defmodule Serum.Markdown do
  @moduledoc false

  _moduledocp = """
  This module provides functions related to dealing with markdown data.
  """

  alias Serum.Project

  @re_media ~r/(?<type>href|src)="(?:%|%25)media:(?<url>[^"]*)"/
  @re_post ~r/(?<type>href|src)="(?:%|%25)post:(?<url>[^"]*)"/
  @re_page ~r/(?<type>href|src)="(?:%|%25)page:(?<url>[^"]*)"/
  @re_tag ~r/(?<type>href|src)="(?:%|%25)tag:(?<url>[^"]*)"/

  @doc "Converts a markdown document into HTML."
  @spec to_html(binary(), Project.t()) :: {binary(), map()}
  def to_html(markdown, proj) do
    {html, meta} =
      Md.generate(markdown,
        parser: Serum.Md.Parser,
        format: [*: :none, p: :indent, article: :indent],
        walker:
          {:post,
           fn
             {:p, _, [title]} = _elem, acc when not is_map_key(acc, :title) ->
               {"", Map.put(acc, :title, title)}

             {:a, %{"data-tag": tag}, _} = elem, acc ->
               {elem, Map.update(acc, :tags, [tag], &[tag | &1])}

             elem, acc ->
               {elem, acc}
           end}
      )

    {process_links(html, proj), meta}
  end

  @spec process_links(binary(), Project.t()) :: binary()
  defp process_links(data, proj) do
    data
    |> replace_media_links(proj)
    |> replace_tag_links(proj)
    |> replace_page_links(proj)
    |> replace_post_links(proj)
  end

  @spec replace_media_links(binary(), Project.t()) :: binary()
  defp replace_media_links(data, proj) do
    Regex.replace(@re_media, data, fn _, attr, val ->
      make_html_attr(attr, Path.join([proj.base_url, "media", val]))
    end)
  end

  @spec replace_tag_links(binary(), Project.t()) :: binary()
  defp replace_tag_links(data, proj) do
    Regex.replace(@re_tag, data, fn _, attr, val ->
      make_html_attr(attr, Path.join([proj.base_url, proj.tags_path, val]))
    end)
  end

  @spec replace_page_links(binary(), Project.t()) :: binary()
  defp replace_page_links(data, proj) do
    Regex.replace(@re_page, data, fn _, attr, val ->
      make_html_attr(attr, Path.join([proj.base_url, val <> ".html"]))
    end)
  end

  @spec replace_post_links(binary(), Project.t()) :: binary()
  defp replace_post_links(data, proj) do
    suffix = post_suffix(proj.pretty_urls)

    Regex.replace(@re_post, data, fn _, attr, val ->
      make_html_attr(attr, Path.join([proj.base_url, "posts", val <> suffix]))
    end)
  end

  @spec make_html_attr(binary(), binary()) :: binary()
  defp make_html_attr(attr, value) do
    <<attr::binary, "=\"", value::binary, "\"">>
  end

  @spec post_suffix(Project.pretty_urls()) :: binary()
  defp post_suffix(pretty_urls)
  defp post_suffix(true), do: ""
  defp post_suffix(:posts), do: ""
  defp post_suffix(_pretty_urls), do: ".html"
end