refactor activation logic / defaults to simplify Manager class

[samandmoore]

based on this suggestion here from @smudge https://github.com/Betterment/webvalve/pull/34#discussion_r341619281

I wonder if in some earlier routine it would make sense to do something like this:

def set_defaults!
  if Webvalve.env.in?(ALWAYS_ENABLED_ENVS)
    if ENV.key? 'WEBVALVE_SERVICE_ENABLED_DEFAULT'
      WebValve.logger.warn SERVICE_ENABLED_DEFAULT_WARNING
    end
    if ENV.key? 'WEBVALVE_ENABLED'
      WebValve.logger.warn WEBVALVE_ENABLED_WARNING
    end
    ENV['WEBVALVE_ENABLED'] = '1'
    ENV['WEBVALVE_SERVICE_ENABLED_DEFAULT'] = '0'
  else
    ENV['WEBVALVE_ENABLED'] ||= '0'
    ENV['WEBVALVE_SERVICE_ENABLED_DEFAULT'] ||= '1'
  end
end

And then inside of Manager there doesn't need to be a concept of "always" or "explicit" - it can more naively trust that the two ENV vars are set and mean what they say they mean:

def enabled?
  ENABLED_VALUES.include?(ENV.fetch('WEBVALVE_ENABLED'))
end

def services_enabled_by_default?
  ENABLED_VALUES.include?(ENV.fetch('WEBVALVE_SERVICE_ENABLED_DEFAULT'))
end

def allowing?
  enabled? && services_enabled_by_default?
end

def intercepting?
  enabled? && !services_enabled_by_default?
end

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This issue has been automatically closed because it has not had recent activity. Thank you for your contributions.