Maybe/app/models/rule/condition.rb

class Rule::Condition < ApplicationRecord
  belongs_to :rule, optional: -> { where.not(parent_id: nil) }
  belongs_to :parent, class_name: "Rule::Condition", optional: true, inverse_of: :sub_conditions

  has_many :sub_conditions, class_name: "Rule::Condition", foreign_key: :parent_id, dependent: :destroy, inverse_of: :parent

  validates :condition_type, presence: true
  validates :operator, presence: true
  validates :value, presence: true, unless: -> { compound? }

  accepts_nested_attributes_for :sub_conditions, allow_destroy: true

  # We don't store rule_id on sub_conditions, so "walk up" to the parent rule
  def rule
    parent&.rule || super
  end

  def compound?
    condition_type == "compound"
  end

  def apply(scope)
    if compound?
      build_compound_scope(scope)
    else
      filter.apply(scope, operator, value)
    end
  end

  def prepare(scope)
    if compound?
      sub_conditions.reduce(scope) { |s, sub| sub.prepare(s) }
    else
      filter.prepare(scope)
    end
  end

  def value_display
    if value.present?
      if options
        options.find { |option| option.last == value }&.first
      else
        value
      end
    else
      ""
    end
  end

  def options
    filter.options
  end

  def operators
    filter.operators
  end

  def filter
    rule.registry.get_filter!(condition_type)
  end

  private
    def build_compound_scope(scope)
      if operator == "or"
        combined_scope = sub_conditions
          .map { |sub| sub.apply(scope) }
          .reduce { |acc, s| acc.or(s) }

        combined_scope || scope
      else
        sub_conditions.reduce(scope) { |s, sub| sub.apply(s) }
      end
    end
end