module Mixins
  module UniqueFinder
    def self.prepended(model_class)
      unless model_class.respond_to? :unique_attribute
        raise "Missing :unique_attribute accessor on ##{model_class}"
      end

      model_class.singleton_class.prepend ClassMethods
    end

    module ClassMethods
      ##
      # Returns the first model that matches (in this order), either:
      # 1. The given ID
      # 2. The given unique attribute
      def find_by_unique(unique_or_id)
        matches = where(id: unique_or_id).or(where(unique_attribute => unique_or_id)).to_a

        case matches.length
        when 0
          nil
        when 1
          matches.first
        else
          matches.find { |user| user.id.to_s == unique_or_id.to_s }
        end
      end

      ##
      # Returns the first model that matches (in this order), either:
      # 1. The given ID
      # 2. The given unique attribute
      #
      # Raise ActiveRecord::RecordNotFound when no match is found.
      def find_by_unique!(unique_or_id)
        match = find_by_unique(unique_or_id)

        if match.nil?
          raise ActiveRecord::RecordNotFound
        else
          match
        end
      end
    end
  end
end