Recursive flattening json object

flatten.rb

def flatten_hash(param, prefix=nil)
  param.each_pair.reduce({}) do |a, (k, v)|
    if v.is_a?(Array)
      v = v.map.with_index { |x, i| [i, x] }.to_h
    end

    if v.is_a?(Hash)
      a.merge(flatten_hash(v, "#{prefix}#{k}."))
    else
      a.merge("#{prefix}#{k}".to_sym => v)
    end
  end
end