defmodule SEO.Breadcrumb.List do
  @moduledoc """
  A `SEO.Breadcrumb.List` is list of items consisting of a chain of linked Web pages, typically
  described using at least their URL and their name, and typically ending with the current page.

  The `:position` property is used to reconstruct the order of the items in a `SEO.Breadcrumb.List`.
  The convention is that a breadcrumb list has an `itemListOrder` of `ItemListOrderAscending`
  (lower values listed first), and that the first items in this list correspond to the "top"
  or beginning of the breadcrumb trail, e.g. with a site or section homepage. The specific values
  of 'position' are not assigned meaning for a BreadcrumbList, but they should be integers,
  e.g. beginning with '1' for the first item in the list.
  """

  alias SEO.Breadcrumb.ListItem

  defstruct "@context": "https://schema.org",
            "@type": "BreadcrumbList",
            itemListElement: []

  @type t :: %__MODULE__{
          "@context": String.t(),
          "@type": String.t(),
          itemListElement: list(ListItem.t())
        }

  @doc """
  Build a list of items that represent breadcrumbs for your item.

  You may build the list with `SEO.Breadcrumb.ListItem` or with attributes that will build
  a ListItem. The position will be inferred from the list provided, but if you need to
  supply the position manually, you must supply `SEO.Breadcrumb.ListItem`.

  For example:

  ```elixir
  SEO.Breadcrumb.List.build([
    %{name: "Posts", item: Routes.blog_url(@endpoint, :index)},
    %{name: "My Post", item: Routes.blog_url(@endpoint, :show, my_id)}
  ])
  ```
  """

  @spec build(t() | list(map() | Keyword.t()) | nil, SEO.config()) :: t() | nil
  def build(attrs, _default \\ nil)

  def build([], _default), do: nil

  def build(attrs, _default) when is_list(attrs) do
    case format_items(attrs) do
      [] -> nil
      items -> %__MODULE__{itemListElement: items}
    end
  end

  def build(%__MODULE__{} = attrs, _default), do: attrs

  def build(_attrs, _default), do: nil

  @doc false
  def to_map(%__MODULE__{} = item) do
    %{item | itemListElement: Enum.map(item.itemListElement, &ListItem.to_map/1)}
    |> Map.from_struct()
  end

  defp reject_empty(items) do
    Enum.reject(items, fn
      %{} = map when map_size(map) == 0 -> true
      [] -> true
      _ -> false
    end)
  end

  defp format_items([]), do: nil

  defp format_items(items) do
    items
    |> reject_empty()
    |> Enum.with_index(1)
    |> Enum.map(fn {item, i} ->
      case item do
        %ListItem{position: pos} = list_item ->
          %{list_item | position: pos || i}

        attrs when is_list(attrs) or is_map(attrs) ->
          ListItem.build(attrs, position: i)

        {k, v} ->
          ListItem.build([{k, v}], position: i)
      end
    end)
  end
end