#!/usr/bin/env python3

import collections

def uuid(): 
   uuid.counter += 1
   return 'UUID(%s)' % uuid.counter
uuid.counter = 0

class FieldTree(object): 
   def __init__(self, pairs): 
      self.fields = collections.OrderedDict()

      for key, value in pairs: 
         if isinstance(value, list): 
            value = FieldTree(value)
         self.add(key, value)

   def __len__(self): 
      result = 0
      for value in self.fields.values(): 
         if not isinstance(value, FieldTree): 
            result += 1
         else: result += len(value)
      return result

   def add(self, key, value): 
      key = key if (key is not None) else uuid()
      self.fields[key] = value

   def get(self, i): 
      counter = 1
      for key, value in self.fields.items(): 
         print(i, counter, key, value)
         if counter == i: 
            return value
         if isinstance(value, FieldTree): 
            try: result = value.get(i - counter)
            except ValueError: 
               counter += len(value)
            else: return result
         counter += 1
      raise ValueError()

def test(): 
   a = FieldTree((
      ('id', 1234), 
      ('name', 'John Smith'), 
      ('phone', '555-1212')
   ))

   print(a.fields)
   print(a.get(1))

   b = FieldTree([
      ('tag', 'table'), 
      ('contents', 
         [('id', 
            [('tag', 'tr'), 
             ('contents', 
               [(None, 
                   [('tag', 'td'), 
                    ('contents', 
                      [(None, 'id')])]), 
                (None, 
                   [('tag', 'td'), 
                    ('contents', 
                      [(None, 
                         [('tag', 'input'), 
                          ('type', 'text'), 
                          ('value', 1234)])])])])]), 
         ('name', ...), 
         ('phone', ...)])
   ])
   print(b.get(15))

b = """
tag: "table"
contents
  id
  | tag: "tr"
  | contents
  | +
  | | tag: "td"
  | | contents
  | |   +: "id"
  | +
  |   tag: "td"
  |   contents
  |     +
  |       tag: "input"
  |       type: "text"
  |       value: "1234"
  name: ...
  phone: ...
"""

if __name__ == '__main__': 
   test()