Nimble Publisher: how to hand image refs in markdown and how to control how HTML is emitted?

I have a couple of (relative) newb questions about Nimble Publisher that I can’t quite work out.

I have it (more or less) working but two questions remain:

  1. What is the best way to handle a markdown file with an image ref in it? For example, let’s say that the original markdown file was in a directory called dir/ and in that directory is an image called dir/image.png. If the markdown file is in the same directory (ie dir/markdown.md I could use the standard markdown image reference tag ![image](./image.png)and the markdown viewer or renderer would create an <img src="./image.png">… tag from the markdown. However, because of the way that the routes are set up, that image url ends up being interpreted as an id for a blog post, which of course it can’t find. I can’t be the first person to ever try to do this so there must be an idiomatic way to handle URIs embedded in the markdown file or a way to configure the routes so that markdown is handled by nimble by images are and other content are treated as normal urls.

  2. I want to control the way that the HTML is emitted from the markdown processor so that I can style it. At the moment, a markdown # Heading is being rendered simply as <h1>Heading</h1>. But what I need to do is control the styling of the emitted HTML. Again, I can’t be the first person who has ever needed to do this, but I can’t find from the docs what the best way to handle this would be.

Any ideas or even a link to an example or some docs for either problem would be very helpful. Thanks.

PS: I originally posted this on GitHub to the NimblePublisher repo here, but was asked to cross-post here by @josevalim.

Ok, so for what it’s worth, I changed the standard NimblePublisher Post module to look like this:

defmodule Msdc.Blog.Post do
  @enforce_keys [:blog, :id, :author, :title, :body, :description, :tags, :date, :long_date]
  defstruct [:blog, :id, :author, :title, :body, :description, :tags, :date, :long_date]

  @style_map %{
    "h1" => "text-4xl font-bold tracking-tight text-zinc-800 sm:text-5xl dark:text-zinc-100",
    "h2" => "text-m font-bold text-zinc-800 dark:text-zinc-100",
    "h3" => "text-base font-semibold tracking-tight text-zinc-800 dark:text-zinc-100",
    "h4" => "text-3xl tracking-tight text-zinc-800 sm:text-3xl dark:text-zinc-100",
    "p" => "mt-6 text-base text-zinc-600 dark:text-zinc-400",
    "a" => "text-m font-medium text-teal-500",
    "img" => ""
  }

  def build(filename, attrs, body) do
    [blog, year, _month_day_id_dir, month_day_id] = filename |> Path.rootname() |> Path.split() |> Enum.take(-4)
    [month, day, id] = String.split(month_day_id, "-", parts: 3)
    date = Date.from_iso8601!("#{year}-#{month}-#{day}")
    long_date = Calendar.strftime(date, "%B, %d")
    struct!(__MODULE__, [blog: blog, id: id, date: date, long_date: long_date, body: inject_style(@style_map, body)] ++ Map.to_list(attrs))
  end

  def inject_style(style_map, html_content) do
    Enum.reduce(style_map, html_content, fn {tag, class_str}, acc ->
      regex = ~r/(<#{tag}[^>]*)(>)/
      replacement = "\\1 class=\"#{class_str}\"\\2"
      String.replace(acc, regex, replacement)
    end)
  end

end

The inject_style/2 function is a bit of a mess, but what it does is add a class="…" attribute for each HTML tag it finds in the raw blog post content where the value of the class is taken from the map of HTML elements onto class strings kept in @style_map.

I know that it is far from robust, but as a PoC, it serves my purpose for now.

Here’s my approach for 2 (but with your styles substituted).

I’ve added the following to my post.ex:

  def earmark_options do
    Earmark.Options.make_options!(postprocessor: Earmark.AstTools.node_only_fn(&add_tag_class/1))
  end

  @tag_to_class %{
    "h1" => "text-4xl font-bold tracking-tight text-zinc-800 sm:text-5xl dark:text-zinc-100",
    "h2" => "text-m font-bold text-zinc-800 dark:text-zinc-100",
    "h3" => "text-base font-semibold tracking-tight text-zinc-800 dark:text-zinc-100",
    "h4" => "text-3xl tracking-tight text-zinc-800 sm:text-3xl dark:text-zinc-100",
    "p" => "mt-6 text-base text-zinc-600 dark:text-zinc-400",
    "a" => "text-m font-medium text-teal-500"
  }
  defp add_tag_class({tag, attrs, ignored, meta}) do
    new_attrs = if class = @tag_to_class[tag], do: [{"class", class}], else: []
    {tag, attrs ++ new_attrs, ignored, meta}
  end

Then the following to my use NimblePublisher invocation:

  use NimblePublisher,
    # ...
    earmark_options: Post.earmark_options(),
    # ...

The postprocessor option gives you a hook which lets you work with the AST.

I also had to add this to my tailwind.config.js:

module.exports = {
  content: [
    // ...
    "../lib/path/to/post.ex",
    // ...
  ],

So it would pickup the new classes.

That’s a neat way to solve this (and more robust than my ropey attempt). Thanks!

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