Transform json schema v3 required to v4

schema_transform.rb

class Stack < Array
  def add_frame
    Stack.new(self + [[]])
  end

  def frames_ago n
    return self[-n]
  end
end

def remap(schema, parent_key = nil, stack = Stack.new)
  schema.each_with_object({}) do |(k, v), copy|
    if v.is_a?(Hash)
      new_stack = stack.add_frame
      copy[k] = remap(v, k, new_stack)
      copy["required"] = new_stack.last unless new_stack.last.empty?
    elsif k == "required"
      stack.frames_ago(2) << parent_key if v
    else
      copy[k] = v
    end
  end
end

require 'json'
file = ARGF.read
schema = JSON.parse(file)
begin
  new_schema = remap(schema)
  puts new_schema.to_json
rescue Exception => err
  $stderr.puts "#{ARGF.filename} #{err}"
  puts file
end