mflask

defmodule Mflask.Middleware.Static do
  @moduledoc """
  Static file serving middleware.

  ## Usage

      use Mflask
      plug Mflask.Middleware.Static, at: "/static", from: "priv/static"

  ## Options

  - `:at`   — URL prefix to serve under (default: `"/static"`)
  - `:from` — filesystem path to serve files from (default: `"priv/static"`)

  ## Example

  A request to `/static/app.css` will serve `priv/static/app.css`.
  """

  @behaviour Plug

  @impl true
  def init(opts) do
    %{
      at: Keyword.get(opts, :at, "/static"),
      from: Keyword.get(opts, :from, "priv/static")
    }
  end

  @impl true
  def call(conn, %{at: at, from: from}) do
    prefix = String.trim_leading(at, "/")

    case conn.path_info do
      [^prefix | rest] ->
        rel_path = Path.join(rest)
        abs_path = Path.join([from, rel_path])

        if File.exists?(abs_path) and not File.dir?(abs_path) do
          mime = MIME.from_path(abs_path)

          conn
          |> Plug.Conn.put_resp_content_type(mime)
          |> Plug.Conn.send_file(200, abs_path)
          |> Plug.Conn.halt()
        else
          conn
        end

      _ ->
        conn
    end
  end
end