Class: ConvenientService::Common::Plugins::HasAroundCallbacks::Middleware

Inherits:
MethodChainMiddleware
  • Object
show all
Includes:
Support::DependencyContainer::Import
Defined in:
lib/convenient_service/common/plugins/has_around_callbacks/middleware.rb

Instance Method Summary collapse

Methods included from Support::Concern

included

Instance Method Details

#next(*args, **kwargs, &block) ⇒ Object 



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# File 'lib/convenient_service/common/plugins/has_around_callbacks/middleware.rb', line 18

def next(*args, **kwargs, &block)
  ##
  # A variable that stores return value of middleware `chain.next` aka `original_value`.
  # It is reassigned later by the `initial_around_callback`.
  #
  original_value = nil

  ##
  # A list of around callbacks.
  #
  # class Service
  #   around do |chain|
  #     # part before `chain.yield`
  #     original_value = chain.yield
  #     # part after `chain.yield`
  #   end
  # end
  #
  # class Service
  #   around do |chain, arguments|
  #     # part before `chain.yield`
  #     original_value = chain.yield
  #     # part after `chain.yield`
  #   end
  # end
  #
  around_callbacks = entity.callbacks.for([:around, method])

  ##
  #
  #
  initial_around_callback = entities.Callback.new(
    types: [:around, method],
    block: proc { original_value = chain.next(*args, **kwargs, &block) }
  )

  ##
  # Let's suppose that we have 3 `around` callbacks:
  #
  # class Service
  #   # first
  #   around do |chain|
  #     # part before `chain.yield`
  #     original_value = chain.yield
  #     # part after `chain.yield`
  #   end
  #
  #   # second
  #   around do |chain|
  #     # part before `chain.yield`
  #     original_value = chain.yield
  #     # part after `chain.yield`
  #   end
  #
  #   # third
  #   around do |chain|
  #     # part before `chain.yield`
  #     original_value = chain.yield
  #     # part after `chain.yield`
  #   end
  # end
  #
  # NOTE: if a user forgets to call `chain.yield` - an error is raised.
  #
  # Then `composed` may be built with the following preudocode (that is why `reverse` is needed):
  #
  #   composed = original
  #   composed = proc { instance_exec(composed, &third) }
  #   composed = proc { instance_exec(composed, &second) }
  #   composed = proc { instance_exec(composed, &first) }
  #
  # Where `first`, `second`, `third` are taken from `entity.callbacks.for([:around, method])`.
  #
  # Original implementation is modified in order to return `original_value` from all `chain.yield` calls.
  #
  #   # Original implementation:
  #   composed =
  #     callbacks.for([:around, method]).reverse.reduce(original) do |composed, callback|
  #       proc { instance_exec(composed, &callback) }
  #     end
  #
  # Original implementation is modified for the second time in order to raise an error
  # if a user forgets to call `chain.yield` inside an around callback.
  #
  # rubocop:disable Style/Semicolon
  composed =
    around_callbacks.reverse.reduce(initial_around_callback) do |composed, callback|
      proc { callback.call_in_context_with_value_and_arguments(entity, composed, *args, **kwargs, &block); original_value }
    end
  # rubocop:enable Style/Semicolon

  ##
  # Call sequence:
  #
  #   composed.call
  #   proc { instance_exec(composed, &first) }.call  # part before `chain.yield`
  #   proc { instance_exec(composed, &second) }.call # part before `chain.yield`
  #   proc { instance_exec(composed, &third) }.call  # part before `chain.yield`
  #   initial_around_callback
  #   proc { instance_exec(composed, &third) }.call  # part after `chain.yield`
  #   proc { instance_exec(composed, &second) }.call # part after `chain.yield`
  #   proc { instance_exec(composed, &first) }.call  # part after `chain.yield`
  #
  composed.call

  ##
  #
  #
  ::ConvenientService.raise Exceptions::AroundCallbackChainIsNotContinued.new(callback: Utils::Array.find_last(around_callbacks, &:called?)) if around_callbacks.any?(&:not_called?)

  ##
  #
  #
  ::ConvenientService.raise Exceptions::AroundCallbackChainIsNotContinued.new(callback: around_callbacks.last) if initial_around_callback.not_called?

  original_value
end