method_with_metadata_and_advice.rb

require 'byebug'

module MethodMetadata
  def self.included(base)
    base.extend ClassMethods
  end

  module ClassMethods
    def method_advice(data = {})
      lineno = caller_locations(1, 1).first.lineno

      register(lineno, data)
    end

    def register(lineno, data)
      method_metadata[lineno] = data
    end

    def method_metadata_at(lineno)
      method_metadata[lineno]
    end

    def method_metadata
      @method_metadata ||= {}
    end

    def method_advices
      @method_advices ||= {}
    end

    def execute_with_advice(advice)
      puts "Executing advices #{advice}"

      ##
      # Implement your advices here
      #
      advice.each do |advice_type, args|
        case advice_type
        when :required_envvar
          args.each { |key| ENV.fetch(key) }
        end
      end

      yield
    end

    def attach_advice_with_singleton_method(method_name, advice)
      method_advices[method_name] = advice

      class_eval(<<-CODE, __FILE__, __LINE__ + 1)
        class << self
          alias_method :#{method_name}_without_advice, :#{method_name}
        
          def #{method_name}(*args)
            advice = method_advices.fetch(:#{method_name}, nil)
            execute_with_advice(advice) { #{method_name}_without_advice(*args) } if advice
          end
        end
      CODE
    end

    # FYI: Needs to implement method_added in order to support instance methods          
    def singleton_method_added(method_name)
      return if method_name.to_s.match(/_without_advice$/)

      advice = method_metadata_at(method(method_name).source_location.last - 1)

      attach_advice_with_singleton_method(method_name, advice) if advice
    end
  end
end

module Hello
  include MethodMetadata

  # FYI, currently it has to be just before the method name, but you can extend this method implementation to setup
  # as per your desire range - :singleton_method_added
  # 
  method_advice required_envvar: %w[HELLO WORLD]
  def self.connection(arg1, arg2)
    puts 'Connection'
    puts method_metadata.inspect
  end

  def self.hi_there
    puts 'Hi there'
  end

  def hello
  end
end

Hello.connection(1, 2)