separate front matter parsing

lib/sloane_sh/front_matter.ex

@@ -0,0 +1,17 @@
+defmodule SloaneSH.FrontMatter do
+  @moduledoc """
+  Parses TOML front matter out put files
+  """
+
+  def parse("+++" <> rest, _ctx) do
+    [toml, body] = String.split(rest, ["+++\n", "+++\r\n"], parts: 2)
+
+    with {:ok, attrs} <- Toml.decode(toml, keys: :atoms) do
+      {:ok, attrs, body}
+    end
+  end
+
+  def parse(body, _ctx) do
+    {:ok, %{}, body}
+  end
+end

test/sloane_sh/front_matter_test.exs

@@ -0,0 +1,42 @@
+defmodule SloaneSH.FrontMatterTest do
+  use ExUnit.Case
+
+  alias SloaneSH.FrontMatter
+
+  test "parses TOML front matter" do
+    document = ~S"""
+    +++
+    foo = "bar"
+    +++
+    # Hello, World!
+
+    This is a document with front matter.
+    """
+
+    assert {:ok, %{foo: "bar"}, "# Hello, World!" <> _} = FrontMatter.parse(document, %{})
+  end
+
+  test "returns an empty map is the document doesn't have front matter" do
+    document = ~S"""
+    # Hello, World!
+
+    This is a document with front matter.
+    """
+
+    assert {:ok, %{} = map, document} = FrontMatter.parse(document, %{})
+    assert %{} = map
+  end
+
+  test "errors in TOML front matter produce an error" do
+    document = ~S"""
+    +++
+    foo = "bar
+    +++
+    # Hello, World!
+
+    This is a document with front matter.
+    """
+
+    assert {:error, _} = FrontMatter.parse(document, %{})
+  end
+end