# Coordinates carry their aggregation depth; SQL NULL remains an ordinary axis value.
class CountsPivotLayout
  def self.depths(keys, sorts, measures: true)
    return [] if keys.length < 2 || sorts.first&.first == 'count' ||
        sorts.first&.first&.match?(/\Am[0-9]+\z/)

    relevant = sorts.map(&:first).select { keys.include?(_1) || (measures && (_1 == 'count' ||
        _1.match?(/\Am[0-9]+\z/))) }
    order = (relevant + keys).uniq
    (1...keys.length).select { order.first(_1).sort == keys.first(_1).sort }
  end

  def self.headers(values, depths, next_values: nil, grand: false)
    result = []
    values.each_with_index do |tuple, index|
      result << { values: tuple, kind: 'data' }
      following = values[index + 1] || next_values
      depths.reverse_each do |depth|
        prefix = tuple.first(depth)
        next if following && following.first(depth) == prefix

        result << { values: prefix, kind: 'subtotal' }
      end
    end
    result << { values: [], kind: 'grand_total' } if grand
    result
  end
end