dxpdf 0.2.22

//! Text measurer — resolves text widths through a `FontRegistry`.

use std::cell::RefCell;
use std::collections::HashSet;

use skia_safe::Font;

use crate::render::dimension::Pt;
use crate::render::emoji::resolve::{EmojiFamily, EmojiResolver, EmojiTypeface, RegistryLookup};
use crate::render::emoji::shape::shape_text;
use crate::render::fonts::{self, FontRegistry, TypefaceEntry};

use super::fragment::FontProps;

/// Measures text using Skia fonts resolved through a [`FontRegistry`].
/// Holds a per-instance `FontCache` for `Font` reuse across measurements.
///
/// Also owns the [`EmojiResolver`] for the same render — so emoji typeface
/// lookups dedupe through the same per-instance state, alongside the warn-
/// once dedup set for `Unavailable` clusters.
pub struct TextMeasurer<'r> {
    registry: &'r FontRegistry,
    font_cache: RefCell<fonts::FontCache>,
    emoji_resolver: EmojiResolver<RegistryLookup<'r>>,
    /// Per-render dedup set so we warn at most once per cluster about a
    /// missing color emoji typeface.
    warned_emoji: RefCell<HashSet<String>>,
}

impl<'r> TextMeasurer<'r> {
    pub fn new(registry: &'r FontRegistry) -> Self {
        Self {
            registry,
            font_cache: RefCell::new(fonts::FontCache::new()),
            emoji_resolver: EmojiResolver::new(RegistryLookup { registry }),
            warned_emoji: RefCell::new(HashSet::new()),
        }
    }

    pub fn registry(&self) -> &'r FontRegistry {
        self.registry
    }

    /// Measure a text string with the given font properties.
    /// Returns (width, TextMetrics).
    pub fn measure(
        &self,
        text: &str,
        font_props: &FontProps,
    ) -> (Pt, super::fragment::TextMetrics) {
        let mut cache = self.font_cache.borrow_mut();
        let font = cache.get(
            self.registry,
            &font_props.family,
            font_props.size,
            font_props.bold,
            font_props.italic,
        );

        let (width, _bounds) = font.measure_str(text, None);
        let (_, metrics) = font.metrics();
        let text_metrics = super::fragment::TextMetrics {
            ascent: Pt::new(-metrics.ascent),
            descent: Pt::new(metrics.descent),
            leading: Pt::new(metrics.leading.max(0.0)),
        };

        // §17.3.2.45: scale the glyph advances horizontally per <w:w>.
        // Applies to glyph widths only — character spacing (§17.3.2.35)
        // is independent and is not scaled (the spec keeps the two
        // separate so kerning in points is unchanged by character scale).
        let scaled_width = Pt::new(width * font_props.text_scale);

        // §17.3.2.35: include character spacing in the measured width
        // so line fitting accounts for the extra inter-character space.
        let char_count = text.chars().count();
        let spacing_extra = if char_count > 0 {
            font_props.char_spacing * (char_count as f32)
        } else {
            Pt::ZERO
        };

        (scaled_width + spacing_extra, text_metrics)
    }

    /// Query font metrics for underline positioning.
    /// Returns (underline_position, underline_thickness) in points.
    /// Position is positive below baseline per Skia convention.
    pub fn underline_metrics(&self, font_props: &FontProps) -> (Pt, Pt) {
        let mut cache = self.font_cache.borrow_mut();
        let font = cache.get(
            self.registry,
            &font_props.family,
            font_props.size,
            font_props.bold,
            font_props.italic,
        );
        let (_, metrics) = font.metrics();
        // Skia: underline_position() returns a negative value (below baseline).
        // We negate to get a positive offset below the baseline.
        // If the font doesn't provide metrics, log a warning and use descent as fallback.
        let raw_pos = metrics.underline_position();
        let raw_thick = metrics.underline_thickness();
        if raw_pos.is_none() || raw_thick.is_none() {
            log::warn!(
                "font '{}' ({:?}) missing underline metrics, using descent as fallback",
                font_props.family,
                font_props.size
            );
        }
        let position = Pt::new(-raw_pos.unwrap_or(metrics.descent));
        // Thickness fallback: 1pt (smallest visible line at 72dpi).
        let thickness = Pt::new(raw_thick.unwrap_or(1.0));
        (position, thickness)
    }

    /// Get line height for the default font (used for empty paragraphs).
    /// §17.3.1.33: includes leading so Auto line spacing scales the full
    /// font-recommended height.
    pub fn default_line_height(&self, family: &str, size: Pt) -> Pt {
        let mut cache = self.font_cache.borrow_mut();
        let font = cache.get(self.registry, family, size, false, false);
        let (_, metrics) = font.metrics();
        Pt::new(-metrics.ascent + metrics.descent + metrics.leading.max(0.0))
    }

    // ─── Emoji pipeline integration ────────────────────────────────────────

    /// Resolve a color emoji typeface via the per-render [`EmojiResolver`].
    /// Cached: repeat calls with the same `requested` family are O(1).
    pub fn resolve_emoji(&self, requested: Option<EmojiFamily>) -> EmojiTypeface {
        self.emoji_resolver.resolve(requested)
    }

    /// Measure a cluster directly against a resolved [`TypefaceEntry`],
    /// bypassing the family-name lookup path. Used by the emoji pipeline,
    /// which has already resolved the typeface and needs Skia raster metrics
    /// at the cluster's font size.
    ///
    /// **Shapes via rustybuzz** (GSUB-aware) so multi-codepoint emoji
    /// sequences measure to their *ligated* width, matching what the
    /// rasterizer produces at paint time. Without this, the layout would
    /// reserve `n × glyph_advance` for an `n`-codepoint sequence (cmap-
    /// only) but the rasterizer would draw a ligated single glyph that's
    /// narrower — the painter then stretches the image to fill the over-
    /// sized rect, distorting the emoji.
    ///
    /// Falls back to `font.measure_str` (cmap-only) if shaping fails — a
    /// best-effort policy mirroring the rasterizer's fallback path.
    pub fn measure_with_typeface(
        &self,
        text: &str,
        typeface: &TypefaceEntry,
        size: Pt,
    ) -> (Pt, super::fragment::TextMetrics) {
        let font = Font::from_typeface(typeface.typeface.clone(), f32::from(size));
        let (_, metrics) = font.metrics();
        let text_metrics = super::fragment::TextMetrics {
            ascent: Pt::new(-metrics.ascent),
            descent: Pt::new(metrics.descent),
            leading: Pt::new(metrics.leading.max(0.0)),
        };

        // Try the GSUB-aware advance first; fall back to the cmap-only
        // path if the typeface bytes can't be extracted or shaped.
        let advance = typeface
            .typeface
            .to_font_data()
            .and_then(|(bytes, _)| shape_text(&bytes, text, f32::from(size)).ok())
            .map(|run| run.total_advance)
            .unwrap_or_else(|| Pt::new(font.measure_str(text, None).0));

        (advance, text_metrics)
    }

    /// Log a warning once per cluster when no color emoji typeface is
    /// available on the host. The `attempted` list lets operators know
    /// which packages to install (e.g. `fonts-noto-color-emoji` on Debian).
    pub fn warn_emoji_unavailable_once(&self, cluster: &str, attempted: &[EmojiFamily]) {
        let inserted = self.warned_emoji.borrow_mut().insert(cluster.to_string());
        if inserted {
            log::warn!(
                "no color emoji typeface available for cluster {:?}; \
                 tried {:?}. Install a color emoji font on the host \
                 (e.g. fonts-noto-color-emoji) to render this cluster correctly.",
                cluster,
                attempted
            );
        }
    }
}

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

    fn fp_at_scale(scale: f32) -> FontProps {
        FontProps {
            family: Rc::from("Helvetica"),
            size: Pt::new(12.0),
            bold: false,
            italic: false,
            underline: false,
            char_spacing: Pt::ZERO,
            text_scale: scale,
            underline_position: Pt::ZERO,
            underline_thickness: Pt::ZERO,
        }
    }

    #[test]
    fn measure_scaled_width_is_proportional_to_text_scale() {
        // §17.3.2.45: glyph advances scale linearly with <w:w>. A run at 80%
        // must measure to 0.8× the width of the same text at 100%.
        let registry = FontRegistry::new(skia_safe::FontMgr::new());
        let measurer = TextMeasurer::new(&registry);

        let (w_100, _) = measurer.measure("scaling sample", &fp_at_scale(1.0));
        let (w_80, _) = measurer.measure("scaling sample", &fp_at_scale(0.8));
        let (w_150, _) = measurer.measure("scaling sample", &fp_at_scale(1.5));

        // The relationship must hold even though the absolute value depends
        // on which fallback font Skia picks on the test host.
        if w_100.raw() <= 0.0 {
            // Some headless CI hosts can't measure text — bail rather than
            // assert; the text path is exercised by the integration tests.
            return;
        }
        assert!(
            (w_80.raw() / w_100.raw() - 0.8).abs() < 0.01,
            "80% scale must produce 0.8× width: 100%={}, 80%={}",
            w_100.raw(),
            w_80.raw(),
        );
        assert!(
            (w_150.raw() / w_100.raw() - 1.5).abs() < 0.01,
            "150% scale must produce 1.5× width: 100%={}, 150%={}",
            w_100.raw(),
            w_150.raw(),
        );
    }

    #[test]
    fn measure_char_spacing_not_scaled_by_text_scale() {
        // §17.3.2.45 + §17.3.2.35: w:spacing (inter-character spacing)
        // is independent of w:w. Doubling text_scale must NOT double
        // the spacing contribution.
        let registry = FontRegistry::new(skia_safe::FontMgr::new());
        let measurer = TextMeasurer::new(&registry);

        let mut fp_scale_1 = fp_at_scale(1.0);
        fp_scale_1.char_spacing = Pt::new(2.0);
        let mut fp_scale_2 = fp_at_scale(2.0);
        fp_scale_2.char_spacing = Pt::new(2.0);

        let text = "abcde";
        let (w1, _) = measurer.measure(text, &fp_scale_1);
        let (w2, _) = measurer.measure(text, &fp_scale_2);

        if w1.raw() <= 0.0 {
            return;
        }
        // Spacing contribution = 5 chars × 2pt = 10pt at both scales.
        // Glyph contribution doubles. So w2 - w1 should equal the glyph
        // contribution at scale 1.0 (i.e. w1 minus the spacing extra).
        let expected_glyph_w1 = w1.raw() - 10.0;
        let observed_glyph_delta = w2.raw() - w1.raw();
        assert!(
            (observed_glyph_delta - expected_glyph_w1).abs() < 0.05,
            "char_spacing must not be scaled by text_scale: \
             w1={}, w2={}, expected glyph delta {}, observed {}",
            w1.raw(),
            w2.raw(),
            expected_glyph_w1,
            observed_glyph_delta,
        );
    }
}