defmodule ArcadiaCloud.Cloud do
  @moduledoc """
  Context for cloud resource inventory.

  Single upsert chokepoint (`upsert_resource/2`) handles:
    - insert new (emit `discovered` event)
    - update existing (diff meaningful fields, emit `updated` event only when changed)
    - bump last_seen_at + reset stale_strike_count
    - restore previously-deleted resources

  Stale handling is in `mark_stale/3` — three-strike deletion across syncs.
  """

  import Ecto.Query, warn: false

  alias ArcadiaCloud.Repo
  alias ArcadiaCloud.Cloud.{CloudProject, CloudResource, CloudResourceEvent}

  @meaningful_fields ~w(status name region size_slug tags attrs cloud_project_id
                        tenant_id deployment_id)a

  # ---- projects -------------------------------------------------------------

  def get_project_by_provider(provider, provider_id) do
    Repo.get_by(CloudProject, provider: provider, provider_id: provider_id)
  end

  def ensure_project(attrs) when is_map(attrs) do
    provider = attrs[:provider] || attrs["provider"]
    provider_id = attrs[:provider_id] || attrs["provider_id"]

    case get_project_by_provider(provider, provider_id) do
      nil ->
        %CloudProject{}
        |> CloudProject.changeset(attrs)
        |> Repo.insert()

      project ->
        project
        |> CloudProject.changeset(attrs)
        |> Repo.update()
    end
  end

  def list_projects, do: Repo.all(CloudProject)

  def skyai_internal_project do
    Repo.get_by(CloudProject, purpose: "skyai-infra", name: "skyai-internal")
  end

  # ---- resources ------------------------------------------------------------

  def upsert_resource(attrs, opts \\ []) when is_map(attrs) do
    source = Keyword.get(opts, :source, "sync")
    provider = attrs[:provider] || attrs["provider"]
    provider_id = attrs[:provider_id] || attrs["provider_id"]
    now = DateTime.utc_now() |> DateTime.truncate(:second)

    attrs =
      attrs
      |> Map.put_new(:first_seen_at, now)
      |> Map.put(:last_seen_at, now)
      |> Map.put(:stale_strike_count, 0)

    Repo.transaction(fn ->
      case Repo.get_by(CloudResource, provider: provider, provider_id: provider_id) do
        nil ->
          {:ok, resource} =
            %CloudResource{}
            |> CloudResource.changeset(attrs)
            |> Repo.insert()

          write_event(resource, "discovered", nil, snapshot(resource), source)
          resource

        existing ->
          before_snap = snapshot(existing)

          {:ok, updated} =
            existing
            |> CloudResource.changeset(Map.delete(attrs, :first_seen_at))
            |> Repo.update()

          cond do
            existing.deleted_at != nil ->
              # Was tombstoned; now seen again. Clear deleted_at and emit restore.
              {:ok, restored} =
                updated
                |> Ecto.Changeset.change(deleted_at: nil)
                |> Repo.update()

              write_event(restored, "restored", before_snap, snapshot(restored), source)
              restored

            meaningful_change?(before_snap, snapshot(updated)) ->
              write_event(updated, "updated", before_snap, snapshot(updated), source)
              updated

            true ->
              updated
          end
      end
    end)
  end

  @doc """
  Three-strike deletion: any resource of `kind` whose `last_seen_at` is older
  than `sync_started_at` gets its strike count bumped. At 3 strikes, mark
  deleted. Returns count of strikes + deletions.
  """
  def mark_stale(kind, sync_started_at, opts \\ []) do
    threshold = Keyword.get(opts, :threshold, 3)

    stale_query =
      from r in CloudResource,
        where: r.kind == ^kind,
        where: r.last_seen_at < ^sync_started_at,
        where: is_nil(r.deleted_at)

    # bump strikes
    {struck, _} =
      Repo.update_all(stale_query, inc: [stale_strike_count: 1])

    # mark deleted those at/past threshold
    now = DateTime.utc_now() |> DateTime.truncate(:second)

    delete_query =
      from r in CloudResource,
        where: r.kind == ^kind,
        where: r.stale_strike_count >= ^threshold,
        where: is_nil(r.deleted_at)

    deleted = Repo.all(delete_query)

    Enum.each(deleted, fn r ->
      r
      |> Ecto.Changeset.change(deleted_at: now)
      |> Repo.update!()

      write_event(r, "deleted", snapshot(r), nil, "sync_stale")
    end)

    %{struck: struck, deleted: length(deleted)}
  end

  def list_resources(opts \\ []) do
    base = from r in CloudResource, where: is_nil(r.deleted_at), order_by: [desc: r.updated_at]

    base
    |> filter_by(:kind, opts[:kind])
    |> filter_by(:tenant_id, opts[:tenant_id])
    |> filter_by(:deployment_id, opts[:deployment_id])
    |> Repo.all()
  end

  defp filter_by(query, _field, nil), do: query

  defp filter_by(query, field, value) do
    from(r in query, where: field(r, ^field) == ^value)
  end

  # ---- internals ------------------------------------------------------------

  defp snapshot(%CloudResource{} = r) do
    Map.take(r, @meaningful_fields ++ [:provider_id, :name, :id])
  end

  defp meaningful_change?(a, b) do
    Map.take(a, @meaningful_fields) != Map.take(b, @meaningful_fields)
  end

  defp write_event(%CloudResource{id: id}, event, before, after_, source) do
    %CloudResourceEvent{}
    |> CloudResourceEvent.changeset(%{
      resource_id: id,
      event: event,
      before: before,
      after: after_,
      source: source,
      occurred_at: DateTime.utc_now() |> DateTime.truncate(:second)
    })
    |> Repo.insert!()
  end
end