award_winning_xor.rb

# 0. "trust me it works"

def cancelled_at=(time)
  super.tap do
    if cancelled_at_change && ((!cancelled_at_change.first) ^ (!cancelled_at_change.last))
      time ? self.status_event = "cancel" : self.status_event = "reserve"
    end
  end
end

# 1. remove tap

def cancelled_at=(time)
  result = super

  if cancelled_at_change && ((!cancelled_at_change.first) ^ (!cancelled_at_change.last))
    time ? self.status_event = "cancel" : self.status_event = "reserve"
  end

  result
end

# 2. capture changing attribute without relying on ActiveModel::Dirty tracking

def cancelled_at=(time)
  before_change = cancelled_at
  result = super
  after_change = cancelled_at

  if (before_change != after_change) && ((!before_change) ^ (!after_change))
    time ? self.status_event = "cancel" : self.status_event = "reserve"
  end

  result
end

# 3. expand ternary to if/else, show checking for nil?

def cancelled_at=(time)
  before_change = cancelled_at
  result = super
  after_change = cancelled_at

  if (before_change != after_change) && ((!before_change) ^ (!after_change))
    if time.nil?
      self.status_event = "cancel"
    else
      self.status_event = "reserve"
    end
  end

  result
end

# 4. ! means nil?

def cancelled_at=(time)
  before_change = cancelled_at
  result = super
  after_change = cancelled_at

  if (before_change != after_change) && (before_change.nil? ^ after_change.nil?)
    if time.nil?
      self.status_event = "cancel"
    else
      self.status_event = "reserve"
    end
  end

  result
end

# 5. name the comparisons for before/after

def cancelled_at=(time)
  before_change = cancelled_at
  result = super
  after_change = cancelled_at
  value_changed = (before_change != after_change)
  only_one_is_nil = (before_change.nil? ^ after_change.nil?)
  changing_to_nil = time.nil?

  if value_changed && only_one_is_nil
    if changing_to_nil
      self.status_event = "cancel"
    else
      self.status_event = "reserve"
    end
  end

  result
end

# 6. expand the XOR comparison to && || comparison

def cancelled_at=(time)
  before_change = cancelled_at
  result = super
  after_change = cancelled_at
  value_changed = before_change != after_change
  only_one_is_nil = (before_change.nil? && after_change.present?) || (before_change.present? && after_change.nil?)
  changing_to_nil = time.nil?

  if value_changed && only_one_is_nil
    if changing_to_nil
      self.status_event = "cancel"
    else
      self.status_event = "reserve"
    end
  end

  result
end

# 7. name the parts of the && || comparison

def cancelled_at=(time)
  before_change = cancelled_at
  result = super
  after_change = cancelled_at
  value_changed = before_change != after_change
  changing_nil_to_time = before_change.nil? && after_change.present?
  changing_time_to_nil = before_change.present? && after_change.nil?
  only_one_is_nil = changing_nil_to_time || changing_time_to_nil
  changing_to_nil = time.nil?

  if value_changed && only_one_is_nil
    if changing_to_nil
      self.status_event = "cancel"
    else
      self.status_event = "reserve"
    end
  end

  result
end