index tips

lib/nerves_motd.ex

@@ -26,7 +26,6 @@ defmodule NervesMOTD do
           {:logo, IO.ANSI.ansidata()}
           | {:extra_rows, [row()]}
           | {:show_tip, boolean()}
-          | {:extra_tips, [String.t()]}
 
   @typedoc """
   One row of information
@@ -53,7 +52,6 @@ defmodule NervesMOTD do
   * `:extra_rows` - a list of custom rows or a callback for returning rows.
     The callback can be a 0-arity function reference or MFArgs tuple.
   * `:show_tip` - a boolean flag to show the tip of the day.
-  * `:extra_tips` - additional custom tips as a list of strings.
   """
   @spec print([option()]) :: :ok
   def print(opts \\ []) do
@@ -92,11 +90,13 @@ defmodule NervesMOTD do
   @spec tips([option()]) :: IO.ANSI.ansidata()
   defp tips(opts) do
     if opts[:show_tip] do
-      """
+      case Tips.random() do
+        {:ok, tip} ->
+          ["\n=== Tip of the day ===\n", tip, "\n"]
 
-      === Tip of the day ===
-      #{Tips.random(opts)}
-      """
+        _error ->
+          []
+      end
     else
       []
     end

lib/nerves_motd/tips.ex

@@ -1,29 +1,49 @@
 defmodule NervesMOTD.Tips do
   @moduledoc false
 
-  @divider "\n\n"
-  @default_tips File.read!("config/default_tips.txt")
-                |> String.split(@divider, trim: true)
-                |> Enum.reject(&(&1 == ""))
+  # Returns a tuple list of locaton and byte size of each tip entry in the provided file.
+  index_file = fn filename, divider when is_binary(filename) and is_binary(divider) ->
+    divider_byte_size = byte_size(divider)
 
-  @type tip :: String.t()
+    {indices, _} =
+      File.read!(filename)
+      |> String.trim()
+      |> String.split(divider, trim: true)
+      |> Enum.reduce({[], 0}, fn tip, {indices, current_location} ->
+        how_many_bytes = byte_size(tip)
+        next_location = current_location + how_many_bytes + divider_byte_size
+        new_index = {current_location, how_many_bytes}
 
-  @doc """
-  List all tips
-  """
-  @spec all(keyword) :: [tip]
-  def all(opts \\ []) do
-    extra_tips = Keyword.get(opts, :extra_tips, [])
-    @default_tips ++ extra_tips
+        {[new_index | indices], next_location}
+      end)
+
+    indices
   end
 
+  @default_tips_file "priv/default_tips.txt"
+  @divider "%%%"
+  @indices Application.app_dir(:nerves_motd, [@default_tips_file]) |> index_file.(@divider)
+
+  def indices, do: @indices
+
   @doc """
   Pick one tip randomly
   """
-  @spec random(keyword) :: tip
-  def random(opts \\ []) do
-    all(opts)
-    |> Enum.reject(&(&1 == ""))
-    |> Enum.random()
+  @spec random() :: {:ok, String.t()} | {:error, any}
+  def random() do
+    {location, how_many_bytes} = Enum.random(@indices)
+    read_file_at_location(tips_file(), location, how_many_bytes)
+  end
+
+  defp tips_file do
+    # this is different from the one at compile time
+    Application.app_dir(:nerves_motd, [@default_tips_file])
+  end
+
+  defp read_file_at_location(filename, location, how_many_bytes) do
+    with {:ok, io_device} <- File.open(filename, [:read]),
+         {:ok, data} <- :file.pread(io_device, location, how_many_bytes),
+         :ok <- File.close(io_device),
+         do: {:ok, String.trim(data)}
   end
 end

config/default_tips.txt → priv/default_tips.txt

@@ -1,75 +1,75 @@
 Compiling systems on linux or via `mix nerves.system.shell`? Don't forgot about
 `make help` and other tips from the Buildroot manual (thanks @ericr3r)
 https://buildroot.org/downloads/manual/manual.html#make-tips
-
+%%%
 Configuring the Elixir Logger to show SASL reports can help debug unexpected
 GenServer restarts.
 https://hexdocs.pm/logger/Logger.html#module-erlang-otp-integration
-
+%%%
 Erlinit is a small program that starts the Erlang VM on boot. It has many
 options - especially for debugging startup issues.
 https://hexdocs.pm/nerves/advanced-configuration.html#overriding-erlinit-config-from-mix-config
-
+%%%
 Get all of the default packages for starting a new Nerves project by depending
 on `:nerves_pack` https://github.com/nerves-project/nerves_pack
-
+%%%
 Get some insights to Nerves internals with this high level overview of the
 Nerves architecture and choice to use the BEAM VM https://youtu.be/VzOaSvTcvU4
-
+%%%
 Identify your Nerves devices using a unique ID that's already programmed into
 the hardware using the boardid command. Details at
 https://github.com/nerves-project/boardid/ and the boardid.config file.
-
+%%%
 Make small code changes to your running application by copy/pasting Elixir
 source files at the IEx prompt.
-
+%%%
 Need more than Elixir logs? Run `dmesg` to see log messages from device drivers
 and the Linux kernel. Nerves also routes kernel log messages to the Elixir
 logger.
-
+%%%
 Nerves automatically reboots devices when the Erlang VM exits. This can make
 some debugging harder, but you can easily disable it to let those sessions hang
 for debugging
-
+%%%
 Nerves enables hardware watchdogs and connects them to Erlang's heart feature
 to detect and recover from the Erlang VM hanging. See
 https://embedded-elixir.com/post/2018-12-10-heart/ to learn more about this.
-
+%%%
 Nerves maintains a set of examples for common use-cases with devices. Things
 like running a phoenix app, using SQLite, controlling GPIO, using Zig lang, and
 more! https://github.com/nerves-project/nerves_examples
-
+%%%
 Nerves stores all BEAM files, the Erlang runtime and various support libraries
 and apps in a compressed and read-only SquashFS filesystem. The writable
 application partition is mounted at `/data`
-
+%%%
 Nerves stores all BEAM files, the Erlang runtime and various support
 libraries/apps in a compressed and read-only SquashFS filesystem. Need to write
 to disk? Use the application partition mounted R/W at `/data`
-
+%%%
 Run `Nerves.Runtime.revert` to go back to the previously loaded firmware.
-
+%%%
 See if someone has already implemented support for a sensor or other hardware
 device that you have by checking https://elixir-circuits.github.io/.
-
+%%%
 Sometimes when compiling Nerves systems, order matters! Use `make
 show-build-order` while in `mix nerves.system.shell` to see the compilation
 order and make sure all your 🦆🦆 are in a row (thanks @ericr3r!)
-
+%%%
 Sometimes, you just need to see whats on your Nerves device's disk. Luckily,
 there are a few ways to do that. You can even use VSCode!
 https://embedded-elixir.com/post/2021-05-08-nerves-file-peeking/#sshfs
-
+%%%
 Use `RingLogger.next` to dump the current log buffer to screen. Use
 `log_attach` from `Toolshed` to attach the current session to the Elixir logger
 for live logs. https://hexdocs.pm/toolshed/Toolshed.Log.html#log_attach/1
-
+%%%
 Use `mix firmware.unpack` to decompress a local copy of your firmware on host
 and inspect the files within before installing on device
-
+%%%
 Use the `RamoopsLogger` backend to store log messages in DRAM that can survive
 unexpected reboots. https://github.com/smartrent/ramoops_logger
-
+%%%
 Want more traditional shell tools in your Nerves IEx? Use Toolshed! Its
 included by default and has may familiar functions, such as `cat`, `ls`, or
 even `weather` 🌤️ https://hexdocs.pm/toolshed

test/nerves_motd/tips_test.exs

@@ -3,22 +3,8 @@ defmodule NervesMOTD.TipsTest do
   alias NervesMOTD.Tips
   doctest NervesMOTD.Tips
 
-  @extra_tip """
-  There are only two hard things in Computer Science: cache invalidation and naming things.
-  """
-
-  test "all/1 returns a list of default tips" do
-    assert [tip | _] = Tips.all()
-    assert is_binary(tip)
-  end
-
-  test "all/1 with extra tips returns tips that contain extra tips" do
-    tips = Tips.all(extra_tips: [@extra_tip])
-    assert @extra_tip in tips
-  end
-
-  test "random/1 returns a string" do
-    tip = Tips.random(extra_tips: [@extra_tip])
+  test "random/0 returns a string" do
+    assert {:ok, tip} = Tips.random()
     assert is_binary(tip)
   end
 end