makeover/

font.rs

//! Typography — layer 0, the app override.
//!
//! Wiki `typography-standard`, GO makeover `174ab3c1`. Layer 1 above is what
//! every product shares; this is the one declaration a product is allowed to
//! make for itself:
//!
//! ```text
//! layer 0   app override     per product, optional   MNW display -> Young Serif
//! layer 1   house default    the quasi-* slot font   quasi-mono  -> Quasi Mono
//! layer 2   system generic   one hop, no further     monospace / sans-serif
//! ```
//!
//! The brand tier was already exempt by decision (`cdf8ac09`), and the exemption
//! was enforced by those faces simply not being in the vocabulary — so each
//! product reached its own face through a hardcoded `font-family` and an
//! `@font-face` block it maintained by hand, which is the exact shape the
//! unification is deleting everywhere else. This turns the carve-out into a
//! mechanism: the per-product face is declared once, in the build script that
//! already writes the typography layer, and is readable as an override rather
//! than as a stylesheet nobody unified.
//!
//! It permits overriding `mono` and `sans` too. No product wants that today,
//! and a layer that only allows overriding the slot nobody describes is not a
//! layer, it is the exemption restated.
//!
//! **One declaration per product per slot.** [`Typography::with_override`]
//! panics on a second override of the same slot rather than letting the last
//! one win: a product with two answers for a slot has the vocabulary wrong, and
//! that is the thing to fix.
//!
//! # What a renderer does when it cannot honour one
//!
//! Declare once, renderers honour what they can. Today only the webview surface
//! has a face to honour at all — neither `makeover-tui` nor `makeover-immediate`
//! emits a `font-family` from anywhere, because the terminal owns the face in
//! one and the app loads its own font stack in the other. So an override is
//! honoured by the generated stylesheet and ignored, silently and correctly, by
//! the other two. That last clause was too strong and 2.10.0 corrected it: egui
//! can reach a face perfectly well, it just needs the file rather than a stack.
//! audiofiles honours its override with no stylesheet anywhere in the path. A renderer that gains font control later reads
//! [`Typography::resolve`] rather than the CSS, which is why the resolution is
//! a method on the data and not a string-building detail. Loading a file needs
//! one thing more than the stack — the family name and the source to load it
//! from — so [`Typography::faces`] is the same data read the other way, and
//! between them an egui or TUI surface can honour an override without a
//! stylesheet anywhere in the path. audiofiles is the first to do it.

use crate::{
    FONT_MONO, FONT_SANS, HOUSE_MONO_FAMILY, HOUSE_SANS_FAMILY, HOUSE_WEIGHT_RANGE,
    WEBFONT_MONO_FILE, WEBFONT_SANS_FILE, font_face_css,
};

// Names this module's prose links to, resolved for rustdoc.
#[allow(unused_imports)]
use crate::typography_css_vars;

/// A slot in the house font vocabulary — the unit an override replaces.
///
/// Three, and the third is deliberately empty by default: `display` is the
/// brand tier, it has no house answer, and a product that does not override it
/// leaves the token undefined so whatever the consumer wrote as a fallback
/// renders. The MNW embeds rely on exactly that.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum FontSlot {
    /// Code, data, identifiers, cell grids. [`FONT_MONO`] by default.
    Mono,
    /// Body and UI text: everything that is not mono or brand. [`FONT_SANS`].
    Sans,
    /// The brand / display tier. No house default.
    Display,
}

impl FontSlot {
    /// Every slot, in the order they are emitted.
    pub const ALL: [FontSlot; 3] = [FontSlot::Mono, FontSlot::Sans, FontSlot::Display];

    /// The custom property this slot is read through.
    pub fn token(self) -> &'static str {
        match self {
            FontSlot::Mono => "--font-mono",
            FontSlot::Sans => "--font-sans",
            FontSlot::Display => "--font-display",
        }
    }

    /// The house stack, or `None` for the brand tier.
    pub fn house_default(self) -> Option<&'static str> {
        match self {
            FontSlot::Mono => Some(FONT_MONO),
            FontSlot::Sans => Some(FONT_SANS),
            FontSlot::Display => None,
        }
    }

    /// The house face behind that stack, or `None` for the brand tier.
    ///
    /// The counterpart of [`house_default`](Self::house_default), and the same
    /// split as [`Typography::resolve`] against [`Typography::faces`]: one
    /// names the family that wins, the other names the file behind it. The
    /// house tier was a format string until this existed, so it could be
    /// emitted and not read — which made [`Typography::faces`] answer for the
    /// brand tier and stay silent about the other two.
    ///
    /// The sources are the **web** copies. A native loader wants a `ttf` and
    /// cuts its own through `quasi-type`, whose `cut_native` writes the file
    /// and hands back the family, style and default weight to register it
    /// under; there is no house `ttf` named here, and there should not be. This
    /// crate is on crates.io and `quasi-type` is `publish = false`, so naming a
    /// native file here would assert a path the web build does not write and
    /// save the consumer nothing, since it still has to run the pipeline.
    ///
    /// One hazard travels with that arrangement and is not solved: a native
    /// consumer takes `quasi-type` as a git dep and pins a rev, so a stale pin
    /// ships an older glyph set silently. Advance it deliberately.
    pub fn house_face(self) -> Option<FontFace> {
        let (family, file) = match self {
            FontSlot::Mono => (HOUSE_MONO_FAMILY, WEBFONT_MONO_FILE),
            FontSlot::Sans => (HOUSE_SANS_FAMILY, WEBFONT_SANS_FILE),
            FontSlot::Display => return None,
        };
        Some(
            FontFace::new(family, [file])
                .with_weight(HOUSE_WEIGHT_RANGE)
                .with_style("normal"),
        )
    }
}

/// One `@font-face` an override brings with it.
///
/// A product overriding a slot usually has to ship the face too, and the two
/// halves have to agree on a family name. Declaring them together is what
/// makes that agreement structural rather than a string typed twice.
#[derive(Debug, Clone)]
pub struct FontFace {
    family: String,
    sources: Vec<String>,
    weight: Option<String>,
    style: Option<String>,
}

impl FontFace {
    /// A face named `family`, fetched from `sources`.
    ///
    /// Each source is either a bare filename, resolved against the
    /// [`Typography`] base URL, or an absolute one (`/…` or `https://…`) taken
    /// as written. The `format()` hint is inferred from the extension —
    /// `woff2`, `woff`, `ttf`, `otf` — and omitted for anything else rather
    /// than guessed, since a wrong hint is worse than none.
    pub fn new<S: Into<String>>(
        family: impl Into<String>,
        sources: impl IntoIterator<Item = S>,
    ) -> Self {
        Self {
            family: family.into(),
            sources: sources.into_iter().map(Into::into).collect(),
            weight: None,
            style: None,
        }
    }

    /// `font-weight`, as CSS writes it: `"700"`, or `"200 800"` for a variable
    /// axis. Omitted when unset, which means `normal`.
    ///
    /// A variable face MUST name its range here for the same reason the house
    /// faces do: a `@font-face` with no range makes the browser resolve every
    /// weight to the file's default instance.
    #[must_use]
    pub fn with_weight(mut self, weight: impl Into<String>) -> Self {
        self.weight = Some(weight.into());
        self
    }

    /// `font-style`. Omitted when unset, which means `normal`.
    #[must_use]
    pub fn with_style(mut self, style: impl Into<String>) -> Self {
        self.style = Some(style.into());
        self
    }

    /// The declared `font-weight`, or `None` when the face never named one.
    ///
    /// A renderer loading a variable face directly has to name a weight — the
    /// file's own default instance is whatever the base shipped, which for the
    /// house faces is ExtraLight — so this is the half of the declaration that
    /// stops the load from being a guess.
    pub fn weight(&self) -> Option<&str> {
        self.weight.as_deref()
    }

    /// The declared `font-style`, or `None`, which means `normal`.
    pub fn style(&self) -> Option<&str> {
        self.style.as_deref()
    }

    /// The family name, as the stack has to spell it.
    ///
    /// For a renderer that loads faces rather than emitting CSS this is the
    /// name it registers the file under, and reading it here is what keeps
    /// that name from being typed a second time.
    pub fn family(&self) -> &str {
        &self.family
    }

    /// The sources, unresolved — bare filenames as they were declared, not
    /// joined to any base URL. A renderer loading from disk or from an
    /// `include_bytes!` wants the filename; only the CSS wants the URL.
    pub fn sources(&self) -> &[String] {
        &self.sources
    }

    pub(crate) fn css(&self, base: &str) -> String {
        use std::fmt::Write as _;

        let src = self
            .sources
            .iter()
            .map(|s| {
                let url = if s.starts_with('/') || s.contains("://") {
                    s.clone()
                } else {
                    format!("{base}/{s}")
                };
                match font_format(s) {
                    Some(fmt) => format!("url(\"{url}\") format(\"{fmt}\")"),
                    None => format!("url(\"{url}\")"),
                }
            })
            .collect::<Vec<_>>()
            .join(",\n       ");

        let mut out = format!(
            "@font-face {{\n  font-family: \"{}\";\n  src: {src};\n",
            self.family
        );
        if let Some(w) = &self.weight {
            let _ = writeln!(out, "  font-weight: {w};");
        }
        if let Some(s) = &self.style {
            let _ = writeln!(out, "  font-style: {s};");
        }
        out.push_str("  font-display: swap;\n}\n\n");
        out
    }
}

/// The `format()` hint for a source, by extension. `None` when unrecognised.
fn font_format(source: &str) -> Option<&'static str> {
    match source.rsplit('.').next()?.to_ascii_lowercase().as_str() {
        "woff2" => Some("woff2"),
        "woff" => Some("woff"),
        "ttf" => Some("truetype"),
        "otf" => Some("opentype"),
        _ => None,
    }
}

/// One product's answer for one slot: the stack, and any faces it ships.
#[derive(Debug, Clone)]
pub struct FontOverride {
    slot: FontSlot,
    stack: String,
    faces: Vec<FontFace>,
}

impl FontOverride {
    /// Point `slot` at `stack`.
    ///
    /// `stack` is the CSS value the token takes, written the way the house
    /// stacks are: the family, then one hop to a system generic. Layer 2 is
    /// still one hop and no further — an override is a different answer to the
    /// slot, not a licence to write the fallback chain the standard deleted.
    pub fn new(slot: FontSlot, stack: impl Into<String>) -> Self {
        Self {
            slot,
            stack: stack.into(),
            faces: Vec::new(),
        }
    }

    /// Ship a face with the override.
    #[must_use]
    pub fn with_face(mut self, face: FontFace) -> Self {
        self.faces.push(face);
        self
    }

    /// The slot this answers.
    pub fn slot(&self) -> FontSlot {
        self.slot
    }

    /// The stack it resolves to.
    pub fn stack(&self) -> &str {
        &self.stack
    }

    /// The faces it ships, in declaration order.
    pub fn faces(&self) -> &[FontFace] {
        &self.faces
    }
}

/// The whole typography layer for one product: the house defaults, plus
/// whatever it overrides.
///
/// This is what a build script composes and what
/// `makeover_build::typography_css_from` writes. [`typography_css_vars`] and
/// [`font_face_css`] are the no-override case of it and stay for callers that
/// have nothing to declare.
#[derive(Debug, Clone)]
pub struct Typography {
    base_url: String,
    overrides: Vec<FontOverride>,
}

impl Typography {
    /// The house layer alone, fetching faces from `base_url` — the directory
    /// the consumer serves fonts from, with or without a trailing slash.
    pub fn house(base_url: impl Into<String>) -> Self {
        Self {
            base_url: base_url.into(),
            overrides: Vec::new(),
        }
    }

    /// Add one product override.
    ///
    /// # Panics
    ///
    /// If the slot is already overridden. One declaration per product per
    /// slot: a second is not a merge to resolve, it is two answers to a
    /// question that has one, and the vocabulary is what wants fixing.
    #[must_use]
    pub fn with_override(mut self, ov: FontOverride) -> Self {
        assert!(
            !self.overrides.iter().any(|o| o.slot == ov.slot),
            "{} is overridden twice; one declaration per product per slot",
            ov.slot.token()
        );
        self.overrides.push(ov);
        self
    }

    /// What `slot` resolves to under this layer, or `None` for a brand slot
    /// nobody overrode.
    ///
    /// The resolution, for a renderer that has a face to choose rather than a
    /// stylesheet to emit.
    pub fn resolve(&self, slot: FontSlot) -> Option<&str> {
        self.overrides
            .iter()
            .find(|o| o.slot == slot)
            .map(|o| o.stack.as_str())
            .or_else(|| slot.house_default())
    }

    /// The faces a product ships for `slot`, in declaration order, or an
    /// empty slice for a slot it did not override.
    ///
    /// The other half of [`resolve`](Self::resolve), for a renderer that has
    /// to load a file rather than name a stack: `resolve` says which family
    /// wins, this says where the bytes come from, what to call them, and at
    /// what weight. The
    /// house faces are not here — they belong to the slot rather than to any
    /// one product, and [`FontSlot::house_face`] is where they answer.
    pub fn faces(&self, slot: FontSlot) -> &[FontFace] {
        self.overrides
            .iter()
            .find(|o| o.slot == slot)
            .map_or(&[], |o| o.faces())
    }

    /// The `@font-face` rules: the two house faces, then each override's.
    pub fn font_face_css(&self) -> String {
        let base = self.base_url.trim_end_matches('/');
        let mut out = font_face_css(base);
        for ov in &self.overrides {
            for face in &ov.faces {
                out.push_str(&face.css(base));
            }
        }
        out
    }

    /// The resolved tokens as CSS declarations, no selector.
    pub fn css_declarations(&self) -> String {
        use std::fmt::Write as _;

        let mut out = String::new();
        for slot in FontSlot::ALL {
            if let Some(stack) = self.resolve(slot) {
                let _ = writeln!(out, "  {}: {stack};", slot.token());
            }
        }
        out
    }

    /// The resolved tokens as a `:root { … }` block.
    pub fn css_vars(&self) -> String {
        format!(":root {{\n{}}}\n", self.css_declarations())
    }

    /// Faces then tokens, in the order a stylesheet wants them.
    pub fn css(&self) -> String {
        format!("{}{}", self.font_face_css(), self.css_vars())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // ---- typography, layer 0 ----

    /// The live case: MNW's Young Serif, which reached the page through a
    /// hand-maintained `@font-face` and a `--font-heading` nothing else knew
    /// about.
    fn young_serif() -> FontOverride {
        FontOverride::new(FontSlot::Display, "\"Young Serif\", serif")
            .with_face(FontFace::new("Young Serif", ["ysrf.woff2", "ysrf.ttf"]))
    }

    #[test]
    fn the_house_layer_alone_is_exactly_what_the_free_functions_emit() {
        let t = Typography::house("/static/fonts");
        assert_eq!(t.font_face_css(), font_face_css("/static/fonts"));
        assert_eq!(t.css_vars(), typography_css_vars());
    }

    #[test]
    fn an_unoverridden_display_slot_defines_no_token_at_all() {
        // Not "defined empty": undefined, so the consumer's own fallback in
        // `var(--font-display, …)` renders. The MNW embeds depend on it.
        let t = Typography::house("fonts");
        assert!(!t.css_vars().contains("--font-display"));
        assert_eq!(t.resolve(FontSlot::Display), None);
        assert_eq!(t.css_vars().matches("--font-").count(), 2);
    }

    #[test]
    fn an_override_adds_its_token_and_its_face_without_touching_the_house_two() {
        let t = Typography::house("/static/fonts").with_override(young_serif());

        assert!(
            t.css_vars()
                .contains("  --font-display: \"Young Serif\", serif;\n")
        );
        assert!(
            t.css_vars()
                .contains("  --font-mono: \"Quasi Mono\", monospace;\n")
        );
        assert!(
            t.css_vars()
                .contains("  --font-sans: \"Quasi Body\", sans-serif;\n")
        );
        assert_eq!(t.resolve(FontSlot::Display), Some("\"Young Serif\", serif"));

        let faces = t.font_face_css();
        assert_eq!(faces.matches("@font-face").count(), 3);
        assert!(faces.contains("font-family: \"Young Serif\";"));
        assert!(faces.contains("url(\"/static/fonts/ysrf.woff2\") format(\"woff2\")"));
        assert!(faces.contains("url(\"/static/fonts/ysrf.ttf\") format(\"truetype\")"));

        // The house faces still come first, so a product face never shadows a
        // slot it did not claim.
        assert!(faces.find("Quasi Mono").unwrap() < faces.find("Young Serif").unwrap());
    }

    #[test]
    fn overriding_mono_or_sans_replaces_the_house_stack_rather_than_adding_to_it() {
        // Nobody wants this today. A layer that only permits overriding the
        // slot nobody describes is the exemption restated, not a layer.
        let t = Typography::house("fonts").with_override(FontOverride::new(
            FontSlot::Mono,
            "\"Departure Mono\", monospace",
        ));

        assert!(
            t.css_vars()
                .contains("  --font-mono: \"Departure Mono\", monospace;\n")
        );
        assert!(!t.css_vars().contains("Quasi Mono"));
        assert_eq!(t.css_vars().matches("--font-").count(), 2);
    }

    #[test]
    #[should_panic(expected = "--font-display is overridden twice")]
    fn a_second_override_of_one_slot_is_a_vocabulary_bug_and_says_so() {
        let _ = Typography::house("fonts")
            .with_override(young_serif())
            .with_override(FontOverride::new(FontSlot::Display, "\"Reglo\", serif"));
    }

    #[test]
    fn an_absolute_source_is_taken_as_written_and_a_relative_one_joins_the_base() {
        let t = Typography::house("/static/fonts").with_override(
            FontOverride::new(FontSlot::Display, "\"Reglo\", serif").with_face(
                FontFace::new(
                    "Reglo",
                    ["Reglo-Bold.woff2", "https://cdn.example/reglo.woff2"],
                )
                .with_weight("700"),
            ),
        );
        let faces = t.font_face_css();
        assert!(faces.contains("url(\"/static/fonts/Reglo-Bold.woff2\")"));
        assert!(faces.contains("url(\"https://cdn.example/reglo.woff2\")"));
        assert!(faces.contains("  font-weight: 700;\n"));
    }

    #[test]
    fn the_house_tier_renders_byte_for_byte_what_the_format_string_wrote() {
        // The house faces became `FontFace` values so they could be read as
        // well as emitted. Nothing about the sheet was meant to move, and this
        // is the whole of that claim: the literal the format string produced.
        let expected = concat!(
            "@font-face {\n",
            "  font-family: \"Quasi Mono\";\n",
            "  src: url(\"/static/fonts/QuasiMono.woff2\") format(\"woff2\");\n",
            "  font-weight: 200 800;\n",
            "  font-style: normal;\n",
            "  font-display: swap;\n",
            "}\n\n",
            "@font-face {\n",
            "  font-family: \"Quasi Body\";\n",
            "  src: url(\"/static/fonts/QuasiBody.woff2\") format(\"woff2\");\n",
            "  font-weight: 200 800;\n",
            "  font-style: normal;\n",
            "  font-display: swap;\n",
            "}\n\n",
        );
        assert_eq!(font_face_css("/static/fonts"), expected);
    }

    #[test]
    fn a_house_slot_names_the_same_family_in_its_stack_and_in_its_face() {
        // The family is spelled once as a bare name and once inside a CSS
        // stack, because a stack cannot be built from a const at compile time.
        // A face whose family is not the one the stack names loads and is
        // never asked for.
        for (slot, family) in [
            (FontSlot::Mono, HOUSE_MONO_FAMILY),
            (FontSlot::Sans, HOUSE_SANS_FAMILY),
        ] {
            let face = slot.house_face().expect("a house slot has a house face");
            assert_eq!(face.family(), family);
            assert!(
                slot.house_default()
                    .unwrap()
                    .starts_with(&format!("\"{family}\""))
            );
        }
    }

    #[test]
    fn the_brand_tier_has_no_house_face_the_way_it_has_no_house_stack() {
        assert!(FontSlot::Display.house_face().is_none());
        assert!(FontSlot::Display.house_default().is_none());
    }

    #[test]
    fn a_face_loading_renderer_reads_the_family_and_the_source_off_the_layer() {
        // The egui case, which has no stylesheet in the path at all: the
        // renderer registers the file under a name, and the name has to be
        // the one the stack spells or the two halves drift.
        let t = Typography::house("fonts").with_override(
            FontOverride::new(FontSlot::Display, "\"RecursiveMono\", monospace").with_face(
                FontFace::new("RecursiveMono", ["RecursiveMonoLnrSt-Bold.ttf"]).with_weight("700"),
            ),
        );

        let [face] = t.faces(FontSlot::Display) else {
            panic!("the display slot ships exactly one face");
        };
        assert_eq!(face.family(), "RecursiveMono");
        assert_eq!(face.sources(), ["RecursiveMonoLnrSt-Bold.ttf"]);
        assert!(
            t.resolve(FontSlot::Display)
                .unwrap()
                .contains(face.family())
        );
    }

    #[test]
    fn a_weight_and_style_are_readable_now_that_the_builders_are_not_using_the_names() {
        let bold = FontFace::new("Reglo", ["Reglo-Bold.woff2"]).with_weight("700");
        assert_eq!(bold.weight(), Some("700"));
        assert_eq!(
            bold.style(),
            None,
            "unset means normal, not a stated normal"
        );

        let italic = FontFace::new("Odd", ["odd.woff2"]).with_style("italic");
        assert_eq!(italic.weight(), None);
        assert_eq!(italic.style(), Some("italic"));
    }

    #[test]
    fn the_house_faces_state_the_variable_range_a_direct_loader_has_to_name() {
        // The trap this closes: a variable face's own default instance is
        // whatever the base shipped, which for these is ExtraLight. A loader
        // that does not name a weight gets that and nothing says so.
        for slot in [FontSlot::Mono, FontSlot::Sans] {
            let face = slot.house_face().unwrap();
            assert_eq!(face.weight(), Some(HOUSE_WEIGHT_RANGE));
            assert_eq!(face.style(), Some("normal"));
        }
    }

    #[test]
    fn a_source_is_read_back_unresolved_because_only_the_css_wants_a_url() {
        let t = Typography::house("/static/fonts").with_override(young_serif());
        assert_eq!(
            t.faces(FontSlot::Display)[0].sources(),
            ["ysrf.woff2", "ysrf.ttf"]
        );
        // The same face, joined to the base, in the sheet.
        assert!(
            t.font_face_css()
                .contains("url(\"/static/fonts/ysrf.woff2\")")
        );
    }

    #[test]
    fn a_slot_nobody_overrode_ships_no_faces_including_the_house_two() {
        let t = Typography::house("fonts").with_override(young_serif());
        assert!(t.faces(FontSlot::Mono).is_empty());
        assert!(t.faces(FontSlot::Sans).is_empty());
        assert_eq!(t.faces(FontSlot::Display).len(), 1);
    }

    #[test]
    fn an_unrecognised_extension_gets_no_format_hint_rather_than_a_guessed_one() {
        let t = Typography::house("fonts").with_override(
            FontOverride::new(FontSlot::Display, "\"Odd\", serif")
                .with_face(FontFace::new("Odd", ["odd.eot"])),
        );
        assert!(t.font_face_css().contains("url(\"fonts/odd.eot\");"));
        assert!(!t.font_face_css().contains("format(\"eot\")"));
    }

    #[test]
    fn css_puts_the_faces_before_the_tokens_that_name_them() {
        let t = Typography::house("fonts").with_override(young_serif());
        let css = t.css();
        assert!(css.starts_with("@font-face"));
        assert!(css.find("@font-face").unwrap() < css.find(":root").unwrap());
    }
}