From a777c9a8b349611ae25bf0a02bb275d9a4541d67 Mon Sep 17 00:00:00 2001
From: Inhji <johnnie@posteo.de>
Date: Tue, 4 Jul 2023 22:46:00 +0200
Subject: [PATCH] include internal link rendering

---
 lib/chiya_web/markdown.ex        | 64 ++++++++++++++++++++---
 lib/chiya_web/references.ex      | 89 ++++++++++++++++++++++++++++++++
 test/chiya_web/markdown_test.exs | 25 +++++++++
 3 files changed, 171 insertions(+), 7 deletions(-)
 create mode 100644 lib/chiya_web/references.ex
 create mode 100644 test/chiya_web/markdown_test.exs

diff --git a/lib/chiya_web/markdown.ex b/lib/chiya_web/markdown.ex
index 030cd81..c2c0cac 100644
--- a/lib/chiya_web/markdown.ex
+++ b/lib/chiya_web/markdown.ex
@@ -1,13 +1,63 @@
 defmodule ChiyaWeb.Markdown do
-  @options [
-    footnotes: true,
-    breaks: true,
-    escape: true,
-    wikilinks: true
-  ]
+  @moduledoc """
+  Module used for rendering markdown. 
 
+  Rendering also collects and replaces internal [references](`Mirage.References`) to other entities like Lists and Tags.
+  """
+
+  import Ecto.Changeset, only: [get_change: 2, put_change: 3]
+
+  defp options() do
+    %Earmark.Options{
+      code_class_prefix: "lang- language-",
+      footnotes: true,
+      breaks: true,
+      escape: false,
+      registered_processors: processors()
+    }
+  end
+
+  @doc """
+  Renders markdown with Earmark.
+  """
   def render(markdown) do
     markdown
-    |> Earmark.as_html!(@options)
+    |> ChiyaWeb.References.replace_references()
+    |> Earmark.as_html!(options())
+  end
+
+  @doc """
+  Renders markdown to HTML inside a changeset if markdown changed.
+  Markdown field and HTML field can be configured.
+  """
+  def maybe_render(changeset, markdown_field, html_field) do
+    if markdown = get_change(changeset, markdown_field) do
+      html = render(markdown)
+      put_change(changeset, html_field, html)
+    else
+      changeset
+    end
+  end
+
+  def processors() do
+    heading = fn
+      {_, _, [content], _} = n when is_binary(content) ->
+        slug = Slugger.slugify_downcase(content)
+        Earmark.AstTools.merge_atts_in_node(n, id: slug)
+
+      node ->
+        node
+    end
+
+    [
+      Earmark.TagSpecificProcessors.new([
+        {"h1", heading},
+        {"h2", heading},
+        {"h3", heading},
+        {"h4", heading},
+        {"h5", heading},
+        {"h6", heading}
+      ])
+    ]
   end
 end
diff --git a/lib/chiya_web/references.ex b/lib/chiya_web/references.ex
new file mode 100644
index 0000000..e24faea
--- /dev/null
+++ b/lib/chiya_web/references.ex
@@ -0,0 +1,89 @@
+defmodule ChiyaWeb.References do
+  @moduledoc """
+  Finds and replaces references to entities in a string.
+
+  A reference is an internal link like the following examples:
+
+  * `[[sustainablity]]` -> A note named *Sustainability*
+  * `[[a-long-unfitting-slug|A simple title]]` -> A note named *A long unfitting title*
+  """
+
+  @reference_regex ~r/\[\[?(?<id>[\d\w-]+)(?:\|(?<title>[\w\d\s'`äöüß]+))?\]\]/
+
+  @doc """
+  Returns a list of references in `string`.
+  """
+  def get_references(nil), do: []
+
+  def get_references(string) do
+    @reference_regex
+    |> Regex.scan(string, capture: :all)
+    |> Enum.map(&map_to_tuple/1)
+  end
+
+  @doc """
+  Checks each reference returned from `get_references/1` and validates its existence.
+  """
+  def validate_references(references) do
+    Enum.map(references, fn {placeholder, slug, custom_title} ->
+      note = Chiya.Notes.get_note_by_slug_preloaded(slug)
+
+      valid =
+        case note do
+          nil -> false
+          _ -> true
+        end
+
+      # If a custom title was defined, use it, 
+      # otherwise use the note's title
+      title =
+        cond do
+          custom_title != slug ->
+            custom_title
+
+          valid ->
+            note.name
+
+          true ->
+            slug
+        end
+
+      {placeholder, slug, title, valid}
+    end)
+  end
+
+  @doc """
+  Returns a list of slugs that are referenced in `string`, optionally filtering by `filter_type`.
+  """
+  def get_reference_ids(string) do
+    string
+    |> get_references()
+    |> Enum.map(fn {_, note_slug, _} -> note_slug end)
+  end
+
+  @doc """
+  Finds and replaces references with the matching url in `string`.
+  """
+  def replace_references(string) do
+    string
+    |> get_references()
+    |> validate_references()
+    |> Enum.reduce(string, fn {placeholder, slug, title, valid}, s ->
+      String.replace(s, placeholder, get_link(slug, title, valid))
+    end)
+  end
+
+  defp get_link(slug, title, valid) do
+    "[#{title}](/note/#{slug})#{get_link_class(valid)}"
+  end
+
+  defp get_link_class(valid) do
+    if valid, do: "{:.invalid}", else: ""
+  end
+
+  defp map_to_tuple([placeholder, note_slug]),
+    do: {placeholder, note_slug, note_slug}
+
+  defp map_to_tuple([placeholder, note_slug, title]),
+    do: {placeholder, note_slug, title}
+end
diff --git a/test/chiya_web/markdown_test.exs b/test/chiya_web/markdown_test.exs
new file mode 100644
index 0000000..bcb49fb
--- /dev/null
+++ b/test/chiya_web/markdown_test.exs
@@ -0,0 +1,25 @@
+defmodule ChiyaWeb.MarkdownTest do
+	use Chiya.DataCase
+
+	alias ChiyaWeb.Markdown
+
+	describe "render/1" do
+		test "renders simple markdown" do
+			html = Markdown.render("# Title")
+			assert html =~ "id=\"title\""
+			assert html =~ "Title"
+			assert html =~ "</h1>"
+		end
+
+		test "renders a link to a note" do
+			html = Markdown.render("[[foo]]")
+			assert html =~ "/note/foo"
+		end
+
+		test "renders a link to a note with custom title" do
+			html = Markdown.render("[[foo|MyFoo]]")
+			assert html =~ "/note/foo"
+			assert html =~ "MyFoo"
+		end
+	end
+end
\ No newline at end of file