/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */

//! Parsing of the stylesheet contents.

use crate::counter_style::{parse_counter_style_body, parse_counter_style_name_definition};
use crate::custom_properties::parse_name as parse_custom_property_name;
use crate::error_reporting::ContextualParseError;
use crate::font_face::parse_font_face_block;
use crate::media_queries::MediaList;
use crate::parser::{Parse, ParserContext};
use crate::properties::declaration_block::{
    parse_property_declaration_list, DeclarationParserState, PropertyDeclarationBlock,
};
use crate::properties_and_values::rule::{parse_property_block, PropertyRuleName};
use crate::selector_parser::{SelectorImpl, SelectorParser};
use crate::shared_lock::{Locked, SharedRwLock};
use crate::str::starts_with_ignore_ascii_case;
use crate::stylesheets::container_rule::{ContainerCondition, ContainerRule};
use crate::stylesheets::document_rule::DocumentCondition;
use crate::stylesheets::font_feature_values_rule::parse_family_name_list;
use crate::stylesheets::import_rule::{ImportLayer, ImportRule, ImportSupportsCondition};
use crate::stylesheets::keyframes_rule::parse_keyframe_list;
use crate::stylesheets::layer_rule::{LayerBlockRule, LayerName, LayerStatementRule};
use crate::stylesheets::scope_rule::{ScopeBounds, ScopeRule};
use crate::stylesheets::supports_rule::SupportsCondition;
use crate::stylesheets::{
    AllowImportRules, CorsMode, CssRule, CssRuleType, CssRuleTypes, CssRules, DocumentRule,
    FontFeatureValuesRule, FontPaletteValuesRule, KeyframesRule, MarginRule, MarginRuleType,
    MediaRule, NamespaceRule, PageRule, PageSelectors, RulesMutateError, StyleRule,
    StylesheetLoader, SupportsRule, StartingStyleRule, NestedDeclarationsRule, PositionTryRule
};
use crate::values::computed::font::FamilyName;
use crate::values::{CssUrl, CustomIdent, DashedIdent, KeyframesName};
use crate::{Atom, Namespace, Prefix};
use cssparser::{
    AtRuleParser, BasicParseError, BasicParseErrorKind, CowRcStr, DeclarationParser, Parser,
    ParserState, QualifiedRuleParser, RuleBodyItemParser, RuleBodyParser, SourceLocation,
    SourcePosition,
};
use selectors::parser::{ParseRelative, SelectorList};
use servo_arc::Arc;
use style_traits::{ParseError, StyleParseErrorKind};

/// The information we need particularly to do CSSOM insertRule stuff.
pub struct InsertRuleContext<'a> {
    /// The rule list we're about to insert into.
    pub rule_list: &'a [CssRule],
    /// The index we're about to get inserted at.
    pub index: usize,
    /// The containing rule types of our ancestors.
    pub containing_rule_types: CssRuleTypes,
    /// Rule type determining if and how we parse relative selector syntax.
    pub parse_relative_rule_type: Option<CssRuleType>,
}

impl<'a> InsertRuleContext<'a> {
    /// Returns the max rule state allowable for insertion at a given index in
    /// the rule list.
    pub fn max_rule_state_at_index(&self, index: usize) -> State {
        let rule = match self.rule_list.get(index) {
            Some(rule) => rule,
            None => return State::Body,
        };
        match rule {
            CssRule::Import(..) => State::Imports,
            CssRule::Namespace(..) => State::Namespaces,
            CssRule::LayerStatement(..) => {
                // If there are @import / @namespace after this layer, then
                // we're in the early-layers phase, otherwise we're in the body
                // and everything is fair game.
                let next_non_layer_statement_rule = self.rule_list[index + 1..]
                    .iter()
                    .find(|r| !matches!(*r, CssRule::LayerStatement(..)));
                if let Some(non_layer) = next_non_layer_statement_rule {
                    if matches!(*non_layer, CssRule::Import(..) | CssRule::Namespace(..)) {
                        return State::EarlyLayers;
                    }
                }
                State::Body
            },
            _ => State::Body,
        }
    }
}

/// The parser for the top-level rules in a stylesheet.
pub struct TopLevelRuleParser<'a, 'i> {
    /// A reference to the lock we need to use to create rules.
    pub shared_lock: &'a SharedRwLock,
    /// A reference to a stylesheet loader if applicable, for `@import` rules.
    pub loader: Option<&'a dyn StylesheetLoader>,
    /// The top-level parser context.
    pub context: ParserContext<'a>,
    /// The current state of the parser.
    pub state: State,
    /// Whether we have tried to parse was invalid due to being in the wrong
    /// place (e.g. an @import rule was found while in the `Body` state). Reset
    /// to `false` when `take_had_hierarchy_error` is called.
    pub dom_error: Option<RulesMutateError>,
    /// The info we need insert a rule in a list.
    pub insert_rule_context: Option<InsertRuleContext<'a>>,
    /// Whether @import rules will be allowed.
    pub allow_import_rules: AllowImportRules,
    /// Whether to keep declarations into first_declaration_block, rather than turning it into a
    /// nested declarations rule.
    pub wants_first_declaration_block: bool,
    /// The first declaration block, only relevant when wants_first_declaration_block is true.
    pub first_declaration_block: PropertyDeclarationBlock,
    /// Parser state for declaration blocks in either nested rules or style rules.
    pub declaration_parser_state: DeclarationParserState<'i>,
    /// State we keep around only for error reporting purposes. Right now that contains just the
    /// selectors stack for nesting, if any.
    ///
    /// TODO(emilio): This isn't populated properly for `insertRule()` but...
    pub error_reporting_state: Vec<SelectorList<SelectorImpl>>,
    /// The rules we've parsed so far.
    pub rules: Vec<CssRule>,
}

impl<'a, 'i> TopLevelRuleParser<'a, 'i> {
    #[inline]
    fn nested(&mut self) -> &mut NestedRuleParser<'a, 'i> {
        // SAFETY: NestedRuleParser is just a repr(transparent) wrapper over TopLevelRuleParser
        const_assert!(
            std::mem::size_of::<TopLevelRuleParser<'static, 'static>>() ==
                std::mem::size_of::<NestedRuleParser<'static, 'static>>()
        );
        const_assert!(
            std::mem::align_of::<TopLevelRuleParser<'static, 'static>>() ==
                std::mem::align_of::<NestedRuleParser<'static, 'static>>()
        );
        unsafe { &mut *(self as *mut _ as *mut NestedRuleParser<'a, 'i>) }
    }

    /// Returns the current state of the parser.
    #[inline]
    pub fn state(&self) -> State {
        self.state
    }

    /// If we're in a nested state, this returns whether declarations can be parsed. See
    /// RuleBodyItemParser::parse_declarations().
    #[inline]
    pub fn can_parse_declarations(&self) -> bool {
        // We also have to check for page rules here because we currently don't
        // have a bespoke parser for page rules, and parse them as though they
        // are style rules.
        self.in_style_or_page_rule()
    }

    #[inline]
    fn in_style_rule(&self) -> bool {
        self.context
            .nesting_context
            .rule_types
            .contains(CssRuleType::Style)
    }

    #[inline]
    fn in_page_rule(&self) -> bool {
        self.context
            .nesting_context
            .rule_types
            .contains(CssRuleType::Page)
    }

    #[inline]
    fn in_style_or_page_rule(&self) -> bool {
        let types = CssRuleTypes::from_bits(CssRuleType::Style.bit() | CssRuleType::Page.bit());
        self.context.nesting_context.rule_types.intersects(types)
    }

    /// Checks whether we can parse a rule that would transition us to
    /// `new_state`.
    ///
    /// This is usually a simple branch, but we may need more bookkeeping if
    /// doing `insertRule` from CSSOM.
    fn check_state(&mut self, new_state: State) -> bool {
        if self.state > new_state {
            self.dom_error = Some(RulesMutateError::HierarchyRequest);
            return false;
        }

        let ctx = match self.insert_rule_context {
            Some(ref ctx) => ctx,
            None => return true,
        };

        let max_rule_state = ctx.max_rule_state_at_index(ctx.index);
        if new_state > max_rule_state {
            self.dom_error = Some(RulesMutateError::HierarchyRequest);
            return false;
        }

        // If there's anything that isn't a namespace rule (or import rule, but
        // we checked that already at the beginning), reject with a
        // StateError.
        if new_state == State::Namespaces &&
            ctx.rule_list[ctx.index..]
                .iter()
                .any(|r| !matches!(*r, CssRule::Namespace(..)))
        {
            self.dom_error = Some(RulesMutateError::InvalidState);
            return false;
        }

        true
    }
}

/// The current state of the parser.
#[derive(Clone, Copy, Eq, Ord, PartialEq, PartialOrd)]
pub enum State {
    /// We haven't started parsing rules.
    Start = 1,
    /// We're parsing early `@layer` statement rules.
    EarlyLayers = 2,
    /// We're parsing `@import` and early `@layer` statement rules.
    Imports = 3,
    /// We're parsing `@namespace` rules.
    Namespaces = 4,
    /// We're parsing the main body of the stylesheet.
    Body = 5,
}

#[derive(Clone, Debug, MallocSizeOf, ToShmem)]
/// Vendor prefix.
pub enum VendorPrefix {
    /// -moz prefix.
    Moz,
    /// -webkit prefix.
    WebKit,
}

/// A rule prelude for at-rule with block.
pub enum AtRulePrelude {
    /// A @font-face rule prelude.
    FontFace,
    /// A @font-feature-values rule prelude, with its FamilyName list.
    FontFeatureValues(Vec<FamilyName>),
    /// A @font-palette-values rule prelude, with its identifier.
    FontPaletteValues(DashedIdent),
    /// A @counter-style rule prelude, with its counter style name.
    CounterStyle(CustomIdent),
    /// A @media rule prelude, with its media queries.
    Media(Arc<Locked<MediaList>>),
    /// A @container rule prelude.
    Container(Arc<ContainerCondition>),
    /// An @supports rule, with its conditional
    Supports(SupportsCondition),
    /// A @keyframes rule, with its animation name and vendor prefix if exists.
    Keyframes(KeyframesName, Option<VendorPrefix>),
    /// A @page rule prelude, with its page name if it exists.
    Page(PageSelectors),
    /// A @property rule prelude.
    Property(PropertyRuleName),
    /// A @document rule, with its conditional.
    Document(DocumentCondition),
    /// A @import rule prelude.
    Import(
        CssUrl,
        Arc<Locked<MediaList>>,
        Option<ImportSupportsCondition>,
        ImportLayer,
    ),
    /// A @margin rule prelude.
    Margin(MarginRuleType),
    /// A @namespace rule prelude.
    Namespace(Option<Prefix>, Namespace),
    /// A @layer rule prelude.
    Layer(Vec<LayerName>),
    /// A @scope rule prelude.
    Scope(ScopeBounds),
    /// A @starting-style prelude.
    StartingStyle,
    /// A @position-try prelude for Anchor Positioning.
    PositionTry(DashedIdent),
}

impl AtRulePrelude {
    fn name(&self) -> &'static str {
        match *self {
            Self::FontFace => "font-face",
            Self::FontFeatureValues(..) => "font-feature-values",
            Self::FontPaletteValues(..) => "font-palette-values",
            Self::CounterStyle(..) => "counter-style",
            Self::Media(..) => "media",
            Self::Container(..) => "container",
            Self::Supports(..) => "supports",
            Self::Keyframes(..) => "keyframes",
            Self::Page(..) => "page",
            Self::Property(..) => "property",
            Self::Document(..) => "-moz-document",
            Self::Import(..) => "import",
            Self::Margin(..) => "margin",
            Self::Namespace(..) => "namespace",
            Self::Layer(..) => "layer",
            Self::Scope(..) => "scope",
            Self::StartingStyle => "starting-style",
            Self::PositionTry(..) => "position-try",
        }
    }
}

impl<'a, 'i> AtRuleParser<'i> for TopLevelRuleParser<'a, 'i> {
    type Prelude = AtRulePrelude;
    type AtRule = SourcePosition;
    type Error = StyleParseErrorKind<'i>;

    fn parse_prelude<'t>(
        &mut self,
        name: CowRcStr<'i>,
        input: &mut Parser<'i, 't>,
    ) -> Result<AtRulePrelude, ParseError<'i>> {
        match_ignore_ascii_case! { &*name,
            "import" => {
                if !self.check_state(State::Imports) {
                    return Err(input.new_custom_error(StyleParseErrorKind::UnexpectedImportRule))
                }

                if let AllowImportRules::No = self.allow_import_rules {
                    return Err(input.new_custom_error(StyleParseErrorKind::DisallowedImportRule))
                }

                // FIXME(emilio): We should always be able to have a loader
                // around! See bug 1533783.
                if self.loader.is_none() {
                    error!("Saw @import rule, but no way to trigger the load");
                    return Err(input.new_custom_error(StyleParseErrorKind::UnexpectedImportRule))
                }

                let url_string = input.expect_url_or_string()?.as_ref().to_owned();
                let url = CssUrl::parse_from_string(url_string, &self.context, CorsMode::None);

                let (layer, supports) = ImportRule::parse_layer_and_supports(input, &mut self.context);

                let media = MediaList::parse(&self.context, input);
                let media = Arc::new(self.shared_lock.wrap(media));

                return Ok(AtRulePrelude::Import(url, media, supports, layer));
            },
            "namespace" => {
                if !self.check_state(State::Namespaces) {
                    return Err(input.new_custom_error(StyleParseErrorKind::UnexpectedNamespaceRule))
                }

                let prefix = input.try_parse(|i| i.expect_ident_cloned())
                                  .map(|s| Prefix::from(s.as_ref())).ok();
                let maybe_namespace = match input.expect_url_or_string() {
                    Ok(url_or_string) => url_or_string,
                    Err(BasicParseError { kind: BasicParseErrorKind::UnexpectedToken(t), location }) => {
                        return Err(location.new_custom_error(StyleParseErrorKind::UnexpectedTokenWithinNamespace(t)))
                    }
                    Err(e) => return Err(e.into()),
                };
                let url = Namespace::from(maybe_namespace.as_ref());
                return Ok(AtRulePrelude::Namespace(prefix, url));
            },
            // @charset is removed by rust-cssparser if it’s the first rule in the stylesheet
            // anything left is invalid.
            "charset" => {
                self.dom_error = Some(RulesMutateError::HierarchyRequest);
                return Err(input.new_custom_error(StyleParseErrorKind::UnexpectedCharsetRule))
            },
            "layer" => {
                let state_to_check = if self.state <= State::EarlyLayers {
                    // The real state depends on whether there's a block or not.
                    // We don't know that yet, but the parse_block check deals
                    // with that.
                    State::EarlyLayers
                } else {
                    State::Body
                };
                if !self.check_state(state_to_check) {
                    return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
                }
            },
            _ => {
                // All other rules have blocks, so we do this check early in
                // parse_block instead.
            }
        }

        AtRuleParser::parse_prelude(self.nested(), name, input)
    }

    #[inline]
    fn parse_block<'t>(
        &mut self,
        prelude: AtRulePrelude,
        start: &ParserState,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self::AtRule, ParseError<'i>> {
        if !self.check_state(State::Body) {
            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }
        AtRuleParser::parse_block(self.nested(), prelude, start, input)?;
        self.state = State::Body;
        Ok(start.position())
    }

    #[inline]
    fn rule_without_block(
        &mut self,
        prelude: AtRulePrelude,
        start: &ParserState,
    ) -> Result<Self::AtRule, ()> {
        match prelude {
            AtRulePrelude::Import(url, media, supports, layer) => {
                let loader = self
                    .loader
                    .expect("Expected a stylesheet loader for @import");

                let import_rule = loader.request_stylesheet(
                    url,
                    start.source_location(),
                    &self.context,
                    &self.shared_lock,
                    media,
                    supports,
                    layer,
                );

                self.state = State::Imports;
                self.rules.push(CssRule::Import(import_rule))
            },
            AtRulePrelude::Namespace(prefix, url) => {
                let namespaces = self.context.namespaces.to_mut();
                let prefix = if let Some(prefix) = prefix {
                    namespaces.prefixes.insert(prefix.clone(), url.clone());
                    Some(prefix)
                } else {
                    namespaces.default = Some(url.clone());
                    None
                };

                self.state = State::Namespaces;
                self.rules.push(CssRule::Namespace(Arc::new(NamespaceRule {
                    prefix,
                    url,
                    source_location: start.source_location(),
                })));
            },
            AtRulePrelude::Layer(..) => {
                AtRuleParser::rule_without_block(self.nested(), prelude, start)?;
                if self.state <= State::EarlyLayers {
                    self.state = State::EarlyLayers;
                } else {
                    self.state = State::Body;
                }
            },
            _ => AtRuleParser::rule_without_block(self.nested(), prelude, start)?,
        };

        Ok(start.position())
    }
}

impl<'a, 'i> QualifiedRuleParser<'i> for TopLevelRuleParser<'a, 'i> {
    type Prelude = SelectorList<SelectorImpl>;
    type QualifiedRule = SourcePosition;
    type Error = StyleParseErrorKind<'i>;

    #[inline]
    fn parse_prelude<'t>(
        &mut self,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self::Prelude, ParseError<'i>> {
        if !self.check_state(State::Body) {
            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }

        QualifiedRuleParser::parse_prelude(self.nested(), input)
    }

    #[inline]
    fn parse_block<'t>(
        &mut self,
        prelude: Self::Prelude,
        start: &ParserState,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self::QualifiedRule, ParseError<'i>> {
        QualifiedRuleParser::parse_block(self.nested(), prelude, start, input)?;
        self.state = State::Body;
        Ok(start.position())
    }
}

#[repr(transparent)]
#[derive(Deref, DerefMut)]
struct NestedRuleParser<'a, 'i>(TopLevelRuleParser<'a, 'i>);

struct NestedParseResult {
    first_declaration_block: PropertyDeclarationBlock,
    rules: Vec<CssRule>,
}

impl<'a, 'i> NestedRuleParser<'a, 'i> {
    #[inline]
    fn parse_relative(&self) -> ParseRelative {
        self.context.nesting_context.parse_relative
    }

    // https://drafts.csswg.org/css-nesting/#conditionals
    //     In addition to nested style rules, this specification allows nested group rules inside
    //     of style rules: any at-rule whose body contains style rules can be nested inside of a
    //     style rule as well.
    fn at_rule_allowed(&self, prelude: &AtRulePrelude) -> bool {
        match prelude {
            AtRulePrelude::Media(..) |
            AtRulePrelude::Supports(..) |
            AtRulePrelude::Container(..) |
            AtRulePrelude::Document(..) |
            AtRulePrelude::Layer(..) |
            AtRulePrelude::Scope(..) |
            AtRulePrelude::StartingStyle => true,

            AtRulePrelude::Namespace(..) |
            AtRulePrelude::FontFace |
            AtRulePrelude::FontFeatureValues(..) |
            AtRulePrelude::FontPaletteValues(..) |
            AtRulePrelude::CounterStyle(..) |
            AtRulePrelude::Keyframes(..) |
            AtRulePrelude::Page(..) |
            AtRulePrelude::Property(..) |
            AtRulePrelude::Import(..) |
            AtRulePrelude::PositionTry(..) => !self.in_style_or_page_rule(),
            AtRulePrelude::Margin(..) => self.in_page_rule(),
        }
    }

    fn nest_for_rule<R>(&mut self, rule_type: CssRuleType, cb: impl FnOnce(&mut Self) -> R) -> R {
        let old = self.context.nesting_context.save(rule_type);
        let r = cb(self);
        self.context.nesting_context.restore(old);
        r
    }

    fn parse_nested_rules(
        &mut self,
        input: &mut Parser<'i, '_>,
        rule_type: CssRuleType,
        source_location: SourceLocation,
    ) -> Arc<Locked<CssRules>> {
        let rules = self.parse_nested(input, rule_type, /* wants_first_declaration_block = */ false, source_location).rules;
        CssRules::new(rules, &self.shared_lock)
    }

    fn parse_nested(
        &mut self,
        input: &mut Parser<'i, '_>,
        rule_type: CssRuleType,
        wants_first_declaration_block: bool,
        source_location: SourceLocation,
    ) -> NestedParseResult {
        debug_assert!(!self.wants_first_declaration_block, "Should've flushed previous declarations");
        self.nest_for_rule(rule_type, |parser| {
            parser.wants_first_declaration_block = wants_first_declaration_block;
            let parse_declarations = parser.parse_declarations();
            let mut rules = std::mem::take(&mut parser.rules);
            let mut first_declaration_block = std::mem::take(&mut parser.first_declaration_block);
            let mut iter = RuleBodyParser::new(input, parser);
            while let Some(result) = iter.next() {
                match result {
                    Ok(()) => {},
                    Err((error, slice)) => {
                        if parse_declarations {
                            let top = &mut **iter.parser;
                            top.declaration_parser_state
                                .did_error(&top.context, error, slice);
                        } else {
                            let location = error.location;
                            let error = ContextualParseError::InvalidRule(slice, error);
                            iter.parser.context.log_css_error(location, error);
                        }
                    },
                }
            }
            parser.flush_declarations(source_location);
            debug_assert!(
                !parser.wants_first_declaration_block,
                "Flushing declarations should take care of this."
            );
            debug_assert!(
                !parser.declaration_parser_state.has_parsed_declarations(),
                "Parsed but didn't consume declarations"
            );
            std::mem::swap(&mut parser.rules, &mut rules);
            std::mem::swap(&mut parser.first_declaration_block, &mut first_declaration_block);
            NestedParseResult {
                first_declaration_block,
                rules,
            }
        })
    }

    #[inline(never)]
    fn handle_error_reporting_selectors_pre(
        &mut self,
        start: &ParserState,
        selectors: &SelectorList<SelectorImpl>,
    ) {
        use cssparser::ToCss;
        debug_assert!(self.context.error_reporting_enabled());
        self.error_reporting_state.push(selectors.clone());
        'selector_loop: for selector in selectors.slice().iter() {
            let mut current = selector.iter();
            loop {
                let mut found_host = false;
                let mut found_non_host = false;
                for component in &mut current {
                    if component.is_host() {
                        found_host = true;
                    } else {
                        found_non_host = true;
                    }
                    if found_host && found_non_host {
                        self.context.log_css_error(
                            start.source_location(),
                            ContextualParseError::NeverMatchingHostSelector(
                                selector.to_css_string(),
                            ),
                        );
                        continue 'selector_loop;
                    }
                }
                if current.next_sequence().is_none() {
                    break;
                }
            }
        }
    }

    fn handle_error_reporting_selectors_post(&mut self) {
        self.error_reporting_state.pop();
    }

    #[inline]
    fn flush_declarations(&mut self, source_location: SourceLocation) {
        let parser = &mut **self;
        let wants_first_declaration_block = parser.wants_first_declaration_block;
        parser.wants_first_declaration_block = false;
        parser.declaration_parser_state.report_errors_if_needed(&parser.context, &parser.error_reporting_state);
        if !parser.declaration_parser_state.has_parsed_declarations() {
            return;
        }
        let declarations = parser.declaration_parser_state.take_declarations();
        if wants_first_declaration_block {
            debug_assert!(parser.first_declaration_block.is_empty(), "How?");
            parser.first_declaration_block = declarations;
        } else {
            let nested_rule = CssRule::NestedDeclarations(Arc::new(parser.shared_lock.wrap(NestedDeclarationsRule {
                block: Arc::new(parser.shared_lock.wrap(declarations)),
                source_location,
            })));
            parser.rules.push(nested_rule);
        }
    }
}

impl<'a, 'i> AtRuleParser<'i> for NestedRuleParser<'a, 'i> {
    type Prelude = AtRulePrelude;
    type AtRule = ();
    type Error = StyleParseErrorKind<'i>;

    fn parse_prelude<'t>(
        &mut self,
        name: CowRcStr<'i>,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self::Prelude, ParseError<'i>> {
        Ok(match_ignore_ascii_case! { &*name,
            "media" => {
                let media_queries = MediaList::parse(&self.context, input);
                let arc = Arc::new(self.shared_lock.wrap(media_queries));
                AtRulePrelude::Media(arc)
            },
            "supports" => {
                let cond = SupportsCondition::parse(input)?;
                AtRulePrelude::Supports(cond)
            },
            "font-face" => {
                AtRulePrelude::FontFace
            },
            "container" if cfg!(feature = "gecko") => {
                let condition = Arc::new(ContainerCondition::parse(&self.context, input)?);
                AtRulePrelude::Container(condition)
            },
            "layer" => {
                let names = input.try_parse(|input| {
                    input.parse_comma_separated(|input| {
                        LayerName::parse(&self.context, input)
                    })
                }).unwrap_or_default();
                AtRulePrelude::Layer(names)
            },
            "font-feature-values" if cfg!(feature = "gecko") => {
                let family_names = parse_family_name_list(&self.context, input)?;
                AtRulePrelude::FontFeatureValues(family_names)
            },
            "font-palette-values" if static_prefs::pref!("layout.css.font-palette.enabled") => {
                let name = DashedIdent::parse(&self.context, input)?;
                AtRulePrelude::FontPaletteValues(name)
            },
            "counter-style" if cfg!(feature = "gecko") => {
                let name = parse_counter_style_name_definition(input)?;
                AtRulePrelude::CounterStyle(name)
            },
            "keyframes" | "-webkit-keyframes" | "-moz-keyframes" => {
                let prefix = if starts_with_ignore_ascii_case(&*name, "-webkit-") {
                    Some(VendorPrefix::WebKit)
                } else if starts_with_ignore_ascii_case(&*name, "-moz-") {
                    Some(VendorPrefix::Moz)
                } else {
                    None
                };
                if cfg!(feature = "servo") &&
                   prefix.as_ref().map_or(false, |p| matches!(*p, VendorPrefix::Moz)) {
                    // Servo should not support @-moz-keyframes.
                    return Err(input.new_error(BasicParseErrorKind::AtRuleInvalid(name.clone())))
                }
                let name = KeyframesName::parse(&self.context, input)?;
                AtRulePrelude::Keyframes(name, prefix)
            },
            "page" if cfg!(feature = "gecko") => {
                AtRulePrelude::Page(
                    input.try_parse(|i| PageSelectors::parse(&self.context, i)).unwrap_or_default()
                )
            },
            "property" if static_prefs::pref!("layout.css.properties-and-values.enabled") => {
                let name = input.expect_ident_cloned()?;
                let name = parse_custom_property_name(&name).map_err(|_| {
                    input.new_custom_error(StyleParseErrorKind::UnexpectedIdent(name.clone()))
                })?;
                AtRulePrelude::Property(PropertyRuleName(Atom::from(name)))
            },
            "-moz-document" if cfg!(feature = "gecko") => {
                let cond = DocumentCondition::parse(&self.context, input)?;
                AtRulePrelude::Document(cond)
            },
            "scope" if static_prefs::pref!("layout.css.at-scope.enabled") => {
                let bounds = ScopeBounds::parse(&self.context, input, self.parse_relative())?;
                AtRulePrelude::Scope(bounds)
            },
            "starting-style" if static_prefs::pref!("layout.css.starting-style-at-rules.enabled") => {
                AtRulePrelude::StartingStyle
            },
            "position-try" if static_prefs::pref!("layout.css.anchor-positioning.enabled") => {
                let name = DashedIdent::parse(&self.context, input)?;
                AtRulePrelude::PositionTry(name)
            },
            _ => {
                if static_prefs::pref!("layout.css.margin-rules.enabled") {
                    if let Some(margin_rule_type) = MarginRuleType::match_name(&name) {
                        return Ok(AtRulePrelude::Margin(margin_rule_type));
                    }
                }
                return Err(input.new_error(BasicParseErrorKind::AtRuleInvalid(name.clone())))
            },
        })
    }

    fn parse_block<'t>(
        &mut self,
        prelude: AtRulePrelude,
        start: &ParserState,
        input: &mut Parser<'i, 't>,
    ) -> Result<(), ParseError<'i>> {
        if !self.at_rule_allowed(&prelude) {
            self.dom_error = Some(RulesMutateError::HierarchyRequest);
            return Err(input.new_error(BasicParseErrorKind::AtRuleInvalid(prelude.name().into())));
        }
        let source_location = start.source_location();
        self.flush_declarations(source_location);
        let rule = match prelude {
            AtRulePrelude::FontFace => self.nest_for_rule(CssRuleType::FontFace, |p| {
                CssRule::FontFace(Arc::new(p.shared_lock.wrap(
                    parse_font_face_block(&p.context, input, source_location).into(),
                )))
            }),
            AtRulePrelude::FontFeatureValues(family_names) => {
                self.nest_for_rule(CssRuleType::FontFeatureValues, |p| {
                    CssRule::FontFeatureValues(Arc::new(FontFeatureValuesRule::parse(
                        &p.context,
                        input,
                        family_names,
                        source_location,
                    )))
                })
            },
            AtRulePrelude::FontPaletteValues(name) => {
                self.nest_for_rule(CssRuleType::FontPaletteValues, |p| {
                    CssRule::FontPaletteValues(Arc::new(FontPaletteValuesRule::parse(
                        &p.context,
                        input,
                        name,
                        source_location,
                    )))
                })
            },
            AtRulePrelude::CounterStyle(name) => {
                let body = self.nest_for_rule(CssRuleType::CounterStyle, |p| {
                    parse_counter_style_body(name, &p.context, input, source_location)
                })?;
                CssRule::CounterStyle(Arc::new(self.shared_lock.wrap(body)))
            },
            AtRulePrelude::Media(media_queries) => {
                CssRule::Media(Arc::new(MediaRule {
                    media_queries,
                    rules: self.parse_nested_rules(input, CssRuleType::Media, source_location),
                    source_location,
                }))
            },
            AtRulePrelude::Supports(condition) => {
                let enabled =
                    self.nest_for_rule(CssRuleType::Style, |p| condition.eval(&p.context));
                CssRule::Supports(Arc::new(SupportsRule {
                    condition,
                    rules: self.parse_nested_rules(input, CssRuleType::Supports, source_location),
                    enabled,
                    source_location,
                }))
            },
            AtRulePrelude::Keyframes(name, vendor_prefix) => {
                self.nest_for_rule(CssRuleType::Keyframe, |p| {
                    let top = &mut **p;
                    CssRule::Keyframes(Arc::new(top.shared_lock.wrap(KeyframesRule {
                        name,
                        keyframes: parse_keyframe_list(&mut top.context, input, top.shared_lock),
                        vendor_prefix,
                        source_location,
                    })))
                })
            },
            AtRulePrelude::Page(selectors) => {
                let page_rule = if !static_prefs::pref!("layout.css.margin-rules.enabled") {
                    let declarations = self.nest_for_rule(CssRuleType::Page, |p| {
                        parse_property_declaration_list(&p.context, input, &[])
                    });
                    PageRule {
                        selectors,
                        rules: CssRules::new(vec![], self.shared_lock),
                        block: Arc::new(self.shared_lock.wrap(declarations)),
                        source_location,
                    }
                } else {
                    let result = self.parse_nested(input, CssRuleType::Page, true, source_location);
                    PageRule {
                        selectors,
                        rules: CssRules::new(result.rules, self.shared_lock),
                        block: Arc::new(self.shared_lock.wrap(result.first_declaration_block)),
                        source_location,
                    }
                };
                CssRule::Page(Arc::new(self.shared_lock.wrap(page_rule)))
            },
            AtRulePrelude::Property(name) => self.nest_for_rule(CssRuleType::Property, |p| {
                let rule_data =
                    parse_property_block(&p.context, input, name, source_location)?;
                Ok::<CssRule, ParseError<'i>>(CssRule::Property(Arc::new(rule_data)))
            })?,
            AtRulePrelude::Document(condition) => {
                if !cfg!(feature = "gecko") {
                    unreachable!()
                }
                CssRule::Document(Arc::new(DocumentRule {
                    condition,
                    rules: self.parse_nested_rules(input, CssRuleType::Document, source_location),
                    source_location,
                }))
            },
            AtRulePrelude::Container(condition) => {
                let source_location = start.source_location();
                CssRule::Container(Arc::new(ContainerRule {
                    condition,
                    rules: self.parse_nested_rules(input, CssRuleType::Container, source_location),
                    source_location,
                }))
            },
            AtRulePrelude::Layer(names) => {
                let name = match names.len() {
                    0 | 1 => names.into_iter().next(),
                    _ => return Err(input.new_error(BasicParseErrorKind::AtRuleBodyInvalid)),
                };
                CssRule::LayerBlock(Arc::new(LayerBlockRule {
                    name,
                    rules: self.parse_nested_rules(input, CssRuleType::LayerBlock, source_location),
                    source_location,
                }))
            },
            AtRulePrelude::Margin(rule_type) => {
                let declarations = self.nest_for_rule(CssRuleType::Margin, |p| {
                    parse_property_declaration_list(&p.context, input, &[])
                });
                CssRule::Margin(Arc::new(MarginRule {
                    rule_type,
                    block: Arc::new(self.shared_lock.wrap(declarations)),
                    source_location,
                }))
            },
            AtRulePrelude::Import(..) | AtRulePrelude::Namespace(..) => {
                // These rules don't have blocks.
                return Err(input.new_unexpected_token_error(cssparser::Token::CurlyBracketBlock));
            },
            AtRulePrelude::Scope(bounds) => {
                CssRule::Scope(Arc::new(ScopeRule {
                    bounds,
                    rules: self.parse_nested_rules(input, CssRuleType::Scope, source_location),
                    source_location,
                }))
            },
            AtRulePrelude::StartingStyle => {
                CssRule::StartingStyle(Arc::new(StartingStyleRule {
                    rules: self.parse_nested_rules(input, CssRuleType::StartingStyle, source_location),
                    source_location,
                }))
            },
            AtRulePrelude::PositionTry(name) => {
                let declarations = self.nest_for_rule(CssRuleType::PositionTry, |p| {
                    parse_property_declaration_list(&p.context, input, &[])
                });
                CssRule::PositionTry(Arc::new(self.shared_lock.wrap(PositionTryRule {
                    name,
                    block: Arc::new(self.shared_lock.wrap(declarations)),
                    source_location,
                })))
            },
        };
        self.rules.push(rule);
        Ok(())
    }

    #[inline]
    fn rule_without_block(
        &mut self,
        prelude: AtRulePrelude,
        start: &ParserState,
    ) -> Result<(), ()> {
        if self.in_style_rule() {
            return Err(());
        }
        let source_location = start.source_location();
        let rule = match prelude {
            AtRulePrelude::Layer(names) => {
                if names.is_empty() {
                    return Err(());
                }
                CssRule::LayerStatement(Arc::new(LayerStatementRule {
                    names,
                    source_location,
                }))
            },
            _ => return Err(()),
        };
        self.flush_declarations(source_location);
        self.rules.push(rule);
        Ok(())
    }
}

impl<'a, 'i> QualifiedRuleParser<'i> for NestedRuleParser<'a, 'i> {
    type Prelude = SelectorList<SelectorImpl>;
    type QualifiedRule = ();
    type Error = StyleParseErrorKind<'i>;

    fn parse_prelude<'t>(
        &mut self,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self::Prelude, ParseError<'i>> {
        let selector_parser = SelectorParser {
            stylesheet_origin: self.context.stylesheet_origin,
            namespaces: &self.context.namespaces,
            url_data: self.context.url_data,
            for_supports_rule: false,
        };
        SelectorList::parse(&selector_parser, input, self.parse_relative())
    }

    fn parse_block<'t>(
        &mut self,
        selectors: Self::Prelude,
        start: &ParserState,
        input: &mut Parser<'i, 't>,
    ) -> Result<(), ParseError<'i>> {
        let source_location = start.source_location();
        let reporting_errors = self.context.error_reporting_enabled();
        if reporting_errors {
            self.handle_error_reporting_selectors_pre(start, &selectors);
        }
        self.flush_declarations(source_location);
        let result = self.parse_nested(input, CssRuleType::Style, true, source_location);
        if reporting_errors {
            self.handle_error_reporting_selectors_post();
        }
        let block = Arc::new(self.shared_lock.wrap(result.first_declaration_block));
        let top = &mut **self;
        top.rules
            .push(CssRule::Style(Arc::new(top.shared_lock.wrap(StyleRule {
                selectors,
                block,
                rules: if result.rules.is_empty() {
                    None
                } else {
                    Some(CssRules::new(result.rules, top.shared_lock))
                },
                source_location,
            }))));
        Ok(())
    }
}

impl<'a, 'i> DeclarationParser<'i> for NestedRuleParser<'a, 'i> {
    type Declaration = ();
    type Error = StyleParseErrorKind<'i>;
    fn parse_value<'t>(
        &mut self,
        name: CowRcStr<'i>,
        input: &mut Parser<'i, 't>,
    ) -> Result<(), ParseError<'i>> {
        let top = &mut **self;
        top.declaration_parser_state
            .parse_value(&top.context, name, input)
    }
}

impl<'a, 'i> RuleBodyItemParser<'i, (), StyleParseErrorKind<'i>> for NestedRuleParser<'a, 'i> {
    fn parse_qualified(&self) -> bool {
        true
    }

    /// If nesting is disabled, we can't get there for a non-style-rule. If it's enabled, we parse
    /// raw declarations there.
    fn parse_declarations(&self) -> bool {
        self.can_parse_declarations()
    }
}