"""
This module contains classes for parsing and processing CHARMM parameter,
topology, and stream files.

Author: Jason M. Swails
Contributors:
Date: Mar. 26, 2017
"""
from __future__ import absolute_import, division, print_function

import os
import re
import warnings
from copy import copy as _copy
from collections import OrderedDict
from itertools import combinations

from ..constants import TINY
from ..exceptions import CharmmError, ParameterWarning
from ..modeller import PatchTemplate, ResidueTemplate
from ..parameters import ParameterSet
from ..periodic_table import AtomicNum, element_by_mass
from ..topologyobjects import (AngleType, Atom, AtomType, BondType, CmapType,
                               DihedralType, DihedralTypeList, ImproperType,
                               NoUreyBradley, DrudeAtom, DrudeAnisotropy)
from ..utils.io import genopen
from ..utils.six import integer_types, iteritems, string_types
from ..utils.six.moves import zip
from ._charmmfile import CharmmFile, CharmmStreamFile

_penaltyre = re.compile(r'penalty\s*=\s*([\d\.]+)')

class _EmptyStringIterator(object):
    """ Always yields an empty string """
    def __iter__(self):
        while True:
            yield ''
    def __getitem__(self, idx):
        return ''

def _typeconv(name):
    if isinstance(name, integer_types):
        return name
    if name.upper() == name:
        return name.replace('*', 'STR').replace('+', 'P').replace('-', 'M')[:6]
    # Lowercase letters present -- decorate the type name with LTU --
    # Lower To Upper
    return ('%sLTU' % name.upper()).replace('*', 'STR').replace(
            '+', 'P').replace('-', 'M')[:6]

class CharmmImproperMatchingMixin(object):
    """ Implements CHARMM-style improper matching """

    def match_improper_type(self, a1, a2, a3, a4):
        """ Matches an improper type based on atom type names """
        typ = self._match_improper_with_typemap(self.improper_types, a1, a2, a3, a4)
        if typ is None:
            typ = self._match_improper_with_typemap(self.improper_periodic_types, a1, a2, a3, a4)
        return typ

    def _match_improper_with_typemap(self, typemap, a1, a2, a3, a4):

        if (a1, a2, a3, a4) in typemap: return typemap[(a1, a2, a3, a4)]
        if (a4, a3, a2, a1) in typemap: return typemap[(a4, a3, a2, a1)]

        # Now try any of the sortings. The documented CHARMM ordering does not seem to work for
        # all systems CHARMM supports :(

        key = tuple(sorted([a1, a2, a3, a4]))
        if self._improper_key_map.get(key, None) in typemap:
            return typemap[self._improper_key_map[key]]

        for exact1, exact2, exact3 in combinations((a1, a2, a3, a4), 3):
            key = tuple(sorted([exact1, exact2, exact3, 'X']))
            if self._improper_key_map.get(key, None) in typemap:
                return typemap[self._improper_key_map[key]]

        for exact1, exact2 in combinations((a1, a2, a3, a4), 2):
            key = tuple(sorted([exact1, exact2, 'X', 'X']))
            if self._improper_key_map.get(key, None) in typemap:
                return typemap[self._improper_key_map[key]]

        return None

class CharmmParameterSet(ParameterSet, CharmmImproperMatchingMixin):
    """
    Stores a parameter set defined by CHARMM files. It stores the equivalent of
    the information found in the MASS section of the CHARMM topology file
    (TOP/RTF) and all of the information in the parameter files (PAR)

    Parameters
    ----------
    *filenames : variable length arguments of str
        The list of topology, parameter, and stream files to load into the
        parameter set. The following file type suffixes are recognized:
            .rtf, .top -- Residue topology file
            .par, .prm -- Parameter file
            .str -- Stream file
            .inp -- If "par" is in the file name, it is a parameter file. If
                    "top" is in the file name, it is a topology file.
                    Otherwise, ValueError is raised.

    See Also
    --------
    :class:`parmed.parameters.ParameterSet`
    """

    def __copy__(self):
        other = super(CharmmParameterSet, self).__copy__()
        other._declared_nbrules = self._declared_nbrules
        return other

    @staticmethod
    def _convert(data, type, msg='', line_index=None, line=None):
        """
        Converts a data type to a desired type, raising CharmmError if it
        fails
        """
        try:
            return type(data)
        except ValueError:
            msg = 'Could not convert %s to %s\n' % (msg, type)
            if line_index is not None:
                msg += 'input line %d\n' % line_index
            if line is not None:
                msg += 'input line: %s\n' % line
            raise CharmmError(msg)

    def __init__(self, *args):
        # Instantiate the list types
        super(CharmmParameterSet, self).__init__()
        self.parametersets = []
        self._declared_nbrules = False

        # Load all of the files
        tops, pars, strs = [], [], []
        for arg in args:
            if arg.endswith('.rtf') or arg.endswith('.top'):
                tops.append(arg)
            elif arg.endswith('.par') or arg.endswith('.prm'):
                pars.append(arg)
            elif arg.endswith('.str'):
                strs.append(arg)
            elif arg.endswith('.inp'):
                # Only consider the file name (since the directory is likely
                # "toppar" and will screw up file type detection)
                fname = os.path.split(arg)[1]
                if 'par' in fname:
                    pars.append(arg)
                elif 'top' in fname:
                    tops.append(arg)
                else:
                    raise ValueError('Unrecognized file type: %s' % arg)
            else:
                raise ValueError('Unrecognized file type: %s' % arg)
        for top in tops:
            self.read_topology_file(top)
        for par in pars:
            self.read_parameter_file(par)
        for strf in strs:
            self.read_stream_file(strf)

    @classmethod
    def from_parameterset(cls, params, copy=False):
        """
        Instantiates a CharmmParameterSet from another ParameterSet (or
        subclass). The main thing this feature is responsible for is converting
        lower-case atom type names into all upper-case and decorating the name
        to ensure each atom type name is unique.

        Parameters
        ----------
        params : :class:`parmed.parameters.ParameterSet`
            ParameterSet containing the list of parameters to be converted to a
            CHARMM-compatible set
        copy : bool, optional
            If True, the returned parameter set is a deep copy of ``params``. If
            False, the returned parameter set is a shallow copy, and the
            original set may be modified if any lower-case atom type names are
            present. Default is False.

        Returns
        -------
        new_params : CharmmParameterSet
            The parameter set whose atom type names are converted to all
            upper-case
        """
        new_params = cls()
        if copy:
            do_copy = lambda x: _copy(x)
        else:
            do_copy = lambda x: x
        # Convert all parameters
        id_typemap = dict()
        def copy_paramtype(key, typ, dict):
            if isinstance(key, string_types):
                key = _typeconv(key)
            elif isinstance(key, tuple):
                key = tuple(_typeconv(k) for k in key)
            # NoUreyBradley should never be copied
            if typ is NoUreyBradley:
                dict[key] = NoUreyBradley
            elif id(typ) in id_typemap:
                dict[key] = id_typemap[id(typ)]
            else:
                newtype = do_copy(typ)
                id_typemap[id(typ)] = newtype
                dict[key] = newtype

        for key, atom_type in iteritems(params.atom_types_tuple):
            atom_type.name = _typeconv(atom_type.name)
            copy_paramtype(key, atom_type, new_params.atom_types_tuple)
        for typename, atom_type in iteritems(params.atom_types):
            atom_type.name = _typeconv(atom_type.name)
            copy_paramtype(typename, atom_type, new_params.atom_types)
        for idx, atom_type in iteritems(params.atom_types_int):
            atom_type.name = _typeconv(atom_type.name)
            copy_paramtype(idx, atom_type, new_params.atom_types_int)

        for key, typ in iteritems(params.bond_types):
            copy_paramtype(key, typ, new_params.bond_types)
        for key, typ in iteritems(params.angle_types):
            copy_paramtype(key, typ, new_params.angle_types)
        for key, typ in iteritems(params.urey_bradley_types):
            copy_paramtype(key, typ, new_params.urey_bradley_types)
        for key, typ in iteritems(params.dihedral_types):
            copy_paramtype(key, typ, new_params.dihedral_types)
        for key, typ in iteritems(params.improper_periodic_types):
            copy_paramtype(key, typ, new_params.improper_periodic_types)
        for key, typ in iteritems(params.improper_types):
            copy_paramtype(key, typ, new_params.improper_types)
        for key, typ in iteritems(params.cmap_types):
            assert len(key) == 8, '%d-key cmap type detected!' % len(key)
            copy_paramtype(key, typ, new_params.cmap_types)
        for key, typ in iteritems(params.nbfix_types):
            copy_paramtype(key, typ, new_params.nbfix_types)

        return new_params

    @classmethod
    def from_structure(cls, struct):
        """ Extracts known parameters from a Structure instance

        Parameters
        ----------
        struct : :class:`parmed.structure.Structure`
            The parametrized ``Structure`` instance from which to extract
            parameters into a ParameterSet

        Returns
        -------
        params : :class:`ParameterSet`
            The parameter set with all parameters defined in the Structure

        Notes
        -----
        The parameters here are copies of the ones in the Structure, so
        modifying the generated ParameterSet will have no effect on ``struct``.
        Furthermore, the *first* occurrence of each parameter will be used. If
        future ones differ, they will be silently ignored, since this is
        expected behavior in some instances (like with Gromacs topologies in the
        ff99sb-ildn force field).

        Dihedrals are a little trickier. They can be multi-term, which can be
        represented either as a *single* entry in dihedrals with a type of
        DihedralTypeList or multiple entries in dihedrals with a DihedralType
        parameter type. In this case, the parameter is constructed from either
        the first DihedralTypeList found or the first DihedralType of each
        periodicity found if no matching DihedralTypeList is found.
        """
        return cls.from_parameterset(
            ParameterSet.from_structure(struct, allow_unequal_duplicates=False)
        )

    @classmethod
    def load_set(cls, tfile=None, pfile=None, sfiles=None):
        """
        Instantiates a CharmmParameterSet from a Topology file and a Parameter
        file (or just a Parameter file if it has all information)

        Parameters
        ----------
        tfile : str
            The name of the Topology (RTF/TOP) file to parse
        pfile : str
            The name of the Parameter (PAR/PRM) file to parse
        sfiles : list(str)
            Iterable of stream (STR) file names

        Returns
        -------
        New CharmmParameterSet populated with parameters found in the provided
        files

        Notes
        -----
        The RTF file is read first (if provided), followed by the PAR file,
        followed by the list of stream files (in the order they are provided).
        Parameters in each stream file will overwrite those that came before (or
        simply append to the existing set if they are different)
        """
        inst = cls()
        if tfile is not None:
            inst.read_topology_file(tfile)
        if pfile is not None:
            inst.read_parameter_file(pfile)
        if isinstance(sfiles, string_types):
            # The API docstring requests a list, but allow for users to pass a
            # string with a single filename instead
            inst.read_stream_file(sfiles)
        elif sfiles is not None:
            for sfile in sfiles:
                inst.read_stream_file(sfile)
        return inst

    def read_parameter_file(self, pfile, comments=None):
        """
        Reads all of the parameters from a parameter file. Versions 36 and
        later of the CHARMM force field files have an ATOMS section defining
        all of the atom types.  Older versions need to load this information
        from the RTF/TOP files.

        Parameters
        ----------
        pfile : str or list of lines
            Name of the CHARMM parameter file to read or list of lines to parse
            as a file
        comments : list of str, optional
            List of comments on each of the pfile lines (if pfile is a list of
            lines)

        Notes
        -----
        The atom types must all be loaded by the end of this routine.  Either
        supply a PAR file with atom definitions in them or read in a RTF/TOP
        file first. Failure to do so will result in a raised RuntimeError.
        """
        conv = CharmmParameterSet._convert
        if isinstance(pfile, str):
            own_handle = True
            f = CharmmFile(pfile)
        else:
            own_handle = False
            f = pfile
            if not isinstance(f, CharmmFile) and comments is None:
                comments = _EmptyStringIterator()
        # What section are we parsing?
        section = None
        # The current cmap we are building (these span multiple lines)
        current_cmap = None
        current_cmap2 = None
        current_cmap_data = []
        current_cmap_res = 0
        nonbonded_types = dict() # Holder
        parameterset = None
        declared_geometric = False
        for i, line in enumerate(f):
            line = line.strip()
            try:
                comment = f.comment
            except AttributeError:
                comment = comments[i]
            if not line:
                # This is a blank line
                continue
            if parameterset is None and line.strip().startswith('*>>'):
                parameterset = line.strip()[1:78]
                continue
            # Set section if this is a section header
            if line.upper().startswith('ATOM'):
                section = 'ATOMS'
                continue
            if line.upper().startswith('BOND'):
                section = 'BONDS'
                continue
            if line.upper().startswith('ANGLE') or line.upper().startswith('THETA'):
                section = 'ANGLES'
                continue
            if line.upper().startswith('DIHE') or line.upper().startswith('PHI'):
                section = 'DIHEDRALS'
                continue
            if line.upper().startswith('IMPROPER') or line.upper().startswith('IMPHI'):
                section = 'IMPROPER'
                continue
            if line.upper().startswith('CMAP'):
                section = 'CMAP'
                continue
            if line.upper().startswith('NONBONDED'):
                read_first_nonbonded = declared_geometric = False
                section = 'NONBONDED'
                # Get nonbonded keywords
                words = line.split()[1:]
                scee = None
                for i, word in enumerate(words):
                    if word.upper() == 'E14FAC':
                        try:
                            scee = 1 / float(words[i+1])
                        except (ValueError, IndexError):
                            raise CharmmError('Could not parse 1-4 electrostatic scaling factor '
                                              'from NONBONDED card')
                        if self._declared_nbrules:
                            if len(self.dihedral_types) > 0:
                                # We already specified it -- make sure it's the same
                                # as the one we specified before
                                _, dt0 = next(iteritems(self.dihedral_types))
                                diff = abs(dt0[0].scee - scee)
                                if diff > TINY:
                                    raise CharmmError('Inconsistent 1-4 scalings')
                        else:
                            for key, dtl in iteritems(self.dihedral_types):
                                for dt in dtl:
                                    dt.scee = scee
                    elif word.upper().startswith('GEOM'):
                        if self._declared_nbrules and self.combining_rule != 'geometric':
                            raise CharmmError('Cannot combine parameter files with different '
                                              'combining rules')
                        self.combining_rule = 'geometric'
                        declared_geometric = True
                continue
            if line.upper().startswith('NBFIX'):
                section = 'NBFIX'
                continue
            if line.upper().startswith('HBOND'):
                section = None
                continue
            if line.upper().startswith('THOLE'):
                section = None
                continue
            # It seems like files? sections? can be terminated with 'END'
            if line[:3].upper() == 'END':
                section = None
                continue
            # If we have no section, skip
            if section is None: continue
            # See if our comments define a penalty for this line
            pens = _penaltyre.findall(comment)
            if len(pens) == 1:
                penalty = float(pens[0])
            else:
                penalty = None
            # Now handle each section specifically
            if section.upper() == 'ATOMS':
                if not line.upper().startswith('MASS'): continue # Should this happen?
                words = line.split()
                if words[0].upper() == 'END':
                    continue
                try:
                    idx = conv(words[1], int, 'atom type', line_index=i, line=line)
                    name = words[2].upper()
                    mass = conv(words[3], float, 'atom mass', line_index=i, line=line)
                except IndexError:
                    raise CharmmError('Could not parse MASS section.')
                # The parameter file might or might not have an element name
                try:
                    elem = words[4].upper()
                    if len(elem) == 2:
                        elem = elem[0] + elem[1].lower()
                    atomic_number = AtomicNum[elem]
                except (IndexError, KeyError):
                    # Figure it out from the mass
                    atomic_number = AtomicNum[element_by_mass(mass)]
                atype = AtomType(name=name, number=idx, mass=mass, atomic_number=atomic_number)
                self.atom_types_str[atype.name] = atype
                self.atom_types_int[atype.number] = atype
                self.atom_types_tuple[(atype.name, atype.number)] = atype
                continue
            if section.upper() == 'BONDS':
                words = line.split()
                if words[0].upper() == 'END':
                    continue
                try:
                    type1 = words[0].upper()
                    type2 = words[1].upper()
                    k = conv(words[2], float, 'bond force constant', line_index=i, line=line)
                    req = conv(words[3], float, 'bond equilibrium dist', line_index=i, line=line)
                except IndexError:
                    raise CharmmError('Could not parse bonds.')
                key = (min(type1, type2), max(type1, type2))
                bond_type = BondType(k, req)
                if key in self.bond_types:
                    # See if existing bond type has a different value and replaces it with a warning
                    if self.bond_types[key] != bond_type:
                        # Replace. Warn if they are different
                        warnings.warn('Replacing bond %r, %r with %r' %
                                      (key, self.bond_types[key], bond_type), ParameterWarning)
                        self.bond_types[(type1, type2)] = bond_type
                        self.bond_types[(type2, type1)] = bond_type
                else: # key not present
                    self.bond_types[(type1, type2)] = bond_type
                    self.bond_types[(type2, type1)] = bond_type
                bond_type.penalty = penalty
                continue
            if section.upper() == 'ANGLES':
                words = line.split()
                if words[0].upper() == 'END':
                    continue
                try:
                    type1 = words[0].upper()
                    type2 = words[1].upper()
                    type3 = words[2].upper()
                    k = conv(words[3], float, 'angle force constant', line_index=i, line=line)
                    theteq = conv(words[4], float, 'angle equilibrium value', line_index=i, line=line)
                except IndexError:
                    raise CharmmError('Could not parse angles.')

                angle_type = AngleType(k, theteq)
                key = (type1, type2, type3)
                if key in self.angle_types:
                    # See if the existing angle type list has a different value
                    # and replaces it with a warning
                    if self.angle_types[key] != angle_type:
                        # Replace. Warn if they are different
                        warnings.warn('Replacing angle %r, %r with %r' %
                                      (key, self.angle_types[key], angle_type), ParameterWarning)
                        self.angle_types[(type1, type2, type3)] = angle_type
                        self.angle_types[(type3, type2, type1)] = angle_type
                else: # key not present
                    self.angle_types[(type1, type2, type3)] = angle_type
                    self.angle_types[(type3, type2, type1)] = angle_type
                # See if we have a urey-bradley
                try:
                    ubk = conv(words[5], float, 'Urey-Bradley force constant', line_index=i, line=line)
                    ubeq = conv(words[6], float, 'Urey-Bradley equil. value', line_index=i, line=line)
                    ubtype = BondType(ubk, ubeq)
                    ubtype.penalty = penalty
                except IndexError:
                    ubtype = NoUreyBradley
                self.urey_bradley_types[(type1, type2, type3)] = ubtype
                self.urey_bradley_types[(type3, type2, type1)] = ubtype
                angle_type.penalty = penalty
                continue
            if section.upper() == 'DIHEDRALS':
                words = line.split()
                if words[0].upper == 'END':
                    continue
                try:
                    type1 = words[0].upper()
                    type2 = words[1].upper()
                    type3 = words[2].upper()
                    type4 = words[3].upper()
                    k = conv(words[4], float, 'dihedral force constant', line_index=i, line=line)
                    n = conv(words[5], float, 'dihedral periodicity', line_index=i, line=line)
                    phase = conv(words[6], float, 'dihedral phase', line_index=i, line=line)
                except IndexError:
                    raise CharmmError('Could not parse dihedrals.')
                key = (type1, type2, type3, type4)
                # See if this is a second (or more) term of the dihedral group
                # that's already present.
                dihedral = DihedralType(k, n, phase)
                dihedral.penalty = penalty
                if key in self.dihedral_types:
                    # See if the existing dihedral type list has a term with
                    # the same periodicity -- If so, replace it
                    replaced = False
                    for i, dtype in enumerate(self.dihedral_types[key]):
                        if dtype.per == dihedral.per:
                            # Replace. Warn if they are different
                            if dtype != dihedral:
                                warnings.warn('Replacing dihedral %r with %r' % (dtype, dihedral),
                                              ParameterWarning)
                            self.dihedral_types[key][i] = dihedral
                            replaced = True
                            break
                    if not replaced:
                        self.dihedral_types[key].append(dihedral)
                else: # key not present
                    dtl = DihedralTypeList()
                    dtl.append(dihedral)
                    self.dihedral_types[(type1, type2, type3, type4)] = dtl
                    self.dihedral_types[(type4, type3, type2, type1)] = dtl
                continue
            if section.upper() == 'IMPROPER':
                words = line.split()
                if words[0].upper() == 'END':
                    continue
                try:
                    type1 = words[0].upper()
                    type2 = words[1].upper()
                    type3 = words[2].upper()
                    type4 = words[3].upper()
                    k = conv(words[4], float, 'improper force constant', line_index=i, line=line)
                    theteq = conv(words[5], float, 'improper equil. value', line_index=i, line=line)
                except IndexError:
                    raise CharmmError('Could not parse dihedrals.')
                # If we have a 7th column, that is the real psi0 (and the 6th
                # is the multiplicity, which will indicate this is a periodic
                # improper torsion (so it needs to be added to the
                # improper_periodic_types list)
                try:
                    tmp = conv(words[6], float, 'improper equil. value', line_index=i, line=line)
                except IndexError:
                    per = 0
                else:
                    per = int(theteq)
                    theteq = tmp
                # Improper types seem not to always have the central atom
                # defined in the first place, so just have the key a fully
                # sorted list. We still depend on the PSF having properly
                # ordered improper atoms
                key = (type1, type2, type3, type4)
                self._improper_key_map[tuple(sorted(key))] = key
                if per == 0:
                    improp = ImproperType(k, theteq)
                    self.improper_types[key] = improp
                else:
                    improp = DihedralType(k, per, theteq)
                    self.improper_periodic_types[key] = improp
                    improp.improper = True
                improp.penalty = penalty
                continue
            if section.upper() == 'CMAP':
                # This is the most complicated part, since cmap parameters span
                # many lines. We won't do much error catching here.
                words = line.split()
                if words[0].upper() == 'END':
                    continue
                try:
                    holder = [float(w) for w in words]
                    current_cmap_data.extend(holder)
                except ValueError:
                    # We assume this is a definition of a new CMAP, so
                    # terminate the last CMAP if applicable
                    if current_cmap is not None:
                        # We have a map to terminate
                        ty = CmapType(current_cmap_res, current_cmap_data)
                        self.cmap_types[current_cmap] = ty
                        self.cmap_types[current_cmap2] = ty
                    try:
                        type1 = words[0].upper()
                        type2 = words[1].upper()
                        type3 = words[2].upper()
                        type4 = words[3].upper()
                        type5 = words[4].upper()
                        type6 = words[5].upper()
                        type7 = words[6].upper()
                        type8 = words[7].upper()
                        res = conv(words[8], int, 'CMAP resolution', line_index=i, line=line)
                    except IndexError:
                        raise CharmmError('Could not parse CMAP data.')
                    # order the torsions independently
                    k1 = [type1, type2, type3, type4, type5, type6, type7, type8]
                    k2 = [type8, type7, type6, type5, type4, type3, type2, type1]
                    current_cmap = tuple(min(k1, k2))
                    current_cmap2 = tuple(max(k1, k2))
                    current_cmap_res = res
                    current_cmap_data = []
                continue
            if section.upper() == 'NONBONDED':
                # Now get the nonbonded values
                words = line.split()
                if words[0].upper == 'END':
                    continue
                try:
                    atype = words[0].upper()
                    # 1st column is ignored
                    epsilon = conv(words[2], float, 'vdW epsilon term', line_index=i, line=line)
                    rmin = conv(words[3], float, 'vdW Rmin/2 term', line_index=i, line=line)
                except (IndexError, CharmmError):
                    # If we haven't read our first nonbonded term yet, we may
                    # just be parsing the settings that should be used. So
                    # soldier on
                    if read_first_nonbonded: raise
                    for i, word in enumerate(words):
                        if word.upper() == 'E14FAC':
                            try:
                                scee = 1 / float(words[i+1])
                            except (ValueError, IndexError):
                                raise CharmmError('Could not parse electrostatic scaling constant')
                            if self._declared_nbrules:
                                # We already specified it -- make sure it's the
                                # same as the one we specified before
                                _, dt0 = next(iteritems(self.dihedral_types))
                                diff = abs(dt0[0].scee - scee)
                                if diff > TINY:
                                    raise CharmmError('Inconsistent 1-4 scalings')
                            else:
                                for key, dtl in iteritems(self.dihedral_types):
                                    for dt in dtl:
                                        dt.scee = scee
                        elif word.upper().startswith('GEOM'):
                            if self._declared_nbrules and self.combining_rule != 'geometric':
                                raise CharmmError('Cannot combine parameter files with different '
                                                  'combining rules')
                            self.combining_rule = 'geometric'
                            declared_geometric = True
                    continue
                else:
                    # OK, we've read our first nonbonded section for sure now.
                    # Make sure we did not try to read in a str file that did
                    # not define GEOM if a previous file did, since
                    # Lorentz-Berthelot and geometric combining rules are
                    # incompatible
                    if (self._declared_nbrules and self.combining_rule == 'geometric' and
                        not declared_geometric):
                        raise CharmmError('Cannot combine parameter files with '
                                          'different combining rules')
                    read_first_nonbonded = True
                    self._declared_nbrules = True
                # See if we have 1-4 parameters
                try:
                    # 4th column is ignored
                    eps14 = conv(words[5], float, '1-4 vdW epsilon term', line_index=i, line=line)
                    rmin14 = conv(words[6], float, '1-4 vdW Rmin/2 term', line_index=i, line=line)
                except IndexError:
                    eps14 = rmin14 = None
                nonbonded_types[atype] = [epsilon, rmin, eps14, rmin14]
                continue
            if section.upper() == 'NBFIX':
                words = line.split()
                if words[0].upper() == 'END':
                    continue
                try:
                    at1 = words[0].upper()
                    at2 = words[1].upper()
                    emin = abs(conv(words[2], float, 'NBFIX Emin', line_index=i, line=line))
                    rmin = conv(words[3], float, 'NBFIX Rmin', line_index=i, line=line)
                    try:
                        emin14 = abs(conv(words[4], float, 'NBFIX Emin 1-4', line_index=i, line=line))
                        rmin14 = conv(words[5], float, 'NBFIX Rmin 1-4', line_index=i, line=line)
                    except IndexError:
                        emin14 = rmin14 = None
                    try:
                        self.atom_types_str[at1].add_nbfix(at2, rmin, emin, rmin14, emin14)
                        self.atom_types_str[at2].add_nbfix(at1, rmin, emin, rmin14, emin14)
                    except KeyError:
                        # Some stream files define NBFIX terms with an atom that
                        # is defined in another toppar file that does not
                        # necessarily have to be loaded. As a result, not every
                        # NBFIX found here will necessarily need to be applied.
                        # If we can't find a particular atom type, don't bother
                        # adding that nbfix and press on
                        pass
                except IndexError:
                    raise CharmmError('Could not parse NBFIX terms.')
                self.nbfix_types[(min(at1, at2), max(at1, at2))] = (emin, rmin)
        # If we had any CMAP terms, then the last one will not have been added
        # yet. Add it here
        if current_cmap is not None:
            typ = CmapType(current_cmap_res, current_cmap_data)
            self.cmap_types[current_cmap] = typ
            self.cmap_types[current_cmap2] = typ
        # Now we're done. Load the nonbonded types into the relevant AtomType
        # instances. In order for this to work, all keys in nonbonded_types
        # must be in the self.atom_types_str dict. Raise a RuntimeError if this
        # is not satisfied
        try:
            for key in nonbonded_types:
                self.atom_types_str[key].set_lj_params(*nonbonded_types[key])
        except KeyError:
            warnings.warn('Atom type %s not present in AtomType list' % key, ParameterWarning)
        if parameterset is not None:
            self.parametersets.append(parameterset)
        if own_handle:
            f.close()

    def read_topology_file(self, tfile):
        """
        Reads _only_ the atom type definitions from a topology file. This is
        unnecessary for versions 36 and later of the CHARMM force field.

        Parameters
        ----------
        tfile : str
            Name of the CHARMM topology file to read
        """
        conv = CharmmParameterSet._convert
        if isinstance(tfile, str):
            own_handle = True
            f = iter(CharmmFile(tfile))
        else:
            own_handle = False
            f = tfile
        hpatch = tpatch = None # default Head and Tail patches
        residues = OrderedDict()
        patches = OrderedDict()
        hpatches = OrderedDict()
        tpatches = OrderedDict()
        line = next(f)
        line_index = 0
        skip_adding_residue = False
        try:
            while line:
                line = line.strip()
                if line[:4].upper() == 'MASS':
                    words = line.split()
                    try:
                        idx = conv(words[1], int, 'atom type', line_index=line_index, line=line)
                        name = words[2].upper()
                        mass = conv(words[3], float, 'atom mass', line_index=line_index, line=line)
                    except IndexError:
                        raise CharmmError('Could not parse MASS section of %s' % tfile)
                    # The parameter file might or might not have an element name
                    try:
                        elem = words[4].upper()
                        if len(elem) == 2:
                            elem = elem[0] + elem[1].lower()
                        atomic_number = AtomicNum[elem]
                    except (IndexError, KeyError):
                        # Figure it out from the mass
                        atomic_number = AtomicNum[element_by_mass(mass)]
                    atype = AtomType(name=name, number=idx, mass=mass, atomic_number=atomic_number)
                    self.atom_types_str[atype.name] = atype
                    self.atom_types_int[atype.number] = atype
                    self.atom_types_tuple[(atype.name, atype.number)] = atype
                elif line[:4].upper() == 'DECL':
                    pass # Not really sure what this means
                elif line[:4].upper() == 'DEFA':
                    words = line.split()
                    if len(words) < 5:
                        warnings.warn('DEFA line has %d tokens; expected 5' % len(words))
                    else:
                        it = iter(words[1:5])
                        for tok, val in zip(it, it):
                            if val.upper() == 'NONE':
                                val = None
                            if tok.upper().startswith('FIRS'):
                                hpatch = val
                            elif tok.upper() == 'LAST':
                                tpatch = val
                            else:
                                warnings.warn('DEFA patch %s unknown' % val)
                elif line[:4].upper() in ('RESI', 'PRES'):
                    restype = line[:4].upper()
                    # Get the residue definition
                    words = line.split()
                    resname = words[1].upper()
                    if resname in self.residues:
                        warnings.warn('Replacing residue {}'.format(resname), ParameterWarning)
                    # Assign default patches
                    hpatches[resname] = hpatch
                    tpatches[resname] = tpatch
                    try:
                        charge = float(words[2])
                    except (IndexError, ValueError):
                        warnings.warn('No charge for %s' % resname)
                    if restype == 'RESI':
                        res = ResidueTemplate(resname)
                    elif restype == 'PRES':
                        res = PatchTemplate(resname)
                    else:
                        assert False, 'restype != RESI or PRES'
                    skip_adding_residue = False
                    line = next(f)
                    group = []
                    ictable = []
                    while line:
                        line = line.lstrip()
                        if line[:5].upper() == 'GROUP':
                            if group:
                                res.groups.append(group)
                            group = []
                        elif line[:4].upper() == 'ATOM':
                            words = line.split()
                            name = words[1].upper()
                            type = words[2].upper()
                            charge = float(words[3])
                            if 'ALPHA' in words:
                                # This is a polarizable atom.
                                alpha = float(words[words.index('ALPHA')+1])
                                thole = 1.3
                                drude_type = 'DRUD'
                                if 'THOLE' in words:
                                    thole = float(words[words.index('THOLE')+1])
                                if 'TYPE' in words:
                                    drude_type = words[words.index('TYPE')+1]
                                atom = DrudeAtom(name=name, type=type, charge=charge, alpha=alpha, thole=thole, drude_type=drude_type)
                            else:
                                atom = Atom(name=name, type=type, charge=charge)
                            group.append(atom)
                            res.add_atom(atom)
                        elif line[:6].upper() == 'DELETE':
                            words = line.split()
                            name = words[2].upper()
                            entity_type = words[1].upper()
                            if entity_type == 'ATOM':
                                res.delete_atoms.append(name)
                            elif entity_type == 'IMPR':
                                res.delete_impropers.append(words[2:5])
                            else:
                                warnings.warn('WARNING: Ignoring "%s" because entity type %s not '
                                              'used.' % (line.strip(), entity_type))
                        elif line.strip().upper() and line.split()[0].upper() in ('BOND', 'DOUBLE'):
                            it = iter([w.upper() for w in line.split()[1:]])
                            for a1, a2 in zip(it, it):
                                if restype == 'PRES':
                                    # Patches can have bonds that refer to atoms not in the patch, so store these in a list of tuples
                                    order = 1
                                    if line.split()[0].upper() == 'DOUBLE':
                                        order = 2
                                    res.add_bonds.append( (a1, a2, order) )
                                    continue

                                if a1.startswith('-'):
                                    res.head = res[a2]
                                    continue
                                if a2.startswith('-'):
                                    res.head = res[a1]
                                    continue
                                if a1.startswith('+'):
                                    res.tail = res[a2]
                                    continue
                                if a2.startswith('+'):
                                    res.tail = res[a1]
                                    continue
                                res.add_bond(a1, a2)
                        elif line[:4].upper() == 'CMAP':
                            pass
                        elif line[:5].upper() == 'DONOR':
                            pass
                        elif line[:6].upper() == 'ACCEPT':
                            pass
                        elif line[:8].upper() == 'LONEPAIR':
                            # See: https://www.charmm.org/charmm/documentation/by-version/c40b1/params/doc/lonepair/
                            # TODO: This currently doesn't handle some formats, like Note 3 in the above URL
                            words = line.split()
                            lptype_keyword = words[1][0:4].upper()
                            if not skip_adding_residue and lptype_keyword not in ['BISE', 'RELA']:
                                warnings.warn('LONEPAIR type %s not supported; only BISEctor and '
                                              'RELAtive supported' % words[1])
                                skip_adding_residue = True
                                break
                            a1, a2, a3, a4 = words[2:6]
                            keywords = {words[index][0:4].upper() : float(words[index+1])
                                        for index in range(6,len(words),2) }
                            r = keywords['DIST'] # angstrom
                            theta = keywords['ANGL'] # degrees
                            phi = keywords['DIHE'] # degrees
                            lptypes = { 'BISE' : 'bisector', 'RELA' : 'relative' }
                            lonepair = (lptypes[lptype_keyword], a1, a2, a3, a4, r, theta, phi) # TODO: Define a LonePair object?
                            res.lonepairs.append(lonepair)
                        elif line[:2].upper() == 'IC':
                            words = line.split()[1:]
                            ictable.append(([w.upper() for w in words[:4]],
                                            [float(w) for w in words[4:]]))
                        elif line[:3].upper() == 'END':
                            break
                        elif line[:5].upper() == 'PATCH':
                            it = iter(line.split()[1:])
                            for tok, val in zip(it, it):
                                if val.upper() == 'NONE': val = None
                                if tok.upper().startswith('FIRS'):
                                    hpatches[resname] = val
                                elif tok.upper().startswith('LAST'):
                                    tpatches[resname] = val
                        elif line[:4].upper() in ('IMPR', 'IMPH'):
                            it = iter(w.upper() for w in line.split()[1:])
                            for a1, a2, a3, a4 in zip(it, it, it, it):
                                res._impr.append((a1, a2, a3, a4))
                                if a2[0] == '-' or a3[0] == '-' or a4 == '-':
                                    res.head = res[a1]
                        elif line[:10].upper() == 'ANISOTROPY':
                            words = line.split()
                            atoms = [res[name] for name in words[1:5]]
                            keywords = {words[index].upper() : float(words[index+1])
                                        for index in range(5,len(words),2)}
                            a11 = float(keywords['A11'])
                            a22 = float(keywords['A22'])
                            atoms[0].anisotropy = DrudeAnisotropy(*atoms, a11=a11, a22=a22)
                        elif line[:4].upper() in ('RESI', 'PRES', 'MASS'):
                            # Back up a line and bail
                            break
                        line = next(f)
                    if group: res.groups.append(group)
                    _fit_IC_table(res, ictable)
                    if skip_adding_residue:
                        # Do not add this residue to the lookup library
                        continue
                    elif restype == 'RESI':
                        residues[resname] = res
                    elif restype == 'PRES':
                        patches[resname] = res
                    else:
                        assert False, 'restype != RESI or PRES'
                    # We parsed a line we need to look at. So don't update the
                    # iterator
                    continue
                # Get the next line and cycle through
                line = next(f)
                line_index += 1
        except StopIteration:
            pass

        # Go through the patches and add the appropriate one
        self.patches.update(patches)
        for resname, res in iteritems(residues):
            patch_name = hpatches[resname]
            if patch_name is not None:
                try:
                    res.first_patch = self.patches[patch_name]
                except KeyError:
                    warnings.warn('Patch %s not found' % patch_name)

            patch_name = tpatches[resname]
            if patch_name is not None:
                try:
                    res.last_patch = self.patches[patch_name]
                except KeyError:
                    warnings.warn('Patch %s not found' % patch_name)
        # Now update the residues and patches with the ones we parsed here
        self.residues.update(residues)

        if own_handle: f.close()

    def read_stream_file(self, sfile):
        """
        Reads RTF and PAR sections from a stream file and dispatches the
        sections to read_topology_file or read_parameter_file

        Parameters
        ----------
        sfile : str or CharmmStreamFile
            Stream file to parse
        """
        if isinstance(sfile, CharmmStreamFile):
            f = sfile
        else:
            f = CharmmStreamFile(sfile)

        title, section, comments = f.next_section()
        while title is not None and section is not None:
            words = title.lower().split()
            if words[1] == 'rtf':
                # This is a Residue Topology File section.
                self.read_topology_file(iter(section))
            elif words[1].startswith('para'):
                # This is a Parameter file section
                self.read_parameter_file(section, comments)
            title, section, comments = f.next_section()

    def write(self, top=None, par=None, str=None):
        """ Write a CHARMM parameter set to a file

        Parameters
        ----------
        top : str or file-like object, optional
            If provided, the atom types will be written to this file in RTF
            format.
        par : str or file-like object, optional
            If provided, the parameters will be written to this file in PAR
            format. Either this or the ``str`` argument *must* be provided
        str : str or file-like object, optional
            If provided, the atom types and parameters will be written to this
            file as separate RTF and PAR cards that can be read as a CHARMM
            stream file. Either this or the ``par`` argument *must* be provided

        Raises
        ------
        ValueError if both par and str are None
        """
        if par is None and str is None:
            raise ValueError('Must specify either par *or* str')

        if top is not None:
            if isinstance(top, string_types):
                f = genopen(top, 'w')
                ownhandle = True
            else:
                f = top
                ownhandle = False
            f.write('*>>>> CHARMM Topology file generated by ParmEd <<<<\n')
            f.write('*\n')
            self._write_top_to(f, True)
            if ownhandle: f.close()
        if par is not None:
            if isinstance(par, string_types):
                f = genopen(par, 'w')
                ownhandle = True
            else:
                f = par
                ownhandle = False
            f.write('*>>>> CHARMM Parameter file generated by ParmEd <<<<\n')
            f.write('*\n\n')
            self._write_par_to(f)
            if ownhandle: f.close()
        if str is not None:
            if isinstance(str, string_types):
                f = genopen(str, 'w')
                ownhandle = True
            else:
                f = str
                ownhandle = False
            self._write_str_to(f)
            if ownhandle: f.close()

    def _write_str_to(self, f):
        """ Private method to write stream items to open file object """
        f.write('read rtf card\n* Topology generated by ParmEd\n*\n')
        self._write_top_to(f, True)
        f.write('\nread para card\n* Parameters generated by ParmEd\n*\n')
        self._write_par_to(f)

    def _write_top_to(self, f, write_version):
        """ Private method to write topology items to open file object """
        if write_version:
            # This version is known to work
            f.write('36   1\n')
            f.write('\n')
        for i, (_, atom) in enumerate(iteritems(self.atom_types)):
            f.write('MASS %5d %-6s %9.5f\n' % (i+1, atom.name, atom.mass))
        if write_version:
            f.write('\nEND\n')

    def _write_par_to(self, f):
        """ Private method to write parameter items to open file object """
        # Find out what the 1-4 electrostatic scaling factors and the 1-4
        # van der Waals scaling factors are
        scee, scnb = set(), set()
        for _, typ in iteritems(self.dihedral_types):
            for t in typ:
                if t.scee: scee.add(t.scee)
                if t.scnb: scnb.add(t.scnb)
        if len(scee) > 1 or len(scnb) > 1:
            raise ValueError('Mixed 1-4 scaling not supported')
        scee = 1.0 if not scee else scee.pop()
        scnb = 1.0 if not scnb else scnb.pop()

        f.write('ATOMS\n')
        self._write_top_to(f, False)
        f.write('\nBONDS\n')
        written = set()
        for key, typ in iteritems(self.bond_types):
            if key in written: continue
            written.add(key); written.add(tuple(reversed(key)))
            f.write('%-6s %-6s %7.2f %10.4f\n' %
                    (key[0], key[1], typ.k, typ.req))
        f.write('\nANGLES\n')
        written = set()
        for key, typ in iteritems(self.angle_types):
            if key in written: continue
            written.add(key)
            written.add(tuple(reversed(key)))
            f.write('%-6s %-6s %-6s %7.2f %8.2f\n' % (key[0], key[1], key[2], typ.k, typ.theteq))
        f.write('\nDIHEDRALS\n')
        written = set()
        for key, typ in iteritems(self.dihedral_types):
            if key in written: continue
            written.add(key)
            written.add(tuple(reversed(key)))
            for tor in typ:
                f.write('%-6s %-6s %-6s %-6s %11.4f %2d %8.2f\n' %
                        (key[0], key[1], key[2], key[3], tor.phi_k, int(tor.per), tor.phase))
        f.write('\nIMPROPERS\n')
        written = set()
        for key, typ in sorted(iteritems(self.improper_periodic_types), key=lambda x: x[0]):
            f.write('%-6s %-6s %-6s %-6s %11.4f %2d %8.2f\n' %
                    (key[0], key[1], key[2], key[3], typ.phi_k, int(typ.per), typ.phase))
        for key, typ in iteritems(self.improper_types):
            f.write('%-6s %-6s %-6s %-6s %11.4f %2d %8.2f\n' %
                    (key[0], key[1], key[2], key[3], typ.psi_k, 0, typ.psi_eq))
        if self.cmap_types:
            f.write('\nCMAPS\n')
            written = set()
            for key, typ in iteritems(self.cmap_types):
                if key in written: continue
                written.add(key); written.add(tuple(reversed(key)))
                f.write('%-6s %-6s %-6s %-6s %-6s %-6s %-6s %-6s %5d\n\n' %
                        (key[0], key[1], key[2], key[3], key[4], key[5], key[6],
                         key[7], typ.resolution))
                i = 0
                for val in typ.grid:
                    if i:
                        if i % 5 == 0:
                            f.write('\n')
                            if i % typ.resolution == 0:
                                f.write('\n')
                                i = 0
                        elif i % typ.resolution == 0:
                            f.write('\n\n')
                            i = 0
                    i += 1
                    f.write(' %13.6f' % val)
                f.write('\n\n\n')
        f.write('\nNONBONDED  nbxmod  5 atom cdiel fshift vatom vdistance vfswitch -\ncutnb 14.0 '
                'ctofnb 12.0 ctonnb 10.0 eps 1.0 e14fac %s wmin 1.5%s\n\n' %
                (1/scee, ' GEOM' if self.combining_rule == 'geometric' else ''))
        for key, typ in iteritems(self.atom_types):
            f.write('%-6s %14.6f %10.6f %14.6f' % (key, 0.0, -abs(typ.epsilon), typ.rmin))
            if typ.epsilon == typ.epsilon_14 and typ.rmin == typ.rmin_14:
                f.write('%10.6f %10.6f %14.6f\n' % (0, -abs(typ.epsilon)/scnb, typ.rmin))
            else:
                f.write('%10.6f %10.6f %14.6f\n' % (0, -abs(typ.epsilon_14), typ.rmin_14))
        f.write('\nEND\n')

# ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

def _fit_IC_table(res, ictable):
    """
    Determines cartesian coordinates from an internal coordinate table stored in
    CHARMM residue topology files

    Parameters
    ----------
    res : ResidueTemplate
        The residue template for which coordinates are being determined
    ictable : list[tuple(atoms, measurements)]
        The internal coordinate table

    Notes
    -----
    This method assigns an xx, xy, and xz attribute to ``res``. For the time
    being, this is just a placeholder, as its functionality has not yet been
    implemented (CHARMM does not use a 'traditional' Z-matrix, and I don't know
    of any existing code that will compute the proper cartesian coordinates from
    the form used by CHARMM)
    """
    for atom in res:
        atom.xx = atom.xy = atom.xz = 0.0
