feat: show fortune

[mnishiguchi]

revised after developing this separate project called elixir-fortune

Description

resolves #105

• This feature is powered by the elixir-fortune package (support include/exclude options fhunleth/elixir-fortune#1)
• By default, this feature is disabled
• With the fortune: true option specified, one of the default Nerves tips will be printed in the MOTD
• Users can optionally provide custom fortunes in their Elixir projects, and include fortunes provided by dependencies, following the elixir-fortune instructions

Notes

• The default tips are copied from https://tips.nerves-project.org
• The general nerves tips could alternatively live in other projects since elixir-fortune is capable of scanning all the dependencies for fortunes directories at the time users compile their Nerves projects.

TODO

• release elixir-fortune v0.1.0 first
• update fortune dependency (currently path dependency)
• make sure all tests pass
• merge this PR
• release new version of nerves_motd

[jjcarstens]

We chatted about this at standup and are super excited! Some of the proposed changes:

• Shift to one-line tips
  • Store in a file in this repo for now
• Allow users to specify custom tips and/or files as well

[mnishiguchi]

I did some testing locally and it worked well.

Three parts

• elixir-fortune
  • defines default elixir fortune file
  • provides :strfile_compiler compiler
  • provides Fortune.random!(options)

    @typedoc """
      The fortune options
    
      * `:paths` - a list of absolute paths to `fortunes` directories
      * `:include` - a list of applications whose fortunes you want to opt in for
      * `:exclude` - a list of applications whose fortunes you want to opt out of
      """
      @type fortune_option() ::
              {:paths, String.t() | [String.t()] | nil}
              | {:include, atom | [atom] | nil}
              | {:exclude, atom | [atom] | nil}

• nerves_motd
  • depends on elixir-fortune
  • uses :strfile_compiler compiler
  • defines nerves-tips fortune file

    # mix.exs
    compilers: Mix.compilers() ++ [:strfile_compiler]

• user’s Nerves firmware project
  • depends on nerves_motd
  • defines custom fortune file

    # rootfs_overlay/etc/iex.exs
    NervesMOTD.print(fortune: true)

Tip format

• wrapping fortune entries by following rules in fortune files is working well
  • width: 80-ish
  • height: 1-5 lines

Inclusion / exclusion of fortune files

Can be configured in a user project like below.

config :fortune, include: [...]
config :fortune, exclude: [...]
config :fortune, paths: [...]

[fhunleth]

This is looking good.

I think we should start moving to reduce the NervesMOTD code for tips. That way, anyone who doesn't want them won't feel like they're bloating their firmware. I suspect that the reality is that this strings only trivially affect it, but I do know a few people who would prefer to not even have to look.

How about:

1. Start using a separate library for the tips. e.g., :nerves_tips
2. Make the :fortune dependency optional.
3. Make a :nerves_tips dependency just for dev and test. For prod, I don't think we need a dependency on it at all, but I can see how it would be handy for dev and test.
4. Keep the option to show the fortune. I'd propose renaming it to :show_fortune? to make it look more boolean. If it's unset, make it default to true if the :fortune application is available at runtime and :false if not. That way it should just work for most users and they won't need to concern themselves with the configuration.

WDYT?