defmodule SearchAsh do
  @moduledoc """
  An Ash extension that adds multilingual full-text search to a resource with one
  `search do … end` block.

      defmodule MyApp.Post do
        use Ash.Resource,
          domain: MyApp.Blog,
          data_layer: AshPostgres.DataLayer,
          extensions: [SearchAsh]

        search do
          fields [:title, :body]
          language_attribute :language
        end

        # ... attributes :title, :body, :language ...
      end

  From that block the extension generates, at compile time:

    * a `:search_text` string attribute (unless you defined one), holding the
      stemmed tokens;
    * a global change that keeps `:search_text` in sync on create/update, stemming
      each row in its own language via `SearchCore` (the `stemmers` Rust NIF);
    * a GIN expression index `to_tsvector('simple', search_text)` on the Postgres
      table — emitted into your migrations and tracked in the resource snapshot, so
      `mix ash_postgres.generate_migrations` round-trips it cleanly;
    * a `:search` read action taking `query` and `language` arguments, filtering on
      the tsvector with a tsquery built from the *same* pipeline (so a search for
      "chevaux" matches a row that stored "cheval").

  Stemming happens in Elixir, so the Postgres side always uses the `'simple'`
  configuration.
  """

  @search %Spark.Dsl.Section{
    name: :search,
    describe: "Configure multilingual full-text search for this resource.",
    examples: [
      """
      search do
        fields [:title, :body]
        language_attribute :language
      end
      """
    ],
    schema: [
      fields: [
        type: {:list, :atom},
        required: true,
        doc: "Attributes whose text is concatenated and indexed for search."
      ],
      language_attribute: [
        type: :atom,
        default: :language,
        doc: "Attribute holding each row's language (a `Stemmers` language atom)."
      ],
      search_text_attribute: [
        type: :atom,
        default: :search_text,
        doc: "Attribute the stemmed tokens are stored in (added automatically if absent)."
      ],
      index_name: [
        type: :string,
        required: false,
        doc: "Name of the generated GIN index. Defaults to `#{"\#{table}"}_search_idx`."
      ],
      action: [
        type: :atom,
        default: :search,
        doc: "Name of the generated read action."
      ],
      default_language: [
        type: :atom,
        default: :french,
        doc:
          "Language used to stem the query when the `:search` action's `language` " <>
            "argument is omitted (e.g. from a generic list UI)."
      ],
      prefix?: [
        type: :boolean,
        default: true,
        doc:
          "Match the last-typed token as a prefix (search-as-you-type): a query " <>
            "\"boulan\" matches \"boulangerie\". Set false for exact stemmed matching."
      ],
      rank?: [
        type: :boolean,
        default: true,
        doc:
          "Rank results by `ts_rank` (most relevant first) and expose the score as the " <>
            "`:search_rank` calculation. Set false to only filter, leaving ordering to you."
      ]
    ]
  }

  use Spark.Dsl.Extension,
    sections: [@search],
    transformers: [
      SearchAsh.Transformers.AddSearchTextAttribute,
      SearchAsh.Transformers.AddSyncChange,
      SearchAsh.Transformers.AddSearchRank,
      SearchAsh.Transformers.AddSearchAction,
      SearchAsh.Transformers.AddSearchIndex
    ]

  @doc """
  Backfill the unified index for all existing rows of a `SearchAsh.Source` resource.

  Streams the source and upserts each row into its configured index. For a multitenant
  index, pass the tenant (call once per tenant):

      SearchAsh.reindex(MyApp.Sales.BonDeCommande, tenant: "org_42")

  Options are forwarded to the read (`:tenant`, `:domain`, `:authorize?`, …); `:tenant`
  is also used for the upsert.
  """
  def reindex(source_resource, opts \\ []) do
    index = SearchAsh.Source.Info.index(source_resource)
    tenant = opts[:tenant]

    source_resource
    |> Ash.stream!(opts)
    |> Stream.each(fn record ->
      attrs = SearchAsh.Source.Document.to_attrs(source_resource, record)

      index
      |> Ash.Changeset.for_create(:upsert, attrs, tenant: tenant)
      |> Ash.create!()
    end)
    |> Stream.run()
  end
end