"""
List of topology file objects that can be edited in ParmEd. They can be indexed
via either the name of the topology file or by the order in which they were
loaded.
"""

from chemistry.amber.amberformat import AmberFormat
from chemistry.amber.readparm import ChamberParm
try:
   from chemistry.amber.openmmloader import OpenMMAmberParm as AmberParm
   _HAS_OPENMM = True
except ImportError:
   from chemistry.amber.readparm import AmberParm
   _HAS_OPENMM = False
from ParmedTools.exceptions import DuplicateParm, ParmIndexError

class ParmList(object):
   """
   List of AmberParm objects index-able via either prmtop name or prmtop index
   (based on order added)
   """

   openmm_enabled = _HAS_OPENMM

   def __init__(self):
      """ Must be instantiated by itself """
      self._parm_names = []
      self._parm_instances = []
      self.parm = None # The active parm instance
      self.prev = None
      self.current_index = 0

   def set_new_active(self, idx):
      """ Sets a new active parm """
      self.current_index = self.index(idx)
      self.parm = self[self.current_index]

   def add_parm(self, parm):
      """ Add a parm to the list """
      # Make sure this parm is not part of the list already
      if str(parm) in self._parm_names:
         raise DuplicateParm('%s already in ParmList' % parm)
      # Convert a string to an AmberParm or add an AmberParm directly
      if not isinstance(parm, AmberFormat):
         parm = AmberFormat(parm)
         # From the parm data, we should be able to tell whether it was a
         # chamber topology or regular topology. Take the proper view and add it
         # to the list
         if 'CTITLE' in parm.flag_list:
            parm = parm.view(ChamberParm)
         else:
            parm = parm.view(AmberParm)
      # Otherwise, add in the new parm's name
      self._parm_names.append(str(parm))
      self._parm_instances.append(parm)
      # A newly added topology file is the currently active parm
      self.current_index = len(self._parm_instances) - 1
      self.parm = parm

   def index(self, idx):
      """ See what the index of the requested parm is (can be int or str) """
      if isinstance(idx, int):
         if idx < 0 or idx >= len(self._parm_instances):
            raise ParmIndexError('index out of range for ParmList')
         return idx
      else:
         try:
            return self._parm_names.index(str(idx))
         except ValueError:
            raise ParmIndexError('%s prmtop not in ParmList' % idx)

   def __getitem__(self, idx):
      """ Allow an integer index or string index to identify a parm """
      return self._parm_instances[self.index(idx)]

   def __contains__(self, name):
      """ See if a given parm name is in the list """
      if isinstance(name, int):
         return name >= 0 and name < len(self)
      else:
         return str(name) in self._parm_names
   
   def __iter__(self):
      """ Iterate through the prmtop names """
      return iter(self._parm_instances)

   def __len__(self):
      return len(self._parm_instances)

   def empty(self):
      return len(self._parm_instances) == 0