.Accounts.User
  alias Microwaveprop.BeaconMonitors.BeaconMonitor
  alias Microwaveprop.Repo

  @token_bytes 32

  # ── User-facing queries ──────────────────────────────────────────

  @doc """
  Returns all monitors assigned to the given user, newest first.
  Preloads the beacon for display.
  """
  @spec list_monitors_for_user(User.t()) :: [BeaconMonitor.t()]
  def list_monitors_for_user(%User{id: user_id}) do
    Repo.all(
      from m in BeaconMonitor,
        where: m.user_id == ^user_id,
        order_by: [desc: m.inserted_at],
        preload: [:beacon]
    )
  end

  @doc """
  Returns a single monitor. Preloads beacon and user relations.
  """
  @spec get_monitor!(Ecto.UUID.t()) :: BeaconMonitor.t()
  def get_monitor!(monitor_id) do
    BeaconMonitor |> Repo.get!(monitor_id) |> Repo.preload([:beacon, :user])
  end

  @doc """
  Returns a single monitor if owned by the given user, nil otherwise.
  """
  @spec get_monitor_for_user(Ecto.UUID.t(), User.t()) :: BeaconMonitor.t() | nil
  def get_monitor_for_user(monitor_id, %User{id: user_id}) do
    Repo.one(
      from m in BeaconMonitor,
        where: m.id == ^monitor_id and m.user_id == ^user_id,
        preload: [:beacon]
    )
  end

  # ── Admin queries ────────────────────────────────────────────────

  @doc """
  Returns all monitors, newest first, with user and beacon preloaded.
  Accepts preload overrides via options.
  """
  @spec list_all_monitors(keyword()) :: [BeaconMonitor.t()]
  def list_all_monitors(opts \\ []) do
    preloads = Keyword.get(opts, :preload, [:user, :beacon, :assigned_by])

    from(m in BeaconMonitor, order_by: [desc: m.inserted_at])
    |> Repo.all()
    |> Repo.preload(preloads)
  end

  # ── Test / convenience helpers ───────────────────────────────────

  @doc """
  Creates a monitor and assigns it to the given user. The user acts as
  both the assigned owner and the creating admin. Used by tests and
  any legacy callers.
  """
  @spec create_monitor(User.t(), map()) :: {:ok, BeaconMonitor.t()} | {:error, Ecto.Changeset.t()}
  def create_monitor(%User{} = user, attrs) when is_list(attrs) or is_map(attrs) do
    attrs =
      attrs
      |> Map.new(fn {k, v} -> {to_string(k), v} end)
      |> Map.put("user_id", user.id)

    create_hardware(user, attrs)
  end

  # ── Admin provisioning ───────────────────────────────────────────

  @doc """
  Creates a new hardware monitor with the given attrs. Generates a
  unique auth token. Expects `user_id` and `assigned_by_id` to be set
  in attrs.
  """
  @spec create_hardware(User.t(), map()) :: {:ok, BeaconMonitor.t()} | {:error, Ecto.Changeset.t()}
  def create_hardware(%User{} = admin, attrs) do
    attrs = Map.put(attrs, "assigned_by_id", admin.id)

    %BeaconMonitor{token: generate_token()}
    |> BeaconMonitor.provision_changeset(attrs)
    |> Repo.insert()
  end

  @doc """
  Updates the monitor's configuration (beacon, frequency, mode, etc).
  Used by both admins and the assigned user.
  """
  @spec update_config(BeaconMonitor.t(), map()) ::
          {:ok, BeaconMonitor.t()} | {:error, Ecto.Changeset.t()}
  def update_config(%BeaconMonitor{} = monitor, attrs) do
    monitor
    |> BeaconMonitor.config_changeset(attrs)
    |> Repo.update()
  end

  @doc """
  Updates the monitor's hardware provisioning fields. Admin-only.
  """
  @spec update_hardware(BeaconMonitor.t(), map()) ::
          {:ok, BeaconMonitor.t()} | {:error, Ecto.Changeset.t()}
  def update_hardware(%BeaconMonitor{} = monitor, attrs) do
    monitor
    |> BeaconMonitor.provision_changeset(attrs)
    |> Repo.update()
  end

  @doc """
  Reassigns a monitor to a different user. Returns `{:error, :not_found}`
  if the target user does not exist.
  """
  @spec assign_to_user(BeaconMonitor.t(), User.t(), User.t()) ::
          {:ok, BeaconMonitor.t()} | {:error, :not_found | Ecto.Changeset.t()}
  def assign_to_user(%BeaconMonitor{} = monitor, %User{id: _} = admin, %User{id: new_user_id}) do
    monitor
    |> BeaconMonitor.provision_changeset(%{
      user_id: new_user_id,
      assigned_by_id: admin.id
    })
    |> Repo.update()
  end

  @doc """
  Deletes a monitor. Works for both admin and the assigned user.
  """
  @spec delete_monitor(User.t(), Ecto.UUID.t()) ::
          {:ok, BeaconMonitor.t()} | {:error, :not_found}
  def delete_monitor(%User{id: user_id}, monitor_id) do
    query =
      from m in BeaconMonitor,
        where: m.id == ^monitor_id and m.user_id == ^user_id

    case Repo.one(query) do
      nil -> {:error, :not_found}
      monitor -> Repo.delete(monitor)
    end
  rescue
    CastError -> {:error, :not_found}
  end

  @doc """
  Deletes a monitor by its ID without user scoping. Admin-only.
  """
  @spec delete_monitor!(Ecto.UUID.t()) :: {:ok, BeaconMonitor.t()} | {:error, :not_found}
  def delete_monitor!(monitor_id) do
    case Repo.get(BeaconMonitor, monitor_id) do
      nil -> {:error, :not_found}
      monitor -> Repo.delete(monitor)
    end
  rescue
    CastError -> {:error, :not_found}
  end

  # ── Auth / heartbeat ─────────────────────────────────────────────

  @doc """
  Looks up a monitor by its token. Returns nil if not found.
  """
  @spec get_monitor_by_token(String.t()) :: BeaconMonitor.t() | nil
  def get_monitor_by_token(token) when is_binary(token) do
    Repo.get_by(BeaconMonitor, token: token)
  end

  @doc """
  Stamps `last_seen_at` to the given timestamp (defaults to "now") for
  the supplied monitor. Used by the measurement ingest endpoint as
  effectively a heartbeat — every accepted upload nudges the monitor's
  last-seen marker forward.
  """
  @spec touch_last_seen(BeaconMonitor.t(), DateTime.t() | nil) :: {non_neg_integer(), nil}
  def touch_last_seen(%BeaconMonitor{id: id}, at \\ nil) do
    at = DateTime.truncate(at || DateTime.utc_now(), :second)

    Repo.update_all(
      from(m in BeaconMonitor, where: m.id == ^id),
      set: [last_seen_at: at]
    )
  end

  @doc """
  Returns a blank changeset for rendering a new-monitor form.
  """
  @spec change_monitor(map()) :: Ecto.Changeset.t()
  def change_monitor(attrs \\ %{}) do
    BeaconMonitor.provision_changeset(%BeaconMonitor{}, attrs)
  end

  defp generate_token do
    @token_bytes
    |> :crypto.strong_rand_bytes()
    |> Base.url_encode64(padding: false)
  end
end