"""CSS selector parser."""
from __future__ import annotations
import re
from functools import lru_cache
from . import util
from . import css_match as cm
from . import css_types as ct
from .util import SelectorSyntaxError
import warnings
from typing import Match, Any, Iterator, cast
from dataclasses import dataclass
from collections import UserDict
import threading

RE_LOCK = threading.Lock()
SEL_LOCK = threading.RLock()

UNICODE_REPLACEMENT_CHAR = 0xFFFD

SELECTOR_LIMIT = 8192

# Simple pseudo classes that take no parameters
PSEUDO_SIMPLE = {
    ":any-link",
    ":empty",
    ":first-child",
    ":first-of-type",
    ":in-range",
    ":open",
    ":out-of-range",
    ":last-child",
    ":last-of-type",
    ":link",
    ":only-child",
    ":only-of-type",
    ":root",
    ':checked',
    ':default',
    ':disabled',
    ':enabled',
    ':indeterminate',
    ':optional',
    ':placeholder-shown',
    ':read-only',
    ':read-write',
    ':required',
    ':scope',
    ':defined',
    ':muted'
}

# Supported, simple pseudo classes that match nothing in the Soup Sieve environment
PSEUDO_SIMPLE_NO_MATCH = {
    ':active',
    ':autofill',
    ':buffering',
    ':current',
    ':focus',
    ':focus-visible',
    ':focus-within',
    ':fullscreen',
    ':future',
    ':host',
    ':hover',
    ':local-link',
    ':past',
    ':paused',
    ':picture-in-picture',
    ':playing',
    ':popover-open',
    ':seeking',
    ':stalled',
    ':target',
    ':target-within',
    ':user-invalid',
    ':volume-locked',
    ':visited'
}

# Complex pseudo classes that take selector lists
PSEUDO_COMPLEX = {
    ':contains',
    ':-soup-contains',
    ':-soup-contains-own',
    ':has',
    ':is',
    ':matches',
    ':not',
    ':where'
}

PSEUDO_COMPLEX_NO_MATCH = {
    ':current',
    ':host',
    ':host-context'
}

# Complex pseudo classes that take very specific parameters and are handled special
PSEUDO_SPECIAL = {
    ':dir',
    ':lang',
    ':nth-child',
    ':nth-last-child',
    ':nth-last-of-type',
    ':nth-of-type'
}

PSEUDO_SUPPORTED = PSEUDO_SIMPLE | PSEUDO_SIMPLE_NO_MATCH | PSEUDO_COMPLEX | PSEUDO_COMPLEX_NO_MATCH | PSEUDO_SPECIAL

# Sub-patterns parts
# Whitespace
NEWLINE = r'(?:\r\n|(?!\r\n)[\n\f\r])'
WS = fr'(?:[ \t]|{NEWLINE})'
# Comments
COMMENTS = r'(?:/\*(?:[^*]|\*(?!/))*\*/)'
# Whitespace with comments included
WSC = fr'(?:{WS}|{COMMENTS})'
# CSS escapes
CSS_ESCAPES = fr'(?:\\(?:[a-f0-9]{{1,6}}{WS}?|[^\r\n\f]|$))'
CSS_STRING_ESCAPES = fr'(?:\\(?:[a-f0-9]{{1,6}}{WS}?|[^\r\n\f]|$|{NEWLINE}))'
# CSS Identifier
IDENTIFIER = fr'''
(?:(?:--|-?(?:[^\x00-\x2f\x30-\x40\x5B-\x5E\x60\x7B-\x9f]|{CSS_ESCAPES}))
(?:[^\x00-\x2c\x2e\x2f\x3A-\x40\x5B-\x5E\x60\x7B-\x9f]|{CSS_ESCAPES})*)
'''
# `nth` content
NTH = fr'(?:[-+])?(?:[0-9]+n?|n)(?:(?<=n){WSC}*(?:[-+]){WSC}*(?:[0-9]+))?'
# Value: quoted string or identifier
VALUE = fr'''(?:"(?:\\(?:.|{NEWLINE})|[^\\"\r\n\f])*?"|'(?:\\(?:.|{NEWLINE})|[^\\'\r\n\f])*?'|{IDENTIFIER})'''
# Attribute value comparison. `!=` is handled special as it is non-standard.
ATTR = fr'(?:{WSC}*(?P<cmp>[!~^|*$]?=){WSC}*(?P<value>{VALUE})(?:{WSC}*(?P<case>[is]))?)?{WSC}*'

# Selector patterns
# IDs (`#id`)
PAT_ID = fr'\#{IDENTIFIER}'
# Classes (`.class`)
PAT_CLASS = fr'\.{IDENTIFIER}'
# Prefix:Tag (`prefix|tag`)
PAT_TAG = fr'(?P<tag_ns>(?:{IDENTIFIER}|\*)?\|)?(?P<tag_name>{IDENTIFIER}|\*)'
# Attributes (`[attr]`, `[attr=value]`, etc.)
PAT_ATTR = fr'\[{WSC}*(?P<attr_ns>(?:{IDENTIFIER}|\*)?\|)?(?P<attr_name>{IDENTIFIER}){ATTR}\]'
# Pseudo class (`:pseudo-class`, `:pseudo-class(`)
PAT_PSEUDO_CLASS = fr'(?P<name>:{IDENTIFIER})(?P<open>\({WSC}*)?'
# Pseudo class special patterns. Matches `:pseudo-class(` for special case pseudo classes.
PAT_PSEUDO_CLASS_SPECIAL = fr'(?P<name>:{IDENTIFIER})(?P<open>\({WSC}*)'
# Custom pseudo class (`:--custom-pseudo`)
PAT_PSEUDO_CLASS_CUSTOM = fr'(?P<name>:(?=--){IDENTIFIER})'
# Nesting ampersand selector. Matches `&`
PAT_AMP = r'&'
# Closing pseudo group (`)`)
PAT_PSEUDO_CLOSE = fr'{WSC}*\)'
# Pseudo element (`::pseudo-element`)
PAT_PSEUDO_ELEMENT = fr':{PAT_PSEUDO_CLASS}'
# At rule (`@page`, etc.) (not supported)
PAT_AT_RULE = fr'@P{IDENTIFIER}'
# Pseudo class `nth-child` (`:nth-child(an+b [of S]?)`, `:first-child`, etc.)
PAT_PSEUDO_NTH_CHILD = fr'''
(?P<pseudo_nth_child>{PAT_PSEUDO_CLASS_SPECIAL}
(?P<nth_child>{NTH}|even|odd))(?:{WSC}*\)|(?P<of>{COMMENTS}*{WS}{WSC}*of{COMMENTS}*{WS}{WSC}*))
'''
# Pseudo class `nth-of-type` (`:nth-of-type(an+b)`, `:first-of-type`, etc.)
PAT_PSEUDO_NTH_TYPE = fr'''
(?P<pseudo_nth_type>{PAT_PSEUDO_CLASS_SPECIAL}
(?P<nth_type>{NTH}|even|odd)){WSC}*\)
'''
# Pseudo class language (`:lang("*-de", en)`)
PAT_PSEUDO_LANG = fr'{PAT_PSEUDO_CLASS_SPECIAL}(?P<values>{VALUE}(?:{WSC}*,{WSC}*{VALUE})*){WSC}*\)'
# Pseudo class direction (`:dir(ltr)`)
PAT_PSEUDO_DIR = fr'{PAT_PSEUDO_CLASS_SPECIAL}(?P<dir>ltr|rtl){WSC}*\)'
# Combining characters (`>`, `~`, ` `, `+`, `,`)
PAT_COMBINE = fr'{WSC}*?(?P<relation>[,+>~]|{WS}(?![,+>~])){WSC}*'
# Extra: Contains (`:contains(text)`)
PAT_PSEUDO_CONTAINS = fr'{PAT_PSEUDO_CLASS_SPECIAL}(?P<values>{VALUE}(?:{WSC}*,{WSC}*{VALUE})*){WSC}*\)'

# Regular expressions
# CSS escape pattern
RE_CSS_ESC = re.compile(fr'(?:(\\[a-f0-9]{{1,6}}{WSC}?)|(\\[^\r\n\f])|(\\$))', re.I)
RE_CSS_STR_ESC = re.compile(fr'(?:(\\[a-f0-9]{{1,6}}{WS}?)|(\\[^\r\n\f])|(\\$)|(\\{NEWLINE}))', re.I)
# Pattern to break up `nth` specifiers
RE_NTH = re.compile(fr'(?P<s1>[-+])?(?P<a>[0-9]+n?|n)(?:(?<=n){WSC}*(?P<s2>[-+]){WSC}*(?P<b>[0-9]+))?', re.I)
# Pattern to iterate multiple values.
RE_VALUES = re.compile(fr'(?:(?P<value>{VALUE})|(?P<split>{WSC}*,{WSC}*))', re.X)
# Whitespace checks
RE_WS = re.compile(WS)
RE_WS_BEGIN = re.compile(fr'^{WSC}*')
RE_WS_END = re.compile(fr'^(?:[ \t]|(?:\n\r|(?!\n\r)[\n\f\r])|{COMMENTS})*')
RE_CUSTOM = re.compile(fr'^{PAT_PSEUDO_CLASS_CUSTOM}$', re.X)
RE_PSEUDO_CLASS_SPECIAL = re.compile(PAT_PSEUDO_CLASS_SPECIAL, re.I | re.X | re.U)

# Constants
# List split token
COMMA_COMBINATOR = ','
# Relation token for descendant
WS_COMBINATOR = " "

# Parse flags
FLG_PSEUDO = 0x01
FLG_NOT = 0x02
FLG_RELATIVE = 0x04
FLG_DEFAULT = 0x08
FLG_HTML = 0x10
FLG_INDETERMINATE = 0x20
FLG_OPEN = 0x40
FLG_IN_RANGE = 0x80
FLG_OUT_OF_RANGE = 0x100
FLG_PLACEHOLDER_SHOWN = 0x200
FLG_FORGIVE = 0x400

# Maximum cached patterns to store
_MAXCACHE = 500


@lru_cache(maxsize=_MAXCACHE)
def _cached_css_compile(
    pattern: str,
    namespaces: ct.Namespaces | None,
    custom: ct.CustomSelectors | None,
    flags: int
) -> cm.SoupSieve:
    """Cached CSS compile."""

    custom_selectors = process_custom(custom)
    return cm.SoupSieve(
        pattern,
        CSSParser(
            pattern,
            custom=custom_selectors,
            flags=flags
        ).process_selectors(),
        namespaces,
        custom,
        flags
    )


def _purge_cache() -> None:
    """Purge the cache."""

    _cached_css_compile.cache_clear()


def process_custom(custom: ct.CustomSelectors | None) -> dict[str, str | ct.SelectorList]:
    """Process custom."""

    custom_selectors = {}
    if custom is not None:
        for key, value in custom.items():
            name = util.lower(key)
            if RE_CUSTOM.match(name) is None:
                raise SelectorSyntaxError(f"The name '{name}' is not a valid custom pseudo-class name")
            if name in custom_selectors:
                raise KeyError(f"The custom selector '{name}' has already been registered")
            custom_selectors[css_unescape(name)] = value
    return custom_selectors


def css_unescape(content: str, string: bool = False) -> str:
    """
    Unescape CSS value.

    Strings allow for spanning the value on multiple strings by escaping a new line.
    """

    def replace(m: Match[str]) -> str:
        """Replace with the appropriate substitute."""

        if m.group(1):
            codepoint = int(m.group(1)[1:], 16)
            if codepoint == 0:
                codepoint = UNICODE_REPLACEMENT_CHAR
            value = chr(codepoint)
        elif m.group(2):
            value = m.group(2)[1:]
        elif m.group(3):
            value = '\ufffd'
        else:
            value = ''

        return value

    return (RE_CSS_ESC if not string else RE_CSS_STR_ESC).sub(replace, content)


def escape(ident: str) -> str:
    """Escape identifier."""

    string = []
    length = len(ident)
    start_dash = length > 0 and ident[0] == '-'
    if length == 1 and start_dash:
        # Need to escape identifier that is a single `-` with no other characters
        string.append(f'\\{ident}')
    else:
        for index, c in enumerate(ident):
            codepoint = ord(c)
            if codepoint == 0x00:
                string.append('\ufffd')
            elif (0x01 <= codepoint <= 0x1F) or codepoint == 0x7F:
                string.append(f'\\{codepoint:x} ')
            elif (index == 0 or (start_dash and index == 1)) and (0x30 <= codepoint <= 0x39):
                string.append(f'\\{codepoint:x} ')
            elif (
                codepoint in (0x2D, 0x5F) or codepoint >= 0x80 or (0x30 <= codepoint <= 0x39) or
                (0x30 <= codepoint <= 0x39) or (0x41 <= codepoint <= 0x5A) or (0x61 <= codepoint <= 0x7A)
            ):
                string.append(c)
            else:
                string.append(f'\\{c}')
    return ''.join(string)


class SelectorPattern:
    """Selector pattern."""

    def __init__(self, name: str, pattern: str) -> None:
        """Initialize."""

        self.name = name
        self.pattern = pattern
        self._re_pattern: re.Pattern[str] | None = None

    @property
    def re_pattern(self) -> re.Pattern[str]:
        """Retrieve the compiled regular expression pattern."""

        with RE_LOCK:
            if self._re_pattern is None:
                self._re_pattern = re.compile(self.pattern, re.I | re.X | re.U)
        return self._re_pattern

    def get_name(self) -> str:
        """Get name."""

        return self.name

    def match(self, selector: str, index: int, flags: int) -> Match[str] | None:
        """Match the selector."""

        return self.re_pattern.match(selector, index)


class SpecialPseudoPattern(SelectorPattern):
    """Selector pattern."""

    def __init__(self, patterns: tuple[tuple[str, tuple[str, ...], str, type[SelectorPattern]], ...]) -> None:
        """Initialize."""

        self.patterns = {}
        for p in patterns:
            name = p[0]
            pattern = p[3](name, p[2])
            for pseudo in p[1]:
                self.patterns[pseudo] = pattern

        self.matched_name = None  # type: SelectorPattern | None

    def get_name(self) -> str:
        """Get name."""

        return '' if self.matched_name is None else self.matched_name.get_name()

    def match(self, selector: str, index: int, flags: int) -> Match[str] | None:
        """Match the selector."""

        pseudo = None
        m = RE_PSEUDO_CLASS_SPECIAL.match(selector, index)
        if m:
            name = util.lower(css_unescape(m.group('name')))
            pattern = self.patterns.get(name)
            if pattern:
                pseudo = pattern.match(selector, index, flags)
                if pseudo:
                    self.matched_name = pattern

        return pseudo


class _Selector:
    """
    Intermediate selector class.

    This stores selector data for a compound selector as we are acquiring them.
    Once we are done collecting the data for a compound selector, we freeze
    the data in an object that can be pickled and hashed.
    """

    def __init__(self, **kwargs: Any) -> None:
        """Initialize."""

        self.tag = kwargs.get('tag', None)  # type: ct.SelectorTag | None
        self.ids = kwargs.get('ids', [])  # type: list[str]
        self.classes = kwargs.get('classes', [])  # type: list[str]
        self.attributes = kwargs.get('attributes', [])  # type: list[ct.SelectorAttribute]
        self.nth = kwargs.get('nth', [])  # type: list[ct.SelectorNth]
        self.selectors = kwargs.get('selectors', [])  # type: list[ct.SelectorList]
        self.relations = kwargs.get('relations', [])  # type: list[_Selector]
        self.rel_type = kwargs.get('rel_type', None)  # type: str | None
        self.contains = kwargs.get('contains', [])  # type: list[ct.SelectorContains]
        self.lang = kwargs.get('lang', [])  # type: list[ct.SelectorLang]
        self.flags = kwargs.get('flags', 0)  # type: int
        self.no_match = kwargs.get('no_match', False)  # type: bool

    def _freeze_relations(self, relations: list[_Selector]) -> ct.SelectorList:
        """Freeze relation."""

        if relations:
            sel = relations[0]
            sel.relations.extend(relations[1:])
            return ct.SelectorList([sel.freeze()])
        else:
            return ct.SelectorList()

    def freeze(self) -> ct.Selector | ct.SelectorNull:
        """Freeze self."""

        if self.no_match:
            return ct.SelectorNull()
        else:
            return ct.Selector(
                self.tag,
                tuple(self.ids),
                tuple(self.classes),
                tuple(self.attributes),
                tuple(self.nth),
                tuple(self.selectors),
                self._freeze_relations(self.relations),
                self.rel_type,
                tuple(self.contains),
                tuple(self.lang),
                self.flags
            )

    def __str__(self) -> str:  # pragma: no cover
        """String representation."""

        return (
            f'_Selector(tag={self.tag!r}, ids={self.ids!r}, classes={self.classes!r}, attributes={self.attributes!r}, '
            f'nth={self.nth!r}, selectors={self.selectors!r}, relations={self.relations!r}, '
            f'rel_type={self.rel_type!r}, contains={self.contains!r}, lang={self.lang!r}, flags={self.flags!r}, '
            f'no_match={self.no_match!r})'
        )

    __repr__ = __str__


@dataclass
class CSSPattern:
    """A CSS pattern that hasn't been processed by `CSSParser` yet."""

    selector: str
    flags: int


class PseudoSelectorMap(UserDict[str, CSSPattern | ct.SelectorList]):
    """Pseudo selector map."""

    def __setitem__(self, key: str, value: CSSPattern | ct.SelectorList) -> None:
        """Set item."""

        self.data[key] = value

    def __getitem__(self, key: str) -> ct.SelectorList:
        """Get item."""

        with SEL_LOCK:
            value = self.data[key]
            if isinstance(value, CSSPattern):
                value = CSSParser(value.selector).process_selectors(flags=value.flags)
                self.data[key] = value

        return value


# CSS pattern for `:link` and `:any-link`
CSS_LINK = CSSPattern('html|*:is(a, area)[href]', FLG_PSEUDO | FLG_HTML)
# CSS pattern for `:checked`
CSS_CHECKED = CSSPattern(
    '''
    html|*:is(input[type=checkbox], input[type=radio])[checked], html|option[selected]
    ''',
    FLG_PSEUDO | FLG_HTML
)
# CSS pattern for `:default` (must compile CSS_CHECKED first)
CSS_DEFAULT = CSSPattern(
    '''
    :checked,

    /*
    This pattern must be at the end.
    Special logic is applied to the last selector.
    */
    html|form html|*:is(button, input)[type="submit"]
    ''',
    FLG_PSEUDO | FLG_HTML | FLG_DEFAULT
)
# CSS pattern for `:indeterminate`
CSS_INDETERMINATE = CSSPattern(
    '''
    html|input[type="checkbox"][indeterminate],
    html|input[type="radio"]:is(:not([name]), [name=""]):not([checked]),
    html|progress:not([value]),

    /*
    This pattern must be at the end.
    Special logic is applied to the last selector.
    */
    html|input[type="radio"][name]:not([name='']):not([checked])
    ''',
    FLG_PSEUDO | FLG_HTML | FLG_INDETERMINATE
)
# CSS pattern for `:disabled`
CSS_DISABLED = CSSPattern(
    '''
    html|*:is(input:not([type=hidden]), button, select, textarea, fieldset, optgroup, option, fieldset)[disabled],
    html|optgroup[disabled] > html|option,
    html|fieldset[disabled] > html|*:is(input:not([type=hidden]), button, select, textarea, fieldset),
    html|fieldset[disabled] >
        html|*:not(legend:nth-of-type(1)) html|*:is(input:not([type=hidden]), button, select, textarea, fieldset)
    ''',
    FLG_PSEUDO | FLG_HTML
)
# CSS pattern for `:enabled`
CSS_ENABLED = CSSPattern(
    '''
    html|*:is(input:not([type=hidden]), button, select, textarea, fieldset, optgroup, option, fieldset):not(:disabled)
    ''',
    FLG_PSEUDO | FLG_HTML
)
# CSS pattern for `:required`
CSS_REQUIRED = CSSPattern('html|*:is(input, textarea, select)[required]', FLG_PSEUDO | FLG_HTML)
# CSS pattern for `:optional`
CSS_OPTIONAL = CSSPattern('html|*:is(input, textarea, select):not([required])', FLG_PSEUDO | FLG_HTML)
# CSS pattern for `:placeholder-shown`
CSS_PLACEHOLDER_SHOWN = CSSPattern(
    '''
    html|input:is(
        :not([type]),
        [type=""],
        [type=text],
        [type=search],
        [type=url],
        [type=tel],
        [type=email],
        [type=password],
        [type=number]
    )[placeholder]:not([placeholder='']):is(:not([value]), [value=""]),
    html|textarea[placeholder]:not([placeholder=''])
    ''',
    FLG_PSEUDO | FLG_HTML | FLG_PLACEHOLDER_SHOWN
)
# CSS pattern for `:read-write` (CSS_DISABLED must be compiled first)
CSS_READ_WRITE = CSSPattern(
    '''
    html|*:is(
        textarea,
        input:is(
            :not([type]),
            [type=""],
            [type=text],
            [type=search],
            [type=url],
            [type=tel],
            [type=email],
            [type=number],
            [type=password],
            [type=date],
            [type=datetime-local],
            [type=month],
            [type=time],
            [type=week]
        )
    ):not([readonly], :disabled),
    html|*:is([contenteditable=""], [contenteditable="true" i])
    ''',
    FLG_PSEUDO | FLG_HTML
)
# CSS pattern for `:read-only`
CSS_READ_ONLY = CSSPattern('html|*:not(:read-write)', FLG_PSEUDO | FLG_HTML)
# CSS pattern for `:in-range`
CSS_IN_RANGE = CSSPattern(
    '''
    html|input:is(
        [type="date"],
        [type="month"],
        [type="week"],
        [type="time"],
        [type="datetime-local"],
        [type="number"],
        [type="range"]
    ):is(
        [min],
        [max]
    )
    ''',
    FLG_PSEUDO | FLG_HTML | FLG_IN_RANGE
)
# CSS pattern for `:out-of-range`
CSS_OUT_OF_RANGE = CSSPattern(
    '''
    html|input:is(
        [type="date"],
        [type="month"],
        [type="week"],
        [type="time"],
        [type="datetime-local"],
        [type="number"],
        [type="range"]
    ):is(
        [min],
        [max]
    )
    ''',
    FLG_PSEUDO | FLG_HTML | FLG_OUT_OF_RANGE
)
# CSS pattern for :open
CSS_OPEN = CSSPattern('html|*:is(details, dialog)[open]', FLG_PSEUDO | FLG_HTML)
# CSS pattern for :muted
CSS_MUTED = CSSPattern('html|*:is(video, audio)[muted]', FLG_PSEUDO | FLG_HTML)
# CSS pattern default for `:nth-child` "of S" feature
CSS_NTH_OF_S_DEFAULT = CSSPattern("*|*", FLG_PSEUDO)


class CSSParser:
    """Parse CSS selectors."""

    CSS_TOKENS = (
        SelectorPattern("pseudo_close", PAT_PSEUDO_CLOSE),
        SpecialPseudoPattern(
            (
                (
                    "pseudo_contains",
                    (':contains', ':-soup-contains', ':-soup-contains-own'),
                    PAT_PSEUDO_CONTAINS,
                    SelectorPattern
                ),
                ("pseudo_nth_child", (':nth-child', ':nth-last-child'), PAT_PSEUDO_NTH_CHILD, SelectorPattern),
                ("pseudo_nth_type", (':nth-of-type', ':nth-last-of-type'), PAT_PSEUDO_NTH_TYPE, SelectorPattern),
                ("pseudo_lang", (':lang',), PAT_PSEUDO_LANG, SelectorPattern),
                ("pseudo_dir", (':dir',), PAT_PSEUDO_DIR, SelectorPattern)
            )
        ),
        SelectorPattern("pseudo_class_custom", PAT_PSEUDO_CLASS_CUSTOM),
        SelectorPattern("pseudo_class", PAT_PSEUDO_CLASS),
        SelectorPattern("pseudo_element", PAT_PSEUDO_ELEMENT),
        SelectorPattern("amp", PAT_AMP),
        SelectorPattern("at_rule", PAT_AT_RULE),
        SelectorPattern("id", PAT_ID),
        SelectorPattern("class", PAT_CLASS),
        SelectorPattern("tag", PAT_TAG),
        SelectorPattern("attribute", PAT_ATTR),
        SelectorPattern("combine", PAT_COMBINE)
    )

    # Pseudos that expand to selectors
    PSEUDO_SELECTORS = PseudoSelectorMap(
        {
            ':link': CSS_LINK,
            ':any-link': CSS_LINK,
            ':checked': CSS_CHECKED,
            ':default': CSS_DEFAULT,
            ':indeterminate': CSS_INDETERMINATE,
            ':disabled': CSS_DISABLED,
            ':enabled': CSS_ENABLED,
            ':required': CSS_REQUIRED,
            ':muted': CSS_MUTED,
            ':open': CSS_OPEN,
            ':optional': CSS_OPTIONAL,
            ':read-only': CSS_READ_ONLY,
            ':read-write': CSS_READ_WRITE,
            ':in-range': CSS_IN_RANGE,
            ':out-of-range': CSS_OUT_OF_RANGE,
            ':placeholder-shown': CSS_PLACEHOLDER_SHOWN,
            '<nth-of-s>': CSS_NTH_OF_S_DEFAULT
        }
    )

    def __init__(
        self,
        selector: str,
        custom: dict[str, str | ct.SelectorList] | None = None,
        flags: int = 0
    ) -> None:
        """Initialize."""

        self.pattern = selector.replace('\x00', '\ufffd')
        self.flags = flags
        self.debug = self.flags & util.DEBUG
        self.custom = {} if custom is None else custom
        self.count = 0

    def check_count(self) -> None:
        """Check the current selector count."""

        if self.count > SELECTOR_LIMIT:
            raise ValueError(f'Selector exceeds pseudo-class nesting limit of {SELECTOR_LIMIT}')

    def parse_attribute_selector(self, sel: _Selector, m: Match[str], has_selector: bool) -> bool:
        """Create attribute selector from the returned regex match."""

        inverse = False
        op = m.group('cmp')
        case = util.lower(m.group('case')) if m.group('case') else None
        ns = css_unescape(m.group('attr_ns')[:-1]) if m.group('attr_ns') else ''
        attr = css_unescape(m.group('attr_name'))
        is_type = False
        pattern2 = None
        value = ''

        if case:
            flags = (re.I if case == 'i' else 0) | re.DOTALL
        elif util.lower(attr) == 'type':
            flags = re.I | re.DOTALL
            is_type = True
        else:
            flags = re.DOTALL

        if op:
            if m.group('value').startswith(('"', "'")):
                value = css_unescape(m.group('value')[1:-1], True)
            else:
                value = css_unescape(m.group('value'))

        if not op:
            # Attribute name
            pattern = None
        elif op.startswith('^'):
            # Value start with
            # `^=` should match nothing if the value is empty, so use `(?!)` which cannot be matched.
            value = r'(?!)' if not value else re.escape(value)
            pattern = re.compile(r'^%s.*' % value, flags)
        elif op.startswith('$'):
            # Value ends with
            # `$=` should match nothing if the value is empty, so use `(?!)` which cannot be matched.
            value = r'(?!)' if not value else re.escape(value)
            pattern = re.compile(r'.*?%s$' % value, flags)
        elif op.startswith('*'):
            # Value contains
            # `*=` should match nothing if the value is empty, so use `(?!)` which cannot be matched.
            value = r'(?!)' if not value else re.escape(value)
            pattern = re.compile(r'.*?%s.*' % value, flags)
        elif op.startswith('~'):
            # Value contains word within space separated list
            # `*~` should match nothing if the value is empty, so use `(?!)` which cannot be matched.
            value = r'(?!)' if not value or RE_WS.search(value) else re.escape(value)
            pattern = re.compile(r'.*?(?:(?<=^)|(?<=[ \t\r\n\f]))%s(?=(?:[ \t\r\n\f]|$)).*' % value, flags)
        elif op.startswith('|'):
            # Value starts with word in dash separated list
            pattern = re.compile(r'^%s(?:-.*)?$' % re.escape(value), flags)
        else:
            # Value matches
            pattern = re.compile(r'^%s$' % re.escape(value), flags)
            if op.startswith('!'):
                # Equivalent to `:not([attr=value])`
                inverse = True
        if is_type and pattern:
            pattern2 = re.compile(pattern.pattern)

        # Append the attribute selector
        sel_attr = ct.SelectorAttribute(attr, ns, pattern, pattern2)
        if inverse:
            # If we are using `!=`, we need to nest the pattern under a `:not()`.
            sub_sel = _Selector()
            sub_sel.attributes.append(sel_attr)
            not_list = ct.SelectorList([sub_sel.freeze()], True, False)
            sel.selectors.append(not_list)
        else:
            sel.attributes.append(sel_attr)

        has_selector = True
        return has_selector

    def parse_tag_pattern(self, sel: _Selector, m: Match[str], has_selector: bool) -> bool:
        """Parse tag pattern from regex match."""

        prefix = css_unescape(m.group('tag_ns')[:-1]) if m.group('tag_ns') else None
        tag = css_unescape(m.group('tag_name'))
        sel.tag = ct.SelectorTag(tag, prefix)
        has_selector = True
        return has_selector

    def parse_pseudo_class_custom(self, sel: _Selector, m: Match[str], has_selector: bool) -> bool:
        """
        Parse custom pseudo class alias.

        Compile custom selectors as we need them. When compiling a custom selector,
        set it to `None` in the dictionary so we can avoid an infinite loop.
        """

        pseudo = util.lower(css_unescape(m.group('name')))
        selector = self.custom.get(pseudo)
        if selector is None:
            raise SelectorSyntaxError(
                f"Undefined custom selector '{pseudo}' found at position {m.end(0)}",
                self.pattern,
                m.end(0)
            )

        if not isinstance(selector, ct.SelectorList):
            del self.custom[pseudo]
            selector = CSSParser(
                selector, custom=self.custom, flags=self.flags
            ).process_selectors(flags=FLG_PSEUDO)
            self.custom[pseudo] = selector

        self.count += selector.count
        self.check_count()

        sel.selectors.append(selector)
        has_selector = True
        return has_selector

    def parse_pseudo_class(
        self,
        sel: _Selector,
        m: Match[str],
        has_selector: bool,
        iselector: Iterator[tuple[str, Match[str]]],
        is_html: bool
    ) -> tuple[bool, bool]:
        """Parse pseudo class."""

        complex_pseudo = False
        pseudo = util.lower(css_unescape(m.group('name')))
        if m.group('open'):
            complex_pseudo = True
        if complex_pseudo and pseudo in PSEUDO_COMPLEX:
            has_selector = self.parse_pseudo_open(sel, pseudo, has_selector, iselector, m.end(0))
        elif not complex_pseudo and pseudo in PSEUDO_SIMPLE:
            if pseudo == ':root':
                sel.flags |= ct.SEL_ROOT
            elif pseudo == ':defined':
                sel.flags |= ct.SEL_DEFINED
                is_html = True
            elif pseudo == ':scope':
                sel.flags |= ct.SEL_SCOPE
            elif pseudo == ':empty':
                sel.flags |= ct.SEL_EMPTY
            elif pseudo in self.PSEUDO_SELECTORS:
                pseudo_selector = self.PSEUDO_SELECTORS[pseudo]
                self.count += pseudo_selector.count
                self.check_count()
                sel.selectors.append(pseudo_selector)
            elif pseudo == ':first-child':
                sel.nth.append(ct.SelectorNth(1, False, 0, False, False, ct.SelectorList()))
            elif pseudo == ':last-child':
                sel.nth.append(ct.SelectorNth(1, False, 0, False, True, ct.SelectorList()))
            elif pseudo == ':first-of-type':
                sel.nth.append(ct.SelectorNth(1, False, 0, True, False, ct.SelectorList()))
            elif pseudo == ':last-of-type':
                sel.nth.append(ct.SelectorNth(1, False, 0, True, True, ct.SelectorList()))
            elif pseudo == ':only-child':
                sel.nth.extend(
                    [
                        ct.SelectorNth(1, False, 0, False, False, ct.SelectorList()),
                        ct.SelectorNth(1, False, 0, False, True, ct.SelectorList())
                    ]
                )
            elif pseudo == ':only-of-type':
                sel.nth.extend(
                    [
                        ct.SelectorNth(1, False, 0, True, False, ct.SelectorList()),
                        ct.SelectorNth(1, False, 0, True, True, ct.SelectorList())
                    ]
                )
            has_selector = True
        elif complex_pseudo and pseudo in PSEUDO_COMPLEX_NO_MATCH:
            self.parse_selectors(iselector, m.end(0), FLG_PSEUDO | FLG_OPEN)
            sel.no_match = True
            has_selector = True
        elif not complex_pseudo and pseudo in PSEUDO_SIMPLE_NO_MATCH:
            sel.no_match = True
            has_selector = True
        elif pseudo in PSEUDO_SUPPORTED:
            raise SelectorSyntaxError(
                f"Invalid syntax for pseudo class '{pseudo}'",
                self.pattern,
                m.start(0)
            )
        else:
            raise SelectorSyntaxError(
                f"'{pseudo}' was detected as a pseudo-class and is either unsupported or invalid. "
                "If the syntax was not intended to be recognized as a pseudo-class, please escape the colon.",
                self.pattern,
                m.start(0)
            )

        return has_selector, is_html

    def parse_pseudo_nth(
        self,
        sel: _Selector,
        m: Match[str],
        has_selector: bool,
        iselector: Iterator[tuple[str, Match[str]]]
    ) -> bool:
        """Parse `nth` pseudo."""

        mdict = m.groupdict()
        if mdict.get('pseudo_nth_child'):
            postfix = '_child'
        else:
            postfix = '_type'
        mdict['name'] = util.lower(css_unescape(mdict['name']))
        content = util.lower(mdict.get('nth' + postfix))
        if content == 'even':
            # 2n
            s1 = 2
            s2 = 0
            var = True
        elif content == 'odd':
            # 2n+1
            s1 = 2
            s2 = 1
            var = True
        else:
            nth_parts = cast(Match[str], RE_NTH.match(content))
            _s1 = '-' if nth_parts.group('s1') and nth_parts.group('s1') == '-' else ''
            a = nth_parts.group('a')
            var = a.endswith('n')
            if a.startswith('n'):
                _s1 += '1'
            elif var:
                _s1 += a[:-1]
            else:
                _s1 += a
            _s2 = '-' if nth_parts.group('s2') and nth_parts.group('s2') == '-' else ''
            if nth_parts.group('b'):
                _s2 += nth_parts.group('b')
            else:
                _s2 = '0'
            s1 = int(_s1, 10)
            s2 = int(_s2, 10)

        pseudo_sel = mdict['name']
        if postfix == '_child':
            if m.group('of'):
                # Parse the rest of `of S`.
                nth_sel = self.parse_selectors(iselector, m.end(0), FLG_PSEUDO | FLG_OPEN)
            else:
                # Use default `*|*` for `of S`.
                nth_sel = self.PSEUDO_SELECTORS['<nth-of-s>']
                self.count += nth_sel.count
                self.check_count()
            if pseudo_sel == ':nth-child':
                sel.nth.append(ct.SelectorNth(s1, var, s2, False, False, nth_sel))
            elif pseudo_sel == ':nth-last-child':
                sel.nth.append(ct.SelectorNth(s1, var, s2, False, True, nth_sel))
        else:
            if pseudo_sel == ':nth-of-type':
                sel.nth.append(ct.SelectorNth(s1, var, s2, True, False, ct.SelectorList()))
            elif pseudo_sel == ':nth-last-of-type':
                sel.nth.append(ct.SelectorNth(s1, var, s2, True, True, ct.SelectorList()))
        has_selector = True
        return has_selector

    def parse_pseudo_open(
        self,
        sel: _Selector,
        name: str,
        has_selector: bool,
        iselector: Iterator[tuple[str, Match[str]]],
        index: int
    ) -> bool:
        """Parse pseudo with opening bracket."""

        flags = FLG_PSEUDO | FLG_OPEN
        if name == ':not':
            flags |= FLG_NOT
        elif name == ':has':
            flags |= FLG_RELATIVE
        elif name in (':where', ':is'):
            flags |= FLG_FORGIVE

        sel.selectors.append(self.parse_selectors(iselector, index, flags))
        has_selector = True

        return has_selector

    def parse_has_combinator(
        self,
        sel: _Selector,
        m: Match[str],
        has_selector: bool,
        selectors: list[_Selector],
        rel_type: str,
        index: int
    ) -> tuple[bool, _Selector, str]:
        """Parse combinator tokens."""

        combinator = m.group('relation').strip()
        if not combinator:
            combinator = WS_COMBINATOR
        if combinator == COMMA_COMBINATOR:
            sel.rel_type = rel_type
            selectors[-1].relations.append(sel)
            rel_type = ":" + WS_COMBINATOR
            selectors.append(_Selector())
        else:
            if has_selector:
                # End the current selector and associate the leading combinator with this selector.
                sel.rel_type = rel_type
                selectors[-1].relations.append(sel)
            elif rel_type[1:] != WS_COMBINATOR:
                # It's impossible to have two whitespace combinators after each other as the patterns
                # will gobble up trailing whitespace. It is also impossible to have a whitespace
                # combinator after any other kind for the same reason. But we could have
                # multiple non-whitespace combinators. So if the current combinator is not a whitespace,
                # then we've hit the multiple combinator case, so we should fail.
                raise SelectorSyntaxError(
                    f'The multiple combinators at position {index}',
                    self.pattern,
                    index
                )

            # Set the leading combinator for the next selector.
            rel_type = ':' + combinator

        sel = _Selector()
        has_selector = False
        return has_selector, sel, rel_type

    def parse_combinator(
        self,
        sel: _Selector,
        m: Match[str],
        has_selector: bool,
        selectors: list[_Selector],
        relations: list[_Selector],
        is_pseudo: bool,
        is_forgive: bool,
        index: int
    ) -> tuple[bool, _Selector]:
        """Parse combinator tokens."""

        combinator = m.group('relation').strip()
        if not combinator:
            combinator = WS_COMBINATOR
        if not has_selector:
            if not is_forgive or combinator != COMMA_COMBINATOR:
                raise SelectorSyntaxError(
                    f"The combinator '{combinator}' at position {index}, must have a selector before it",
                    self.pattern,
                    index
                )

            # If we are in a forgiving pseudo class, just make the selector a "no match"
            if combinator == COMMA_COMBINATOR:
                sel.no_match = True
                del relations[:]
                selectors.append(sel)
        else:
            if combinator == COMMA_COMBINATOR:
                if not sel.tag and not is_pseudo:
                    # Implied `*`
                    sel.tag = ct.SelectorTag('*', None)
                sel.relations.extend(relations)
                selectors.append(sel)
                del relations[:]
            else:
                sel.relations.extend(relations)
                sel.rel_type = combinator
                del relations[:]
                relations.append(sel)

        sel = _Selector()
        has_selector = False

        return has_selector, sel

    def parse_class_id(self, sel: _Selector, m: Match[str], has_selector: bool) -> bool:
        """Parse HTML classes and ids."""

        selector = m.group(0)
        if selector.startswith('.'):
            sel.classes.append(css_unescape(selector[1:]))
        else:
            sel.ids.append(css_unescape(selector[1:]))
        has_selector = True
        return has_selector

    def parse_pseudo_contains(self, sel: _Selector, m: Match[str], has_selector: bool) -> bool:
        """Parse contains."""

        pseudo = util.lower(css_unescape(m.group('name')))
        if pseudo == ":contains":
            warnings.warn(  # noqa: B028
                "The pseudo class ':contains' is deprecated, ':-soup-contains' should be used moving forward.",
                FutureWarning
            )
        contains_own = pseudo == ":-soup-contains-own"
        values = css_unescape(m.group('values'))
        patterns = []
        for token in RE_VALUES.finditer(values):
            if token.group('split'):
                continue
            value = token.group('value')
            if value.startswith(("'", '"')):
                value = css_unescape(value[1:-1], True)
            else:
                value = css_unescape(value)
            patterns.append(value)
        sel.contains.append(ct.SelectorContains(patterns, contains_own))
        has_selector = True
        return has_selector

    def parse_pseudo_lang(self, sel: _Selector, m: Match[str], has_selector: bool) -> bool:
        """Parse pseudo language."""

        values = m.group('values')
        patterns = []
        for token in RE_VALUES.finditer(values):
            if token.group('split'):
                continue
            value = token.group('value')
            if value.startswith(('"', "'")):
                value = css_unescape(value[1:-1], True)
            else:
                value = css_unescape(value)

            patterns.append(value)

        sel.lang.append(ct.SelectorLang(patterns))
        has_selector = True

        return has_selector

    def parse_pseudo_dir(self, sel: _Selector, m: Match[str], has_selector: bool) -> bool:
        """Parse pseudo direction."""

        value = ct.SEL_DIR_LTR if util.lower(m.group('dir')) == 'ltr' else ct.SEL_DIR_RTL
        sel.flags |= value
        has_selector = True
        return has_selector

    def parse_selectors(
        self,
        iselector: Iterator[tuple[str, Match[str]]],
        index: int = 0,
        flags: int = 0
    ) -> ct.SelectorList:
        """Parse selectors."""

        # Initialize important variables
        sel = _Selector()
        selectors = []
        has_selector = False
        closed = False
        relations = []  # type: list[_Selector]
        rel_type = ":" + WS_COMBINATOR
        count = self.count

        # Setup various flags
        is_open = bool(flags & FLG_OPEN)
        is_pseudo = bool(flags & FLG_PSEUDO)
        is_relative = bool(flags & FLG_RELATIVE)
        is_not = bool(flags & FLG_NOT)
        is_html = bool(flags & FLG_HTML)
        is_default = bool(flags & FLG_DEFAULT)
        is_indeterminate = bool(flags & FLG_INDETERMINATE)
        is_in_range = bool(flags & FLG_IN_RANGE)
        is_out_of_range = bool(flags & FLG_OUT_OF_RANGE)
        is_placeholder_shown = bool(flags & FLG_PLACEHOLDER_SHOWN)
        is_forgive = bool(flags & FLG_FORGIVE)

        # Print out useful debug stuff
        if self.debug:  # pragma: no cover
            if is_pseudo:
                print('    is_pseudo: True')
            if is_open:
                print('    is_open: True')
            if is_relative:
                print('    is_relative: True')
            if is_not:
                print('    is_not: True')
            if is_html:
                print('    is_html: True')
            if is_default:
                print('    is_default: True')
            if is_indeterminate:
                print('    is_indeterminate: True')
            if is_in_range:
                print('    is_in_range: True')
            if is_out_of_range:
                print('    is_out_of_range: True')
            if is_placeholder_shown:
                print('    is_placeholder_shown: True')
            if is_forgive:
                print('    is_forgive: True')

        # The algorithm for relative selectors require an initial selector in the selector list
        if is_relative:
            selectors.append(_Selector())

        try:
            while True:
                key, m = next(iselector)

                if key not in ('combine', 'pseudo_close'):
                    self.count += 1
                    self.check_count()

                # Handle parts
                if key == "at_rule":
                    raise NotImplementedError(f"At-rules found at position {m.start(0)}")
                elif key == "amp":
                    sel.flags |= ct.SEL_SCOPE
                    has_selector = True
                elif key == 'pseudo_class_custom':
                    has_selector = self.parse_pseudo_class_custom(sel, m, has_selector)
                elif key == 'pseudo_class':
                    has_selector, is_html = self.parse_pseudo_class(sel, m, has_selector, iselector, is_html)
                elif key == 'pseudo_element':
                    raise NotImplementedError(f"Pseudo-element found at position {m.start(0)}")
                elif key == 'pseudo_contains':
                    has_selector = self.parse_pseudo_contains(sel, m, has_selector)
                elif key in ('pseudo_nth_type', 'pseudo_nth_child'):
                    has_selector = self.parse_pseudo_nth(sel, m, has_selector, iselector)
                elif key == 'pseudo_lang':
                    has_selector = self.parse_pseudo_lang(sel, m, has_selector)
                elif key == 'pseudo_dir':
                    has_selector = self.parse_pseudo_dir(sel, m, has_selector)
                    # Currently only supports HTML
                    is_html = True
                elif key == 'pseudo_close':
                    if not has_selector:
                        if not is_forgive:
                            raise SelectorSyntaxError(
                                f"Expected a selector at position {m.start(0)}",
                                self.pattern,
                                m.start(0)
                            )
                        sel.no_match = True
                    if is_open:
                        closed = True
                        break
                    else:
                        raise SelectorSyntaxError(
                            f"Unmatched pseudo-class close at position {m.start(0)}",
                            self.pattern,
                            m.start(0)
                        )
                elif key == 'combine':
                    if is_relative:
                        has_selector, sel, rel_type = self.parse_has_combinator(
                            sel, m, has_selector, selectors, rel_type, index
                        )
                    else:
                        has_selector, sel = self.parse_combinator(
                            sel, m, has_selector, selectors, relations, is_pseudo, is_forgive, index
                        )
                elif key == 'attribute':
                    has_selector = self.parse_attribute_selector(sel, m, has_selector)
                elif key == 'tag':
                    if has_selector:
                        raise SelectorSyntaxError(
                            f"Tag name found at position {m.start(0)} instead of at the start",
                            self.pattern,
                            m.start(0)
                        )
                    has_selector = self.parse_tag_pattern(sel, m, has_selector)
                elif key in ('class', 'id'):
                    has_selector = self.parse_class_id(sel, m, has_selector)

                index = m.end(0)
        except StopIteration:
            pass

        # Handle selectors that are not closed
        if is_open and not closed:
            raise SelectorSyntaxError(
                f"Unclosed pseudo-class at position {index}",
                self.pattern,
                index
            )

        # Cleanup completed selector piece
        if has_selector:
            if not sel.tag and not is_pseudo:
                # Implied `*`
                sel.tag = ct.SelectorTag('*', None)
            if is_relative:
                sel.rel_type = rel_type
                selectors[-1].relations.append(sel)
            else:
                sel.relations.extend(relations)
                del relations[:]
                selectors.append(sel)

        # Forgive empty slots in pseudo-classes that have lists (and are forgiving)
        elif is_forgive and (not selectors or not relations):
            # Handle normal pseudo-classes with empty slots like `:is()` etc.
            sel.no_match = True
            del relations[:]
            selectors.append(sel)
            has_selector = True

        if not has_selector:
            # We will always need to finish a selector when `:has()` is used as it leads with combining.
            # May apply to others as well.
            raise SelectorSyntaxError(
                f'Expected a selector at position {index}',
                self.pattern,
                index
            )

        # Some patterns require additional logic, such as default. We try to make these the
        # last pattern, and append the appropriate flag to that selector which communicates
        # to the matcher what additional logic is required.
        if is_default:
            selectors[-1].flags = ct.SEL_DEFAULT
        if is_indeterminate:
            selectors[-1].flags = ct.SEL_INDETERMINATE
        if is_in_range:
            selectors[-1].flags = ct.SEL_IN_RANGE
        if is_out_of_range:
            selectors[-1].flags = ct.SEL_OUT_OF_RANGE
        if is_placeholder_shown:
            selectors[-1].flags = ct.SEL_PLACEHOLDER_SHOWN

        # Return selector list
        return ct.SelectorList([s.freeze() for s in selectors], is_not, is_html, self.count - count)

    def selector_iter(self, pattern: str) -> Iterator[tuple[str, Match[str]]]:
        """Iterate selector tokens."""

        # Ignore whitespace and comments at start and end of pattern
        m = RE_WS_BEGIN.search(pattern)
        index = m.end(0) if m else 0
        m = RE_WS_END.search(pattern[::-1])
        offset = m.end(0) if m else 0
        end = len(pattern) - (1 + offset)

        if self.debug:  # pragma: no cover
            print(f'## PARSING: {pattern!r}')
        while index <= end:
            m = None
            for v in self.CSS_TOKENS:
                m = v.match(pattern, index, self.flags)
                if m:
                    name = v.get_name()
                    if self.debug:  # pragma: no cover
                        print(f"TOKEN: '{name}' --> {m.group(0)!r} at position {m.start(0)}")
                    index = m.end(0)
                    yield name, m
                    break
            if m is None:
                c = pattern[index]
                # If the character represents the start of one of the known selector types,
                # throw an exception mentioning that the known selector type is in error;
                # otherwise, report the invalid character.
                if c == '[':
                    msg = f"Malformed attribute selector at position {index}"
                elif c == '.':
                    msg = f"Malformed class selector at position {index}"
                elif c == '#':
                    msg = f"Malformed id selector at position {index}"
                elif c == ':':
                    msg = f"Malformed pseudo-class selector at position {index}"
                else:
                    msg = f"Invalid character {c!r} position {index}"
                raise SelectorSyntaxError(msg, self.pattern, index)
        if self.debug:  # pragma: no cover
            print('## END PARSING')

    def process_selectors(self, index: int = 0, flags: int = 0) -> ct.SelectorList:
        """Process selectors."""

        return self.parse_selectors(self.selector_iter(self.pattern), index, flags)
