#
# Secret Labs' Regular Expression Engine
#
# convert re-style regular expression to sre pattern
#
# Copyright (c) 1998-2001 by Secret Labs AB.  All rights reserved.
#
# See the __init__.py file for information on usage and redistribution.
#

"""Internal support module for sre"""

# XXX: show string offset and offending character for all errors

from ._constants import *

SPECIAL_CHARS = ".\\[{()*+?^$|"
REPEAT_CHARS = "*+?{"

DIGITS = frozenset("0123456789")

OCTDIGITS = frozenset("01234567")
HEXDIGITS = frozenset("0123456789abcdefABCDEF")
ASCIILETTERS = frozenset("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")

WHITESPACE = frozenset(" \t\n\r\v\f")

_REPEATCODES = frozenset({MIN_REPEAT, MAX_REPEAT, POSSESSIVE_REPEAT})
_UNITCODES = frozenset({ANY, RANGE, IN, LITERAL, NOT_LITERAL, CATEGORY})
_SETITEMCODES = frozenset({LITERAL, CATEGORY})

ESCAPES = {
    r"\a": (LITERAL, ord("\a")),
    r"\b": (LITERAL, ord("\b")),
    r"\f": (LITERAL, ord("\f")),
    r"\n": (LITERAL, ord("\n")),
    r"\r": (LITERAL, ord("\r")),
    r"\t": (LITERAL, ord("\t")),
    r"\v": (LITERAL, ord("\v")),
    r"\\": (LITERAL, ord("\\"))
}

CATEGORIES = {
    r"\A": (AT, AT_BEGINNING_STRING), # start of string
    r"\b": (AT, AT_BOUNDARY),
    r"\B": (AT, AT_NON_BOUNDARY),
    r"\d": (CATEGORY, CATEGORY_DIGIT),
    r"\D": (CATEGORY, CATEGORY_NOT_DIGIT),
    r"\s": (CATEGORY, CATEGORY_SPACE),
    r"\S": (CATEGORY, CATEGORY_NOT_SPACE),
    r"\w": (CATEGORY, CATEGORY_WORD),
    r"\W": (CATEGORY, CATEGORY_NOT_WORD),
    r"\z": (AT, AT_END_STRING), # end of string
    r"\Z": (AT, AT_END_STRING), # end of string (obsolete)
}

FLAGS = {
    # standard flags
    "i": SRE_FLAG_IGNORECASE,
    "L": SRE_FLAG_LOCALE,
    "m": SRE_FLAG_MULTILINE,
    "s": SRE_FLAG_DOTALL,
    "x": SRE_FLAG_VERBOSE,
    # extensions
    "a": SRE_FLAG_ASCII,
    "u": SRE_FLAG_UNICODE,
}

TYPE_FLAGS = SRE_FLAG_ASCII | SRE_FLAG_LOCALE | SRE_FLAG_UNICODE
GLOBAL_FLAGS = SRE_FLAG_DEBUG

# Maximal value returned by SubPattern.getwidth().
# Must be larger than MAXREPEAT, MAXCODE and sys.maxsize.
MAXWIDTH = 1 << 64

class State:
    # keeps track of state for parsing
    def __init__(self):
        self.flags = 0
        self.groupdict = {}
        self.groupwidths = [None]  # group 0
        self.lookbehindgroups = None
        self.grouprefpos = {}
    @property
    def groups(self):
        return len(self.groupwidths)
    def opengroup(self, name=None):
        gid = self.groups
        self.groupwidths.append(None)
        if self.groups > MAXGROUPS:
            raise error("too many groups")
        if name is not None:
            ogid = self.groupdict.get(name, None)
            if ogid is not None:
                raise error("redefinition of group name %r as group %d; "
                            "was group %d" % (name, gid,  ogid))
            self.groupdict[name] = gid
        return gid
    def closegroup(self, gid, p):
        self.groupwidths[gid] = p.getwidth()
    def checkgroup(self, gid):
        return gid < self.groups and self.groupwidths[gid] is not None

    def checklookbehindgroup(self, gid, source):
        if self.lookbehindgroups is not None:
            if not self.checkgroup(gid):
                raise source.error('cannot refer to an open group')
            if gid >= self.lookbehindgroups:
                raise source.error('cannot refer to group defined in the same '
                                   'lookbehind subpattern')

class SubPattern:
    # a subpattern, in intermediate form
    def __init__(self, state, data=None):
        self.state = state
        if data is None:
            data = []
        self.data = data
        self.width = None

    def dump(self, level=0):
        seqtypes = (tuple, list)
        for op, av in self.data:
            print(level*"  " + str(op), end='')
            if op is IN:
                # member sublanguage
                print()
                for op, a in av:
                    print((level+1)*"  " + str(op), a)
            elif op is BRANCH:
                print()
                for i, a in enumerate(av[1]):
                    if i:
                        print(level*"  " + "OR")
                    a.dump(level+1)
            elif op is GROUPREF_EXISTS:
                condgroup, item_yes, item_no = av
                print('', condgroup)
                item_yes.dump(level+1)
                if item_no:
                    print(level*"  " + "ELSE")
                    item_no.dump(level+1)
            elif isinstance(av, SubPattern):
                print()
                av.dump(level+1)
            elif isinstance(av, seqtypes):
                nl = False
                for a in av:
                    if isinstance(a, SubPattern):
                        if not nl:
                            print()
                        a.dump(level+1)
                        nl = True
                    else:
                        if not nl:
                            print(' ', end='')
                        print(a, end='')
                        nl = False
                if not nl:
                    print()
            else:
                print('', av)
    def __repr__(self):
        return repr(self.data)
    def __len__(self):
        return len(self.data)
    def __delitem__(self, index):
        del self.data[index]
    def __getitem__(self, index):
        if isinstance(index, slice):
            return SubPattern(self.state, self.data[index])
        return self.data[index]
    def __setitem__(self, index, code):
        self.data[index] = code
    def insert(self, index, code):
        self.data.insert(index, code)
    def append(self, code):
        self.data.append(code)
    def getwidth(self):
        # determine the width (min, max) for this subpattern
        if self.width is not None:
            return self.width
        lo = hi = 0
        for op, av in self.data:
            if op is BRANCH:
                i = MAXWIDTH
                j = 0
                for av in av[1]:
                    l, h = av.getwidth()
                    i = min(i, l)
                    j = max(j, h)
                lo = lo + i
                hi = hi + j
            elif op is ATOMIC_GROUP:
                i, j = av.getwidth()
                lo = lo + i
                hi = hi + j
            elif op is SUBPATTERN:
                i, j = av[-1].getwidth()
                lo = lo + i
                hi = hi + j
            elif op in _REPEATCODES:
                i, j = av[2].getwidth()
                lo = lo + i * av[0]
                if av[1] == MAXREPEAT and j:
                    hi = MAXWIDTH
                else:
                    hi = hi + j * av[1]
            elif op in _UNITCODES:
                lo = lo + 1
                hi = hi + 1
            elif op is GROUPREF:
                i, j = self.state.groupwidths[av]
                lo = lo + i
                hi = hi + j
            elif op is GROUPREF_EXISTS:
                i, j = av[1].getwidth()
                if av[2] is not None:
                    l, h = av[2].getwidth()
                    i = min(i, l)
                    j = max(j, h)
                else:
                    i = 0
                lo = lo + i
                hi = hi + j
            elif op is SUCCESS:
                break
        self.width = min(lo, MAXWIDTH), min(hi, MAXWIDTH)
        return self.width

class Tokenizer:
    def __init__(self, string):
        self.istext = isinstance(string, str)
        self.string = string
        if not self.istext:
            string = str(string, 'latin1')
        self.decoded_string = string
        self.index = 0
        self.next = None
        self.__next()
    def __next(self):
        index = self.index
        try:
            char = self.decoded_string[index]
        except IndexError:
            self.next = None
            return
        if char == "\\":
            index += 1
            try:
                char += self.decoded_string[index]
            except IndexError:
                raise error("bad escape (end of pattern)",
                            self.string, len(self.string) - 1) from None
        self.index = index + 1
        self.next = char
    def match(self, char):
        if char == self.next:
            self.__next()
            return True
        return False
    def get(self):
        this = self.next
        self.__next()
        return this
    def getwhile(self, n, charset):
        result = ''
        for _ in range(n):
            c = self.next
            if c not in charset:
                break
            result += c
            self.__next()
        return result
    def getuntil(self, terminator, name):
        result = ''
        while True:
            c = self.next
            self.__next()
            if c is None:
                if not result:
                    raise self.error("missing " + name)
                raise self.error("missing %s, unterminated name" % terminator,
                                 len(result))
            if c == terminator:
                if not result:
                    raise self.error("missing " + name, 1)
                break
            result += c
        return result
    @property
    def pos(self):
        return self.index - len(self.next or '')
    def tell(self):
        return self.index - len(self.next or '')
    def seek(self, index):
        self.index = index
        self.__next()

    def error(self, msg, offset=0):
        if not self.istext:
            msg = msg.encode('ascii', 'backslashreplace').decode('ascii')
        return error(msg, self.string, self.tell() - offset)

    def checkgroupname(self, name, offset):
        if not (self.istext or name.isascii()):
            msg = "bad character in group name %a" % name
            raise self.error(msg, len(name) + offset)
        if not name.isidentifier():
            msg = "bad character in group name %r" % name
            raise self.error(msg, len(name) + offset)

def _property_escape(source, escape):
    # handle \p{...} and \P{...} (UTS #18 1.2.4, "Property Syntax")
    from . import _properties
    if not source.match('{'):
        raise source.error("missing {, expected property name")
    name = source.getuntil('}', 'property name')
    code = _properties.parse_property(name, escape[1] == 'P')
    if code is None:
        raise source.error("unknown property name %r" % name,
                           len(name) + len(r'\p{}'))
    return code

def _class_escape(source, escape):
    # handle escape code inside character class
    code = ESCAPES.get(escape)
    if code:
        return code
    code = CATEGORIES.get(escape)
    if code and code[0] is CATEGORY:
        return code
    try:
        c = escape[1:2]
        if c == "x":
            # hexadecimal escape (exactly two digits)
            escape += source.getwhile(2, HEXDIGITS)
            if len(escape) != 4:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "u" and source.istext:
            # unicode escape (exactly four digits)
            escape += source.getwhile(4, HEXDIGITS)
            if len(escape) != 6:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "U" and source.istext:
            # unicode escape (exactly eight digits)
            escape += source.getwhile(8, HEXDIGITS)
            if len(escape) != 10:
                raise source.error("incomplete escape %s" % escape, len(escape))
            c = int(escape[2:], 16)
            chr(c) # raise ValueError for invalid code
            return LITERAL, c
        elif c == "N" and source.istext:
            import unicodedata
            # named unicode escape e.g. \N{EM DASH}
            if not source.match('{'):
                raise source.error("missing {")
            charname = source.getuntil('}', 'character name')
            try:
                c = ord(unicodedata.lookup(charname))
            except (KeyError, TypeError):
                raise source.error("undefined character name %r" % charname,
                                   len(charname) + len(r'\N{}')) from None
            return LITERAL, c
        elif c in "pP" and source.istext:
            return _property_escape(source, escape)
        elif c in OCTDIGITS:
            # octal escape (up to three digits)
            escape += source.getwhile(2, OCTDIGITS)
            c = int(escape[1:], 8)
            if c > 0o377:
                raise source.error('octal escape value %s outside of '
                                   'range 0-0o377' % escape, len(escape))
            return LITERAL, c
        elif c in DIGITS:
            raise ValueError
        if len(escape) == 2:
            if c in ASCIILETTERS:
                raise source.error('bad escape %s' % escape, len(escape))
            return LITERAL, ord(escape[1])
    except ValueError:
        pass
    raise source.error("bad escape %s" % escape, len(escape))

def _escape(source, escape, state):
    # handle escape code in expression
    code = CATEGORIES.get(escape)
    if code:
        return code
    code = ESCAPES.get(escape)
    if code:
        return code
    try:
        c = escape[1:2]
        if c == "x":
            # hexadecimal escape
            escape += source.getwhile(2, HEXDIGITS)
            if len(escape) != 4:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "u" and source.istext:
            # unicode escape (exactly four digits)
            escape += source.getwhile(4, HEXDIGITS)
            if len(escape) != 6:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "U" and source.istext:
            # unicode escape (exactly eight digits)
            escape += source.getwhile(8, HEXDIGITS)
            if len(escape) != 10:
                raise source.error("incomplete escape %s" % escape, len(escape))
            c = int(escape[2:], 16)
            chr(c) # raise ValueError for invalid code
            return LITERAL, c
        elif c == "N" and source.istext:
            import unicodedata
            # named unicode escape e.g. \N{EM DASH}
            if not source.match('{'):
                raise source.error("missing {")
            charname = source.getuntil('}', 'character name')
            try:
                c = ord(unicodedata.lookup(charname))
            except (KeyError, TypeError):
                raise source.error("undefined character name %r" % charname,
                                   len(charname) + len(r'\N{}')) from None
            return LITERAL, c
        elif c in "pP" and source.istext:
            return _property_escape(source, escape)
        elif c == "0":
            # octal escape
            escape += source.getwhile(2, OCTDIGITS)
            return LITERAL, int(escape[1:], 8)
        elif c in DIGITS:
            # octal escape *or* decimal group reference (sigh)
            if source.next in DIGITS:
                escape += source.get()
                if (escape[1] in OCTDIGITS and escape[2] in OCTDIGITS and
                    source.next in OCTDIGITS):
                    # got three octal digits; this is an octal escape
                    escape += source.get()
                    c = int(escape[1:], 8)
                    if c > 0o377:
                        raise source.error('octal escape value %s outside of '
                                           'range 0-0o377' % escape,
                                           len(escape))
                    return LITERAL, c
            # not an octal escape, so this is a group reference
            group = int(escape[1:])
            if group < state.groups:
                if not state.checkgroup(group):
                    raise source.error("cannot refer to an open group",
                                       len(escape))
                state.checklookbehindgroup(group, source)
                return GROUPREF, group
            raise source.error("invalid group reference %d" % group, len(escape) - 1)
        if len(escape) == 2:
            if c in ASCIILETTERS:
                raise source.error("bad escape %s" % escape, len(escape))
            return LITERAL, ord(escape[1])
    except ValueError:
        pass
    raise source.error("bad escape %s" % escape, len(escape))

def _uniq(items):
    return list(dict.fromkeys(items))

def _parse_sub(source, state, verbose, nested):
    # parse an alternation: a|b|c

    items = []
    itemsappend = items.append
    sourcematch = source.match
    while True:
        itemsappend(_parse(source, state, verbose, nested + 1,
                           not nested and not items))
        if not sourcematch("|"):
            break
        if not nested:
            verbose = state.flags & SRE_FLAG_VERBOSE

    if len(items) == 1:
        return items[0]

    subpattern = SubPattern(state)

    # check if all items share a common prefix
    while True:
        prefix = None
        for item in items:
            if not item:
                break
            if prefix is None:
                prefix = item[0]
            elif item[0] != prefix:
                break
        else:
            # all subitems start with a common "prefix".
            # move it out of the branch
            for item in items:
                del item[0]
            subpattern.append(prefix)
            continue # check next one
        break

    # check if the branch can be replaced by a character set
    set = []
    for item in items:
        if len(item) != 1:
            break
        op, av = item[0]
        if op in _SETITEMCODES:
            set.append((op, av))
        elif op is IN and av[0][0] is not NEGATE:
            set.extend(av)
        else:
            break
    else:
        # we can store this as a character set instead of a
        # branch (the compiler may optimize this even more)
        subpattern.append((IN, _uniq(set)))
        return subpattern

    subpattern.append((BRANCH, (None, items)))
    return subpattern

def _charset_node(items):
    # One element matching a character in the union `items`.  A lone LITERAL or
    # CATEGORY is already a one-character matcher and needs no IN wrapper.
    if len(items) == 1 and items[0][0] in _SETITEMCODES:
        return items[0]
    return (IN, items)

def _flat_items(elements, complement=False):
    # The items if `elements` is a single flat charset, else None -- the dual
    # of _charset_node: a lone LITERAL or CATEGORY is an item.  A complemented
    # charset (a NEGATE-bearing IN) qualifies only when `complement` is true.
    if len(elements) == 1:
        op, av = elements[0]
        if op in _SETITEMCODES:
            return [elements[0]]
        if op is IN:
            if not complement:
                for o, _av in av:
                    if o is NEGATE:
                        return None
            return av
    return None

def _union(left, right, state):
    # A || B: merge two flat character classes into one charset where possible,
    # else alternate the one-character matchers.
    left_items = _flat_items(left)
    right_items = _flat_items(right)
    if left_items is not None and right_items is not None:
        return [_charset_node(_uniq(left_items + right_items))]
    return [(BRANCH, (None, [SubPattern(state, left),
                             SubPattern(state, right)]))]

def _intersect(left, right, state):
    # A && B: A, then require the same character to also match B (lookbehind).
    return left + [(ASSERT, (-1, SubPattern(state, right)))]

def _difference(left, right, state):
    # A -- B: A, then require the character not to match B (lookbehind).
    return left + [(ASSERT_NOT, (-1, SubPattern(state, right)))]

# Map a set-operator token to the function combining the accumulated result
# with the next operand.
_SETOPS = {'||': _union, '&&': _intersect, '--': _difference}

def _operand_elements(set, compound, negated, state):
    # The operand's elements: a standalone nested set, else the member union,
    # with any negated-property members alternated in (see addmember).
    if compound is not None:
        return compound
    result = [_charset_node(_uniq(set))] if set or not negated else None
    for neg in negated:
        result = [neg] if result is None else _union(result, [neg], state)
    return result

def _parse_operand(source, state, nested, here, allow_nested):
    # Read one operand, stopping at a set operator or the closing ']'.  An
    # operand is either a union of members/ranges/escapes or, when allow_nested,
    # a single nested set ([...]) -- not a mix.  Return (elements, terminator),
    # where terminator is the operator that ended the operand, or None at the end
    # of the class.
    _ord = ord
    sourceget = source.get
    sourcematch = source.match
    set = []
    setappend = set.append
    negated = []        # \P{...} negated-range props, alternated in at the end
    def addmember(code):
        # Flatten a \p{...} property's IN into the member set; a negated one is a
        # complemented charset, set aside to _union in (it can't join the union).
        if code[0] is IN:
            if code[1][0][0] is NEGATE:
                negated.append(code)
            else:
                set.extend(code[1])
        else:
            setappend(code)
    compound = None     # elements of a standalone nested-set operand
    if allow_nested and sourcematch("["):
        # A nested set after an operator is the whole operand, used as-is (not
        # wrapped in a group); it cannot be combined with loose members.
        compound = _parse_charset(source, state, nested + 1)
    while True:
        this = sourceget()
        if this is None:
            raise source.error("unterminated character set",
                               source.tell() - here)
        if set or compound is not None or negated:
            if this == "]":
                return _operand_elements(set, compound, negated, state), None
            if this in '-&|~' and source.next == this:
                if this == '~':
                    import warnings
                    warnings.warn(
                        'Possible set symmetric difference at position %d'
                        % (source.tell() - 1),
                        FutureWarning, stacklevel=nested + 8
                    )
                else:
                    # '--', '&&' or '||' ends this operand and starts the next.
                    sourceget()  # consume the second operator character
                    return _operand_elements(set, compound, negated, state), this + this
        if this[0] == "\\":
            code1 = _class_escape(source, this)
        else:
            code1 = LITERAL, _ord(this)
        if compound is not None:
            # A standalone nested set cannot be combined with other members.
            raise source.error("unsupported nested set operand",
                               source.tell() - here)
        # Past this point the operand is a plain member set (compound is None).
        if sourcematch("-"):
            # potential range
            that = sourceget()
            if that is None:
                raise source.error("unterminated character set",
                                   source.tell() - here)
            if that == "]":
                # A trailing '-' is a literal.
                addmember(code1)
                setappend((LITERAL, _ord("-")))
                return _operand_elements(set, None, negated, state), None
            if that == "-":
                # 'X--': difference, not a range.  '--' after a single member
                # lands here because the range probe consumed the first '-'.
                addmember(code1)
                return _operand_elements(set, None, negated, state), "--"
            if that[0] == "\\":
                code2 = _class_escape(source, that)
            else:
                code2 = LITERAL, _ord(that)
            if code1[0] != LITERAL or code2[0] != LITERAL:
                msg = "bad character range %s-%s" % (this, that)
                raise source.error(msg, len(this) + 1 + len(that))
            lo = code1[1]
            hi = code2[1]
            if hi < lo:
                msg = "bad character range %s-%s" % (this, that)
                raise source.error(msg, len(this) + 1 + len(that))
            setappend((RANGE, (lo, hi)))
        else:
            addmember(code1)

def _complement(elements, state):
    # The complement of `elements` (a single matcher, or a set operation as a
    # head followed by lookbehind assertions).  De Morgan pushes the negation in
    # -- recursively through nested set operations -- so no lookahead is needed.
    op, av = elements[0]
    if op is LITERAL:
        result = [(NOT_LITERAL, av)]
    elif op is NOT_LITERAL:
        result = [(LITERAL, av)]
    elif op is CATEGORY:
        result = [(CATEGORY, CH_NEGATE[av])]
    elif op is IN:
        # Negate by toggling a leading NEGATE: a doubly negated set flips back
        # to positive instead of stacking a second NEGATE.
        if av[0][0] is NEGATE:
            result = [(IN, av[1:])]
        else:
            result = [(IN, [(NEGATE, None)] + av)]
    else:
        # An un-merged union (A||B as an alternation).  De Morgan:
        # ~(A | B | ...) = ~A & ~B & ... -- intersect the operand complements.
        assert op is BRANCH
        branches = av[1]
        result = _complement(branches[0].data, state)
        for sub in branches[1:]:
            result = _intersect(result, _complement(sub.data, state), state)
    # A set operation: a head followed by lookbehind assertions.  De Morgan:
    #   ~(head & ~B & C ...) = ~head | B | ~C ...
    for op, av in elements[1:]:
        if op is ASSERT_NOT:      # '--' operand B: union with B
            result = _union(result, av[1].data, state)
        else:                     # '&&' operand B (ASSERT): union with [^B]
            result = _union(result, _complement(av[1].data, state), state)
    return result

def _parse_charset(source, state, nested):
    # Parse a character set, assuming the opening '[' has been consumed, up to
    # and including the closing ']'.  Return a list of subpattern elements that
    # together consume exactly one character.
    #
    # A set operation (UTS #18 RL1.3) maps to assertions on, or alternatives of,
    # the matched character:
    #   [A--B]  ->  A (?<![B])           difference
    #   [A&&B]  ->  A (?<=[B])           intersection
    #   [A||B]  ->  [AB] or (?:A|B)      union
    # A flat-operand difference [A--B] is later fused back into a single charset
    # by Lib/re/_optimizer.py (see that module).
    # Operators chain left-to-right with no precedence.  A leading '^' negates by
    # De Morgan, pushing the negation into the operands (no lookahead needed):
    #   [^A--B] -> [^A] | B ; [^A&&B] -> [^A] | [^B] ; [^A||B] -> [^A] && [^B]
    # Each operand compiles in its own flag context, so this is IGNORECASE-safe.
    here = source.tell() - 1
    if source.next == '[':
        # A '[' at the start of a class stays a literal (the first operand never
        # needs grouping), but the position is reserved -- keep warning.
        import warnings
        warnings.warn(
            'Possible nested set at position %d' % source.tell(),
            FutureWarning, stacklevel=nested + 7
        )
    negate = source.match("^")
    result, term = _parse_operand(source, state, nested, here, False)
    while term is not None:
        combine = _SETOPS[term]
        operand, term = _parse_operand(source, state, nested, here, True)
        result = combine(result, operand, state)
    if negate:
        # Push the negation into the operands by De Morgan (see above).
        result = _complement(result, state)

    # A single one-character matcher, or a set operation (head + assertions);
    # the caller groups a multi-element result if a quantifier could follow.
    return result

def _parse(source, state, verbose, nested, first=False):
    # parse a simple pattern
    subpattern = SubPattern(state)

    # precompute constants into local variables
    subpatternappend = subpattern.append
    sourceget = source.get
    sourcematch = source.match
    _len = len
    _ord = ord

    while True:

        this = source.next
        if this is None:
            break # end of pattern
        if this in "|)":
            break # end of subpattern
        sourceget()

        if verbose:
            # skip whitespace and comments
            if this in WHITESPACE:
                continue
            if this == "#":
                while True:
                    this = sourceget()
                    if this is None or this == "\n":
                        break
                continue

        if this[0] == "\\":
            code = _escape(source, this, state)
            subpatternappend(code)

        elif this not in SPECIAL_CHARS:
            subpatternappend((LITERAL, _ord(this)))

        elif this == "[":
            charset = _parse_charset(source, state, nested)
            if len(charset) == 1:
                code = charset[0]
            else:
                # Wrap a multi-element set operation in a non-capturing group so
                # a following quantifier (e.g. [a-z--[aeiou]]+) binds the whole
                # operation, not just its trailing assertion.
                code = (SUBPATTERN, (None, 0, 0, SubPattern(state, charset)))
            subpatternappend(code)

        elif this in REPEAT_CHARS:
            # repeat previous item
            here = source.tell()
            if this == "?":
                min, max = 0, 1
            elif this == "*":
                min, max = 0, MAXREPEAT

            elif this == "+":
                min, max = 1, MAXREPEAT
            elif this == "{":
                if source.next == "}":
                    subpatternappend((LITERAL, _ord(this)))
                    continue

                min, max = 0, MAXREPEAT
                lo = hi = ""
                while source.next in DIGITS:
                    lo += sourceget()
                if sourcematch(","):
                    while source.next in DIGITS:
                        hi += sourceget()
                else:
                    hi = lo
                if not sourcematch("}"):
                    subpatternappend((LITERAL, _ord(this)))
                    source.seek(here)
                    continue

                if lo:
                    min = int(lo)
                    if min >= MAXREPEAT:
                        raise OverflowError("the repetition number is too large")
                if hi:
                    max = int(hi)
                    if max >= MAXREPEAT:
                        raise OverflowError("the repetition number is too large")
                    if max < min:
                        raise source.error("min repeat greater than max repeat",
                                           source.tell() - here)
            else:
                raise AssertionError("unsupported quantifier %r" % (char,))
            # figure out which item to repeat
            if subpattern:
                item = subpattern[-1:]
            else:
                item = None
            if not item or item[0][0] is AT:
                raise source.error("nothing to repeat",
                                   source.tell() - here + len(this))
            if item[0][0] in _REPEATCODES:
                raise source.error("multiple repeat",
                                   source.tell() - here + len(this))
            if item[0][0] is SUBPATTERN:
                group, add_flags, del_flags, p = item[0][1]
                if group is None and not add_flags and not del_flags:
                    item = p
            if sourcematch("?"):
                # Non-Greedy Match
                subpattern[-1] = (MIN_REPEAT, (min, max, item))
            elif sourcematch("+"):
                # Possessive Match (Always Greedy)
                subpattern[-1] = (POSSESSIVE_REPEAT, (min, max, item))
            else:
                # Greedy Match
                subpattern[-1] = (MAX_REPEAT, (min, max, item))

        elif this == ".":
            subpatternappend((ANY, None))

        elif this == "(":
            start = source.tell() - 1
            capture = True
            atomic = False
            name = None
            add_flags = 0
            del_flags = 0
            if sourcematch("?"):
                # options
                char = sourceget()
                if char is None:
                    raise source.error("unexpected end of pattern")
                if char == "P":
                    # python extensions
                    if sourcematch("<"):
                        # named group: skip forward to end of name
                        name = source.getuntil(">", "group name")
                        source.checkgroupname(name, 1)
                    elif sourcematch("="):
                        # named backreference
                        name = source.getuntil(")", "group name")
                        source.checkgroupname(name, 1)
                        gid = state.groupdict.get(name)
                        if gid is None:
                            msg = "unknown group name %r" % name
                            raise source.error(msg, len(name) + 1)
                        if not state.checkgroup(gid):
                            raise source.error("cannot refer to an open group",
                                               len(name) + 1)
                        state.checklookbehindgroup(gid, source)
                        subpatternappend((GROUPREF, gid))
                        continue

                    else:
                        char = sourceget()
                        if char is None:
                            raise source.error("unexpected end of pattern")
                        raise source.error("unknown extension ?P" + char,
                                           len(char) + 2)
                elif char == ":":
                    # non-capturing group
                    capture = False
                elif char == "#":
                    # comment
                    while True:
                        if source.next is None:
                            raise source.error("missing ), unterminated comment",
                                               source.tell() - start)
                        if sourceget() == ")":
                            break
                    continue

                elif char in "=!<":
                    # lookahead assertions
                    dir = 1
                    if char == "<":
                        char = sourceget()
                        if char is None:
                            raise source.error("unexpected end of pattern")
                        if char not in "=!":
                            raise source.error("unknown extension ?<" + char,
                                               len(char) + 2)
                        dir = -1 # lookbehind
                        lookbehindgroups = state.lookbehindgroups
                        if lookbehindgroups is None:
                            state.lookbehindgroups = state.groups
                    p = _parse_sub(source, state, verbose, nested + 1)
                    if dir < 0:
                        if lookbehindgroups is None:
                            state.lookbehindgroups = None
                    if not sourcematch(")"):
                        raise source.error("missing ), unterminated subpattern",
                                           source.tell() - start)
                    if char == "=":
                        subpatternappend((ASSERT, (dir, p)))
                    elif p:
                        subpatternappend((ASSERT_NOT, (dir, p)))
                    else:
                        subpatternappend((FAILURE, ()))
                    continue

                elif char == "(":
                    # conditional backreference group
                    condname = source.getuntil(")", "group name")
                    if not (condname.isdecimal() and condname.isascii()):
                        source.checkgroupname(condname, 1)
                        condgroup = state.groupdict.get(condname)
                        if condgroup is None:
                            msg = "unknown group name %r" % condname
                            raise source.error(msg, len(condname) + 1)
                    else:
                        condgroup = int(condname)
                        if not condgroup:
                            raise source.error("bad group number",
                                               len(condname) + 1)
                        if condgroup >= MAXGROUPS:
                            msg = "invalid group reference %d" % condgroup
                            raise source.error(msg, len(condname) + 1)
                        if condgroup not in state.grouprefpos:
                            state.grouprefpos[condgroup] = (
                                source.tell() - len(condname) - 1
                            )
                    state.checklookbehindgroup(condgroup, source)
                    item_yes = _parse(source, state, verbose, nested + 1)
                    if source.match("|"):
                        item_no = _parse(source, state, verbose, nested + 1)
                        if source.next == "|":
                            raise source.error("conditional backref with more than two branches")
                    else:
                        item_no = None
                    if not source.match(")"):
                        raise source.error("missing ), unterminated subpattern",
                                           source.tell() - start)
                    subpatternappend((GROUPREF_EXISTS, (condgroup, item_yes, item_no)))
                    continue

                elif char == ">":
                    # non-capturing, atomic group
                    capture = False
                    atomic = True
                elif char in FLAGS or char == "-":
                    # flags
                    flags = _parse_flags(source, state, char)
                    if flags is None:  # global flags
                        if not first or subpattern:
                            raise source.error('global flags not at the start '
                                               'of the expression',
                                               source.tell() - start)
                        verbose = state.flags & SRE_FLAG_VERBOSE
                        continue

                    add_flags, del_flags = flags
                    capture = False
                else:
                    raise source.error("unknown extension ?" + char,
                                       len(char) + 1)

            # parse group contents
            if capture:
                try:
                    group = state.opengroup(name)
                except error as err:
                    raise source.error(err.msg, len(name) + 1) from None
            else:
                group = None
            sub_verbose = ((verbose or (add_flags & SRE_FLAG_VERBOSE)) and
                           not (del_flags & SRE_FLAG_VERBOSE))
            p = _parse_sub(source, state, sub_verbose, nested + 1)
            if not source.match(")"):
                raise source.error("missing ), unterminated subpattern",
                                   source.tell() - start)
            if group is not None:
                state.closegroup(group, p)
            if atomic:
                assert group is None
                subpatternappend((ATOMIC_GROUP, p))
            else:
                subpatternappend((SUBPATTERN, (group, add_flags, del_flags, p)))

        elif this == "^":
            subpatternappend((AT, AT_BEGINNING))

        elif this == "$":
            subpatternappend((AT, AT_END))

        else:
            raise AssertionError("unsupported special character %r" % (char,))

    # unpack non-capturing groups
    for i in range(len(subpattern))[::-1]:
        op, av = subpattern[i]
        if op is SUBPATTERN:
            group, add_flags, del_flags, p = av
            if group is None and not add_flags and not del_flags:
                subpattern[i: i+1] = p

    return subpattern

def _parse_flags(source, state, char):
    sourceget = source.get
    add_flags = 0
    del_flags = 0
    if char != "-":
        while True:
            flag = FLAGS[char]
            if source.istext:
                if char == 'L':
                    msg = "bad inline flags: cannot use 'L' flag with a str pattern"
                    raise source.error(msg)
            else:
                if char == 'u':
                    msg = "bad inline flags: cannot use 'u' flag with a bytes pattern"
                    raise source.error(msg)
            add_flags |= flag
            if (flag & TYPE_FLAGS) and (add_flags & TYPE_FLAGS) != flag:
                msg = "bad inline flags: flags 'a', 'u' and 'L' are incompatible"
                raise source.error(msg)
            char = sourceget()
            if char is None:
                raise source.error("missing -, : or )")
            if char in ")-:":
                break
            if char not in FLAGS:
                msg = "unknown flag" if char.isalpha() else "missing -, : or )"
                raise source.error(msg, len(char))
    if char == ")":
        state.flags |= add_flags
        return None
    if add_flags & GLOBAL_FLAGS:
        raise source.error("bad inline flags: cannot turn on global flag", 1)
    if char == "-":
        char = sourceget()
        if char is None:
            raise source.error("missing flag")
        if char not in FLAGS:
            msg = "unknown flag" if char.isalpha() else "missing flag"
            raise source.error(msg, len(char))
        while True:
            flag = FLAGS[char]
            if flag & TYPE_FLAGS:
                msg = "bad inline flags: cannot turn off flags 'a', 'u' and 'L'"
                raise source.error(msg)
            del_flags |= flag
            char = sourceget()
            if char is None:
                raise source.error("missing :")
            if char == ":":
                break
            if char not in FLAGS:
                msg = "unknown flag" if char.isalpha() else "missing :"
                raise source.error(msg, len(char))
    assert char == ":"
    if del_flags & GLOBAL_FLAGS:
        raise source.error("bad inline flags: cannot turn off global flag", 1)
    if add_flags & del_flags:
        raise source.error("bad inline flags: flag turned on and off", 1)
    return add_flags, del_flags

def fix_flags(src, flags):
    # Check and fix flags according to the type of pattern (str or bytes)
    if isinstance(src, str):
        if flags & SRE_FLAG_LOCALE:
            raise ValueError("cannot use LOCALE flag with a str pattern")
        if not flags & SRE_FLAG_ASCII:
            flags |= SRE_FLAG_UNICODE
        elif flags & SRE_FLAG_UNICODE:
            raise ValueError("ASCII and UNICODE flags are incompatible")
    else:
        if flags & SRE_FLAG_UNICODE:
            raise ValueError("cannot use UNICODE flag with a bytes pattern")
        if flags & SRE_FLAG_LOCALE and flags & SRE_FLAG_ASCII:
            raise ValueError("ASCII and LOCALE flags are incompatible")
    return flags

def parse(str, flags=0, state=None):
    # parse 're' pattern into list of (opcode, argument) tuples

    source = Tokenizer(str)

    if state is None:
        state = State()
    state.flags = flags
    state.str = str

    p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
    p.state.flags = fix_flags(str, p.state.flags)

    if source.next is not None:
        assert source.next == ")"
        raise source.error("unbalanced parenthesis")

    for g in p.state.grouprefpos:
        if g >= p.state.groups:
            msg = "invalid group reference %d" % g
            raise error(msg, str, p.state.grouprefpos[g])

    if flags & SRE_FLAG_DEBUG:
        p.dump()

    return p

def parse_template(source, pattern):
    # parse 're' replacement string into list of literals and
    # group references
    s = Tokenizer(source)
    sget = s.get
    result = []
    literal = []
    lappend = literal.append
    def addliteral():
        if s.istext:
            result.append(''.join(literal))
        else:
            # The tokenizer implicitly decodes bytes objects as latin-1, we must
            # therefore re-encode the final representation.
            result.append(''.join(literal).encode('latin-1'))
        del literal[:]
    def addgroup(index, pos):
        if index > pattern.groups:
            raise s.error("invalid group reference %d" % index, pos)
        addliteral()
        result.append(index)
    groupindex = pattern.groupindex
    while True:
        this = sget()
        if this is None:
            break # end of replacement string
        if this[0] == "\\":
            # group
            c = this[1]
            if c == "g":
                if not s.match("<"):
                    raise s.error("missing <")
                name = s.getuntil(">", "group name")
                if not (name.isdecimal() and name.isascii()):
                    s.checkgroupname(name, 1)
                    try:
                        index = groupindex[name]
                    except KeyError:
                        raise IndexError("unknown group name %r" % name) from None
                else:
                    index = int(name)
                    if index >= MAXGROUPS:
                        raise s.error("invalid group reference %d" % index,
                                      len(name) + 1)
                addgroup(index, len(name) + 1)
            elif c == "0":
                if s.next in OCTDIGITS:
                    this += sget()
                    if s.next in OCTDIGITS:
                        this += sget()
                lappend(chr(int(this[1:], 8) & 0xff))
            elif c in DIGITS:
                isoctal = False
                if s.next in DIGITS:
                    this += sget()
                    if (c in OCTDIGITS and this[2] in OCTDIGITS and
                        s.next in OCTDIGITS):
                        this += sget()
                        isoctal = True
                        c = int(this[1:], 8)
                        if c > 0o377:
                            raise s.error('octal escape value %s outside of '
                                          'range 0-0o377' % this, len(this))
                        lappend(chr(c))
                if not isoctal:
                    addgroup(int(this[1:]), len(this) - 1)
            else:
                try:
                    this = chr(ESCAPES[this][1])
                except KeyError:
                    if c in ASCIILETTERS:
                        raise s.error('bad escape %s' % this, len(this)) from None
                lappend(this)
        else:
            lappend(this)
    addliteral()
    return result