user_search_service.rb

class UserSearchService
  def initialize(search_term, limit = nil, offset = nil)
    @search_term = if search_term.is_a?(String)
      search_term.split(" ")
    else
      search_term.values.reject(&:blank?)
    end
    @limit = limit
    @offset = offset
  end

  def call
    if @limit.present? || @offset.present?
      paginated_results(@limit || 0, @offset || 0)
    else
      complete_results
    end
  end

  alias_method :search_users, :call

  private

  attr_reader :search_term

  def paginated_results(limit, offset)
    paginated_query = base_query.tap do |q|
      q.limit(limit) if limit.positive?
    end.tap do |q|
      q.offset(offset) if offset.positive?
    end

    user_results = paginated_query.to_a
    user_result_count = user_results.count

    address_user_results = if limit.zero? || user_result_count < limit
                             address_query(*user_results.map(&:id)).tap do |q|
                               q.limit(limit - users_count) if limit.positive?
                             end.tap do |q|
                               q.offset(offset - users_count) if offset.positive? && users_count < offset
                             end.map(&:user)
                           else
                             []
                           end

    user_results + address_user_results
  end

  def complete_results
    user_results = base_query.to_a

    address_user_results = address_query(*user_results.map(&:id)).map(&:user)

    user_results + address_user_results
  end

  def full_text_search_term
    search_term.map { |t| "#{t}:*" }.join(" & ")
  end

  def base_query
    Spree::User.quick_search(full_text_search_term)
  end

  def address_query(*user_ids)
    Spree::Address
      .includes(:user)
      .where("user_id NOT IN (?)", user_ids << 0)
      .where("user_id IS NOT NULL")
      .quick_search(full_text_search_term)
  end
end