defmodule SukaatoWeb.Theme do
  @moduledoc """
  Manage website themes.
  """

  @rel_proj_root "../.."
  @central_sass "export.sass"
  @site_config Toml.decode_file(Path.expand(@rel_proj_root <> "/site.toml", __DIR__))
  @theme_filepath Path.expand(@rel_proj_root <> "/assets/sass/themes/" <> elem(@site_config, 1)["site"]["theme"] <> "/" <> @central_sass, __DIR__)
  @theme_glob Path.expand(@rel_proj_root <> "/assets/sass/themes/*/" <> @central_sass, __DIR__)
  @theme_linkpath Path.expand(@rel_proj_root <> "/assets/sass/app.sass", __DIR__)

  defp get_installed() do
    path_list = Path.wildcard(@theme_glob)
    extract_theme = fn theme_path -> Enum.at(Path.split(theme_path), length(Path.split(theme_path)) - 2) end
    installed = Enum.map(path_list, fn p -> extract_theme.(p) end)

    installed
  end

  @doc """
  List installed website themes.
  """
  def list() do
    get_installed()
  end

  defp get_current() do
    if File.exists?(@theme_linkpath) do
      link_path = File.read_link(@theme_linkpath)

      if elem(link_path, 0) == :ok do
        split_path = Path.split(elem(link_path, 1))
        current_theme = Enum.at(split_path, length(split_path) - 2)
        {:ok, current_theme}
      else
        {:error, "link not traceable--sure its a link?"}
      end
    else
      {:error, "symbolic link does not exist"}
    end
  end

  @doc """
  List website themes under project root's 'assets/sass/themes' path.
  """
  def list(status) do
    case status do
      :installed ->
        get_installed()
      :current ->
        elem(get_current(), 1)
    end
  end

  defp change_theme_path(theme_name) do
    Path.expand(@rel_proj_root <> "/assets/sass/themes/" <> theme_name <> "/" <> @central_sass, __DIR__)
  end

  @doc """
  Update website theme based on stored website settings, refreshes current theme otherwise.
  """
  def update() do
    if File.exists?(@theme_filepath) do
      result = File.ln_s(@theme_filepath, @theme_linkpath)

      if result == :ok do
        {:ok, @theme_linkpath}
      else
        {:error, {@theme_filepath, @theme_linkpath}}
      end
    else
      link_path = File.read_link(@theme_linkpath)

      if Enum.at(link_path, 0) == :ok do
        split_path = Path.split(Enum.at(link_path, 1))
        current_theme = Enum.at(split_path, length(split_path) - 2)

        # @TODO find some way to notify theme could not be found
        current_path = change_theme_path(current_theme)
        result = File.ln_s(current_path, @theme_linkpath)

        if result == :ok do
          {:ok, "current theme '" <> current_theme <> "' reinstated as no declared theme"}
        else
          result = File.ln_s(change_theme_path("default"), @theme_linkpath)

          if result == :ok do
            {:ok, "current theme '" <> current_theme <> "' unavailable, successful fallback to default theme"}
          else
            {:error, "current theme '" <> current_theme <> "' unavailable, failed fallback to default theme"}
          end
        end
      else
        {:error, @theme_linkpath}
      end
    end
  end

  @doc """
  Update website theme in-memory, independent of stored website settings.
  """
  def update(theme_name) do
    theme_path = change_theme_path(theme_name)

    if File.exists?(theme_path) do
      # @TODO find some way to notify theme could not be found
      result = File.ln_s(theme_path, @theme_linkpath)

      if result == :ok do
        {:ok, @theme_linkpath}
      else
        update()
      end
    else
      update()
    end
  end

  def grab(), do: nil

  def unpack(), do: nil

  def install(), do: nil

  def remove(theme_name) do
    theme_path = change_theme_path(theme_name)

    if theme_name != "default" do
      result = File.rm_rf(theme_path)
      result
    else
      {:error, theme_name <> " cannot be uninstalled"}
    end
  end
end