Add hook system

[jbanass]

Problem

Given the purpose for Onesie is to run scripts that largely account for changing data, there are times where an artifact is necessary that records actions taken, and subsequently uploaded for later analysis. This is especially useful in continuous delivery circumstances where these onesies are ran without human intervention.

With that said, it's also understood that this gems purpose is to not handle uploading of artifacts.

Proposal

Add support for a hooks system (akin to RSpec's before(:each)) that allows for either onesie set up or tear down that enables consumers to do things such as:

• prep storage providers for artifact upload
• clean up things that a onesie may have created
• Post a slack message stating this onesie's about to run

Could possibly take advantage of https://github.com/rails/rails/tree/main/activesupport for callback?

[timlkelly]

Thanks for bringing up the topic! It makes sense to me to have a more configurable callback system, and I see the usefulness of being able to act before or after a task is run. And I agree that Onesie itself should not know anything about the custom task being done before/after a task is run.

Onesie already employs a basic approach to wrap each task to perform a few validations and housekeeping tasks.
When Task objects are instantiated, they're wrapped with the TaskWrapper:

onesie/lib/onesie/task_proxy.rb

Lines 35 to 37 in 8381959

	klass = "Onesie::Tasks::#{name}".constantize
	klass.class_eval { prepend Onesie::TaskWrapper }
	klass.new(name, version)

TaskWrapper#run is called before the actual Task's #run method and executes a few guards and records that the task was run afterward.

onesie/lib/onesie/task_wrapper.rb

Lines 9 to 18 in 8381959

	def run(manual_override: false)
	return unless allowed_environment?
	return if task_record_present?
	return if manual_task? && !manual_override
	puts "Running #{name}...".magenta
	super()
	record_task
	puts "Done running #{name}!".green
	end

This could be expanded to provide a basic before or after callback.

ActiveSupport::Callbacks is probably a more powerful and better callback system that provides before, after, and around callbacks out of the box.

I'd be okay with adding this dependency, given Onesie is already tightly dependent on other libraries from Rails.

If ActiveSupport::Callbacks is used, we should ensure that it complements the existing Task lifecycle.
Custom before and after callbacks should execute after the internal before actions and internal after actions. Perhaps the wrapper could even be completely replaced with Callbacks.

Post a slack message stating this onesie's about to run

With this example, would higher-level callbacks be useful? For instance, define a custom callback that happens after every task but is configured at a "system" level so you aren't appending after :notifiy_slack to each Task. Alternatively, there could be callbacks after each Onesie "run" instead of before/after each task.