text: #------------------------------------------------------------------------------
  # Copyright (c) 2013, Nucleic Development Team.
  #
  # Distributed under the terms of the Modified BSD License.
  #
  # The full license is in the file COPYING.txt, distributed with this software.
  #------------------------------------------------------------------------------
  from collections import Iterable
  
  from atom.api import Atom, Int, Instance, List, Typed, Value
  from atom.datastructures.api import sortedmap
  
  from .compiler_nodes import new_scope
  from .declarative import d_
  from .pattern import Pattern
  
  
  class Iteration(Atom):
      """ A container to hold data for items in the Looper.
  
      """
      #: Index within the Looper's iterable
      index = Int()
  
      #: Item from the Looper's iterable
      item = Value()
  
      #: Nodes generated by the Looper
      nodes = List()
  
  
  class Looper(Pattern):
      """ A pattern object that repeats its children over an iterable.
  
      The children of a `Looper` are used as a template when creating new
      objects for each item in the given `iterable`. Each iteration of the
      loop will be given an independent scope which is the union of the
      outer scope and any identifiers created during the iteration. This
      scope will also contain a `loop` variable which has `item` and `index`
      members to access the index and value of the iterable, respectively.
  
      All items created by the looper will be added as children of the
      parent of the `Looper`. The `Looper` keeps ownership of all items
      it creates. When the iterable for the looper is changed, the looper
      will only create and destroy children for the items in the iterable
      which have changed. When an item in the iterable is moved the
      `loop.index` will be updated to reflect the new index.
  
      The Looper works under the assumption that the values stored in the
      iterable are unique.
  
      The `loop_item` and `loop_index` scope variables are depreciated in favor
      of `loop.item` and `loop.index` respectively. This is because the old
      `loop_index` variable may become invalid when items are moved.
  
      """
      #: The iterable to use when creating the items for the looper.
      #: The items in the iterable must be unique. This allows the
      #: Looper to optimize the creation and destruction of widgets.
      iterable = d_(Instance(Iterable))
  
      #: The list of items created by the conditional. Each item in the
      #: list represents one iteration of the loop and is a list of the
      #: items generated during that iteration. This list should not be
      #: manipulated directly by user code.
      items = List()
  
      #: Private data storage which maps the user iterable data to the
      #: list of items created for that iteration. This allows the looper
      #: to only create and destroy the items which have changed.
      _iter_data = Typed(sortedmap, ())
  
      #--------------------------------------------------------------------------
      # Lifetime API
      #--------------------------------------------------------------------------
      def destroy(self):
          """ A reimplemented destructor.
  
          The looper will release the owned items on destruction.
  
          """
          super(Looper, self).destroy()
          del self.iterable
          del self.items
          del self._iter_data
  
      #--------------------------------------------------------------------------
      # Observers
      #--------------------------------------------------------------------------
      def _observe_iterable(self, change):
          """ A private observer for the `iterable` attribute.
  
          If the iterable changes while the looper is active, the loop
          items will be refreshed.
  
          """
          if change['type'] == 'update' and self.is_initialized:
              self.refresh_items()
  
      #--------------------------------------------------------------------------
      # Pattern API
      #--------------------------------------------------------------------------
      def pattern_items(self):
          """ Get a list of items created by the pattern.
  
          """
          return sum(self.items, [])
  
      def refresh_items(self):
          """ Refresh the items of the pattern.
  
          This method destroys the old items and creates and initializes
          the new items.
  
          """
          old_items = self.items[:]
          old_iter_data = self._iter_data
          iterable = self.iterable
          pattern_nodes = self.pattern_nodes
          new_iter_data = sortedmap()
          new_items = []
  
          if iterable is not None and len(pattern_nodes) > 0:
              for loop_index, loop_item in enumerate(iterable):
                  iter_data = old_iter_data.get(loop_item)
                  if iter_data is not None:
                      new_iter_data[loop_item] = iter_data
                      iteration = iter_data.nodes
                      new_items.append(iteration)
                      old_items.remove(iteration)
                      iter_data.index = loop_index
                      continue
                  iter_data = Iteration(index=loop_index, item=loop_item)
                  iteration = iter_data.nodes
                  new_iter_data[loop_item] = iter_data
                  new_items.append(iteration)
                  for nodes, key, f_locals in pattern_nodes:
                      with new_scope(key, f_locals) as f_locals:
                          # Retain for compatibility reasons
                          f_locals['loop_index'] = loop_index
                          f_locals['loop_item'] = loop_item
                          f_locals['loop'] = iter_data
                          for node in nodes:
                              child = node(None)
                              if isinstance(child, list):
                                  iteration.extend(child)
                              else:
                                  iteration.append(child)
  
          for iteration in old_items:
              for old in iteration:
                  if not old.is_destroyed:
                      old.destroy()
  
          if len(new_items) > 0:
              expanded = []
              recursive_expand(sum(new_items, []), expanded)
              self.parent.insert_children(self, expanded)
  
          self.items = new_items
          self._iter_data = new_iter_data
  
  
  def recursive_expand(items, expanded):
      """ Recursively expand the list of items created by the looper.
  
      This allows the final list to be inserted into the parent and
      maintain the proper ordering of children.
  
      Parameters
      ----------
      items : list
          The list of items to expand. This should be composed of
          Pattern and other Object instances.
  
      expanded : list
          The output list. This list will be modified in-place.
  
      """
      for item in items:
          if isinstance(item, Pattern):
              recursive_expand(item.pattern_items(), expanded)
          expanded.append(item)
  