defmodule Wiki.SiteMatrix do
  @moduledoc """
  Retrieves sites from a wiki farm with the SiteMatrix extension installed.
  """

  @metawiki_api "https://meta.wikimedia.org/w/api.php"

  alias Wiki.Error

  defmodule Spec do
    @moduledoc """
    Container for a single site.
    """

    @type t :: %__MODULE__{
            base_url: String.t(),
            closed: boolean(),
            dbname: String.t(),
            dir: String.t(),
            lang: String.t(),
            name: String.t(),
            private: boolean()
          }

    @enforce_keys [:base_url]
    defstruct [
      :base_url,
      :closed,
      :dbname,
      :dir,
      :lang,
      :name,
      :private
    ]
  end

  @type client_options :: [Wiki.Action.client_option() | {:api, binary()}]

  @doc """
  ## Options

  - `api` - Action API URL for a site participating in the farm.
    Defaults to #{@metawiki_api}.
  """
  @opaque sitematrix_state :: %{
            api: binary(),
            sites: %{binary() => Spec.t()}
          }

  @spec new(client_options()) :: sitematrix_state()
  def new(opts \\ []) do
    api = opts[:api] || @metawiki_api

    %{
      api: api,
      sites: do_get_all(api, opts)
    }
  end

  @doc """
  Get all sites for a wiki farm.

  ## Arguments

  * `sitematrix` - Result of Sitematrix.new()

  ## Return value

  List of site specifications.
  """
  @spec get_all(sitematrix_state()) :: {:ok, [Spec.t()]} | {:error, any}
  def get_all(sitematrix) do
    {:ok, Map.values(sitematrix.sites)}
  end

  @spec action_client(binary(), client_options()) :: Wiki.Action.Session.t()
  defp action_client(api, opts) do
    api
    |> Wiki.Action.new(opts)
  end

  @spec do_get_all(binary(), client_options()) :: map()
  defp do_get_all(api, opts) do
    action_client(api, opts)
    |> fetch_sitematrix()
    |> Enum.map(&site_spec/1)
    |> Map.new(fn site -> {site.dbname, site} end)
  end

  defp site_spec(site) do
    %Spec{
      base_url: site["url"],
      closed: site["closed"] == true,
      dbname: site["dbname"],
      dir: site["dir"] || "ltr",
      lang: site["lang"],
      name: site["name"] || site["sitename"],
      private: site["private"] == true
    }
  end

  defp fetch_sitematrix(client) do
    client
    |> Wiki.Action.stream(
      action: :sitematrix,
      smsiteprop: [:dbname, :lang, :sitename, :url]
    )
    |> Enum.flat_map(fn response ->
      flatten_sitematrix(response["sitematrix"])
    end)
  end

  defp flatten_sitematrix(all) do
    (all
     |> Map.drop(["count", "specials"])
     |> flatten_language_wikis()) ++
      (all["specials"] || [])
  end

  defp flatten_language_wikis(language_sites) do
    language_sites
    |> Map.delete("specials")
    |> Map.values()
    |> Enum.flat_map(fn group ->
      group["site"]
      |> Enum.map(fn site ->
        site
        |> Map.merge(%{
          "dir" => group["dir"],
          # FIXME: Lacking translation and grammar
          "name" => group["localname"] <> " " <> site["sitename"]
        })
      end)
    end)
  end

  @doc """
  Get a single site, matching on dbname

  ## Arguments

  * `sitematrix` - Result of Sitematrix.new()
  * `dbname` - Wiki ID, for example "enwiki"

  ## Return value

  Site spec or error
  """
  @spec get(sitematrix_state(), String.t()) :: {:ok, Spec.t()} | {:error, any}
  def get(sitematrix, dbname) do
    Map.fetch(sitematrix.sites, dbname)
    |> case do
      :error -> {:error, %Error{message: "Site #{dbname} not found."}}
      x -> x
    end
  end

  @doc """
  Assertive variant of `get`.
  """
  @spec get!(sitematrix_state(), String.t()) :: Spec.t()
  def get!(sitematrix, dbname) do
    case get(sitematrix, dbname) do
      {:ok, site} -> site
      {:error, error} -> raise error
    end
  end

  @doc """
  Get the Action API for a known site

  ```elixir
  Wiki.SiteMatrix.new()
  |> Wiki.SiteMatrix.get("enwiki")
  |> Wiki.SiteMatrix.action_api()

  # "https://en.wikipedia.org/w/api.php"
  ```

  As a convenience, the site can be referenced as a bare string, in which case
  it will be looked up in the default Wikimedia farm.  Note that this will be
  uncached and so inappropriate for most production use.

  ```elixir
  Wiki.SiteMatrix.action_api("dewiki")
  ```

  ## Arguments

  * `site` - Populated site structure.

  ## Return value

  Calculated Action API.
  """
  @spec action_api(String.t() | Spec.t()) :: String.t()
  def action_api(site)

  def action_api(site) when is_binary(site) do
    # FIXME: Globally cached site matrix for this case
    new()
    |> get!(site)
    |> action_api()
  end

  def action_api(site) do
    site.base_url <>
      "/w/api.php"
  end
end