/* 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/. */

//! CSS handling for the specified value of
//! [`position`][position]s
//!
//! [position]: https://drafts.csswg.org/css-backgrounds-3/#position

use crate::parser::{Parse, ParserContext};
use crate::selector_map::PrecomputedHashMap;
use crate::str::HTML_SPACE_CHARACTERS;
use crate::values::computed::LengthPercentage as ComputedLengthPercentage;
use crate::values::computed::{Context, Percentage, ToComputedValue};
use crate::values::generics::position::Position as GenericPosition;
use crate::values::generics::position::PositionComponent as GenericPositionComponent;
use crate::values::generics::position::PositionOrAuto as GenericPositionOrAuto;
use crate::values::generics::position::ZIndex as GenericZIndex;
use crate::values::generics::position::{AnchorSide, AspectRatio as GenericAspectRatio};
use crate::values::generics::position::{GenericAnchorFunction, GenericInset};
use crate::values::specified;
use crate::values::specified::{AllowQuirks, Integer, LengthPercentage, NonNegativeNumber};
use crate::values::DashedIdent;
use crate::{Atom, Zero};
use cssparser::Parser;
use selectors::parser::SelectorParseErrorKind;
use servo_arc::Arc;
use smallvec::{smallvec, SmallVec};
use std::collections::hash_map::Entry;
use std::fmt::{self, Write};
use style_traits::arc_slice::ArcSlice;
use style_traits::values::specified::AllowedNumericType;
use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};

/// The specified value of a CSS `<position>`
pub type Position = GenericPosition<HorizontalPosition, VerticalPosition>;

/// The specified value of an `auto | <position>`.
pub type PositionOrAuto = GenericPositionOrAuto<Position>;

/// The specified value of a horizontal position.
pub type HorizontalPosition = PositionComponent<HorizontalPositionKeyword>;

/// The specified value of a vertical position.
pub type VerticalPosition = PositionComponent<VerticalPositionKeyword>;

/// The specified value of a component of a CSS `<position>`.
#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
pub enum PositionComponent<S> {
    /// `center`
    Center,
    /// `<length-percentage>`
    Length(LengthPercentage),
    /// `<side> <length-percentage>?`
    Side(S, Option<LengthPercentage>),
}

/// A keyword for the X direction.
#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    Hash,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[allow(missing_docs)]
#[repr(u8)]
pub enum HorizontalPositionKeyword {
    Left,
    Right,
}

/// A keyword for the Y direction.
#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    Hash,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[allow(missing_docs)]
#[repr(u8)]
pub enum VerticalPositionKeyword {
    Top,
    Bottom,
}

impl Parse for Position {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        let position = Self::parse_three_value_quirky(context, input, AllowQuirks::No)?;
        if position.is_three_value_syntax() {
            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }
        Ok(position)
    }
}

impl Position {
    /// Parses a `<bg-position>`, with quirks.
    pub fn parse_three_value_quirky<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
        allow_quirks: AllowQuirks,
    ) -> Result<Self, ParseError<'i>> {
        match input.try_parse(|i| PositionComponent::parse_quirky(context, i, allow_quirks)) {
            Ok(x_pos @ PositionComponent::Center) => {
                if let Ok(y_pos) =
                    input.try_parse(|i| PositionComponent::parse_quirky(context, i, allow_quirks))
                {
                    return Ok(Self::new(x_pos, y_pos));
                }
                let x_pos = input
                    .try_parse(|i| PositionComponent::parse_quirky(context, i, allow_quirks))
                    .unwrap_or(x_pos);
                let y_pos = PositionComponent::Center;
                return Ok(Self::new(x_pos, y_pos));
            },
            Ok(PositionComponent::Side(x_keyword, lp)) => {
                if input
                    .try_parse(|i| i.expect_ident_matching("center"))
                    .is_ok()
                {
                    let x_pos = PositionComponent::Side(x_keyword, lp);
                    let y_pos = PositionComponent::Center;
                    return Ok(Self::new(x_pos, y_pos));
                }
                if let Ok(y_keyword) = input.try_parse(VerticalPositionKeyword::parse) {
                    let y_lp = input
                        .try_parse(|i| LengthPercentage::parse_quirky(context, i, allow_quirks))
                        .ok();
                    let x_pos = PositionComponent::Side(x_keyword, lp);
                    let y_pos = PositionComponent::Side(y_keyword, y_lp);
                    return Ok(Self::new(x_pos, y_pos));
                }
                let x_pos = PositionComponent::Side(x_keyword, None);
                let y_pos = lp.map_or(PositionComponent::Center, PositionComponent::Length);
                return Ok(Self::new(x_pos, y_pos));
            },
            Ok(x_pos @ PositionComponent::Length(_)) => {
                if let Ok(y_keyword) = input.try_parse(VerticalPositionKeyword::parse) {
                    let y_pos = PositionComponent::Side(y_keyword, None);
                    return Ok(Self::new(x_pos, y_pos));
                }
                if let Ok(y_lp) =
                    input.try_parse(|i| LengthPercentage::parse_quirky(context, i, allow_quirks))
                {
                    let y_pos = PositionComponent::Length(y_lp);
                    return Ok(Self::new(x_pos, y_pos));
                }
                let y_pos = PositionComponent::Center;
                let _ = input.try_parse(|i| i.expect_ident_matching("center"));
                return Ok(Self::new(x_pos, y_pos));
            },
            Err(_) => {},
        }
        let y_keyword = VerticalPositionKeyword::parse(input)?;
        let lp_and_x_pos: Result<_, ParseError> = input.try_parse(|i| {
            let y_lp = i
                .try_parse(|i| LengthPercentage::parse_quirky(context, i, allow_quirks))
                .ok();
            if let Ok(x_keyword) = i.try_parse(HorizontalPositionKeyword::parse) {
                let x_lp = i
                    .try_parse(|i| LengthPercentage::parse_quirky(context, i, allow_quirks))
                    .ok();
                let x_pos = PositionComponent::Side(x_keyword, x_lp);
                return Ok((y_lp, x_pos));
            };
            i.expect_ident_matching("center")?;
            let x_pos = PositionComponent::Center;
            Ok((y_lp, x_pos))
        });
        if let Ok((y_lp, x_pos)) = lp_and_x_pos {
            let y_pos = PositionComponent::Side(y_keyword, y_lp);
            return Ok(Self::new(x_pos, y_pos));
        }
        let x_pos = PositionComponent::Center;
        let y_pos = PositionComponent::Side(y_keyword, None);
        Ok(Self::new(x_pos, y_pos))
    }

    /// `center center`
    #[inline]
    pub fn center() -> Self {
        Self::new(PositionComponent::Center, PositionComponent::Center)
    }

    /// Returns true if this uses a 3 value syntax.
    #[inline]
    fn is_three_value_syntax(&self) -> bool {
        self.horizontal.component_count() != self.vertical.component_count()
    }
}

impl ToCss for Position {
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: Write,
    {
        match (&self.horizontal, &self.vertical) {
            (
                x_pos @ &PositionComponent::Side(_, Some(_)),
                &PositionComponent::Length(ref y_lp),
            ) => {
                x_pos.to_css(dest)?;
                dest.write_str(" top ")?;
                y_lp.to_css(dest)
            },
            (
                &PositionComponent::Length(ref x_lp),
                y_pos @ &PositionComponent::Side(_, Some(_)),
            ) => {
                dest.write_str("left ")?;
                x_lp.to_css(dest)?;
                dest.write_char(' ')?;
                y_pos.to_css(dest)
            },
            (x_pos, y_pos) => {
                x_pos.to_css(dest)?;
                dest.write_char(' ')?;
                y_pos.to_css(dest)
            },
        }
    }
}

impl<S: Parse> Parse for PositionComponent<S> {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        Self::parse_quirky(context, input, AllowQuirks::No)
    }
}

impl<S: Parse> PositionComponent<S> {
    /// Parses a component of a CSS position, with quirks.
    pub fn parse_quirky<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
        allow_quirks: AllowQuirks,
    ) -> Result<Self, ParseError<'i>> {
        if input
            .try_parse(|i| i.expect_ident_matching("center"))
            .is_ok()
        {
            return Ok(PositionComponent::Center);
        }
        if let Ok(lp) =
            input.try_parse(|i| LengthPercentage::parse_quirky(context, i, allow_quirks))
        {
            return Ok(PositionComponent::Length(lp));
        }
        let keyword = S::parse(context, input)?;
        let lp = input
            .try_parse(|i| LengthPercentage::parse_quirky(context, i, allow_quirks))
            .ok();
        Ok(PositionComponent::Side(keyword, lp))
    }
}

impl<S> GenericPositionComponent for PositionComponent<S> {
    fn is_center(&self) -> bool {
        match *self {
            PositionComponent::Center => true,
            PositionComponent::Length(LengthPercentage::Percentage(ref per)) => per.0 == 0.5,
            // 50% from any side is still the center.
            PositionComponent::Side(_, Some(LengthPercentage::Percentage(ref per))) => per.0 == 0.5,
            _ => false,
        }
    }
}

impl<S> PositionComponent<S> {
    /// `0%`
    pub fn zero() -> Self {
        PositionComponent::Length(LengthPercentage::Percentage(Percentage::zero()))
    }

    /// Returns the count of this component.
    fn component_count(&self) -> usize {
        match *self {
            PositionComponent::Length(..) | PositionComponent::Center => 1,
            PositionComponent::Side(_, ref lp) => {
                if lp.is_some() {
                    2
                } else {
                    1
                }
            },
        }
    }
}

impl<S: Side> ToComputedValue for PositionComponent<S> {
    type ComputedValue = ComputedLengthPercentage;

    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
        match *self {
            PositionComponent::Center => ComputedLengthPercentage::new_percent(Percentage(0.5)),
            PositionComponent::Side(ref keyword, None) => {
                let p = Percentage(if keyword.is_start() { 0. } else { 1. });
                ComputedLengthPercentage::new_percent(p)
            },
            PositionComponent::Side(ref keyword, Some(ref length)) if !keyword.is_start() => {
                let length = length.to_computed_value(context);
                // We represent `<end-side> <length>` as `calc(100% - <length>)`.
                ComputedLengthPercentage::hundred_percent_minus(length, AllowedNumericType::All)
            },
            PositionComponent::Side(_, Some(ref length)) |
            PositionComponent::Length(ref length) => length.to_computed_value(context),
        }
    }

    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
        PositionComponent::Length(ToComputedValue::from_computed_value(computed))
    }
}

impl<S: Side> PositionComponent<S> {
    /// The initial specified value of a position component, i.e. the start side.
    pub fn initial_specified_value() -> Self {
        PositionComponent::Side(S::start(), None)
    }
}

/// https://drafts.csswg.org/css-anchor-position-1/#propdef-anchor-name
#[repr(transparent)]
#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[css(comma)]
pub struct AnchorName(
    #[css(iterable, if_empty = "none")]
    #[ignore_malloc_size_of = "Arc"]
    pub crate::ArcSlice<DashedIdent>,
);

impl AnchorName {
    /// Return the `none` value.
    pub fn none() -> Self {
        Self(Default::default())
    }

    /// Returns whether this is the `none` value.
    pub fn is_none(&self) -> bool {
        self.0.is_empty()
    }
}

impl Parse for AnchorName {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        let location = input.current_source_location();
        let first = input.expect_ident()?;
        if first.eq_ignore_ascii_case("none") {
            return Ok(Self::none());
        }
        // The common case is probably just to have a single anchor name, so
        // space for four on the stack should be plenty.
        let mut idents: SmallVec<[DashedIdent; 4]> =
            smallvec![DashedIdent::from_ident(location, first,)?];
        while input.try_parse(|input| input.expect_comma()).is_ok() {
            idents.push(DashedIdent::parse(context, input)?);
        }
        Ok(AnchorName(ArcSlice::from_iter(idents.drain(..))))
    }
}

/// https://drafts.csswg.org/css-anchor-position-1/#propdef-scope
#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(u8)]
pub enum AnchorScope {
    /// `none`
    None,
    /// `all`
    All,
    /// `<dashed-ident>#`
    #[css(comma)]
    Idents(
        #[css(iterable)]
        #[ignore_malloc_size_of = "Arc"]
        crate::ArcSlice<DashedIdent>,
    ),
}

impl AnchorScope {
    /// Return the `none` value.
    pub fn none() -> Self {
        Self::None
    }

    /// Returns whether this is the `none` value.
    pub fn is_none(&self) -> bool {
        *self == Self::None
    }
}

impl Parse for AnchorScope {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        let location = input.current_source_location();
        let first = input.expect_ident()?;
        if first.eq_ignore_ascii_case("none") {
            return Ok(Self::None);
        }
        if first.eq_ignore_ascii_case("all") {
            return Ok(Self::All);
        }
        // Authors using more than a handful of anchored elements is likely
        // uncommon, so we only pre-allocate for 8 on the stack here.
        let mut idents: SmallVec<[DashedIdent; 8]> =
            smallvec![DashedIdent::from_ident(location, first,)?];
        while input.try_parse(|input| input.expect_comma()).is_ok() {
            idents.push(DashedIdent::parse(context, input)?);
        }
        Ok(AnchorScope::Idents(ArcSlice::from_iter(idents.drain(..))))
    }
}

/// https://drafts.csswg.org/css-anchor-position-1/#propdef-position-anchor
#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(u8)]
pub enum PositionAnchor {
    /// `auto`
    Auto,
    /// `<dashed-ident>`
    Ident(DashedIdent),
}

impl PositionAnchor {
    /// Return the `auto` value.
    pub fn auto() -> Self {
        Self::Auto
    }

    /// Returns whether this is the `auto` value.
    pub fn is_auto(&self) -> bool {
        *self == Self::Auto
    }
}

#[derive(
    Clone,
    Copy,
    Debug,
    Default,
    Eq,
    MallocSizeOf,
    Parse,
    PartialEq,
    Serialize,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(u8)]
/// How to swap values for the automatically-generated position tactic.
pub enum PositionTryFallbacksTryTacticKeyword {
    /// Magic value for no change.
    #[css(skip)]
    #[default]
    None,
    /// Swap the values in the block axis.
    FlipBlock,
    /// Swap the values in the inline axis.
    FlipInline,
    /// Swap the values in the start properties.
    FlipStart,
}

impl PositionTryFallbacksTryTacticKeyword {
    fn is_none(&self) -> bool {
        *self == Self::None
    }
}

#[derive(
    Clone,
    Copy,
    Debug,
    Default,
    Eq,
    MallocSizeOf,
    PartialEq,
    Serialize,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
/// Changes for the automatically-generated position option.
/// Note that this is order-dependent - e.g. `flip-start flip-inline` != `flip-inline flip-start`.
///
/// https://drafts.csswg.org/css-anchor-position-1/#typedef-position-try-fallbacks-try-tactic
pub struct PositionTryFallbacksTryTactic(
    pub PositionTryFallbacksTryTacticKeyword,
    pub PositionTryFallbacksTryTacticKeyword,
    pub PositionTryFallbacksTryTacticKeyword,
);

impl Parse for PositionTryFallbacksTryTactic {
    fn parse<'i, 't>(
        _context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        let first = input.try_parse(PositionTryFallbacksTryTacticKeyword::parse)?;
        let second = input.try_parse(PositionTryFallbacksTryTacticKeyword::parse).unwrap_or_default();
        let third = input.try_parse(PositionTryFallbacksTryTacticKeyword::parse).unwrap_or_default();
        if first == second || first == third || (!second.is_none() && second == third) {
            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }
        Ok(Self(first, second, third))
    }
}

impl PositionTryFallbacksTryTactic {
    fn is_empty(&self) -> bool {
        self.0.is_none()
    }
}

#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
/// https://drafts.csswg.org/css-anchor-position-1/#propdef-position-try-fallbacks
/// <dashed-ident> || <try-tactic>
pub struct DashedIdentAndOrTryTactic {
    /// `<dashed-ident>`
    pub ident: DashedIdent,
    /// `<try-tactic>`
    pub try_tactic: PositionTryFallbacksTryTactic,
}

impl Parse for DashedIdentAndOrTryTactic {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        let mut result = Self {
            ident: DashedIdent::empty(),
            try_tactic: PositionTryFallbacksTryTactic::default(),
        };

        loop {
            if result.ident.is_empty() {
                if let Ok(ident) = input.try_parse(|i| DashedIdent::parse(context, i)) {
                    result.ident = ident;
                    continue;
                }
            }
            if result.try_tactic.is_empty() {
                if let Ok(try_tactic) =
                    input.try_parse(|i| PositionTryFallbacksTryTactic::parse(context, i))
                {
                    result.try_tactic = try_tactic;
                    continue;
                }
            }
            break;
        }

        if result.ident.is_empty() && result.try_tactic.is_empty() {
            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }
        return Ok(result);
    }
}

#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(u8)]
/// https://drafts.csswg.org/css-anchor-position-1/#propdef-position-try-fallbacks
/// [ [<dashed-ident> || <try-tactic>] | <'position-area'> ]
pub enum PositionTryFallbacksItem {
    /// `<dashed-ident> || <try-tactic>`
    IdentAndOrTactic(DashedIdentAndOrTryTactic),
    #[parse(parse_fn = "PositionArea::parse_except_none")]
    /// `<position-area>`
    PositionArea(PositionArea),
}

#[derive(
    Clone,
    Debug,
    Default,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[css(comma)]
#[repr(C)]
/// https://drafts.csswg.org/css-anchor-position-1/#position-try-fallbacks
pub struct PositionTryFallbacks(
    #[css(iterable, if_empty = "none")]
    #[ignore_malloc_size_of = "Arc"]
    pub crate::ArcSlice<PositionTryFallbacksItem>,
);

impl PositionTryFallbacks {
    #[inline]
    /// Return the `none` value.
    pub fn none() -> Self {
        Self(Default::default())
    }

    /// Returns whether this is the `none` value.
    pub fn is_none(&self) -> bool {
        self.0.is_empty()
    }
}

impl Parse for PositionTryFallbacks {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        if input.try_parse(|i| i.expect_ident_matching("none")).is_ok() {
            return Ok(Self::none());
        }
        // The common case is unlikely to include many alternate positioning
        // styles, so space for four on the stack should typically be enough.
        let mut items: SmallVec<[PositionTryFallbacksItem; 4]> =
            smallvec![PositionTryFallbacksItem::parse(context, input)?];
        while input.try_parse(|input| input.expect_comma()).is_ok() {
            items.push(PositionTryFallbacksItem::parse(context, input)?);
        }
        Ok(Self(ArcSlice::from_iter(items.drain(..))))
    }
}

/// https://drafts.csswg.org/css-anchor-position-1/#position-try-order-property
#[derive(
    Clone,
    Copy,
    Debug,
    Default,
    Eq,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(u8)]
pub enum PositionTryOrder {
    #[default]
    /// `normal`
    Normal,
    /// `most-width`
    MostWidth,
    /// `most-height`
    MostHeight,
    /// `most-block-size`
    MostBlockSize,
    /// `most-inline-size`
    MostInlineSize,
}

impl PositionTryOrder {
    #[inline]
    /// Return the `auto` value.
    pub fn normal() -> Self {
        Self::Normal
    }

    /// Returns whether this is the `auto` value.
    pub fn is_normal(&self) -> bool {
        *self == Self::Normal
    }
}

#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    MallocSizeOf,
    Parse,
    PartialEq,
    Serialize,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[css(bitflags(single = "always", mixed = "anchors-valid,anchors-visible,no-overflow"))]
#[repr(C)]
/// Specified keyword values for the position-visibility property.
pub struct PositionVisibility(u8);
bitflags! {
    impl PositionVisibility: u8 {
        /// Element is displayed without regard for its anchors or its overflowing status.
        const ALWAYS = 0;
        /// anchors-valid
        const ANCHORS_VALID = 1 << 0;
        /// anchors-visible
        const ANCHORS_VISIBLE = 1 << 1;
        /// no-overflow
        const NO_OVERFLOW = 1 << 2;
    }
}

impl Default for PositionVisibility {
    fn default() -> Self {
        Self::ALWAYS
    }
}

impl PositionVisibility {
    #[inline]
    /// Returns the initial value of position-visibility
    pub fn always() -> Self {
        Self::ALWAYS
    }
}

#[derive(
    Clone,
    Copy,
    Debug,
    Default,
    Eq,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[allow(missing_docs)]
#[repr(u8)]
/// Possible values for the `position-area` preperty's keywords.
/// https://drafts.csswg.org/css-anchor-position-1/#propdef-position-area
pub enum PositionAreaKeyword {
    #[default]
    None,

    // Common (shared) keywords:
    Center,
    SpanAll,

    // Horizontal keywords:
    Left,
    Right,
    SpanLeft,
    SpanRight,
    XStart,
    XEnd,
    SpanXStart,
    SpanXEnd,
    XSelfStart,
    XSelfEnd,
    SpanXSelfStart,
    SpanXSelfEnd,
    // Vertical keywords:
    Top,
    Bottom,
    SpanTop,
    SpanBottom,
    YStart,
    YEnd,
    SpanYStart,
    SpanYEnd,
    YSelfStart,
    YSelfEnd,
    SpanYSelfStart,
    SpanYSelfEnd,

    // Block keywords:
    BlockStart,
    BlockEnd,
    SpanBlockStart,
    SpanBlockEnd,
    // Inline keywords:
    InlineStart,
    InlineEnd,
    SpanInlineStart,
    SpanInlineEnd,

    // "Self" block keywords:
    SelfBlockStart,
    SelfBlockEnd,
    SpanSelfBlockStart,
    SpanSelfBlockEnd,
    // "Self" inline keywords:
    SelfInlineStart,
    SelfInlineEnd,
    SpanSelfInlineStart,
    SpanSelfInlineEnd,

    // Inferred axis keywords:
    Start,
    End,
    SpanStart,
    SpanEnd,

    // "Self" inferred axis keywords:
    SelfStart,
    SelfEnd,
    SpanSelfStart,
    SpanSelfEnd,
}

#[allow(missing_docs)]
impl PositionAreaKeyword {
    #[inline]
    pub fn none() -> Self {
        Self::None
    }

    pub fn is_none(&self) -> bool {
        *self == Self::None
    }

    /// Is a value that's common to all compatible keyword groupings.
    pub fn is_common(&self) -> bool {
        *self == Self::Center || *self == Self::SpanAll
    }

    pub fn is_horizontal(&self) -> bool {
        matches!(
            self,
            Self::Left |
                Self::Right |
                Self::SpanLeft |
                Self::SpanRight |
                Self::XStart |
                Self::XEnd |
                Self::SpanXStart |
                Self::SpanXEnd |
                Self::XSelfStart |
                Self::XSelfEnd |
                Self::SpanXSelfStart |
                Self::SpanXSelfEnd
        )
    }
    pub fn is_vertical(&self) -> bool {
        matches!(
            self,
            Self::Top |
                Self::Bottom |
                Self::SpanTop |
                Self::SpanBottom |
                Self::YStart |
                Self::YEnd |
                Self::SpanYStart |
                Self::SpanYEnd |
                Self::YSelfStart |
                Self::YSelfEnd |
                Self::SpanYSelfStart |
                Self::SpanYSelfEnd
        )
    }

    pub fn is_block(&self) -> bool {
        matches!(
            self,
            Self::BlockStart | Self::BlockEnd | Self::SpanBlockStart | Self::SpanBlockEnd
        )
    }
    pub fn is_inline(&self) -> bool {
        matches!(
            self,
            Self::InlineStart | Self::InlineEnd | Self::SpanInlineStart | Self::SpanInlineEnd
        )
    }

    pub fn is_self_block(&self) -> bool {
        matches!(
            self,
            Self::SelfBlockStart |
                Self::SelfBlockEnd |
                Self::SpanSelfBlockStart |
                Self::SpanSelfBlockEnd
        )
    }
    pub fn is_self_inline(&self) -> bool {
        matches!(
            self,
            Self::SelfInlineStart |
                Self::SelfInlineEnd |
                Self::SpanSelfInlineStart |
                Self::SpanSelfInlineEnd
        )
    }

    pub fn is_inferred_logical(&self) -> bool {
        matches!(
            self,
            Self::Start | Self::End | Self::SpanStart | Self::SpanEnd
        )
    }

    pub fn is_self_inferred_logical(&self) -> bool {
        matches!(
            self,
            Self::SelfStart | Self::SelfEnd | Self::SpanSelfStart | Self::SpanSelfEnd
        )
    }
}

#[inline]
fn is_compatible_pairing(first: PositionAreaKeyword, second: PositionAreaKeyword) -> bool {
    if first.is_none() || second.is_none() {
        // `none` is not allowed as one of the keywords when two keywords are
        // provided.
        return false;
    }
    if first.is_common() || second.is_common() {
        return true;
    }
    if first.is_horizontal() {
        return second.is_vertical();
    }
    if first.is_vertical() {
        return second.is_horizontal();
    }
    if first.is_block() {
        return second.is_inline();
    }
    if first.is_inline() {
        return second.is_block();
    }
    if first.is_self_block() {
        return second.is_self_inline();
    }
    if first.is_self_inline() {
        return second.is_self_block();
    }
    if first.is_inferred_logical() {
        return second.is_inferred_logical();
    }
    if first.is_self_inferred_logical() {
        return second.is_self_inferred_logical();
    }

    debug_assert!(false, "Not reached");

    // Return false to increase the chances of this being reported to us if we
    // ever were to get here.
    false
}

#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
/// https://drafts.csswg.org/css-anchor-position-1/#propdef-position-area
pub struct PositionArea {
    /// First keyword, if any.
    pub first: PositionAreaKeyword,
    /// Second keyword, if any.
    #[css(skip_if = "PositionAreaKeyword::is_none")]
    pub second: PositionAreaKeyword,
}

#[allow(missing_docs)]
impl PositionArea {
    #[inline]
    pub fn none() -> Self {
        Self {
            first: PositionAreaKeyword::None,
            second: PositionAreaKeyword::None,
        }
    }

    #[inline]
    pub fn is_none(&self) -> bool {
        self.first.is_none()
    }

    pub fn parse_except_none<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        Self::parse_internal(context, input, /*allow_none*/ false)
    }

    fn parse_internal<'i, 't>(
        _context: &ParserContext,
        input: &mut Parser<'i, 't>,
        allow_none: bool,
    ) -> Result<Self, ParseError<'i>> {
        let mut location = input.current_source_location();
        let mut first = PositionAreaKeyword::parse(input)?;
        if first.is_none() {
            if allow_none {
                return Ok(Self::none());
            }
            return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }

        location = input.current_source_location();
        let second = input.try_parse(PositionAreaKeyword::parse);
        if let Ok(PositionAreaKeyword::None) = second {
            // `none` is only allowed as a single value
            return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }
        let mut second = second.unwrap_or(PositionAreaKeyword::None);
        if second.is_none() {
            // Either there was no second keyword and try_parse returned a
            // BasicParseErrorKind::EndOfInput, or else the second "keyword"
            // was invalid. We assume the former case here, and if it's the
            // latter case then our caller detects the error (try_parse will,
            // have rewound, leaving an unparsed token).
            return Ok(Self { first, second });
        }

        if !is_compatible_pairing(first, second) {
            return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }

        // Normalize by applying the shortest serialization principle:
        // https://drafts.csswg.org/cssom/#serializing-css-values
        if first.is_inferred_logical() ||
            second.is_inferred_logical() ||
            first.is_self_inferred_logical() ||
            second.is_self_inferred_logical() ||
            (first.is_common() && second.is_common())
        {
            // In these cases we must not change the order of the keywords
            // since their meaning is inferred from their order. However, if
            // both keywords are the same, only one should be set.
            if first == second {
                second = PositionAreaKeyword::None;
            }
        } else if second == PositionAreaKeyword::SpanAll {
            // Span-all is the default behavior, so specifying `span-all` is
            // superfluous.
            second = PositionAreaKeyword::None;
        } else if first == PositionAreaKeyword::SpanAll {
            // Same here, but the non-superfluous keyword must come first.
            first = second;
            second = PositionAreaKeyword::None;
        } else if first.is_vertical() ||
            second.is_horizontal() ||
            first.is_inline() ||
            second.is_block() ||
            first.is_self_inline() ||
            second.is_self_block()
        {
            // Canonical order is horizontal before vertical, block before inline.
            std::mem::swap(&mut first, &mut second);
        }

        Ok(Self { first, second })
    }
}

impl Parse for PositionArea {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        Self::parse_internal(context, input, /*allow_none*/ true)
    }
}

/// Represents a side, either horizontal or vertical, of a CSS position.
pub trait Side {
    /// Returns the start side.
    fn start() -> Self;

    /// Returns whether this side is the start side.
    fn is_start(&self) -> bool;
}

impl Side for HorizontalPositionKeyword {
    #[inline]
    fn start() -> Self {
        HorizontalPositionKeyword::Left
    }

    #[inline]
    fn is_start(&self) -> bool {
        *self == Self::start()
    }
}

impl Side for VerticalPositionKeyword {
    #[inline]
    fn start() -> Self {
        VerticalPositionKeyword::Top
    }

    #[inline]
    fn is_start(&self) -> bool {
        *self == Self::start()
    }
}

/// Controls how the auto-placement algorithm works specifying exactly how auto-placed items
/// get flowed into the grid: [ row | column ] || dense
/// https://drafts.csswg.org/css-grid-2/#grid-auto-flow-property
#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToResolvedValue,
    ToShmem,
)]
#[css(bitflags(
    mixed = "row,column,dense",
    validate_mixed = "Self::validate_and_simplify"
))]
#[repr(C)]
pub struct GridAutoFlow(u8);
bitflags! {
    impl GridAutoFlow: u8 {
        /// 'row' - mutually exclusive with 'column'
        const ROW = 1 << 0;
        /// 'column' - mutually exclusive with 'row'
        const COLUMN = 1 << 1;
        /// 'dense'
        const DENSE = 1 << 2;
    }
}

impl GridAutoFlow {
    /// [ row | column ] || dense
    fn validate_and_simplify(&mut self) -> bool {
        if self.contains(Self::ROW | Self::COLUMN) {
            // row and column are mutually exclusive.
            return false;
        }
        if *self == Self::DENSE {
            // If there's no column, default to row.
            self.insert(Self::ROW);
        }
        true
    }
}

impl ToCss for GridAutoFlow {
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: Write,
    {
        let dense = self.intersects(Self::DENSE);
        if self.intersects(Self::ROW) {
            return if dense {
                dest.write_str("dense")
            } else {
                dest.write_str("row")
            };
        }
        debug_assert!(self.intersects(Self::COLUMN));
        if dense {
            dest.write_str("column dense")
        } else {
            dest.write_str("column")
        }
    }
}

#[repr(u8)]
#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
/// Masonry auto-placement algorithm packing.
pub enum MasonryPlacement {
    /// Place the item in the track(s) with the smallest extent so far.
    Pack,
    /// Place the item after the last item, from start to end.
    Next,
}

#[repr(u8)]
#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
/// Masonry auto-placement algorithm item sorting option.
pub enum MasonryItemOrder {
    /// Place all items with a definite placement before auto-placed items.
    DefiniteFirst,
    /// Place items in `order-modified document order`.
    Ordered,
}

#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
/// Controls how the Masonry layout algorithm works
/// specifying exactly how auto-placed items get flowed in the masonry axis.
pub struct MasonryAutoFlow {
    /// Specify how to pick a auto-placement track.
    #[css(contextual_skip_if = "is_pack_with_non_default_order")]
    pub placement: MasonryPlacement,
    /// Specify how to pick an item to place.
    #[css(skip_if = "is_item_order_definite_first")]
    pub order: MasonryItemOrder,
}

#[inline]
fn is_pack_with_non_default_order(placement: &MasonryPlacement, order: &MasonryItemOrder) -> bool {
    *placement == MasonryPlacement::Pack && *order != MasonryItemOrder::DefiniteFirst
}

#[inline]
fn is_item_order_definite_first(order: &MasonryItemOrder) -> bool {
    *order == MasonryItemOrder::DefiniteFirst
}

impl MasonryAutoFlow {
    #[inline]
    /// Get initial `masonry-auto-flow` value.
    pub fn initial() -> MasonryAutoFlow {
        MasonryAutoFlow {
            placement: MasonryPlacement::Pack,
            order: MasonryItemOrder::DefiniteFirst,
        }
    }
}

impl Parse for MasonryAutoFlow {
    /// [ definite-first | ordered ] || [ pack | next ]
    fn parse<'i, 't>(
        _context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<MasonryAutoFlow, ParseError<'i>> {
        let mut value = MasonryAutoFlow::initial();
        let mut got_placement = false;
        let mut got_order = false;
        while !input.is_exhausted() {
            let location = input.current_source_location();
            let ident = input.expect_ident()?;
            let success = match_ignore_ascii_case! { &ident,
                "pack" if !got_placement => {
                    got_placement = true;
                    true
                },
                "next" if !got_placement => {
                    value.placement = MasonryPlacement::Next;
                    got_placement = true;
                    true
                },
                "definite-first" if !got_order => {
                    got_order = true;
                    true
                },
                "ordered" if !got_order => {
                    value.order = MasonryItemOrder::Ordered;
                    got_order = true;
                    true
                },
                _ => false
            };
            if !success {
                return Err(location
                    .new_custom_error(SelectorParseErrorKind::UnexpectedIdent(ident.clone())));
            }
        }

        if got_placement || got_order {
            Ok(value)
        } else {
            Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
        }
    }
}

#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
/// https://drafts.csswg.org/css-grid/#named-grid-area
pub struct TemplateAreas {
    /// `named area` containing for each template area
    #[css(skip)]
    pub areas: crate::OwnedSlice<NamedArea>,
    /// The simplified CSS strings for serialization purpose.
    /// https://drafts.csswg.org/css-grid/#serialize-template
    // Note: We also use the length of `strings` when computing the explicit grid end line number
    // (i.e. row number).
    #[css(iterable)]
    pub strings: crate::OwnedSlice<crate::OwnedStr>,
    /// The number of columns of the grid.
    #[css(skip)]
    pub width: u32,
}

/// Parser for grid template areas.
#[derive(Default)]
pub struct TemplateAreasParser {
    areas: Vec<NamedArea>,
    area_indices: PrecomputedHashMap<Atom, usize>,
    strings: Vec<crate::OwnedStr>,
    width: u32,
    row: u32,
}

impl TemplateAreasParser {
    /// Parse a single string.
    pub fn try_parse_string<'i>(
        &mut self,
        input: &mut Parser<'i, '_>,
    ) -> Result<(), ParseError<'i>> {
        input.try_parse(|input| {
            self.parse_string(input.expect_string()?)
                .map_err(|()| input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
        })
    }

    /// Parse a single string.
    fn parse_string(&mut self, string: &str) -> Result<(), ()> {
        self.row += 1;
        let mut simplified_string = String::new();
        let mut current_area_index: Option<usize> = None;
        let mut column = 0u32;
        for token in TemplateAreasTokenizer(string) {
            column += 1;
            if column > 1 {
                simplified_string.push(' ');
            }
            let name = if let Some(token) = token? {
                simplified_string.push_str(token);
                Atom::from(token)
            } else {
                if let Some(index) = current_area_index.take() {
                    if self.areas[index].columns.end != column {
                        return Err(());
                    }
                }
                simplified_string.push('.');
                continue;
            };
            if let Some(index) = current_area_index {
                if self.areas[index].name == name {
                    if self.areas[index].rows.start == self.row {
                        self.areas[index].columns.end += 1;
                    }
                    continue;
                }
                if self.areas[index].columns.end != column {
                    return Err(());
                }
            }
            match self.area_indices.entry(name) {
                Entry::Occupied(ref e) => {
                    let index = *e.get();
                    if self.areas[index].columns.start != column ||
                        self.areas[index].rows.end != self.row
                    {
                        return Err(());
                    }
                    self.areas[index].rows.end += 1;
                    current_area_index = Some(index);
                },
                Entry::Vacant(v) => {
                    let index = self.areas.len();
                    let name = v.key().clone();
                    v.insert(index);
                    self.areas.push(NamedArea {
                        name,
                        columns: UnsignedRange {
                            start: column,
                            end: column + 1,
                        },
                        rows: UnsignedRange {
                            start: self.row,
                            end: self.row + 1,
                        },
                    });
                    current_area_index = Some(index);
                },
            }
        }
        if column == 0 {
            // Each string must produce a valid token.
            // https://github.com/w3c/csswg-drafts/issues/5110
            return Err(());
        }
        if let Some(index) = current_area_index {
            if self.areas[index].columns.end != column + 1 {
                debug_assert_ne!(self.areas[index].rows.start, self.row);
                return Err(());
            }
        }
        if self.row == 1 {
            self.width = column;
        } else if self.width != column {
            return Err(());
        }

        self.strings.push(simplified_string.into());
        Ok(())
    }

    /// Return the parsed template areas.
    pub fn finish(self) -> Result<TemplateAreas, ()> {
        if self.strings.is_empty() {
            return Err(());
        }
        Ok(TemplateAreas {
            areas: self.areas.into(),
            strings: self.strings.into(),
            width: self.width,
        })
    }
}

impl TemplateAreas {
    fn parse_internal(input: &mut Parser) -> Result<Self, ()> {
        let mut parser = TemplateAreasParser::default();
        while parser.try_parse_string(input).is_ok() {}
        parser.finish()
    }
}

impl Parse for TemplateAreas {
    fn parse<'i, 't>(
        _: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        Self::parse_internal(input)
            .map_err(|()| input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
    }
}

/// Arc type for `Arc<TemplateAreas>`
#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(transparent)]
pub struct TemplateAreasArc(#[ignore_malloc_size_of = "Arc"] pub Arc<TemplateAreas>);

impl Parse for TemplateAreasArc {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        let parsed = TemplateAreas::parse(context, input)?;
        Ok(TemplateAreasArc(Arc::new(parsed)))
    }
}

/// A range of rows or columns. Using this instead of std::ops::Range for FFI
/// purposes.
#[repr(C)]
#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToResolvedValue,
    ToShmem,
)]
pub struct UnsignedRange {
    /// The start of the range.
    pub start: u32,
    /// The end of the range.
    pub end: u32,
}

#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
/// Not associated with any particular grid item, but can be referenced from the
/// grid-placement properties.
pub struct NamedArea {
    /// Name of the `named area`
    pub name: Atom,
    /// Rows of the `named area`
    pub rows: UnsignedRange,
    /// Columns of the `named area`
    pub columns: UnsignedRange,
}

/// Tokenize the string into a list of the tokens,
/// using longest-match semantics
struct TemplateAreasTokenizer<'a>(&'a str);

impl<'a> Iterator for TemplateAreasTokenizer<'a> {
    type Item = Result<Option<&'a str>, ()>;

    fn next(&mut self) -> Option<Self::Item> {
        let rest = self.0.trim_start_matches(HTML_SPACE_CHARACTERS);
        if rest.is_empty() {
            return None;
        }
        if rest.starts_with('.') {
            self.0 = &rest[rest.find(|c| c != '.').unwrap_or(rest.len())..];
            return Some(Ok(None));
        }
        if !rest.starts_with(is_name_code_point) {
            return Some(Err(()));
        }
        let token_len = rest.find(|c| !is_name_code_point(c)).unwrap_or(rest.len());
        let token = &rest[..token_len];
        self.0 = &rest[token_len..];
        Some(Ok(Some(token)))
    }
}

fn is_name_code_point(c: char) -> bool {
    c >= 'A' && c <= 'Z' ||
        c >= 'a' && c <= 'z' ||
        c >= '\u{80}' ||
        c == '_' ||
        c >= '0' && c <= '9' ||
        c == '-'
}

/// This property specifies named grid areas.
///
/// The syntax of this property also provides a visualization of the structure
/// of the grid, making the overall layout of the grid container easier to
/// understand.
#[repr(C, u8)]
#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
pub enum GridTemplateAreas {
    /// The `none` value.
    None,
    /// The actual value.
    Areas(TemplateAreasArc),
}

impl GridTemplateAreas {
    #[inline]
    /// Get default value as `none`
    pub fn none() -> GridTemplateAreas {
        GridTemplateAreas::None
    }
}

/// A specified value for the `z-index` property.
pub type ZIndex = GenericZIndex<Integer>;

/// A specified value for the `aspect-ratio` property.
pub type AspectRatio = GenericAspectRatio<NonNegativeNumber>;

impl Parse for AspectRatio {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        use crate::values::generics::position::PreferredRatio;
        use crate::values::specified::Ratio;

        let location = input.current_source_location();
        let mut auto = input.try_parse(|i| i.expect_ident_matching("auto"));
        let ratio = input.try_parse(|i| Ratio::parse(context, i));
        if auto.is_err() {
            auto = input.try_parse(|i| i.expect_ident_matching("auto"));
        }

        if auto.is_err() && ratio.is_err() {
            return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }

        Ok(AspectRatio {
            auto: auto.is_ok(),
            ratio: match ratio {
                Ok(ratio) => PreferredRatio::Ratio(ratio),
                Err(..) => PreferredRatio::None,
            },
        })
    }
}

impl AspectRatio {
    /// Returns Self by a valid ratio.
    pub fn from_mapped_ratio(w: f32, h: f32) -> Self {
        use crate::values::generics::position::PreferredRatio;
        use crate::values::generics::ratio::Ratio;
        AspectRatio {
            auto: true,
            ratio: PreferredRatio::Ratio(Ratio(
                NonNegativeNumber::new(w),
                NonNegativeNumber::new(h),
            )),
        }
    }
}

/// A specified value for inset types.
pub type Inset = GenericInset<specified::Percentage, LengthPercentage>;

impl Inset {
    /// Parses an inset type, allowing the unitless length quirk.
    /// <https://quirks.spec.whatwg.org/#the-unitless-length-quirk>
    #[inline]
    pub fn parse_quirky<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
        allow_quirks: AllowQuirks,
    ) -> Result<Self, ParseError<'i>> {
        if let Ok(l) = input.try_parse(|i| LengthPercentage::parse_quirky(context, i, allow_quirks))
        {
            return Ok(Self::LengthPercentage(l));
        }
        if input.try_parse(|i| i.expect_ident_matching("auto")).is_ok() {
            return Ok(Self::Auto);
        }
        if let Ok(inner) = input.try_parse(|i| AnchorFunction::parse(context, i)) {
            return Ok(Self::AnchorFunction(Box::new(inner)));
        }
        Ok(Self::AnchorSizeFunction(Box::new(
            specified::AnchorSizeFunction::parse(context, input)?,
        )))
    }
}

impl Parse for Inset {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        Self::parse_quirky(context, input, AllowQuirks::No)
    }
}

/// A specified value for `anchor()` function.
pub type AnchorFunction = GenericAnchorFunction<specified::Percentage, LengthPercentage>;

impl Parse for AnchorFunction {
    fn parse<'i, 't>(
        context: &ParserContext,
        input: &mut Parser<'i, 't>,
    ) -> Result<Self, ParseError<'i>> {
        if !static_prefs::pref!("layout.css.anchor-positioning.enabled") {
            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
        }
        input.expect_function_matching("anchor")?;
        input.parse_nested_block(|i| {
            let target_element = i.try_parse(|i| DashedIdent::parse(context, i)).ok();
            let side = AnchorSide::parse(context, i)?;
            let target_element = if target_element.is_none() {
                i.try_parse(|i| DashedIdent::parse(context, i)).ok()
            } else {
                target_element
            };
            let fallback = i
                .try_parse(|i| {
                    i.expect_comma()?;
                    LengthPercentage::parse(context, i)
                })
                .ok();
            Ok(Self {
                target_element: target_element.unwrap_or_else(DashedIdent::empty),
                side,
                fallback: fallback.into(),
            })
        })
    }
}