Improve posts extension with slugs, filename as default slug, and config-based default for layout

lib/tableau/extensions/post_extension.ex

@@ -1,7 +1,18 @@
 defmodule Tableau.PostExtension.Config do
+  @moduledoc """
+  Configuration for PostExtension.
+
+  ## Options
+    - `:enabled` - boolean - Extension is active or not.
+    - `:dir` - string - Directory to scan for markdown files. Defaults to `_posts`
+    - `:future` - boolean - Show posts that have dates later than the current timestamp, or time at which the site is generated.
+    - `:permalink` - string - Default output path for posts. Accepts `:title` as a replacement keyword, replaced with the post's provided title. If a post has a `:permalink` provided, that will override this value _for that post_.
+    - `layout` - string - Elixir module providing page layout for posts. Default is nil
+  """
+
   import Schematic
 
-  defstruct enabled: true, dir: "_posts", future: false
+  defstruct enabled: true, dir: "_posts", future: false, permalink: nil, layout: nil
 
   def new(input), do: unify(schematic(), input)
 
@@ -11,7 +22,9 @@ defmodule Tableau.PostExtension.Config do
       %{
         optional(:enabled) => bool(),
         optional(:dir) => str(),
-        optional(:future) => bool()
+        optional(:future) => bool(),
+        optional(:permalink) => str(),
+        optional(:layout) => str()
       },
       convert: false
     )
@@ -22,30 +35,56 @@ defmodule Tableau.PostExtension.Posts.Post do
   def build(filename, attrs, body) do
     {:ok, config} = Tableau.Config.new(Map.new(Application.get_env(:tableau, :config, %{})))
 
+    {:ok, post_config} =
+      Tableau.PostExtension.Config.new(
+        Map.new(Application.get_env(:tableau, Tableau.PostExtension, %{}))
+      )
+
     attrs
     |> Map.put(:body, body)
     |> Map.put(:file, filename)
-    |> Map.put(:layout, Module.concat([attrs.layout]))
+    |> Map.put(:layout, Module.concat([attrs.layout || post_config.layout]))
     |> Map.put(
       :date,
       DateTime.from_naive!(
         Code.eval_string(attrs.date) |> elem(0),
         config.timezone
       )
     )
-    |> Map.put(
-      :permalink,
-      attrs.permalink
-      |> String.replace(":title", attrs.title)
-      |> String.replace(" ", "-")
-      |> String.replace(~r/[^[:alnum:]\/\-]/, "")
-      |> String.downcase()
-    )
+    |> build_permalink(post_config)
   end
 
   def parse(_file_path, content) do
     Tableau.YamlFrontMatter.parse!(content, atoms: true)
   end
+
+  defp build_permalink(%{permalink: permalink} = attrs, _config) do
+    permalink
+    |> transform_permalink(attrs)
+    |> then(&Map.put(attrs, :permalink, &1))
+  end
+
+  defp build_permalink(%{title: _title} = attrs, %{permalink: permalink})
+       when not is_nil(permalink) do
+    permalink
+    |> transform_permalink(attrs)
+    |> then(&Map.put(attrs, :permalink, &1))
+  end
+
+  defp build_permalink(%{file: filename} = attrs, _) do
+    filename
+    |> Path.rootname()
+    |> transform_permalink(attrs)
+    |> then(&Map.put(attrs, :permalink, &1))
+  end
+
+  defp transform_permalink(path, attrs) do
+    path
+    |> String.replace(":title", attrs.title)
+    |> String.replace(" ", "-")
+    |> String.replace(~r/[^[:alnum:]\/\-]/, "")
+    |> String.downcase()
+  end
 end
 
 defmodule Tableau.PostExtension do
@@ -60,7 +99,7 @@ defmodule Tableau.PostExtension do
 
   * `:id` - An Elixir module to be used when compiling the backing `Tableau.Page`
   * `:title` - The title of the post
-  * `:permalink` - The permalink of the post. `:title` will be replaced with the posts title and non alphanumeric characters removed
+  * `:permalink` - The permalink of the post. `:title` will be replaced with the posts title and non alphanumeric characters removed. Optional.
   * `:date` - An Elixir `NaiveDateTime`, often presented as a `sigil_N`
   * `:layout` - A Tableau layout module.
 
@@ -75,6 +114,16 @@ defmodule Tableau.PostExtension do
   layout: "ElixirTools.PostLayout"
   ---
   ```
+
+  ## URL generation
+
+  If a `:permalink` is specified in the front matter, whatever is there _will_ be the post's permalink.
+
+  If a global `:permalink` is set, it's rules will be used. See `Tableau.PostExtension.Config` for details.
+
+  If permalink is set in either location, the file's name and path will be used
+
+  In all cases, permalinks are stripped of non-alphanumeric characters.
   """
 
   {:ok, config} =

mix.exs

@@ -44,7 +44,6 @@ defmodule Tableau.MixProject do
       {:makeup_elixir, ">= 0.0.0"},
       {:tz, "~> 0.26.2"},
 
-
       # {:yaml_front_matter, "~> 1.0"},
       # {:jason, "~> 1.4"},
       # {:req, "~> 0.3", only: :test},