# AUTO-GENERATED FILE - DO NOT EDIT
# This file was automatically generated by the XDK build tool.
# Any manual changes will be overwritten on the next generation.

defmodule Xdk.Paginator do
  @moduledoc """
  Cursor-based pagination helper.

  Wraps any paginated endpoint function into a lazy `Stream` that
  automatically follows `next_token` / `pagination_token`.

  ## Example

      fetch = fn token ->
        opts = [query: "elixir", max_results: 100]
        opts = if token, do: Keyword.put(opts, :pagination_token, token), else: opts
        Xdk.Posts.search_recent(client, opts)
      end

      Xdk.Paginator.stream(fetch)
      |> Stream.flat_map(fn {:ok, page} -> page["data"] || [] end)
      |> Enum.take(500)
  """

  @type fetch_fun :: (String.t() | nil -> {:ok, map()} | {:error, term()})

  @spec stream(fetch_fun(), keyword()) :: Enumerable.t()
  def stream(fetch_fun, _opts \\ []) do
    Stream.resource(
      fn -> nil end,
      fn
        :halt ->
          {:halt, :halt}

        token ->
          case fetch_fun.(token) do
            {:ok, page} ->
              next = extract_next_token(page)
              next_state = if next, do: next, else: :halt
              {[{:ok, page}], next_state}

            {:error, _} = err ->
              {[err], :halt}
          end
      end,
      fn _ -> :ok end
    )
  end

  @spec items(fetch_fun(), keyword()) :: Enumerable.t()
  def items(fetch_fun, opts \\ []) do
    data_key = Keyword.get(opts, :data_key, "data")

    stream(fetch_fun, opts)
    |> Stream.flat_map(fn
      {:ok, page} -> page[data_key] || []
      {:error, _} -> []
    end)
  end

  defp extract_next_token(page) do
    meta = page["meta"] || %{}
    meta["next_token"] || meta["pagination_token"]
  end
end