selector.rs

use crate::compat::Feature;
use crate::error::{ParserError, PrinterError};
use crate::printer::Printer;
use crate::properties::custom::TokenList;
use crate::rules::{StyleContext, ToCssWithContext};
use crate::stylesheet::{ParserOptions, PrinterOptions};
use crate::targets::Browsers;
use crate::traits::{Parse, ToCss};
use crate::vendor_prefix::VendorPrefix;
use crate::{macros::enum_property, values::string::CowArcStr};
use cssparser::*;
use parcel_selectors::parser::SelectorParseErrorKind;
use parcel_selectors::{
  attr::{AttrSelectorOperator, ParsedAttrSelectorOperation, ParsedCaseSensitivity},
  parser::{Combinator, Component, Selector, SelectorImpl},
  SelectorList,
};
use std::collections::HashMap;
use std::collections::HashSet;
use std::fmt;
use std::fmt::Write;

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Selectors;

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub struct SelectorString<'a>(pub CowArcStr<'a>);

impl<'a> std::convert::From<CowRcStr<'a>> for SelectorString<'a> {
  fn from(s: CowRcStr<'a>) -> SelectorString<'a> {
    SelectorString(s.into())
  }
}

impl<'a> cssparser::ToCss for SelectorString<'a> {
  fn to_css<W>(&self, dest: &mut W) -> std::fmt::Result
  where
    W: std::fmt::Write,
  {
    write!(CssStringWriter::new(dest), "{}", &self.0)
  }
}

impl<'a> SelectorString<'a> {
  pub fn write_identifier<W>(&self, dest: &mut W) -> Result<(), PrinterError>
  where
    W: fmt::Write,
  {
    serialize_identifier(&self.0, dest)?;
    Ok(())
  }
}

#[derive(Debug, Clone, PartialEq, Eq, Default, Hash)]
pub struct SelectorIdent<'i>(pub CowArcStr<'i>);

impl<'a> std::convert::From<CowRcStr<'a>> for SelectorIdent<'a> {
  fn from(s: CowRcStr<'a>) -> SelectorIdent {
    SelectorIdent(s.into())
  }
}

impl<'i> cssparser::ToCss for SelectorIdent<'i> {
  fn to_css<W>(&self, dest: &mut W) -> std::fmt::Result
  where
    W: std::fmt::Write,
  {
    serialize_identifier(&self.0, dest)
  }
}

impl<'i> SelectorImpl<'i> for Selectors {
  type AttrValue = SelectorString<'i>;
  type Identifier = SelectorIdent<'i>;
  type LocalName = SelectorIdent<'i>;
  type NamespacePrefix = SelectorIdent<'i>;
  type NamespaceUrl = SelectorIdent<'i>;
  type BorrowedNamespaceUrl = SelectorIdent<'i>;
  type BorrowedLocalName = SelectorIdent<'i>;

  type NonTSPseudoClass = PseudoClass<'i>;
  type PseudoElement = PseudoElement<'i>;
  type VendorPrefix = VendorPrefix;

  type ExtraMatchingData = ();

  fn to_css<W: fmt::Write>(selectors: &SelectorList<'i, Self>, dest: &mut W) -> std::fmt::Result {
    let mut printer = Printer::new(dest, PrinterOptions::default());
    serialize_selector_list(selectors.0.iter(), &mut printer, None, false).map_err(|_| std::fmt::Error)
  }
}

pub struct SelectorParser<'a, 'o, 'i> {
  pub default_namespace: &'a Option<CowArcStr<'i>>,
  pub namespace_prefixes: &'a HashMap<CowArcStr<'i>, CowArcStr<'i>>,
  pub is_nesting_allowed: bool,
  pub options: &'a ParserOptions<'o, 'i>,
}

impl<'a, 'o, 'i> parcel_selectors::parser::Parser<'i> for SelectorParser<'a, 'o, 'i> {
  type Impl = Selectors;
  type Error = ParserError<'i>;

  fn parse_non_ts_pseudo_class(
    &self,
    loc: SourceLocation,
    name: CowRcStr<'i>,
  ) -> Result<PseudoClass<'i>, ParseError<'i, Self::Error>> {
    use PseudoClass::*;
    let pseudo_class = match_ignore_ascii_case! { &name,
      // https://drafts.csswg.org/selectors-4/#useraction-pseudos
      "hover" => Hover,
      "active" => Active,
      "focus" => Focus,
      "focus-visible" => FocusVisible,
      "focus-within" => FocusWithin,

      // https://drafts.csswg.org/selectors-4/#time-pseudos
      "current" => Current,
      "past" => Past,
      "future" => Future,

      // https://drafts.csswg.org/selectors-4/#resource-pseudos
      "playing" => Playing,
      "paused" => Paused,
      "seeking" => Seeking,
      "buffering" => Buffering,
      "stalled" => Stalled,
      "muted" => Muted,
      "volume-locked" => VolumeLocked,

      // https://fullscreen.spec.whatwg.org/#:fullscreen-pseudo-class
      "fullscreen" => Fullscreen(VendorPrefix::None),
      "-webkit-full-screen" => Fullscreen(VendorPrefix::WebKit),
      "-moz-full-screen" => Fullscreen(VendorPrefix::Moz),
      "-ms-fullscreen" => Fullscreen(VendorPrefix::Ms),

      // https://drafts.csswg.org/selectors-4/#the-defined-pseudo
      "defined" => Defined,

      // https://drafts.csswg.org/selectors-4/#location
      "any-link" => AnyLink(VendorPrefix::None),
      "-webkit-any-link" => AnyLink(VendorPrefix::WebKit),
      "-moz-any-link" => AnyLink(VendorPrefix::Moz),
      "link" => Link,
      "local-link" => LocalLink,
      "target" => Target,
      "target-within" => TargetWithin,
      "visited" => Visited,

      // https://drafts.csswg.org/selectors-4/#input-pseudos
      "enabled" => Enabled,
      "disabled" => Disabled,
      "read-only" => ReadOnly(VendorPrefix::None),
      "-moz-read-only" => ReadOnly(VendorPrefix::Moz),
      "read-write" => ReadWrite(VendorPrefix::None),
      "-moz-read-write" => ReadWrite(VendorPrefix::Moz),
      "placeholder-shown" => PlaceholderShown(VendorPrefix::None),
      "-moz-placeholder-shown" => PlaceholderShown(VendorPrefix::Moz),
      "-ms-placeholder-shown" => PlaceholderShown(VendorPrefix::Ms),
      "default" => Default,
      "checked" => Checked,
      "indeterminate" => Indeterminate,
      "blank" => Blank,
      "valid" => Valid,
      "invalid" => Invalid,
      "in-range" => InRange,
      "out-of-range" => OutOfRange,
      "required" => Required,
      "optional" => Optional,
      "user-valid" => UserValid,
      "user-invalid" => UserInvalid,

      // https://html.spec.whatwg.org/multipage/semantics-other.html#selector-autofill
      "autofill" => Autofill(VendorPrefix::None),
      "-webkit-autofill" => Autofill(VendorPrefix::WebKit),
      "-o-autofill" => Autofill(VendorPrefix::O),

      // https://webkit.org/blog/363/styling-scrollbars/
      "horizontal" => WebKitScrollbar(WebKitScrollbarPseudoClass::Horizontal),
      "vertical" => WebKitScrollbar(WebKitScrollbarPseudoClass::Vertical),
      "decrement" => WebKitScrollbar(WebKitScrollbarPseudoClass::Decrement),
      "increment" => WebKitScrollbar(WebKitScrollbarPseudoClass::Increment),
      "start" => WebKitScrollbar(WebKitScrollbarPseudoClass::Start),
      "end" => WebKitScrollbar(WebKitScrollbarPseudoClass::End),
      "double-button" => WebKitScrollbar(WebKitScrollbarPseudoClass::DoubleButton),
      "single-button" => WebKitScrollbar(WebKitScrollbarPseudoClass::SingleButton),
      "no-button" => WebKitScrollbar(WebKitScrollbarPseudoClass::NoButton),
      "corner-present" => WebKitScrollbar(WebKitScrollbarPseudoClass::CornerPresent),
      "window-inactive" => WebKitScrollbar(WebKitScrollbarPseudoClass::WindowInactive),

      _ => {
        if !name.starts_with('-') {
          self.options.warn(loc.new_custom_error(SelectorParseErrorKind::UnsupportedPseudoClassOrElement(name.clone())));
        }
        Custom(name.into())
      }
    };

    Ok(pseudo_class)
  }

  fn parse_non_ts_functional_pseudo_class<'t>(
    &self,
    name: CowRcStr<'i>,
    parser: &mut cssparser::Parser<'i, 't>,
  ) -> Result<PseudoClass<'i>, ParseError<'i, Self::Error>> {
    use PseudoClass::*;
    let pseudo_class = match_ignore_ascii_case! { &name,
      "lang" => {
        let langs = parser.parse_comma_separated(|parser| {
          parser.expect_ident_or_string()
            .map(|s| s.into())
            .map_err(|e| e.into())
        })?;
        Lang(langs)
      },
      "dir" => Dir(Direction::parse(parser)?),
      "local" if self.options.css_modules.is_some() => Local(Box::new(parcel_selectors::parser::Selector::parse(self, parser)?)),
      "global" if self.options.css_modules.is_some() => Global(Box::new(parcel_selectors::parser::Selector::parse(self, parser)?)),
      _ => {
        if !name.starts_with('-') {
          self.options.warn(parser.new_custom_error(SelectorParseErrorKind::UnsupportedPseudoClassOrElement(name.clone())));
        }
        CustomFunction(name.into(), TokenList::parse(parser, &self.options, 0)?)
      },
    };

    Ok(pseudo_class)
  }

  fn parse_any_prefix<'t>(&self, name: &str) -> Option<VendorPrefix> {
    match_ignore_ascii_case! { &name,
      "-webkit-any" => Some(VendorPrefix::WebKit),
      "-moz-any" => Some(VendorPrefix::Moz),
      _ => None
    }
  }

  fn parse_pseudo_element(
    &self,
    loc: SourceLocation,
    name: CowRcStr<'i>,
  ) -> Result<PseudoElement<'i>, ParseError<'i, Self::Error>> {
    use PseudoElement::*;
    let pseudo_element = match_ignore_ascii_case! { &name,
      "before" => Before,
      "after" => After,
      "first-line" => FirstLine,
      "first-letter" => FirstLetter,
      "cue" => Cue,
      "cue-region" => CueRegion,
      "selection" => Selection(VendorPrefix::None),
      "-moz-selection" => Selection(VendorPrefix::Moz),
      "placeholder" => Placeholder(VendorPrefix::None),
      "-webkit-input-placeholder" => Placeholder(VendorPrefix::WebKit),
      "-moz-placeholder" => Placeholder(VendorPrefix::Moz),
      "-ms-input-placeholder" => Placeholder(VendorPrefix::Moz),
      "marker" => Marker,
      "backdrop" => Backdrop(VendorPrefix::None),
      "-webkit-backdrop" => Backdrop(VendorPrefix::WebKit),
      "file-selector-button" => FileSelectorButton(VendorPrefix::None),
      "-webkit-file-upload-button" => FileSelectorButton(VendorPrefix::WebKit),
      "-ms-browse" => FileSelectorButton(VendorPrefix::Ms),

      "-webkit-scrollbar" => WebKitScrollbar(WebKitScrollbarPseudoElement::Scrollbar),
      "-webkit-scrollbar-button" => WebKitScrollbar(WebKitScrollbarPseudoElement::Button),
      "-webkit-scrollbar-track" => WebKitScrollbar(WebKitScrollbarPseudoElement::Track),
      "-webkit-scrollbar-track-piece" => WebKitScrollbar(WebKitScrollbarPseudoElement::TrackPiece),
      "-webkit-scrollbar-thumb" => WebKitScrollbar(WebKitScrollbarPseudoElement::Thumb),
      "-webkit-scrollbar-corner" => WebKitScrollbar(WebKitScrollbarPseudoElement::Corner),
      "-webkit-resizer" => WebKitScrollbar(WebKitScrollbarPseudoElement::Resizer),

      _ => {
        if !name.starts_with('-') {
          self.options.warn(loc.new_custom_error(SelectorParseErrorKind::UnsupportedPseudoClassOrElement(name.clone())));
        }
        Custom(name.into())
      }
    };

    Ok(pseudo_element)
  }

  fn parse_functional_pseudo_element<'t>(
    &self,
    name: CowRcStr<'i>,
    arguments: &mut Parser<'i, 't>,
  ) -> Result<<Self::Impl as SelectorImpl<'i>>::PseudoElement, ParseError<'i, Self::Error>> {
    use PseudoElement::*;
    let pseudo_element = match_ignore_ascii_case! { &name,
      "cue" => CueFunction(Box::new(Selector::parse(self, arguments)?)),
      "cue-region" => CueRegionFunction(Box::new(Selector::parse(self, arguments)?)),
      _ => {
        if !name.starts_with('-') {
          self.options.warn(arguments.new_custom_error(SelectorParseErrorKind::UnsupportedPseudoClassOrElement(name.clone())));
        }
        CustomFunction(name.into(), TokenList::parse(arguments, &self.options, 0)?)
      }
    };

    Ok(pseudo_element)
  }

  #[inline]
  fn parse_slotted(&self) -> bool {
    true
  }

  #[inline]
  fn parse_host(&self) -> bool {
    true
  }

  #[inline]
  fn parse_is_and_where(&self) -> bool {
    true
  }

  #[inline]
  fn parse_part(&self) -> bool {
    true
  }

  fn default_namespace(&self) -> Option<SelectorIdent<'i>> {
    self.default_namespace.clone().map(SelectorIdent)
  }

  fn namespace_for_prefix(&self, prefix: &SelectorIdent<'i>) -> Option<SelectorIdent<'i>> {
    self.namespace_prefixes.get(&prefix.0).cloned().map(SelectorIdent)
  }

  #[inline]
  fn is_nesting_allowed(&self) -> bool {
    self.is_nesting_allowed
  }
}

enum_property! {
  #[derive(Eq)]
  pub enum Direction {
    Ltr,
    Rtl,
  }
}

/// https://drafts.csswg.org/selectors-4/#structural-pseudos
#[derive(Clone, PartialEq)]
pub enum PseudoClass<'i> {
  // https://drafts.csswg.org/selectors-4/#linguistic-pseudos
  Lang(Vec<CowArcStr<'i>>),
  Dir(Direction),

  // https://drafts.csswg.org/selectors-4/#useraction-pseudos
  Hover,
  Active,
  Focus,
  FocusVisible,
  FocusWithin,

  // https://drafts.csswg.org/selectors-4/#time-pseudos
  Current,
  Past,
  Future,

  // https://drafts.csswg.org/selectors-4/#resource-pseudos
  Playing,
  Paused,
  Seeking,
  Buffering,
  Stalled,
  Muted,
  VolumeLocked,

  // https://fullscreen.spec.whatwg.org/#:fullscreen-pseudo-class
  Fullscreen(VendorPrefix),

  // https://drafts.csswg.org/selectors-4/#the-defined-pseudo
  Defined,

  // https://drafts.csswg.org/selectors-4/#location
  AnyLink(VendorPrefix),
  Link,
  LocalLink,
  Target,
  TargetWithin,
  Visited,

  // https://drafts.csswg.org/selectors-4/#input-pseudos
  Enabled,
  Disabled,
  ReadOnly(VendorPrefix),
  ReadWrite(VendorPrefix),
  PlaceholderShown(VendorPrefix),
  Default,
  Checked,
  Indeterminate,
  Blank,
  Valid,
  Invalid,
  InRange,
  OutOfRange,
  Required,
  Optional,
  UserValid,
  UserInvalid,

  // https://html.spec.whatwg.org/multipage/semantics-other.html#selector-autofill
  Autofill(VendorPrefix),

  // CSS modules
  Local(Box<parcel_selectors::parser::Selector<'i, Selectors>>),
  Global(Box<parcel_selectors::parser::Selector<'i, Selectors>>),

  // https://webkit.org/blog/363/styling-scrollbars/
  WebKitScrollbar(WebKitScrollbarPseudoClass),

  Custom(CowArcStr<'i>),
  CustomFunction(CowArcStr<'i>, TokenList<'i>),
}

/// https://webkit.org/blog/363/styling-scrollbars/
#[derive(Clone, Eq, PartialEq)]
pub enum WebKitScrollbarPseudoClass {
  Horizontal,
  Vertical,
  Decrement,
  Increment,
  Start,
  End,
  DoubleButton,
  SingleButton,
  NoButton,
  CornerPresent,
  WindowInactive,
}

impl<'i> parcel_selectors::parser::NonTSPseudoClass<'i> for PseudoClass<'i> {
  type Impl = Selectors;

  fn is_active_or_hover(&self) -> bool {
    matches!(*self, PseudoClass::Active | PseudoClass::Hover)
  }

  fn is_user_action_state(&self) -> bool {
    matches!(
      *self,
      PseudoClass::Active
        | PseudoClass::Hover
        | PseudoClass::Focus
        | PseudoClass::FocusWithin
        | PseudoClass::FocusVisible
    )
  }

  fn is_valid_before_webkit_scrollbar(&self) -> bool {
    !matches!(*self, PseudoClass::WebKitScrollbar(..))
  }

  fn is_valid_after_webkit_scrollbar(&self) -> bool {
    // https://github.com/WebKit/WebKit/blob/02fbf9b7aa435edb96cbf563a8d4dcf1aa73b4b3/Source/WebCore/css/parser/CSSSelectorParser.cpp#L285
    matches!(
      *self,
      PseudoClass::WebKitScrollbar(..)
        | PseudoClass::Enabled
        | PseudoClass::Disabled
        | PseudoClass::Hover
        | PseudoClass::Active
    )
  }
}

impl<'i> cssparser::ToCss for PseudoClass<'i> {
  fn to_css<W>(&self, _: &mut W) -> std::fmt::Result
  where
    W: fmt::Write,
  {
    unreachable!()
  }
}

impl<'a, 'i> ToCssWithContext<'a, 'i> for PseudoClass<'i> {
  fn to_css_with_context<W>(
    &self,
    dest: &mut Printer<W>,
    context: Option<&StyleContext<'a, 'i>>,
  ) -> Result<(), PrinterError>
  where
    W: fmt::Write,
  {
    use PseudoClass::*;
    match &self {
      Lang(lang) => {
        dest.write_str(":lang(")?;
        let mut first = true;
        for lang in lang {
          if first {
            first = false;
          } else {
            dest.delim(',', false)?;
          }
          serialize_identifier(lang, dest)?;
        }
        return dest.write_str(")");
      }
      Dir(dir) => {
        dest.write_str(":dir(")?;
        dir.to_css(dest)?;
        return dest.write_str(")");
      }
      _ => {}
    }

    macro_rules! write_prefixed {
      ($prefix: ident, $val: expr) => {{
        dest.write_char(':')?;
        // If the printer has a vendor prefix override, use that.
        let vp = if !dest.vendor_prefix.is_empty() {
          dest.vendor_prefix
        } else {
          *$prefix
        };
        vp.to_css(dest)?;
        dest.write_str($val)
      }};
    }

    macro_rules! pseudo {
      ($key: ident, $s: literal) => {{
        let class = if let Some(pseudo_classes) = &dest.pseudo_classes {
          pseudo_classes.$key
        } else {
          None
        };

        if let Some(class) = class {
          dest.write_char('.')?;
          dest.write_ident(class)
        } else {
          dest.write_str($s)
        }
      }};
    }

    match &self {
      // https://drafts.csswg.org/selectors-4/#useraction-pseudos
      Hover => pseudo!(hover, ":hover"),
      Active => pseudo!(active, ":active"),
      Focus => pseudo!(focus, ":focus"),
      FocusVisible => pseudo!(focus_visible, ":focus-visible"),
      FocusWithin => pseudo!(focus_within, ":focus-within"),

      // https://drafts.csswg.org/selectors-4/#time-pseudos
      Current => dest.write_str(":current"),
      Past => dest.write_str(":past"),
      Future => dest.write_str(":future"),

      // https://drafts.csswg.org/selectors-4/#resource-pseudos
      Playing => dest.write_str(":playing"),
      Paused => dest.write_str(":paused"),
      Seeking => dest.write_str(":seeking"),
      Buffering => dest.write_str(":buffering"),
      Stalled => dest.write_str(":stalled"),
      Muted => dest.write_str(":muted"),
      VolumeLocked => dest.write_str(":volume-locked"),

      // https://fullscreen.spec.whatwg.org/#:fullscreen-pseudo-class
      Fullscreen(prefix) => {
        dest.write_char(':')?;
        let vp = if !dest.vendor_prefix.is_empty() {
          dest.vendor_prefix
        } else {
          *prefix
        };
        vp.to_css(dest)?;
        if vp == VendorPrefix::WebKit || vp == VendorPrefix::Moz {
          dest.write_str("full-screen")
        } else {
          dest.write_str("fullscreen")
        }
      }

      // https://drafts.csswg.org/selectors-4/#the-defined-pseudo
      Defined => dest.write_str(":defined"),

      // https://drafts.csswg.org/selectors-4/#location
      AnyLink(prefix) => write_prefixed!(prefix, "any-link"),
      Link => dest.write_str(":link"),
      LocalLink => dest.write_str(":local-link"),
      Target => dest.write_str(":target"),
      TargetWithin => dest.write_str(":target-within"),
      Visited => dest.write_str(":visited"),

      // https://drafts.csswg.org/selectors-4/#input-pseudos
      Enabled => dest.write_str(":enabled"),
      Disabled => dest.write_str(":disabled"),
      ReadOnly(prefix) => write_prefixed!(prefix, "read-only"),
      ReadWrite(prefix) => write_prefixed!(prefix, "read-write"),
      PlaceholderShown(prefix) => write_prefixed!(prefix, "placeholder-shown"),
      Default => dest.write_str(":default"),
      Checked => dest.write_str(":checked"),
      Indeterminate => dest.write_str(":indeterminate"),
      Blank => dest.write_str(":blank"),
      Valid => dest.write_str(":valid"),
      Invalid => dest.write_str(":invalid"),
      InRange => dest.write_str(":in-range"),
      OutOfRange => dest.write_str(":out-of-range"),
      Required => dest.write_str(":required"),
      Optional => dest.write_str(":optional"),
      UserValid => dest.write_str(":user-valid"),
      UserInvalid => dest.write_str(":user-invalid"),

      // https://html.spec.whatwg.org/multipage/semantics-other.html#selector-autofill
      Autofill(prefix) => write_prefixed!(prefix, "autofill"),

      Local(selector) => selector.to_css_with_context(dest, context),
      Global(selector) => {
        let css_module = std::mem::take(&mut dest.css_module);
        selector.to_css_with_context(dest, context)?;
        dest.css_module = css_module;
        Ok(())
      }

      // https://webkit.org/blog/363/styling-scrollbars/
      WebKitScrollbar(s) => {
        use WebKitScrollbarPseudoClass::*;
        dest.write_str(match s {
          Horizontal => ":horizontal",
          Vertical => ":vertical",
          Decrement => ":decrement",
          Increment => ":increment",
          Start => ":start",
          End => ":end",
          DoubleButton => ":double-button",
          SingleButton => ":single-button",
          NoButton => ":no-button",
          CornerPresent => ":corner-present",
          WindowInactive => ":window-inactive",
        })
      }

      Lang(_) | Dir(_) => unreachable!(),
      Custom(val) => {
        dest.write_char(':')?;
        return dest.write_str(&val);
      }
      CustomFunction(name, args) => {
        dest.write_char(':')?;
        dest.write_str(name)?;
        dest.write_char('(')?;
        args.to_css(dest, false)?;
        dest.write_char(')')
      }
    }
  }
}

impl<'i> PseudoClass<'i> {
  pub fn is_equivalent(&self, other: &PseudoClass<'i>) -> bool {
    use PseudoClass::*;
    match (self, other) {
      (Fullscreen(_), Fullscreen(_))
      | (AnyLink(_), AnyLink(_))
      | (ReadOnly(_), ReadOnly(_))
      | (ReadWrite(_), ReadWrite(_))
      | (PlaceholderShown(_), PlaceholderShown(_))
      | (Autofill(_), Autofill(_)) => true,
      (a, b) => a == b,
    }
  }

  pub fn get_prefix(&self) -> VendorPrefix {
    use PseudoClass::*;
    match self {
      Fullscreen(p) | AnyLink(p) | ReadOnly(p) | ReadWrite(p) | PlaceholderShown(p) | Autofill(p) => *p,
      _ => VendorPrefix::empty(),
    }
  }

  pub fn get_necessary_prefixes(&self, targets: Browsers) -> VendorPrefix {
    use crate::prefixes::Feature;
    use PseudoClass::*;
    let feature = match self {
      Fullscreen(p) if *p == VendorPrefix::None => Feature::PseudoClassFullscreen,
      AnyLink(p) if *p == VendorPrefix::None => Feature::PseudoClassAnyLink,
      ReadOnly(p) if *p == VendorPrefix::None => Feature::PseudoClassReadOnly,
      ReadWrite(p) if *p == VendorPrefix::None => Feature::PseudoClassReadWrite,
      PlaceholderShown(p) if *p == VendorPrefix::None => Feature::PseudoClassPlaceholderShown,
      Autofill(p) if *p == VendorPrefix::None => Feature::PseudoClassAutofill,
      _ => return VendorPrefix::empty(),
    };

    feature.prefixes_for(targets)
  }
}

#[derive(PartialEq, Clone, Debug)]
pub enum PseudoElement<'i> {
  After,
  Before,
  FirstLine,
  FirstLetter,
  Selection(VendorPrefix),
  Placeholder(VendorPrefix),
  Marker,
  Backdrop(VendorPrefix),
  FileSelectorButton(VendorPrefix),
  WebKitScrollbar(WebKitScrollbarPseudoElement),
  Cue,
  CueRegion,
  CueFunction(Box<Selector<'i, Selectors>>),
  CueRegionFunction(Box<Selector<'i, Selectors>>),
  Custom(CowArcStr<'i>),
  CustomFunction(CowArcStr<'i>, TokenList<'i>),
}

#[derive(PartialEq, Eq, Clone, Debug, Hash)]
pub enum WebKitScrollbarPseudoElement {
  /// ::-webkit-scrollbar
  Scrollbar,
  /// ::-webkit-scrollbar-button
  Button,
  /// ::-webkit-scrollbar-track
  Track,
  /// ::-webkit-scrollbar-track-piece
  TrackPiece,
  /// ::-webkit-scrollbar-thumb
  Thumb,
  /// ::-webkit-scrollbar-corner
  Corner,
  /// ::-webkit-resizer
  Resizer,
}

impl<'i> cssparser::ToCss for PseudoElement<'i> {
  fn to_css<W>(&self, _: &mut W) -> std::fmt::Result
  where
    W: fmt::Write,
  {
    unreachable!();
  }
}

impl<'i> ToCss for PseudoElement<'i> {
  fn to_css<W>(&self, dest: &mut Printer<W>) -> Result<(), PrinterError>
  where
    W: fmt::Write,
  {
    use PseudoElement::*;

    macro_rules! write_prefix {
      ($prefix: ident) => {{
        dest.write_str("::")?;
        // If the printer has a vendor prefix override, use that.
        let vp = if !dest.vendor_prefix.is_empty() {
          dest.vendor_prefix
        } else {
          *$prefix
        };
        vp.to_css(dest)?;
        vp
      }};
    }

    macro_rules! write_prefixed {
      ($prefix: ident, $val: expr) => {{
        write_prefix!($prefix);
        dest.write_str($val)
      }};
    }

    match &self {
      // CSS2 pseudo elements support a single colon syntax in addition
      // to the more correct double colon for other pseudo elements.
      // We use that here because it's supported everywhere and is shorter.
      After => dest.write_str(":after"),
      Before => dest.write_str(":before"),
      FirstLine => dest.write_str(":first-line"),
      FirstLetter => dest.write_str(":first-letter"),
      Marker => dest.write_str("::marker"),
      Selection(prefix) => write_prefixed!(prefix, "selection"),
      Cue => dest.write_str("::cue"),
      CueRegion => dest.write_str("::cue-region"),
      CueFunction(selector) => {
        dest.write_str("::cue(")?;
        selector.to_css_with_context(dest, None)?;
        dest.write_char(')')
      }
      CueRegionFunction(selector) => {
        dest.write_str("::cue-region(")?;
        selector.to_css_with_context(dest, None)?;
        dest.write_char(')')
      }
      Placeholder(prefix) => {
        let vp = write_prefix!(prefix);
        if vp == VendorPrefix::WebKit || vp == VendorPrefix::Ms {
          dest.write_str("input-placeholder")
        } else {
          dest.write_str("placeholder")
        }
      }
      Backdrop(prefix) => write_prefixed!(prefix, "backdrop"),
      FileSelectorButton(prefix) => {
        let vp = write_prefix!(prefix);
        if vp == VendorPrefix::WebKit {
          dest.write_str("file-upload-button")
        } else if vp == VendorPrefix::Ms {
          dest.write_str("browse")
        } else {
          dest.write_str("file-selector-button")
        }
      }
      WebKitScrollbar(s) => {
        use WebKitScrollbarPseudoElement::*;
        dest.write_str(match s {
          Scrollbar => "::-webkit-scrollbar",
          Button => "::-webkit-scrollbar-button",
          Track => "::-webkit-scrollbar-track",
          TrackPiece => "::-webkit-scrollbar-track-piece",
          Thumb => "::-webkit-scrollbar-thumb",
          Corner => "::-webkit-scrollbar-corner",
          Resizer => "::-webkit-resizer",
        })
      }
      Custom(val) => {
        dest.write_str("::")?;
        return dest.write_str(val);
      }
      CustomFunction(name, args) => {
        dest.write_str("::")?;
        dest.write_str(name)?;
        dest.write_char('(')?;
        args.to_css(dest, false)?;
        dest.write_char(')')
      }
    }
  }
}

impl<'i> parcel_selectors::parser::PseudoElement<'i> for PseudoElement<'i> {
  type Impl = Selectors;

  fn accepts_state_pseudo_classes(&self) -> bool {
    // Be lenient.
    true
  }

  fn valid_after_slotted(&self) -> bool {
    // ::slotted() should support all tree-abiding pseudo-elements, see
    // https://drafts.csswg.org/css-scoping/#slotted-pseudo
    // https://drafts.csswg.org/css-pseudo-4/#treelike
    matches!(
      *self,
      PseudoElement::Before
        | PseudoElement::After
        | PseudoElement::Marker
        | PseudoElement::Placeholder(_)
        | PseudoElement::FileSelectorButton(_)
    )
  }

  fn is_webkit_scrollbar(&self) -> bool {
    matches!(*self, PseudoElement::WebKitScrollbar(..))
  }
}

impl<'i> PseudoElement<'i> {
  pub fn is_equivalent(&self, other: &PseudoElement<'i>) -> bool {
    use PseudoElement::*;
    match (self, other) {
      (Selection(_), Selection(_))
      | (Placeholder(_), Placeholder(_))
      | (Backdrop(_), Backdrop(_))
      | (FileSelectorButton(_), FileSelectorButton(_)) => true,
      (a, b) => a == b,
    }
  }

  pub fn get_prefix(&self) -> VendorPrefix {
    use PseudoElement::*;
    match self {
      Selection(p) | Placeholder(p) | Backdrop(p) | FileSelectorButton(p) => *p,
      _ => VendorPrefix::empty(),
    }
  }

  pub fn get_necessary_prefixes(&self, targets: Browsers) -> VendorPrefix {
    use crate::prefixes::Feature;
    use PseudoElement::*;
    let feature = match self {
      Selection(p) if *p == VendorPrefix::None => Feature::PseudoElementSelection,
      Placeholder(p) if *p == VendorPrefix::None => Feature::PseudoElementPlaceholder,
      Backdrop(p) if *p == VendorPrefix::None => Feature::PseudoElementBackdrop,
      FileSelectorButton(p) if *p == VendorPrefix::None => Feature::PseudoElementFileSelectorButton,
      _ => return VendorPrefix::empty(),
    };

    feature.prefixes_for(targets)
  }
}

impl<'a, 'i> ToCssWithContext<'a, 'i> for SelectorList<'i, Selectors> {
  fn to_css_with_context<W>(
    &self,
    dest: &mut Printer<W>,
    context: Option<&StyleContext<'a, 'i>>,
  ) -> Result<(), PrinterError>
  where
    W: fmt::Write,
  {
    serialize_selector_list(self.0.iter(), dest, context, false)
  }
}

impl ToCss for Combinator {
  fn to_css<W>(&self, dest: &mut Printer<W>) -> Result<(), PrinterError>
  where
    W: fmt::Write,
  {
    match *self {
      Combinator::Child => dest.delim('>', true),
      Combinator::Descendant => dest.write_str(" "),
      Combinator::NextSibling => dest.delim('+', true),
      Combinator::LaterSibling => dest.delim('~', true),
      Combinator::PseudoElement | Combinator::Part | Combinator::SlotAssignment => Ok(()),
    }
  }
}

// Copied from the selectors crate and modified to override to_css implementation.
impl<'a, 'i> ToCssWithContext<'a, 'i> for parcel_selectors::parser::Selector<'i, Selectors> {
  fn to_css_with_context<W>(
    &self,
    dest: &mut Printer<W>,
    context: Option<&StyleContext<'a, 'i>>,
  ) -> Result<(), PrinterError>
  where
    W: fmt::Write,
  {
    serialize_selector(self, dest, context, false)
  }
}

fn serialize_selector<'a, 'i, W>(
  selector: &parcel_selectors::parser::Selector<'i, Selectors>,
  dest: &mut Printer<W>,
  context: Option<&StyleContext<'a, 'i>>,
  mut is_relative: bool,
) -> Result<(), PrinterError>
where
  W: fmt::Write,
{
  use parcel_selectors::parser::*;
  // Compound selectors invert the order of their contents, so we need to
  // undo that during serialization.
  //
  // This two-iterator strategy involves walking over the selector twice.
  // We could do something more clever, but selector serialization probably
  // isn't hot enough to justify it, and the stringification likely
  // dominates anyway.
  //
  // NB: A parse-order iterator is a Rev<>, which doesn't expose as_slice(),
  // which we need for |split|. So we split by combinators on a match-order
  // sequence and then reverse.

  let mut combinators = selector.iter_raw_match_order().rev().filter_map(|x| x.as_combinator());
  let compound_selectors = selector.iter_raw_match_order().as_slice().split(|x| x.is_combinator()).rev();

  let mut combinators_exhausted = false;
  for mut compound in compound_selectors {
    debug_assert!(!combinators_exhausted);

    // Skip implicit :scope in relative selectors (e.g. :has(:scope > foo) -> :has(> foo))
    if is_relative && matches!(compound.get(0), Some(Component::Scope)) {
      if let Some(combinator) = combinators.next() {
        combinator.to_css(dest)?;
      }
      compound = &compound[1..];
      is_relative = false;
    }

    // https://drafts.csswg.org/cssom/#serializing-selectors
    if compound.is_empty() {
      continue;
    }

    let has_leading_nesting = matches!(compound[0], Component::Nesting);
    let first_index = if has_leading_nesting { 1 } else { 0 };

    // 1. If there is only one simple selector in the compound selectors
    //    which is a universal selector, append the result of
    //    serializing the universal selector to s.
    //
    // Check if `!compound.empty()` first--this can happen if we have
    // something like `... > ::before`, because we store `>` and `::`
    // both as combinators internally.
    //
    // If we are in this case, after we have serialized the universal
    // selector, we skip Step 2 and continue with the algorithm.
    let (can_elide_namespace, first_non_namespace) = match compound.get(first_index) {
      Some(Component::ExplicitAnyNamespace)
      | Some(Component::ExplicitNoNamespace)
      | Some(Component::Namespace(..)) => (false, first_index + 1),
      Some(Component::DefaultNamespace(..)) => (true, first_index + 1),
      _ => (true, first_index),
    };
    let mut perform_step_2 = true;
    let next_combinator = combinators.next();
    if first_non_namespace == compound.len() - 1 {
      match (next_combinator, &compound[first_non_namespace]) {
        // We have to be careful here, because if there is a
        // pseudo element "combinator" there isn't really just
        // the one simple selector. Technically this compound
        // selector contains the pseudo element selector as well
        // -- Combinator::PseudoElement, just like
        // Combinator::SlotAssignment, don't exist in the
        // spec.
        (Some(Combinator::PseudoElement), _) | (Some(Combinator::SlotAssignment), _) => (),
        (_, &Component::ExplicitUniversalType) => {
          // Iterate over everything so we serialize the namespace
          // too.
          let mut iter = compound.iter();
          let swap_nesting = has_leading_nesting && context.is_some();
          if swap_nesting {
            // Swap nesting and type selector (e.g. &div -> div&).
            iter.next();
          }

          for simple in iter {
            simple.to_css_with_context(dest, context)?;
          }

          if swap_nesting {
            serialize_nesting(dest, context, false)?;
          }

          // Skip step 2, which is an "otherwise".
          perform_step_2 = false;
        }
        _ => (),
      }
    }

    // 2. Otherwise, for each simple selector in the compound selectors
    //    that is not a universal selector of which the namespace prefix
    //    maps to a namespace that is not the default namespace
    //    serialize the simple selector and append the result to s.
    //
    // See https://github.com/w3c/csswg-drafts/issues/1606, which is
    // proposing to change this to match up with the behavior asserted
    // in cssom/serialize-namespaced-type-selectors.html, which the
    // following code tries to match.
    if perform_step_2 {
      let mut iter = compound.iter();
      if has_leading_nesting && context.is_some() && is_type_selector(compound.get(first_non_namespace)) {
        // Swap nesting and type selector (e.g. &div -> div&).
        // This ensures that the compiled selector is valid. e.g. (div.foo is valid, .foodiv is not).
        let nesting = iter.next().unwrap();
        let local = iter.next().unwrap();
        local.to_css_with_context(dest, context)?;

        // Also check the next item in case of namespaces.
        if first_non_namespace > first_index {
          let local = iter.next().unwrap();
          local.to_css_with_context(dest, context)?;
        }

        nesting.to_css_with_context(dest, context)?;
      } else if has_leading_nesting && context.is_some() {
        // Nesting selector may serialize differently if it is leading, due to type selectors.
        iter.next();
        serialize_nesting(dest, context, true)?;
      }

      for simple in iter {
        if let Component::ExplicitUniversalType = *simple {
          // Can't have a namespace followed by a pseudo-element
          // selector followed by a universal selector in the same
          // compound selector, so we don't have to worry about the
          // real namespace being in a different `compound`.
          if can_elide_namespace {
            continue;
          }
        }
        simple.to_css_with_context(dest, context)?;
      }
    }

    // 3. If this is not the last part of the chain of the selector
    //    append a single SPACE (U+0020), followed by the combinator
    //    ">", "+", "~", ">>", "||", as appropriate, followed by another
    //    single SPACE (U+0020) if the combinator was not whitespace, to
    //    s.
    match next_combinator {
      Some(c) => c.to_css(dest)?,
      None => combinators_exhausted = true,
    };

    // 4. If this is the last part of the chain of the selector and
    //    there is a pseudo-element, append "::" followed by the name of
    //    the pseudo-element, to s.
    //
    // (we handle this above)
  }

  Ok(())
}

impl<'a, 'i> ToCssWithContext<'a, 'i> for Component<'i, Selectors> {
  fn to_css_with_context<W>(
    &self,
    dest: &mut Printer<W>,
    context: Option<&StyleContext<'a, 'i>>,
  ) -> Result<(), PrinterError>
  where
    W: fmt::Write,
  {
    use Component::*;
    match &self {
      Combinator(ref c) => c.to_css(dest),
      AttributeInNoNamespace {
        ref local_name,
        operator,
        ref value,
        case_sensitivity,
        ..
      } => {
        use cssparser::ToCss;
        dest.write_char('[')?;
        local_name.to_css(dest)?;
        cssparser::ToCss::to_css(operator, dest)?;

        if dest.minify {
          // Serialize as both an identifier and a string and choose the shorter one.
          let mut id = String::new();
          value.write_identifier(&mut id)?;

          let mut s = String::new();
          value.to_css(&mut s)?;

          if id.len() > 0 && id.len() < s.len() + 2 {
            dest.write_str(&id)?;
          } else {
            dest.write_char('"')?;
            dest.write_str(&s)?;
            dest.write_char('"')?;
          }
        } else {
          dest.write_char('"')?;
          value.to_css(dest)?;
          dest.write_char('"')?;
        }

        match case_sensitivity {
          parcel_selectors::attr::ParsedCaseSensitivity::CaseSensitive
          | parcel_selectors::attr::ParsedCaseSensitivity::AsciiCaseInsensitiveIfInHtmlElementInHtmlDocument => {}
          parcel_selectors::attr::ParsedCaseSensitivity::AsciiCaseInsensitive => dest.write_str(" i")?,
          parcel_selectors::attr::ParsedCaseSensitivity::ExplicitCaseSensitive => dest.write_str(" s")?,
        }
        dest.write_char(']')
      }
      Is(ref list) | Where(ref list) | Negation(ref list) | Any(_, ref list) => {
        match *self {
          Where(..) => dest.write_str(":where(")?,
          Is(..) => {
            let vp = dest.vendor_prefix;
            if vp.intersects(VendorPrefix::WebKit | VendorPrefix::Moz) {
              dest.write_char(':')?;
              vp.to_css(dest)?;
              dest.write_str("any(")?;
            } else {
              dest.write_str(":is(")?;
            }
          }
          Negation(..) => return serialize_negation(list.iter(), dest, context),
          Any(ref prefix, ..) => {
            dest.write_char(':')?;
            prefix.to_css(dest)?;
            dest.write_str("any(")?;
          }
          _ => unreachable!(),
        }
        serialize_selector_list(list.iter(), dest, context, false)?;
        dest.write_str(")")
      }
      Has(ref list) => {
        dest.write_str(":has(")?;
        serialize_selector_list(list.iter(), dest, context, true)?;
        dest.write_str(")")
      }
      NonTSPseudoClass(pseudo) => pseudo.to_css_with_context(dest, context),
      PseudoElement(pseudo) => pseudo.to_css(dest),
      Nesting => serialize_nesting(dest, context, false),
      Class(ref class) => {
        dest.write_char('.')?;
        dest.write_ident(&class.0)
      }
      ID(ref id) => {
        dest.write_char('#')?;
        dest.write_ident(&id.0)
      }
      _ => {
        cssparser::ToCss::to_css(self, dest)?;
        Ok(())
      }
    }
  }
}

fn serialize_nesting<W>(
  dest: &mut Printer<W>,
  context: Option<&StyleContext>,
  first: bool,
) -> Result<(), PrinterError>
where
  W: fmt::Write,
{
  if let Some(ctx) = context {
    // If there's only one simple selector, just serialize it directly.
    // Otherwise, use an :is() pseudo class.
    // Type selectors are only allowed at the start of a compound selector,
    // so use :is() if that is not the case.
    if ctx.rule.selectors.0.len() == 1
      && (first || (!has_type_selector(&ctx.rule.selectors.0[0]) && is_simple(&ctx.rule.selectors.0[0])))
    {
      ctx.rule.selectors.0.first().unwrap().to_css_with_context(dest, ctx.parent)
    } else {
      dest.write_str(":is(")?;
      serialize_selector_list(ctx.rule.selectors.0.iter(), dest, ctx.parent, false)?;
      dest.write_char(')')
    }
  } else {
    dest.write_char('&')
  }
}

#[inline]
fn has_type_selector(selector: &parcel_selectors::parser::Selector<Selectors>) -> bool {
  let mut iter = selector.iter_raw_parse_order_from(0);
  let first = iter.next();
  if is_namespace(first) {
    is_type_selector(iter.next())
  } else {
    is_type_selector(first)
  }
}

#[inline]
fn is_simple(selector: &parcel_selectors::parser::Selector<Selectors>) -> bool {
  !selector.iter_raw_match_order().any(|component| component.is_combinator())
}

#[inline]
fn is_type_selector(component: Option<&Component<Selectors>>) -> bool {
  matches!(
    component,
    Some(Component::LocalName(_)) | Some(Component::ExplicitUniversalType)
  )
}

#[inline]
fn is_namespace(component: Option<&Component<Selectors>>) -> bool {
  matches!(
    component,
    Some(Component::ExplicitAnyNamespace)
      | Some(Component::ExplicitNoNamespace)
      | Some(Component::Namespace(..))
      | Some(Component::DefaultNamespace(_))
  )
}

fn serialize_selector_list<'a, 'i: 'a, I, W>(
  iter: I,
  dest: &mut Printer<W>,
  context: Option<&StyleContext<'_, 'i>>,
  is_relative: bool,
) -> Result<(), PrinterError>
where
  I: Iterator<Item = &'a Selector<'i, Selectors>>,
  W: fmt::Write,
{
  let mut first = true;
  for selector in iter {
    if !first {
      dest.delim(',', false)?;
    }
    first = false;
    serialize_selector(selector, dest, context, is_relative)?;
  }
  Ok(())
}

fn serialize_negation<'a, 'i: 'a, I, W>(
  iter: I,
  dest: &mut Printer<W>,
  context: Option<&StyleContext<'_, 'i>>,
) -> Result<(), PrinterError>
where
  I: Iterator<Item = &'a Selector<'i, Selectors>>,
  W: fmt::Write,
{
  // Downlevel :not(.a, .b) -> :not(.a):not(.b) if not list is unsupported.
  let is_supported = if let Some(targets) = dest.targets {
    Feature::CssNotSelList.is_compatible(targets)
  } else {
    true
  };

  if is_supported {
    dest.write_str(":not(")?;
    serialize_selector_list(iter, dest, context, false)?;
    dest.write_char(')')?;
  } else {
    for selector in iter {
      dest.write_str(":not(")?;
      selector.to_css_with_context(dest, context)?;
      dest.write_char(')')?;
    }
  }

  Ok(())
}

pub fn is_compatible(selectors: &SelectorList<Selectors>, targets: Option<Browsers>) -> bool {
  for selector in &selectors.0 {
    let iter = selector.iter();
    for component in iter {
      let feature = match component {
        Component::ID(_) | Component::Class(_) | Component::LocalName(_) => continue,

        Component::ExplicitAnyNamespace
        | Component::ExplicitNoNamespace
        | Component::DefaultNamespace(_)
        | Component::Namespace(_, _) => Feature::CssNamespaces,

        Component::ExplicitUniversalType => Feature::CssSel2,

        Component::AttributeInNoNamespaceExists { .. } => Feature::CssSel2,
        Component::AttributeInNoNamespace {
          operator,
          case_sensitivity,
          ..
        } => {
          if *case_sensitivity != ParsedCaseSensitivity::CaseSensitive {
            Feature::CssCaseInsensitive
          } else {
            match operator {
              AttrSelectorOperator::Equal | AttrSelectorOperator::Includes | AttrSelectorOperator::DashMatch => {
                Feature::CssSel2
              }
              AttrSelectorOperator::Prefix | AttrSelectorOperator::Substring | AttrSelectorOperator::Suffix => {
                Feature::CssSel3
              }
            }
          }
        }
        Component::AttributeOther(attr) => match attr.operation {
          ParsedAttrSelectorOperation::Exists => Feature::CssSel2,
          ParsedAttrSelectorOperation::WithValue {
            operator,
            case_sensitivity,
            ..
          } => {
            if case_sensitivity != ParsedCaseSensitivity::CaseSensitive {
              Feature::CssCaseInsensitive
            } else {
              match operator {
                AttrSelectorOperator::Equal | AttrSelectorOperator::Includes | AttrSelectorOperator::DashMatch => {
                  Feature::CssSel2
                }
                AttrSelectorOperator::Prefix | AttrSelectorOperator::Substring | AttrSelectorOperator::Suffix => {
                  Feature::CssSel3
                }
              }
            }
          }
        },

        Component::FirstChild => Feature::CssSel2,

        Component::Empty
        | Component::FirstOfType
        | Component::LastChild
        | Component::LastOfType
        | Component::Negation(_)
        | Component::NthChild(_, _)
        | Component::NthLastChild(_, _)
        | Component::NthLastOfType(_, _)
        | Component::NthOfType(_, _)
        | Component::OnlyChild
        | Component::OnlyOfType
        | Component::Root => Feature::CssSel3,

        Component::Is(_) | Component::Nesting => Feature::CssMatchesPseudo,
        Component::Any(..) => Feature::AnyPseudo,
        Component::Has(_) => Feature::CssHas,

        Component::Scope | Component::Host(_) | Component::Slotted(_) => Feature::Shadowdomv1,

        Component::Part(_) | Component::Where(_) => return false, // TODO: find this data in caniuse-lite

        Component::NonTSPseudoClass(pseudo) => {
          match pseudo {
            PseudoClass::Link
            | PseudoClass::Visited
            | PseudoClass::Active
            | PseudoClass::Hover
            | PseudoClass::Focus
            | PseudoClass::Lang(_) => Feature::CssSel2,

            PseudoClass::Checked | PseudoClass::Disabled | PseudoClass::Enabled | PseudoClass::Target => {
              Feature::CssSel3
            }

            PseudoClass::AnyLink(prefix) if *prefix == VendorPrefix::None => Feature::CssAnyLink,
            PseudoClass::Indeterminate => Feature::CssIndeterminatePseudo,

            PseudoClass::Fullscreen(prefix) if *prefix == VendorPrefix::None => Feature::Fullscreen,

            PseudoClass::FocusVisible => Feature::CssFocusVisible,
            PseudoClass::FocusWithin => Feature::CssFocusWithin,
            PseudoClass::Default => Feature::CssDefaultPseudo,
            PseudoClass::Dir(_) => Feature::CssDirPseudo,
            PseudoClass::Optional => Feature::CssOptionalPseudo,
            PseudoClass::PlaceholderShown(prefix) if *prefix == VendorPrefix::None => Feature::CssPlaceholderShown,

            PseudoClass::ReadOnly(prefix) | PseudoClass::ReadWrite(prefix) if *prefix == VendorPrefix::None => {
              Feature::CssReadOnlyWrite
            }

            PseudoClass::Valid | PseudoClass::Invalid | PseudoClass::Required => Feature::FormValidation,

            PseudoClass::InRange | PseudoClass::OutOfRange => Feature::CssInOutOfRange,

            PseudoClass::Autofill(prefix) if *prefix == VendorPrefix::None => Feature::CssAutofill,

            // Experimental, no browser support.
            PseudoClass::Current
            | PseudoClass::Past
            | PseudoClass::Future
            | PseudoClass::Playing
            | PseudoClass::Paused
            | PseudoClass::Seeking
            | PseudoClass::Stalled
            | PseudoClass::Buffering
            | PseudoClass::Muted
            | PseudoClass::VolumeLocked
            | PseudoClass::TargetWithin
            | PseudoClass::LocalLink
            | PseudoClass::Blank
            | PseudoClass::UserInvalid
            | PseudoClass::UserValid
            | PseudoClass::Defined => return false,

            PseudoClass::Custom(_) | _ => return false,
          }
        }

        Component::PseudoElement(pseudo) => match pseudo {
          PseudoElement::After | PseudoElement::Before => Feature::CssGencontent,
          PseudoElement::FirstLine => Feature::CssFirstLine,
          PseudoElement::FirstLetter => Feature::CssFirstLetter,
          PseudoElement::Selection(prefix) if *prefix == VendorPrefix::None => Feature::CssSelection,
          PseudoElement::Placeholder(prefix) if *prefix == VendorPrefix::None => Feature::CssPlaceholder,
          PseudoElement::Marker => Feature::CssMarkerPseudo,
          PseudoElement::Backdrop(prefix) if *prefix == VendorPrefix::None => Feature::Dialog,
          PseudoElement::Cue => Feature::Cue,
          PseudoElement::CueFunction(_) => Feature::CueFunction,
          PseudoElement::Custom(_) | _ => return false,
        },

        Component::Combinator(combinator) => match combinator {
          Combinator::Child | Combinator::NextSibling => Feature::CssSel2,
          Combinator::LaterSibling => Feature::CssSel3,
          _ => continue,
        },
      };

      if let Some(targets) = targets {
        if !feature.is_compatible(targets) {
          return false;
        }
      } else {
        return false;
      }
    }
  }

  true
}

/// Returns whether two selector lists are equivalent, i.e. the same minus any vendor prefix differences.
pub fn is_equivalent<'i>(selectors: &SelectorList<'i, Selectors>, other: &SelectorList<'i, Selectors>) -> bool {
  if selectors.0.len() != other.0.len() {
    return false;
  }

  for (i, a) in selectors.0.iter().enumerate() {
    let b = &other.0[i];
    if a.len() != b.len() {
      return false;
    }

    for (a, b) in a.iter().zip(b.iter()) {
      let is_equivalent = match (a, b) {
        (Component::NonTSPseudoClass(a_ps), Component::NonTSPseudoClass(b_ps)) => a_ps.is_equivalent(b_ps),
        (Component::PseudoElement(a_pe), Component::PseudoElement(b_pe)) => a_pe.is_equivalent(b_pe),
        (a, b) => a == b,
      };

      if !is_equivalent {
        return false;
      }
    }
  }

  true
}

/// Returns the vendor prefix (if any) used in the given selector list.
/// If multiple vendor prefixes are seen, this is invalid, and an empty result is returned.
pub fn get_prefix(selectors: &SelectorList<Selectors>) -> VendorPrefix {
  let mut prefix = VendorPrefix::empty();
  for selector in &selectors.0 {
    for component in selector.iter() {
      let p = match component {
        // Return none rather than empty for these so that we call downlevel_selectors.
        Component::NonTSPseudoClass(PseudoClass::Lang(..))
        | Component::NonTSPseudoClass(PseudoClass::Dir(..))
        | Component::Is(..) => VendorPrefix::None,
        Component::NonTSPseudoClass(pc) => pc.get_prefix(),
        Component::PseudoElement(pe) => pe.get_prefix(),
        _ => VendorPrefix::empty(),
      };

      if !p.is_empty() {
        if prefix.is_empty() || prefix == p {
          prefix = p;
        } else {
          return VendorPrefix::empty();
        }
      }
    }
  }

  prefix
}

const RTL_LANGS: &[&str] = &[
  "ae", "ar", "arc", "bcc", "bqi", "ckb", "dv", "fa", "glk", "he", "ku", "mzn", "nqo", "pnb", "ps", "sd", "ug",
  "ur", "yi",
];

/// Downlevels the given selectors to be compatible with the given browser targets.
/// Returns the necessary vendor prefixes.
pub fn downlevel_selectors(selectors: &mut SelectorList<Selectors>, targets: Browsers) -> VendorPrefix {
  let mut necessary_prefixes = VendorPrefix::empty();
  for selector in &mut selectors.0 {
    for component in selector.iter_mut_raw_match_order() {
      necessary_prefixes |= downlevel_component(component, targets);
    }
  }

  necessary_prefixes
}

fn downlevel_component<'i>(component: &mut Component<'i, Selectors>, targets: Browsers) -> VendorPrefix {
  match component {
    Component::NonTSPseudoClass(pc) => {
      match pc {
        PseudoClass::Dir(dir) => {
          if !Feature::CssDirPseudo.is_compatible(targets) {
            *component = downlevel_dir(*dir, targets);
            downlevel_component(component, targets)
          } else {
            VendorPrefix::empty()
          }
        }
        PseudoClass::Lang(langs) => {
          // :lang() with multiple languages is not supported everywhere.
          // compile this to :is(:lang(a), :lang(b)) etc.
          if langs.len() > 1 && !Feature::LangList.is_compatible(targets) {
            *component = Component::Is(lang_list_to_selectors(&langs));
            downlevel_component(component, targets)
          } else {
            VendorPrefix::empty()
          }
        }
        _ => pc.get_necessary_prefixes(targets),
      }
    }
    Component::PseudoElement(pe) => pe.get_necessary_prefixes(targets),
    Component::Is(ref selectors) => {
      // Convert :is to :-webkit-any/:-moz-any if needed.
      // All selectors must be simple, no combinators are supported.
      if !Feature::CssMatchesPseudo.is_compatible(targets)
        && selectors.iter().all(|selector| !selector.has_combinator())
      {
        crate::prefixes::Feature::AnyPseudo.prefixes_for(targets)
      } else {
        VendorPrefix::empty()
      }
    }
    _ => VendorPrefix::empty(),
  }
}

fn lang_list_to_selectors<'i>(langs: &Vec<CowArcStr<'i>>) -> Box<[Selector<'i, Selectors>]> {
  langs
    .iter()
    .map(|lang| Selector::from_vec2(vec![Component::NonTSPseudoClass(PseudoClass::Lang(vec![lang.clone()]))]))
    .collect::<Vec<Selector<Selectors>>>()
    .into_boxed_slice()
}

fn downlevel_dir<'i>(dir: Direction, targets: Browsers) -> Component<'i, Selectors> {
  // Convert :dir to :lang. If supported, use a list of languages in a single :lang,
  // otherwise, use :is/:not, which may be further downleveled to e.g. :-webkit-any.
  let langs = RTL_LANGS.iter().map(|lang| (*lang).into()).collect();
  if Feature::LangList.is_compatible(targets) {
    let c = Component::NonTSPseudoClass(PseudoClass::Lang(langs));
    if dir == Direction::Ltr {
      Component::Negation(vec![Selector::from_vec2(vec![c])].into_boxed_slice())
    } else {
      c
    }
  } else {
    if dir == Direction::Ltr {
      Component::Negation(lang_list_to_selectors(&langs))
    } else {
      Component::Is(lang_list_to_selectors(&langs))
    }
  }
}

/// Determines whether a selector list contains only unused selectors.
/// A selector is considered unused if it contains a class or id component that exists in the set of unused symbols.
pub fn is_unused(
  selectors: &mut std::slice::Iter<Selector<Selectors>>,
  unused_symbols: &HashSet<String>,
  parent_is_unused: bool,
) -> bool {
  if unused_symbols.is_empty() {
    return false;
  }

  selectors.all(|selector| {
    for component in selector.iter_raw_match_order() {
      match component {
        Component::Class(name) | Component::ID(name) => {
          if unused_symbols.contains(&name.0.to_string()) {
            return true;
          }
        }
        Component::Is(is) | Component::Where(is) | Component::Any(_, is) => {
          if is_unused(&mut is.iter(), unused_symbols, parent_is_unused) {
            return true;
          }
        }
        Component::Nesting => {
          if parent_is_unused {
            return true;
          }
        }
        _ => {}
      }
    }

    false
  })
}

#[cfg(feature = "serde")]
pub fn serialize_selectors<S>(selectors: &SelectorList<Selectors>, s: S) -> Result<S::Ok, S::Error>
where
  S: serde::Serializer,
{
  use serde::Serialize;
  selectors
    .0
    .iter()
    .map(|selector| {
      let mut dest = String::new();
      let mut printer = Printer::new(&mut dest, PrinterOptions::default());
      serialize_selector(selector, &mut printer, None, false).unwrap();
      dest
    })
    .collect::<Vec<String>>()
    .serialize(s)
}

#[cfg(feature = "serde")]
pub fn deserialize_selectors<'i, 'de: 'i, D>(deserializer: D) -> Result<SelectorList<'i, Selectors>, D::Error>
where
  D: serde::Deserializer<'de>,
{
  use serde::Deserialize;

  let selector_parser = SelectorParser {
    default_namespace: &None,
    namespace_prefixes: &HashMap::new(),
    is_nesting_allowed: false,
    options: &ParserOptions::default(),
  };

  let selectors = Vec::<&'i str>::deserialize(deserializer)?
    .into_iter()
    .map(|selector| {
      let mut input = ParserInput::new(selector);
      let mut parser = Parser::new(&mut input);
      Selector::parse(&selector_parser, &mut parser).unwrap()
    })
    .collect();
  Ok(SelectorList(selectors))
}