feat: add engine subcommands to expert

[rmand97]

closes #209

Taking a stab at the issue. Hoping I understood it correctly.

[mhanberg]

Can you make this return the exit code, and put the System.halt(exit_code) part here?

That'll make the unit tests easier to write, as well as pull the halting part up to the top level.

This way it's very clear that the program stops after this code runs.

[rmand97]

Will do.
Just a quick question. Would you like it to always return success (0), event though it fails deleting a file?

like if its fails the middle one of 3 files in expert clean --force it will continue after failing, logging something went wrong, and delete the last one and return 0. Or would like it to stop after failing and return 1?

[mhanberg]

If it fails any, lets return a non zero exit code (1).

[mhanberg]

Let's also add help text to each subcommand, and the options can be presented for the relevant subcommand.

So in the existing help text here, we won't have any options, and the --force option will show up in the help text for the clean subcommand

[mhanberg]

@rmand97 looks like there are some failing tests.

[mhanberg]

Suggested change

	case argv do
	["engine" | engine_args] ->
	engine_args
	|> Expert.Engine.run()
	|> System.halt()
	_ ->
	:noop
	end
	with ["engine" | engine_args] <- argv do
	engine_args
	|> Expert.Engine.run()
	|> System.halt()
	end

[mhanberg]

I think at this level, we would only want a help option.

[mhanberg]

I believe the way to accomplish the "subcommand" cli we are wanting is to parse the options, get the subcommand, then parse the options again.

Also not we use parse_head instead of parse.

So for example

{opts, rest, _invalid} =
      OptionParser.parse_head(args,
        strict: [help: :boolean],
        aliases: [h: :help]
      )

case rest do
  ["clean" | clean_opts] -> clean_engines(clean_opts) 
  # the rest
end

defp clean_engines(argv) do
  {opts, _rest, _invalid} =
      OptionParser.parse_head(argv,
        strict: [force: :boolean, help: :boolean],
        aliases: [f: :force, h: :help]
      )

  # do the rest

end