import re
import sys

from .utils import get_regexp_width

Py36 = (sys.version_info[:2] >= (3, 6))


###{standalone
def is_terminal(sym):
    return sym.isupper()

class GrammarError(Exception):
    pass

class ParseError(Exception):
    pass

class UnexpectedToken(ParseError):
    def __init__(self, token, expected, seq, index, considered_rules=None):
        self.token = token
        self.expected = expected
        self.line = getattr(token, 'line', '?')
        self.column = getattr(token, 'column', '?')
        self.considered_rules = considered_rules

        try:
            context = ' '.join(['%r(%s)' % (t.value, t.type) for t in seq[index:index+5]])
        except AttributeError:
            context = seq[index:index+5]
        except TypeError:
            context = "<no context>"
        message = ("Unexpected token %r at line %s, column %s.\n"
                   "Expected: %s\n"
                   "Context: %s" % (token, self.line, self.column, expected, context))

        super(UnexpectedToken, self).__init__(message)


###}



class LexerConf:
    def __init__(self, tokens, ignore=(), postlex=None, callbacks=None):
        self.tokens = tokens
        self.ignore = ignore
        self.postlex = postlex
        self.callbacks = callbacks or {}

class ParserConf:
    def __init__(self, rules, callback, start):
        self.rules = rules
        self.callback = callback
        self.start = start



class Pattern(object):
    def __init__(self, value, flags=()):
        self.value = value
        self.flags = frozenset(flags)

    def __repr__(self):
        return repr(self.to_regexp())

    # Pattern Hashing assumes all subclasses have a different priority!
    def __hash__(self):
        return hash((type(self), self.value, self.flags))
    def __eq__(self, other):
        return type(self) == type(other) and self.value == other.value and self.flags == other.flags

    if Py36:
        # Python 3.6 changed syntax for flags in regular expression
        def _get_flags(self, value):
            for f in self.flags:
                value = ('(?%s:%s)' % (f, value))
            return value

    else:
        def _get_flags(self, value):
            for f in self.flags:
                value = ('(?%s)' % f) + value
            return value

class PatternStr(Pattern):
    def to_regexp(self):
        return self._get_flags(re.escape(self.value))

    @property
    def min_width(self):
        return len(self.value)
    max_width = min_width

class PatternRE(Pattern):
    def to_regexp(self):
        return self._get_flags(self.value)

    @property
    def min_width(self):
        return get_regexp_width(self.to_regexp())[0]
    @property
    def max_width(self):
        return get_regexp_width(self.to_regexp())[1]

class TokenDef(object):
    def __init__(self, name, pattern, priority=1):
        assert isinstance(pattern, Pattern), pattern
        self.name = name
        self.pattern = pattern
        self.priority = priority

    def __repr__(self):
        return '%s(%r, %r)' % (type(self).__name__, self.name, self.pattern)