#!/usr/bin/env python
#
# $Id: compat.py 712 2010-10-20 15:25:57Z g.rodola $
#

"""Module which provides compatibility with older Python versions."""

from operator import itemgetter as _itemgetter
from keyword import iskeyword as _iskeyword
import sys as _sys


def namedtuple(typename, field_names, verbose=False, rename=False):
    """A collections.namedtuple implementation written in Python
    to support Python versions < 2.6.

    Taken from: http://code.activestate.com/recipes/500261/
    """
    # Parse and validate the field names.  Validation serves two
    # purposes, generating informative error messages and preventing
    # template injection attacks.
    if isinstance(field_names, basestring):
         # names separated by whitespace and/or commas
        field_names = field_names.replace(',', ' ').split()
    field_names = tuple(map(str, field_names))
    if rename:
        names = list(field_names)
        seen = set()
        for i, name in enumerate(names):
            if (not min(c.isalnum() or c=='_' for c in name) or _iskeyword(name)
                or not name or name[0].isdigit() or name.startswith('_')
                or name in seen):
                    names[i] = '_%d' % i
            seen.add(name)
        field_names = tuple(names)
    for name in (typename,) + field_names:
        if not min(c.isalnum() or c=='_' for c in name):
            raise ValueError('Type names and field names can only contain ' \
                             'alphanumeric characters and underscores: %r'
                             % name)
        if _iskeyword(name):
            raise ValueError('Type names and field names cannot be a keyword: %r' \
                             % name)
        if name[0].isdigit():
            raise ValueError('Type names and field names cannot start with a ' \
                             'number: %r' % name)
    seen_names = set()
    for name in field_names:
        if name.startswith('_') and not rename:
            raise ValueError('Field names cannot start with an underscore: %r'
                             % name)
        if name in seen_names:
            raise ValueError('Encountered duplicate field name: %r' % name)
        seen_names.add(name)

    # Create and fill-in the class template
    numfields = len(field_names)
    # tuple repr without parens or quotes
    argtxt = repr(field_names).replace("'", "")[1:-1]
    reprtxt = ', '.join('%s=%%r' % name for name in field_names)
    template = '''class %(typename)s(tuple):
        '%(typename)s(%(argtxt)s)' \n
        __slots__ = () \n
        _fields = %(field_names)r \n
        def __new__(_cls, %(argtxt)s):
            return _tuple.__new__(_cls, (%(argtxt)s)) \n
        @classmethod
        def _make(cls, iterable, new=tuple.__new__, len=len):
            'Make a new %(typename)s object from a sequence or iterable'
            result = new(cls, iterable)
            if len(result) != %(numfields)d:
                raise TypeError('Expected %(numfields)d arguments, got %%d' %% len(result))
            return result \n
        def __repr__(self):
            return '%(typename)s(%(reprtxt)s)' %% self \n
        def _asdict(self):
            'Return a new dict which maps field names to their values'
            return dict(zip(self._fields, self)) \n
        def _replace(_self, **kwds):
            'Return a new %(typename)s object replacing specified fields with new values'
            result = _self._make(map(kwds.pop, %(field_names)r, _self))
            if kwds:
                raise ValueError('Got unexpected field names: %%r' %% kwds.keys())
            return result \n
        def __getnewargs__(self):
            return tuple(self) \n\n''' % locals()
    for i, name in enumerate(field_names):
        template += '        %s = _property(_itemgetter(%d))\n' % (name, i)
    if verbose:
        print template

    # Execute the template string in a temporary namespace
    namespace = dict(_itemgetter=_itemgetter, __name__='namedtuple_%s' % typename,
                     _property=property, _tuple=tuple)
    try:
        exec template in namespace
    except SyntaxError, e:
        raise SyntaxError(e.message + ':\n' + template)
    result = namespace[typename]

    # For pickling to work, the __module__ variable needs to be set
    # to the frame where the named tuple is created.  Bypass this
    # step in enviroments where sys._getframe is not defined (Jython
    # for example) or sys._getframe is not defined for arguments
    # greater than 0 (IronPython).
    try:
        result.__module__ = _sys._getframe(1).f_globals.get('__name__', '__main__')
    except (AttributeError, ValueError):
        pass

    return result
