defmodule SEO.Facebook do
  @moduledoc """
  Facebook originally developed the OpenGraph standard, so much of social-sharing techniques
  are contained in `SEO.OpenGraph`, however there remains one Facebook-specific attribute: the `:app_id`.

  Resources:
  - https://developers.facebook.com/docs/sharing/webmaster
  """

  defstruct [:app_id]

  @type t :: %__MODULE__{
          app_id: String.t()
        }

  @doc """
  In order to use Facebook Insights you must add the `:app_id` to your page. Insights lets you view analytics for traffic
  to your site from Facebook. Find the app ID in your Facebook App Dashboard.
  """

  @spec build(SEO.attrs(), SEO.config()) :: t() | nil
  def build(attrs, default \\ nil)

  def build(attrs, default) do
    SEO.Utils.merge_defaults(__MODULE__, attrs, default)
  end

  use Phoenix.Component

  attr(:item, __MODULE__, default: nil)
  attr(:config, :any, default: nil)

  def meta(assigns) do
    assigns = assign(assigns, :item, build(assigns[:item], assigns[:config]))

    ~H"""
    <%= if @item do %>
    <%= if @item.app_id do %>
    <meta name="fb:app_id" content={@item.app_id} />
    <% end %>
    <% end %>
    """
  end
end