module ActiveRecord::AttributeMethods::Dirty

def _field_changed?(attr, old, value)
  if column = column_for_attribute(attr)
    if column.number? && (changes_from_nil_to_empty_string?(column, old, value) ||
                          changes_from_zero_to_string?(old, value))
      value = nil
    else
      value = column.type_cast(value)
    end
  end
  old != value
end

def changes_from_nil_to_empty_string?(column, old, value)
  # For nullable numeric columns, NULL gets stored in database for blank (i.e. '') values.
  # Hence we don't record it as a change if the value changes from nil to ''.
  # If an old value of 0 is set to '' we want this to get changed to nil as otherwise it'll
  # be typecast back to 0 (''.to_i => 0)
  column.null && (old.nil? || old == 0) && value.blank?
end

def changes_from_zero_to_string?(old, value)
  # For columns with old 0 and value non-empty string
  old == 0 && value.is_a?(String) && value.present? && non_zero?(value)
end

def create_record(*)
  partial_writes? ? super(keys_for_partial_write) : super
end

def init_changed_attributes
  @changed_attributes = nil
  # Intentionally avoid using #column_defaults since overridden defaults (as is done in
  # optimistic locking) won't get written unless they get marked as changed
  self.class.columns.each do |c|
    attr, orig_value = c.name, c.default
    changed_attributes[attr] = orig_value if _field_changed?(attr, orig_value, @attributes[attr])
  end
end

def initialize_dup(other) # :nodoc:
  super
  init_changed_attributes
end

def initialize_internals_callback
  super
  init_changed_attributes
end

def keys_for_partial_write
  changed
end

def non_zero?(value)
  value !~ /\A0+(\.0+)?\z/
end

def reload(*)
  super.tap do
    reset_changes
  end
end

def save(*)
  if status = super
    changes_applied
  end
  status
end

def save!(*)
  super.tap do
    changes_applied
  end
end

def save_changed_attribute(attr, value)
  # The attribute already has an unsaved change.
  if attribute_changed?(attr)
    old = changed_attributes[attr]
    changed_attributes.delete(attr) unless _field_changed?(attr, old, value)
  else
    old = clone_attribute_value(:read_attribute, attr)
    changed_attributes[attr] = old if _field_changed?(attr, old, value)
  end
end

def update_record(*)
  partial_writes? ? super(keys_for_partial_write) : super
end

def write_attribute(attr, value)
  attr = attr.to_s
  save_changed_attribute(attr, value)
  super(attr, value)
end