typst/crates/typst-layout/src/math/fragment.rs

use std::fmt::{self, Debug, Formatter};

use rustybuzz::Feature;
use ttf_parser::gsub::{AlternateSubstitution, SingleSubstitution, SubstitutionSubtable};
use ttf_parser::opentype_layout::LayoutTable;
use ttf_parser::{GlyphId, Rect};
use typst_library::foundations::StyleChain;
use typst_library::introspection::Tag;
use typst_library::layout::{
    Abs, Axis, Corner, Em, Frame, FrameItem, Point, Size, VAlignment,
};
use typst_library::math::{EquationElem, MathSize};
use typst_library::text::{Font, Glyph, Lang, Region, TextElem, TextItem};
use typst_library::visualize::Paint;
use typst_syntax::Span;
use typst_utils::default_math_class;
use unicode_math_class::MathClass;

use super::{stretch_glyph, MathContext, Scaled};
use crate::modifiers::{FrameModifiers, FrameModify};

#[derive(Debug, Clone)]
pub enum MathFragment {
    Glyph(GlyphFragment),
    Variant(VariantFragment),
    Frame(FrameFragment),
    Spacing(Abs, bool),
    Space(Abs),
    Linebreak,
    Align,
    Tag(Tag),
}

impl MathFragment {
    pub fn size(&self) -> Size {
        Size::new(self.width(), self.height())
    }

    pub fn width(&self) -> Abs {
        match self {
            Self::Glyph(glyph) => glyph.width,
            Self::Variant(variant) => variant.frame.width(),
            Self::Frame(fragment) => fragment.frame.width(),
            Self::Spacing(amount, _) => *amount,
            Self::Space(amount) => *amount,
            _ => Abs::zero(),
        }
    }

    pub fn height(&self) -> Abs {
        match self {
            Self::Glyph(glyph) => glyph.height(),
            Self::Variant(variant) => variant.frame.height(),
            Self::Frame(fragment) => fragment.frame.height(),
            _ => Abs::zero(),
        }
    }

    pub fn ascent(&self) -> Abs {
        match self {
            Self::Glyph(glyph) => glyph.ascent,
            Self::Variant(variant) => variant.frame.ascent(),
            Self::Frame(fragment) => fragment.frame.baseline(),
            _ => Abs::zero(),
        }
    }

    pub fn descent(&self) -> Abs {
        match self {
            Self::Glyph(glyph) => glyph.descent,
            Self::Variant(variant) => variant.frame.descent(),
            Self::Frame(fragment) => fragment.frame.descent(),
            _ => Abs::zero(),
        }
    }

    pub fn is_ignorant(&self) -> bool {
        match self {
            Self::Frame(fragment) => fragment.ignorant,
            Self::Tag(_) => true,
            _ => false,
        }
    }

    pub fn class(&self) -> MathClass {
        match self {
            Self::Glyph(glyph) => glyph.class,
            Self::Variant(variant) => variant.class,
            Self::Frame(fragment) => fragment.class,
            Self::Spacing(_, _) => MathClass::Space,
            Self::Space(_) => MathClass::Space,
            Self::Linebreak => MathClass::Space,
            Self::Align => MathClass::Special,
            Self::Tag(_) => MathClass::Special,
        }
    }

    pub fn math_size(&self) -> Option<MathSize> {
        match self {
            Self::Glyph(glyph) => Some(glyph.math_size),
            Self::Variant(variant) => Some(variant.math_size),
            Self::Frame(fragment) => Some(fragment.math_size),
            _ => None,
        }
    }

    pub fn font_size(&self) -> Option<Abs> {
        match self {
            Self::Glyph(glyph) => Some(glyph.font_size),
            Self::Variant(variant) => Some(variant.font_size),
            Self::Frame(fragment) => Some(fragment.font_size),
            _ => None,
        }
    }

    pub fn set_class(&mut self, class: MathClass) {
        match self {
            Self::Glyph(glyph) => glyph.class = class,
            Self::Variant(variant) => variant.class = class,
            Self::Frame(fragment) => fragment.class = class,
            _ => {}
        }
    }

    pub fn set_limits(&mut self, limits: Limits) {
        match self {
            Self::Glyph(glyph) => glyph.limits = limits,
            Self::Variant(variant) => variant.limits = limits,
            Self::Frame(fragment) => fragment.limits = limits,
            _ => {}
        }
    }

    pub fn is_spaced(&self) -> bool {
        if self.class() == MathClass::Fence {
            return true;
        }

        matches!(
            self,
            MathFragment::Frame(FrameFragment {
                spaced: true,
                class: MathClass::Normal | MathClass::Alphabetic,
                ..
            })
        )
    }

    pub fn is_text_like(&self) -> bool {
        match self {
            Self::Glyph(glyph) => !glyph.extended_shape,
            Self::Variant(variant) => !variant.extended_shape,
            MathFragment::Frame(frame) => frame.text_like,
            _ => false,
        }
    }

    pub fn italics_correction(&self) -> Abs {
        match self {
            Self::Glyph(glyph) => glyph.italics_correction,
            Self::Variant(variant) => variant.italics_correction,
            Self::Frame(fragment) => fragment.italics_correction,
            _ => Abs::zero(),
        }
    }

    pub fn accent_attach(&self) -> (Abs, Abs) {
        match self {
            Self::Glyph(glyph) => glyph.accent_attach,
            Self::Variant(variant) => variant.accent_attach,
            Self::Frame(fragment) => fragment.accent_attach,
            _ => (self.width() / 2.0, self.width() / 2.0),
        }
    }

    pub fn into_frame(self) -> Frame {
        match self {
            Self::Glyph(glyph) => glyph.into_frame(),
            Self::Variant(variant) => variant.frame,
            Self::Frame(fragment) => fragment.frame,
            Self::Tag(tag) => {
                let mut frame = Frame::soft(Size::zero());
                frame.push(Point::zero(), FrameItem::Tag(tag));
                frame
            }
            _ => Frame::soft(self.size()),
        }
    }

    pub fn limits(&self) -> Limits {
        match self {
            MathFragment::Glyph(glyph) => glyph.limits,
            MathFragment::Variant(variant) => variant.limits,
            MathFragment::Frame(fragment) => fragment.limits,
            _ => Limits::Never,
        }
    }

    /// If no kern table is provided for a corner, a kerning amount of zero is
    /// assumed.
    pub fn kern_at_height(&self, ctx: &MathContext, corner: Corner, height: Abs) -> Abs {
        match self {
            Self::Glyph(glyph) => {
                kern_at_height(ctx, glyph.font_size, glyph.id, corner, height)
                    .unwrap_or_default()
            }
            _ => Abs::zero(),
        }
    }
}

impl From<GlyphFragment> for MathFragment {
    fn from(glyph: GlyphFragment) -> Self {
        Self::Glyph(glyph)
    }
}

impl From<VariantFragment> for MathFragment {
    fn from(variant: VariantFragment) -> Self {
        Self::Variant(variant)
    }
}

impl From<FrameFragment> for MathFragment {
    fn from(fragment: FrameFragment) -> Self {
        Self::Frame(fragment)
    }
}

#[derive(Clone)]
pub struct GlyphFragment {
    pub id: GlyphId,
    pub c: char,
    pub font: Font,
    pub lang: Lang,
    pub region: Option<Region>,
    pub fill: Paint,
    pub shift: Abs,
    pub width: Abs,
    pub ascent: Abs,
    pub descent: Abs,
    pub italics_correction: Abs,
    pub accent_attach: (Abs, Abs),
    pub font_size: Abs,
    pub class: MathClass,
    pub math_size: MathSize,
    pub span: Span,
    pub modifiers: FrameModifiers,
    pub limits: Limits,
    pub extended_shape: bool,
}

impl GlyphFragment {
    pub fn new(ctx: &MathContext, styles: StyleChain, c: char, span: Span) -> Self {
        let id = ctx.ttf.glyph_index(c).unwrap_or_default();
        let id = Self::adjust_glyph_index(ctx, id);
        Self::with_id(ctx, styles, c, id, span)
    }

    pub fn try_new(
        ctx: &MathContext,
        styles: StyleChain,
        c: char,
        span: Span,
    ) -> Option<Self> {
        let id = ctx.ttf.glyph_index(c)?;
        let id = Self::adjust_glyph_index(ctx, id);
        Some(Self::with_id(ctx, styles, c, id, span))
    }

    pub fn with_id(
        ctx: &MathContext,
        styles: StyleChain,
        c: char,
        id: GlyphId,
        span: Span,
    ) -> Self {
        let class = EquationElem::class_in(styles)
            .or_else(|| default_math_class(c))
            .unwrap_or(MathClass::Normal);

        let mut fragment = Self {
            id,
            c,
            font: ctx.font.clone(),
            lang: TextElem::lang_in(styles),
            region: TextElem::region_in(styles),
            fill: TextElem::fill_in(styles).as_decoration(),
            shift: TextElem::baseline_in(styles),
            font_size: TextElem::size_in(styles),
            math_size: EquationElem::size_in(styles),
            width: Abs::zero(),
            ascent: Abs::zero(),
            descent: Abs::zero(),
            limits: Limits::for_char(c),
            italics_correction: Abs::zero(),
            accent_attach: (Abs::zero(), Abs::zero()),
            class,
            span,
            modifiers: FrameModifiers::get_in(styles),
            extended_shape: false,
        };
        fragment.set_id(ctx, id);
        fragment
    }

    /// Apply GSUB substitutions.
    fn adjust_glyph_index(ctx: &MathContext, id: GlyphId) -> GlyphId {
        if let Some(glyphwise_tables) = &ctx.glyphwise_tables {
            glyphwise_tables.iter().fold(id, |id, table| table.apply(id))
        } else {
            id
        }
    }

    /// Sets element id and boxes in appropriate way without changing other
    /// styles. This is used to replace the glyph with a stretch variant.
    pub fn set_id(&mut self, ctx: &MathContext, id: GlyphId) {
        let advance = ctx.ttf.glyph_hor_advance(id).unwrap_or_default();
        let italics = italics_correction(ctx, id, self.font_size).unwrap_or_default();
        let bbox = ctx.ttf.glyph_bounding_box(id).unwrap_or(Rect {
            x_min: 0,
            y_min: 0,
            x_max: 0,
            y_max: 0,
        });

        let mut width = advance.scaled(ctx, self.font_size);

        // The fallback for accents is half the width plus or minus the italics
        // correction. This is similar to how top and bottom attachments are
        // shifted. For bottom accents we do not use the accent attach of the
        // base as it is meant for top acccents.
        let top_accent_attach =
            accent_attach(ctx, id, self.font_size).unwrap_or((width + italics) / 2.0);
        let bottom_accent_attach = (width - italics) / 2.0;

        let extended_shape = is_extended_shape(ctx, id);
        if !extended_shape {
            width += italics;
        }

        self.id = id;
        self.width = width;
        self.ascent = bbox.y_max.scaled(ctx, self.font_size);
        self.descent = -bbox.y_min.scaled(ctx, self.font_size);
        self.italics_correction = italics;
        self.accent_attach = (top_accent_attach, bottom_accent_attach);
        self.extended_shape = extended_shape;
    }

    pub fn height(&self) -> Abs {
        self.ascent + self.descent
    }

    pub fn into_variant(self) -> VariantFragment {
        VariantFragment {
            c: self.c,
            font_size: self.font_size,
            italics_correction: self.italics_correction,
            accent_attach: self.accent_attach,
            class: self.class,
            math_size: self.math_size,
            span: self.span,
            limits: self.limits,
            extended_shape: self.extended_shape,
            frame: self.into_frame(),
            mid_stretched: None,
        }
    }

    pub fn into_frame(self) -> Frame {
        let item = TextItem {
            font: self.font.clone(),
            size: self.font_size,
            fill: self.fill,
            lang: self.lang,
            region: self.region,
            text: self.c.into(),
            stroke: None,
            glyphs: vec![Glyph {
                id: self.id.0,
                x_advance: Em::from_length(self.width, self.font_size),
                x_offset: Em::zero(),
                range: 0..self.c.len_utf8() as u16,
                span: (self.span, 0),
            }],
        };
        let size = Size::new(self.width, self.ascent + self.descent);
        let mut frame = Frame::soft(size);
        frame.set_baseline(self.ascent);
        frame.push(Point::with_y(self.ascent + self.shift), FrameItem::Text(item));
        frame.modify(&self.modifiers);
        frame
    }

    pub fn make_script_size(&mut self, ctx: &MathContext) {
        let alt_id =
            ctx.ssty_table.as_ref().and_then(|ssty| ssty.try_apply(self.id, None));
        if let Some(alt_id) = alt_id {
            self.set_id(ctx, alt_id);
        }
    }

    pub fn make_script_script_size(&mut self, ctx: &MathContext) {
        let alt_id = ctx.ssty_table.as_ref().and_then(|ssty| {
            // We explicitly request to apply the alternate set with value 1,
            // as opposed to the default value in ssty, as the former
            // corresponds to second level scripts and the latter corresponds
            // to first level scripts.
            ssty.try_apply(self.id, Some(1))
                .or_else(|| ssty.try_apply(self.id, None))
        });
        if let Some(alt_id) = alt_id {
            self.set_id(ctx, alt_id);
        }
    }

    pub fn make_dotless_form(&mut self, ctx: &MathContext) {
        let alt_id =
            ctx.dtls_table.as_ref().and_then(|dtls| dtls.try_apply(self.id, None));
        if let Some(alt_id) = alt_id {
            self.set_id(ctx, alt_id);
        }
    }

    pub fn make_flattened_accent_form(&mut self, ctx: &MathContext) {
        let alt_id =
            ctx.flac_table.as_ref().and_then(|flac| flac.try_apply(self.id, None));
        if let Some(alt_id) = alt_id {
            self.set_id(ctx, alt_id);
        }
    }

    /// Try to stretch a glyph to a desired height.
    pub fn stretch_vertical(
        self,
        ctx: &mut MathContext,
        height: Abs,
        short_fall: Abs,
    ) -> VariantFragment {
        stretch_glyph(ctx, self, height, short_fall, Axis::Y)
    }

    /// Try to stretch a glyph to a desired width.
    pub fn stretch_horizontal(
        self,
        ctx: &mut MathContext,
        width: Abs,
        short_fall: Abs,
    ) -> VariantFragment {
        stretch_glyph(ctx, self, width, short_fall, Axis::X)
    }
}

impl Debug for GlyphFragment {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(f, "GlyphFragment({:?})", self.c)
    }
}

#[derive(Clone)]
pub struct VariantFragment {
    pub c: char,
    pub italics_correction: Abs,
    pub accent_attach: (Abs, Abs),
    pub frame: Frame,
    pub font_size: Abs,
    pub class: MathClass,
    pub math_size: MathSize,
    pub span: Span,
    pub limits: Limits,
    pub mid_stretched: Option<bool>,
    pub extended_shape: bool,
}

impl VariantFragment {
    /// Vertically adjust the fragment's frame so that it is centered
    /// on the axis.
    pub fn center_on_axis(&mut self, ctx: &MathContext) {
        self.align_on_axis(ctx, VAlignment::Horizon)
    }

    /// Vertically adjust the fragment's frame so that it is aligned
    /// to the given alignment on the axis.
    pub fn align_on_axis(&mut self, ctx: &MathContext, align: VAlignment) {
        let h = self.frame.height();
        let axis = ctx.constants.axis_height().scaled(ctx, self.font_size);
        self.frame.set_baseline(align.inv().position(h + axis * 2.0));
    }
}

impl Debug for VariantFragment {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(f, "VariantFragment({:?})", self.c)
    }
}

#[derive(Debug, Clone)]
pub struct FrameFragment {
    pub frame: Frame,
    pub font_size: Abs,
    pub class: MathClass,
    pub math_size: MathSize,
    pub limits: Limits,
    pub spaced: bool,
    pub base_ascent: Abs,
    pub base_descent: Abs,
    pub italics_correction: Abs,
    pub accent_attach: (Abs, Abs),
    pub text_like: bool,
    pub ignorant: bool,
}

impl FrameFragment {
    pub fn new(styles: StyleChain, frame: Frame) -> Self {
        let base_ascent = frame.ascent();
        let base_descent = frame.descent();
        let accent_attach = frame.width() / 2.0;
        Self {
            frame: frame.modified(&FrameModifiers::get_in(styles)),
            font_size: TextElem::size_in(styles),
            class: EquationElem::class_in(styles).unwrap_or(MathClass::Normal),
            math_size: EquationElem::size_in(styles),
            limits: Limits::Never,
            spaced: false,
            base_ascent,
            base_descent,
            italics_correction: Abs::zero(),
            accent_attach: (accent_attach, accent_attach),
            text_like: false,
            ignorant: false,
        }
    }

    pub fn with_class(self, class: MathClass) -> Self {
        Self { class, ..self }
    }

    pub fn with_limits(self, limits: Limits) -> Self {
        Self { limits, ..self }
    }

    pub fn with_spaced(self, spaced: bool) -> Self {
        Self { spaced, ..self }
    }

    pub fn with_base_ascent(self, base_ascent: Abs) -> Self {
        Self { base_ascent, ..self }
    }

    pub fn with_base_descent(self, base_descent: Abs) -> Self {
        Self { base_descent, ..self }
    }

    pub fn with_italics_correction(self, italics_correction: Abs) -> Self {
        Self { italics_correction, ..self }
    }

    pub fn with_accent_attach(self, accent_attach: (Abs, Abs)) -> Self {
        Self { accent_attach, ..self }
    }

    pub fn with_text_like(self, text_like: bool) -> Self {
        Self { text_like, ..self }
    }

    pub fn with_ignorant(self, ignorant: bool) -> Self {
        Self { ignorant, ..self }
    }
}

/// Look up the italics correction for a glyph.
fn italics_correction(ctx: &MathContext, id: GlyphId, font_size: Abs) -> Option<Abs> {
    Some(
        ctx.table
            .glyph_info?
            .italic_corrections?
            .get(id)?
            .scaled(ctx, font_size),
    )
}

/// Loop up the top accent attachment position for a glyph.
fn accent_attach(ctx: &MathContext, id: GlyphId, font_size: Abs) -> Option<Abs> {
    Some(
        ctx.table
            .glyph_info?
            .top_accent_attachments?
            .get(id)?
            .scaled(ctx, font_size),
    )
}

/// Look up whether a glyph is an extended shape.
fn is_extended_shape(ctx: &MathContext, id: GlyphId) -> bool {
    ctx.table
        .glyph_info
        .and_then(|info| info.extended_shapes)
        .and_then(|info| info.get(id))
        .is_some()
}

/// Look up a kerning value at a specific corner and height.
fn kern_at_height(
    ctx: &MathContext,
    font_size: Abs,
    id: GlyphId,
    corner: Corner,
    height: Abs,
) -> Option<Abs> {
    let kerns = ctx.table.glyph_info?.kern_infos?.get(id)?;
    let kern = match corner {
        Corner::TopLeft => kerns.top_left,
        Corner::TopRight => kerns.top_right,
        Corner::BottomRight => kerns.bottom_right,
        Corner::BottomLeft => kerns.bottom_left,
    }?;

    let mut i = 0;
    while i < kern.count() && height > kern.height(i)?.scaled(ctx, font_size) {
        i += 1;
    }

    Some(kern.kern(i)?.scaled(ctx, font_size))
}

/// Describes in which situation a frame should use limits for attachments.
#[derive(Debug, Copy, Clone)]
pub enum Limits {
    /// Always scripts.
    Never,
    /// Display limits only in `display` math.
    Display,
    /// Always limits.
    Always,
}

impl Limits {
    /// The default limit configuration if the given character is the base.
    pub fn for_char(c: char) -> Self {
        match default_math_class(c) {
            Some(MathClass::Large) => {
                if is_integral_char(c) {
                    Limits::Never
                } else {
                    Limits::Display
                }
            }
            Some(MathClass::Relation) => Limits::Always,
            _ => Limits::Never,
        }
    }

    /// The default limit configuration for a math class.
    pub fn for_class(class: MathClass) -> Self {
        match class {
            MathClass::Large => Self::Display,
            MathClass::Relation => Self::Always,
            _ => Self::Never,
        }
    }

    /// Whether limits should be displayed in this context.
    pub fn active(&self, styles: StyleChain) -> bool {
        match self {
            Self::Always => true,
            Self::Display => EquationElem::size_in(styles) == MathSize::Display,
            Self::Never => false,
        }
    }
}

/// Determines if the character is one of a variety of integral signs.
fn is_integral_char(c: char) -> bool {
    ('∫'..='∳').contains(&c) || ('⨋'..='⨜').contains(&c)
}

/// An OpenType substitution table that is applicable to glyph-wise substitutions.
pub enum GlyphwiseSubsts<'a> {
    Single(SingleSubstitution<'a>),
    Alternate(AlternateSubstitution<'a>, u32),
}

impl<'a> GlyphwiseSubsts<'a> {
    pub fn new(gsub: Option<LayoutTable<'a>>, feature: Feature) -> Option<Self> {
        let gsub = gsub?;
        let table = gsub
            .features
            .find(feature.tag)
            .and_then(|feature| feature.lookup_indices.get(0))
            .and_then(|index| gsub.lookups.get(index))?;
        let table = table.subtables.get::<SubstitutionSubtable>(0)?;
        match table {
            SubstitutionSubtable::Single(single_glyphs) => {
                Some(Self::Single(single_glyphs))
            }
            SubstitutionSubtable::Alternate(alt_glyphs) => {
                Some(Self::Alternate(alt_glyphs, feature.value))
            }
            _ => None,
        }
    }

    pub fn try_apply(
        &self,
        glyph_id: GlyphId,
        alt_value: Option<u32>,
    ) -> Option<GlyphId> {
        match self {
            Self::Single(single) => match single {
                SingleSubstitution::Format1 { coverage, delta } => coverage
                    .get(glyph_id)
                    .map(|_| GlyphId(glyph_id.0.wrapping_add(*delta as u16))),
                SingleSubstitution::Format2 { coverage, substitutes } => {
                    coverage.get(glyph_id).and_then(|idx| substitutes.get(idx))
                }
            },
            Self::Alternate(alternate, value) => alternate
                .coverage
                .get(glyph_id)
                .and_then(|idx| alternate.alternate_sets.get(idx))
                .and_then(|set| set.alternates.get(alt_value.unwrap_or(*value) as u16)),
        }
    }

    pub fn apply(&self, glyph_id: GlyphId) -> GlyphId {
        self.try_apply(glyph_id, None).unwrap_or(glyph_id)
    }
}