serve images, not HTML

lib/labelmaker_web/controllers/label_controller.ex

@@ -0,0 +1,48 @@
+defmodule LabelmakerWeb.LabelController do
+  use LabelmakerWeb, :controller
+  alias LabelmakerWeb.Constants
+
+  @label_dir Path.join(:code.priv_dir(:labelmaker), "static/labels")
+  File.mkdir_p!(@label_dir)
+
+  def show(conn, params) do
+    options =
+      Constants.defaults()
+      |> Map.merge(params)
+      |> Map.take(Constants.permitted_keys())
+
+    filename =
+      options
+      |> inspect()
+      |> (fn str -> :crypto.hash(:sha256, str) end).()
+      |> Base.encode16(case: :lower)
+
+    filename = filename <> ".png"
+    filepath = Path.join(@label_dir, filename)
+
+    unless File.exists?(filepath) do
+      generate_image(options, filepath)
+    end
+
+    conn
+    |> put_resp_content_type("image/png")
+    |> send_file(200, filepath)
+  end
+
+  defp generate_image(options, filepath) do
+    args = [
+      "-background",
+      "none",
+      "-fill",
+      options["color"],
+      "-pointsize",
+      options["size"],
+      "-font",
+      options["font"],
+      "label:#{options["label"]}",
+      filepath
+    ]
+
+    {_, 0} = System.cmd("magick", args)
+  end
+end