Feature: OG Social media cards

Not Original Gangsta, but ObjectGraph

Reason: images were showing on LinkedIn, but small.

app/lib/firehose_web/components/layouts.ex

@@ -12,6 +12,27 @@ defmodule FirehoseWeb.Layouts do
 
   embed_templates "layouts/*"
 
+  @doc """
+  Stores content in the connection for later rendering in layouts.
+
+  Used to inject dynamic meta tags into the `<head>` section.
+  """
+  def put_content_for(conn, key, content) do
+    content_for = Map.get(conn.assigns, :content_for, %{})
+    new_content_for = Map.update(content_for, key, [content], &(&1 ++ [content]))
+    Plug.Conn.assign(conn, :content_for, new_content_for)
+  end
+
+  @doc """
+  Retrieves content stored via `put_content_for/3`.
+
+  Can be called from HEEx templates with `get_content_for(assigns, :meta_tags)`.
+  """
+  def get_content_for(assigns, key) do
+    content_for = assigns[:content_for]
+    if is_map(content_for), do: Map.get(content_for, key, []), else: []
+  end
+
   @doc """
   Shows the flash group with standard titles and content.