rustyfi-html 0.1.2

//! `PureHorzBox` → inline HTML ("Inline level"), appending into an
//! already-open paragraph's (or inline frame's) text buffer — never
//! absolutely positioned, never carrying an x/y of its own; the browser
//! lays every span out in normal inline flow.
//!
//! Slice 1 renders `InnerString` (styled + escaped text), the three glue
//! variants (collapsed to a plain space — the browser re-breaks, so the
//! exact stretch/shrink amounts have no reflow meaning), `Discretionary`
//! (a soft hyphen), and `Frame` (a real inline `<span>`, contents recursed).
//!
//! Slice 2 (design doc §4/§6 "S2") replaces the `Math`/`Graphics` PLACEHOLDER
//! `<span>`s with real, self-contained inline `<svg>` — see
//! [`emit_math_svg`]/[`emit_graphics_box`] — and gives `Frame` real `<a
//! href>`/`id=` treatment when its `DecoId` matches an observed link/
//! destination (`Ctx::links`/`Ctx::dests`, sourced from `DocumentValue::
//! reflow_links`/`reflow_dests`). `GraphicsOuter`/`Image`/`Footnote` remain
//! inert PLACEHOLDER `<span>`s (`GraphicsOuter` in particular is a
//! lang-side-only DEFERRED callback — `resolve_outer_graphics_in_contents`,
//! `rustyfi-lang/src/primitives.rs:3917`, always resolves it to a plain
//! `Graphics` box during `line-break`, well before `reflow_source` is
//! captured, so this arm is realistically unreachable; kept as an honest
//! placeholder rather than assumed-dead code).
//! `HookPageBreak`/`FrameMarker` render nothing (no reflow meaning, same as
//! both the faithful HTML writer and the PDF writer's own wildcard arms).
//!
//! Slice 3 (design doc §6 "S3", `structure.rs`'s doc comment) replaces the
//! `Tabular` PLACEHOLDER `<span>` with a real `<table>` — see this module's
//! own `Tabular` arm below for why it delegates to `structure::render_table`
//! (`block.rs` handles the common top-level case directly, since a `<table>`
//! is block-level and needs to flush the surrounding paragraph first; this
//! arm is only the fallback for a `Tabular` nested inside inline content).
//!
//! Slice 4 ("Inline level") handles the new `InlineMark` box:
//! `EmphStart`/`EmphEnd` open/close a real `<em>`/`<strong>` (via
//! `Ctx::emph_stack`, since `EmphEnd` alone doesn't say which tag to close —
//! see that field's doc comment), and `BulletStart`/`BulletEnd` fence a
//! drawn bullet/number glyph run so it renders NOTHING
//! (`Ctx::bullet_suppress`) — the real marker comes from the `<ul>`/`<ol>`
//! `block.rs` now emits instead.

use std::fmt::Write as _;

use rustyfi_backend::{
    AnnotAction, Color, GraphicsElem, HorzStringInfo, InlineMarkKind, MathGlyph, PureHorzBox,
};

use super::Ctx;
use crate::image;

/// Append `bx`'s reflow rendering to `out`. Never touches `out`'s
/// surrounding whitespace/paragraph bookkeeping — that is the caller's
/// (`block.rs`'s) job.
pub(crate) fn emit_inline(out: &mut String, bx: &PureHorzBox, ctx: &Ctx) {
    match bx {
        // S4: handled FIRST, unconditionally of `ctx.bullet_suppress` below
        // — a `BulletEnd` reached WHILE suppressed must still clear the
        // counter, and an `EmphStart`/`EmphEnd` reached while suppressed
        // (should not happen — `itemize.satyh` never nests emphasis inside
        // its own bullet fence — but stays correct regardless) must still
        // keep the tag stack balanced.
        PureHorzBox::InlineMark(kind) => match kind {
            InlineMarkKind::EmphStart { strong } => {
                close_run(out, ctx);
                ctx.emph_stack.borrow_mut().push(*strong);
                out.push_str(if *strong { "<strong>" } else { "<em>" });
            }
            InlineMarkKind::EmphEnd => {
                close_run(out, ctx);
                // An unmatched `EmphEnd` (should not happen) closes `</em>`
                // rather than panicking.
                let strong = ctx.emph_stack.borrow_mut().pop().unwrap_or(false);
                out.push_str(if strong { "</strong>" } else { "</em>" });
            }
            InlineMarkKind::BulletStart => {
                *ctx.bullet_suppress.borrow_mut() += 1;
            }
            InlineMarkKind::BulletEnd => {
                let mut n = ctx.bullet_suppress.borrow_mut();
                *n = n.saturating_sub(1);
            }
        },

        // `inline-frame-breakable` does NOT build a `Frame`: it splices its
        // contents between a marker PAIR so the frame can split across lines,
        // which means the wrapper has to be opened and closed positionally
        // rather than around a recursion. Same lookup as the `Frame` arm
        // below, keyed on the MARKER's own `DecoId`. Without this arm every
        // `\href`/`\ref` that goes through the breakable frame — which is
        // how `annot.satyh` writes them — renders its text unwrapped, with
        // no error anywhere.
        //
        // Handled here, ahead of the `bullet_suppress` guard below, for the
        // same reason `InlineMark` is: a marker skipped while suppressed
        // would leave the stack unbalanced and mis-close a later wrapper. A
        // link inside a bullet fence should not happen, but the tags stay
        // balanced regardless — while suppressed the stack is still
        // maintained and only the emission is dropped.
        PureHorzBox::InlineFrameMarker { id, end, .. } => {
            let suppressed = *ctx.bullet_suppress.borrow() > 0;
            close_run(out, ctx);
            if *end {
                let close = ctx
                    .iframe_stack
                    .borrow_mut()
                    .pop()
                    .map_or("</span>", |(_, close)| close);
                if !suppressed {
                    out.push_str(close);
                }
            } else {
                let (open, reopen, close) = wrapper_tags(id, ctx);
                if !suppressed {
                    out.push_str(&open);
                }
                ctx.iframe_stack.borrow_mut().push((reopen, close));
            }
        }

        // S4: while a `BulletStart`/`BulletEnd` fence is open, every OTHER
        // box (the bullet's `Graphics` circle / the enumerate index's
        // `InnerString` digit, and anything else that happened to ride
        // along) renders nothing — the real marker comes from the `<ul>`/
        // `<ol>` `block.rs` now emits. Matched here, ahead of every
        // concrete arm below, via a guarded wildcard (still fully
        // exhaustive together with the explicit arms that follow it — see
        // `rustc`'s own exhaustiveness check, which accepts this).
        _ if *ctx.bullet_suppress.borrow() > 0 => {}

        PureHorzBox::InnerString { info, text, .. } => emit_run(out, info, text, ctx),

        // Glue does NOT become a space here — it is RECORDED, and judged
        // once the following character is known. The box stream puts glue
        // between every pair of CJK characters and inside every hyphenatable
        // Latin word, so "glue means space" (what this arm used to do)
        // rendered Japanese as `研 究 計 画` and `\LaTeX` as `L AT EX`. See
        // `text.rs`'s doc comment for the whole argument and `wants_space`
        // for the rule.
        PureHorzBox::OuterEmpty { natural, .. } => ctx.note_glue(natural.0),
        // `inline-fil`: infinite stretch, no natural width. Never a space;
        // `block.rs` reads its POSITION instead, as the alignment signal it
        // is (leading + trailing fil = centred, leading only = flush right).
        PureHorzBox::OuterFil => ctx.note_glue(0.0),
        // `inline-skip`: an explicit, deliberately-sized, non-breakable gap.
        // Above a visible threshold it keeps its width as an inline-block
        // strut (intrinsic sizing, not positioning — the same licence math
        // and graphics have); below it, it is a kern and goes through the
        // ordinary glue rule, which drops it.
        PureHorzBox::FixedEmpty { width } => {
            if width.0 >= HSKIP_MIN_PT {
                ctx.resolve_glue(out, None);
                close_run(out, ctx);
                let _ = write!(
                    out,
                    "<span class=\"hskip\" style=\"width:{}pt;\"></span>",
                    width.0
                );
            } else {
                // A kern: recorded as zero-width glue, i.e. as nothing. A
                // sub-2pt `inline-skip` is a micro-adjustment, never a word
                // space — word spaces arrive as `OuterEmpty`.
                ctx.note_glue(0.0);
            }
        }

        // A break point that may or may not be taken. When it carries text
        // in `pre_break` it is a real hyphenation point (the pattern
        // dictionary's, `Latex&shy;Cmds`) and a soft hyphen is exactly
        // right: the browser re-breaks and shows the hyphen only if it
        // breaks there. When `pre_break` is bare glue it is a UAX#14 chunk
        // boundary — a soft hyphen there would invite the browser to
        // hyphenate `Con-tributors` at a point the dictionary never
        // sanctioned, and between two CJK characters it would be nonsense —
        // so it goes through the ordinary glue rule instead.
        PureHorzBox::Discretionary { pre_break, .. } => {
            if pre_break_carries_text(pre_break) {
                out.push_str("&shy;");
            } else {
                ctx.note_glue(glue_width(pre_break));
            }
        }

        // A real inline frame: no atomic-width fitting to preserve (that
        // was only ever needed for the eager line-breaker) — just recurse
        // its contents into one wrapper for CSS-hook purposes.
        //
        // S2 (design doc §4 "Links/metadata"): if THIS frame's `DecoId`
        // matches an observed `register-link-to-uri`/`-to-location` call
        // (`ctx.links`, `annot.satyh`'s `\href`), wrap the contents in a
        // real `<a href>` instead of a plain `<span>` — `Uri` maps to the
        // literal URL, `GotoName` to an in-document `#anchor` (the matching
        // destination is placed by `block.rs`'s `FrameStart`/`ctx.dests`
        // lookup, or by this SAME arm's `dest` fallback below when the
        // named-destination frame happens to be inline rather than block).
        // Falls back to `ctx.dests` (a `register-location-frame` used
        // inline rather than as a block frame) for a plain `id=` anchor
        // when there's no link action, then to the Slice-1 inert `<span>`.
        PureHorzBox::Frame { deco, contents, .. } => {
            let (open, _, close) = wrapper_tags(deco, ctx);
            close_run(out, ctx);
            out.push_str(&open);
            for (_, cbx) in contents {
                emit_inline(out, cbx, ctx);
            }
            close_run(out, ctx);
            out.push_str(close);
        }

        // Math is flattened to positioned glyphs at eval time (design doc
        // §4) — no fraction/sub/sup structure survives to render as MathML,
        // so (Slice 2, design doc §4's "the honest option") this renders the
        // SAME way the faithful backend's approximation does: each glyph as
        // positioned text, each rule (fraction bar/radical) as an SVG path
        // — but bundled into ONE self-contained, intrinsically-sized inline
        // `<svg>` (see [`emit_math_svg`]) instead of the faithful mode's
        // page-absolute `<span>`s, since reflow has no page to be absolute
        // WITHIN.
        PureHorzBox::Math {
            width,
            height,
            depth,
            glyphs,
            rules,
        } => emit_math_svg(out, width.0, height.0, depth.0, glyphs, rules, ctx),

        // Slice 2 (design doc §6/§4 "reuse svg::emit_graphics verbatim"):
        // real inline SVG, sized to the box's own metrics — see
        // [`emit_graphics_box`].
        PureHorzBox::Graphics {
            width,
            height,
            depth,
            elems,
            origin_independent: _,
        } => emit_graphics_box(out, width.0, height.0, depth.0, elems, ctx),

        // `GraphicsOuter` is a DEFERRED lang-side callback (`GraphicsFnId`,
        // resolved only by `resolve_outer_graphics_in_contents` at
        // `line-break` time, well before `reflow_source` is captured — see
        // this module's doc comment); the backend has no way to run it, same
        // limitation the faithful writer has (its own `emit_box` has no arm
        // for this variant at all, silently matching its wildcard). Kept as
        // an honest placeholder rather than silently dropped.
        PureHorzBox::GraphicsOuter { .. } => {
            open_opaque(out, ctx);
            out.push_str(
                "<span class=\"gfx-placeholder\" title=\"unresolved inline-graphics-outer (lang-side callback)\"></span>",
            );
        }
        // A real `<img>` with a self-contained data URI, sized in the
        // document's own points but capped at the column width so a figure
        // wider than a narrow viewport shrinks instead of overflowing
        // (`css.rs`'s `img.img` rule) — the reflowable counterpart of the
        // faithful backend's absolutely-positioned `<img>`, sharing
        // `crate::image::data_uri` verbatim with it.
        PureHorzBox::Image {
            width,
            height,
            image,
        } => {
            open_opaque(out, ctx);
            match ctx.images.get(image.0) {
                // `load-pdf-image`: an imported PDF page carries no raster
                // samples at all (`ImageResource::pdf`), and rasterizing one
                // is out of scope for an HTML writer, so this keeps an
                // honestly-labelled box at the right size rather than
                // emitting a degenerate 0x0 `<img>`. The faithful backend
                // does exactly the same.
                Some(res) if res.pdf.is_some() => {
                    let _ = write!(
                        out,
                        "<span class=\"pdf-image\" style=\"width:{}pt; height:{}pt;\" \
                         title=\"embedded PDF page (not rasterized)\"></span>",
                        width.0, height.0,
                    );
                }
                // Placed more than once: its bytes go into the stylesheet
                // ONCE (`css.rs`'s `shared_image_rules`) and every placement
                // is a sized box referencing that rule. A data URI is
                // typically hundreds of kilobytes, so repeating it per
                // placement is the difference between a 13 MB file and a
                // 1.9 MB one for a manual that shows the same two figures
                // seventeen times. The element is `aria-hidden` rather than
                // an `<img>`, which costs nothing here: SATySFi carries no
                // alt text, so the `<img>` below is `alt=""` — decorative —
                // and the two are equivalent to a screen reader.
                Some(_) if ctx.image_sharing(image.0).1 => {
                    let canon = ctx.image_sharing(image.0).0;
                    let mut shared = ctx.shared_images.borrow_mut();
                    if !shared.contains(&canon) {
                        shared.push(canon);
                    }
                    drop(shared);
                    let _ = write!(
                        out,
                        "<span class=\"img shared-img-{canon}\" style=\"width:{}pt; height:{}pt;\" \
                         aria-hidden=\"true\"></span>",
                        width.0, height.0,
                    );
                }
                Some(res) => {
                    let _ = write!(
                        out,
                        "<img class=\"img\" src=\"{}\" style=\"width:{}pt; height:{}pt;\" alt=\"\">",
                        image::data_uri(res),
                        width.0,
                        height.0,
                    );
                }
                // Out-of-range `ImageId` — should not happen; the faithful
                // writer and the PDF writer both skip rather than panic.
                None => {}
            }
        }
        // S3 ("S3", `structure.rs`'s "Tables — genuinely recoverable"): a
        // real `<table>`. `block.rs`'s own `VertBox::Line` walk already
        // special- cases the common top-level case (flushing the open
        // paragraph first, since a `<table>` is block-level); THIS arm is
        // the fallback for a `Tabular` nested inside inline content this
        // module recurses into on its own (a `Frame`'s `contents`, or a
        // table cell that itself contains a nested `Tabular`) — no
        // surrounding paragraph to flush here, so no `extra_attrs` margin.
        PureHorzBox::Tabular(tab) => {
            open_opaque(out, ctx);
            super::structure::render_table(out, tab, "", ctx)
        }
        // A footnote has nowhere to be collected TO in a continuous
        // document — there is no page foot any more — so it becomes a
        // numbered reference here and its body is queued for `block.rs`'s
        // `flush_para` to place as an `<aside>` immediately after the
        // paragraph that referenced it. See the `reflow` module's doc
        // comment for why "just after the paragraph" was chosen over
        // "collected at the end".
        PureHorzBox::Footnote { block } => {
            open_opaque(out, ctx);
            let n = ctx.footnote_seq.get() + 1;
            ctx.footnote_seq.set(n);
            // Render the body NOW, at the point the marker rides, so it sees
            // the surrounding context — but into its own buffer, and with
            // the inline-flow state saved/restored around it, since the
            // footnote's own last character must not decide the spacing of
            // the word after the reference in the main text.
            let saved = (ctx.pending_glue.take(), ctx.last_char.take());
            // Park the queue too: the nested walk drains whatever it finds
            // there when it finishes, and an earlier sibling footnote from
            // this same paragraph must not end up nested inside this one.
            let parked = std::mem::take(&mut *ctx.footnotes.borrow_mut());
            let mut body = String::new();
            super::block::walk_vboxes(&mut body, block, ctx);
            ctx.pending_glue.set(saved.0);
            ctx.last_char.set(saved.1);
            let mut queue = ctx.footnotes.borrow_mut();
            *queue = parked;
            queue.push((n, body));
            drop(queue);
            // An EMPTY anchor, not a visible marker.
            //
            // The document has already typeset its own reference marker —
            // `stdjabook`'s `\footnote` sets a superscript `*1` in the text
            // immediately after this box — so emitting a numbered `<sup>`
            // here put `1*1` on the page, and the note's body then repeated
            // the document's number a third time. What is missing is not a
            // marker but a link TARGET, which is all this is; the
            // `<aside>`'s back-link points at it. Forward navigation is not
            // worth duplicating the marker for, since the note lands a
            // couple of lines below rather than pages away.
            let _ = write!(out, "<span class=\"fnref\" id=\"fnref-{n}\"></span>");
        }

        // `EmbeddedBlock` is handled one level up, in `block.rs`'s own
        // per-`Line`-contents loop (it needs to CLOSE the open paragraph,
        // which this function's `&mut String` signature has no way to do)
        // — unreachable in practice, kept as an explicit inert arm rather
        // than a silent catch-all so a future new `PureHorzBox` variant
        // still forces a compile error here instead of silently falling
        // through.
        PureHorzBox::EmbeddedBlock { .. } => {}

        // No reflow meaning (zero-width markers/hooks; matches the
        // faithful writer's own wildcard treatment of these two).
        PureHorzBox::HookPageBreak { .. } | PureHorzBox::FrameMarker { .. } => {}
    }
}

/// A `FixedEmpty` (`inline-skip`) at least this wide (pt) survives as a real
/// sized strut; anything narrower is a KERN and renders as nothing at all.
///
/// Two points separates the two populations cleanly in the corpus. Above it
/// sit the deliberate gaps — a paragraph indent (one em, 10.56pt), a table
/// cell's padding (6pt), the space after a section number (10pt) — which a
/// reader would miss. Below it sit micro-adjustments: the `\LaTeX` logo's
/// four kerns, and the 1pt gaps between the dots of a table-of-contents
/// leader, of which `enumitem`'s manual has some hundreds. Rendering those
/// as struts broke a leader into one `<span>` per dot; rendering them as
/// spaces would be wider than the kern they stand for. Nothing is right for
/// both.
const HSKIP_MIN_PT: f64 = 2.0;

/// One `InnerString` run.
///
/// The text is written as TEXT: a run set in the document's body style (see
/// `text::BodyStyle`, which `css.rs` puts on `body`) gets no element around
/// it at all, so a paragraph of ordinary prose serialises as ordinary prose
/// rather than as one `<span style="font-size:10.56pt">` per syllable. Only
/// the properties that genuinely differ from the body style are emitted, and
/// the size as an `em` RATIO rather than an absolute point size, so the
/// whole document rescales from the single value on `body`.
///
/// Still no `left`/`top`/`position` — this is flowing content, not a placed
/// box; `vertical-align` (not `position`) handles a non-zero `rising`, since
/// it needs no positioned ancestor and composes with the inline flow.
fn emit_run(out: &mut String, info: &HorzStringInfo, text: &str, ctx: &Ctx) {
    if text.is_empty() {
        return;
    }
    ctx.resolve_glue(out, text.chars().next());
    ctx.last_char.set(text.chars().next_back());
    ctx.mono_run.set(ctx.is_monospace(Some(info.font)));

    let mut style = String::new();
    if !ctx.body.matches(info.font, info.size.0) {
        if Some(info.font) != ctx.body.font {
            if let Some(stack) = ctx.font_family_for(info.font) {
                let _ = write!(style, "font-family:{stack};");
            }
        } else {
            // Same face as the body, so the `@font-face` rule for it is
            // needed even though this run names no family of its own.
            let _ = ctx.font_family_for(info.font);
        }
        if (info.size.0 - ctx.body.size).abs() >= 0.005 {
            let _ = write!(style, "font-size:{:.4}em;", info.size.0 / ctx.body.size);
        }
    } else {
        // Body-styled: still record the face as used, so `font_face_rules`
        // embeds it for the `body` rule that names it.
        let _ = ctx.font_family_for(info.font);
    }
    // Non-black only, mirroring the faithful writer's own guard, so a plain
    // black run stays unwrapped.
    if info.color != Color::Gray(0.0) {
        let _ = write!(style, "color:{};", crate::svg::css_color(info.color));
    }
    if info.rising.0 != 0.0 {
        let _ = write!(style, "vertical-align:{}pt;", info.rising.0);
    }

    let escaped = crate::escape_html(text);
    if style.is_empty() {
        close_run(out, ctx);
        out.push_str(&escaped);
        return;
    }
    // Same style as the span already open: keep writing into it. This is
    // what turns the box stream's one-`InnerString`-per-CJK-character (and
    // one-per-hyphenation-chunk) into a single span of readable text.
    let mut open = ctx.open_run.borrow_mut();
    match open.as_deref() {
        Some(current) if current == style => {}
        _ => {
            if open.is_some() {
                out.push_str("</span>");
            }
            let _ = write!(out, "<span class=\"run\" style=\"{style}\">");
            *open = Some(style);
        }
    }
    out.push_str(&escaped);
}

/// Close the `<span class="run">` left open by [`emit_run`], if any. Called
/// by everything that writes something which is not part of the run's text —
/// a wrapper tag, a strut, an `<svg>`, an `<img>`, the end of a paragraph or
/// a table cell. A space and a soft hyphen do NOT call it: they carry no
/// style and belong inside the word.
pub(crate) fn close_run(out: &mut String, ctx: &Ctx) {
    if ctx.open_run.borrow_mut().take().is_some() {
        out.push_str("</span>");
    }
}

/// The opening and closing tags a decorated inline region gets, from its
/// `DecoId` alone. Shared by the `Frame` arm (a wrapper around a recursion)
/// and the `InlineFrameMarker` arm (the same wrapper, opened and closed
/// positionally because `inline-frame-breakable` splices rather than nests)
/// so the two can never disagree about what a given `DecoId` means:
///
/// - an observed `register-link-to-uri`/`-to-location`
///   (`Ctx::links`, `annot.satyh`'s `\href`) → a real `<a href>`, `Uri` to
///   the literal URL and `GotoName` to an in-document `#anchor`;
/// - an observed `register-destination` (`Ctx::dests`,
///   `register-location-frame`) → a plain `<span>` carrying the `id=` that
///   anchor lands on;
/// - neither → an inert `<span class="iframe">`, kept as a CSS hook.
/// Returns `(open, reopen, close)`. `reopen` differs from `open` only for a
/// destination wrapper, whose `id=` must appear once and only once even if
/// the region has to be split across a paragraph boundary
/// (`Ctx::iframe_stack`).
fn wrapper_tags(deco: &rustyfi_backend::DecoId, ctx: &Ctx) -> (String, String, &'static str) {
    if let Some(action) = ctx.links.get(deco) {
        let href = match action {
            AnnotAction::Uri(uri) => crate::escape_html(uri),
            AnnotAction::GotoName(name) => format!("#{}", crate::escape_html(name)),
        };
        let tag = format!("<a class=\"link\" href=\"{href}\">");
        (tag.clone(), tag, "</a>")
    } else if let Some(name) = ctx.dests.get(deco) {
        (
            format!(
                "<span class=\"iframe\" id=\"{}\">",
                crate::escape_html(name)
            ),
            "<span class=\"iframe\">".to_string(),
            "</span>",
        )
    } else {
        (
            "<span class=\"iframe\">".to_string(),
            "<span class=\"iframe\">".to_string(),
            "</span>",
        )
    }
}

/// Close every inline wrapper this block opened, innermost first, and leave
/// the stack in place so [`reopen_wrappers`] can restore them. Called by
/// `block.rs` when a paragraph is flushed mid-wrapper.
///
/// `base` is the stack depth its `walk_vboxes` was entered at, so only the
/// wrappers THIS block opened are closed. A nested walk — an
/// `EmbeddedBlock`, a footnote body, a table cell — runs with the enclosing
/// paragraph already flushed but its wrapper stack deliberately still
/// standing; without the base it would emit that paragraph's closing tags a
/// second time, inside the nested block.
pub(crate) fn close_open_wrappers(out: &mut String, ctx: &Ctx, base: usize) {
    close_run(out, ctx);
    for (_, close) in ctx.iframe_stack.borrow().iter().skip(base).rev() {
        out.push_str(close);
    }
}

/// Re-open, outermost first, every wrapper [`close_open_wrappers`] closed.
pub(crate) fn reopen_wrappers(out: &mut String, ctx: &Ctx, base: usize) {
    for (reopen, _) in ctx.iframe_stack.borrow().iter().skip(base) {
        out.push_str(reopen);
    }
}

/// Does a `Discretionary`'s `pre_break` carry a visible character (the
/// hyphenation dictionary's hyphen), as opposed to bare glue?
fn pre_break_carries_text(pre_break: &[PureHorzBox]) -> bool {
    pre_break.iter().any(|b| match b {
        PureHorzBox::InnerString { text, .. } => !text.is_empty(),
        _ => false,
    })
}

/// The total natural width of a `Discretionary`'s `pre_break` glue, fed to
/// the ordinary glue rule when there is no hyphen to show.
fn glue_width(pre_break: &[PureHorzBox]) -> f64 {
    pre_break
        .iter()
        .map(|b| match b {
            PureHorzBox::OuterEmpty { natural, .. } => natural.0,
            PureHorzBox::FixedEmpty { width } => width.0,
            _ => 0.0,
        })
        .sum()
}

/// Write an opaque, non-textual inline element (`<svg>`, `<img>`,
/// `<table>`, a footnote reference): settle any pending glue against "no
/// following character", then forget the last character, since the next
/// glue has nothing textual on its left to be judged against.
fn open_opaque(out: &mut String, ctx: &Ctx) {
    ctx.resolve_glue(out, None);
    close_run(out, ctx);
    ctx.last_char.set(None);
}

/// Slice 2 (design doc §4 "Graphics — inline SVG, reuse `svg::emit_graphics`
/// verbatim"): wrap a graphics-bearing box's `elems` in an intrinsically
/// sized `<span>` (`position:relative; display:inline-block`, sized to the
/// box's own `width×(height+depth)` and baseline-aligned via
/// `vertical-align:-depth`) and reuse [`crate::svg::emit_graphics`] UNCHANGED
/// inside it, anchored at the wrapper's own top-left `(0, height)` — exactly
/// the design doc's "supplies its own anchor (0,0 for an inline-block
/// wrapper)". [`crate::svg::emit_graphics`]'s own `<svg>` carries
/// `position:absolute; left:0; top:0`, which is why the WRAPPER (not the
/// page) must be `position:relative`: that scopes the absolute positioning
/// to this one inline box, so it composes with normal flow instead of
/// escaping to the nearest positioned ancestor (which could be the `.doc`
/// root, or nothing at all) — this is the one place `position:absolute`
/// legitimately appears in this module's output, and it never affects
/// block-level layout (the design doc's own "inline SVG for math/graphics is
/// fine — that's intrinsic sizing, not page positioning").
///
/// `nested` (for `GraphicsElem::Text`/`draw-text`, the one arm that steps
/// outside the local coordinate frame — see `svg.rs`'s own doc comment)
/// re-enters THIS module's [`emit_inline`] rather than the faithful writer's
/// page-absolute `emit_box`, since reflow has no page coordinates to place
/// nested content at; the `_x`/`_y` callback args are therefore unused here
/// (a `draw-text` run's nested boxes render inline, at their natural flow
/// position within the wrapper, not at their SVG-local point — a documented
/// approximation for this rare construction, same spirit as the faithful
/// mode's own `Math.glyph.gid` approximation).
fn emit_graphics_box(
    out: &mut String,
    width: f64,
    height: f64,
    depth: f64,
    elems: &[GraphicsElem],
    ctx: &Ctx,
) {
    if elems.is_empty() {
        return;
    }
    // A graphics box whose every element is a `draw-text` DRAWS nothing: the
    // `<svg>` comes out with an empty `<g>` and all the content goes to
    // `nested`. Emitting the wrapper anyway reserved the box's full size a
    // second time, on top of the content's own — `easytable` wraps each table
    // in exactly this shape, and every table in a document arrived under a
    // table-sized rectangle of blank space.
    if elems.iter().all(is_pure_text) {
        // The overlaid halves of one table are visible together only here —
        // see `Ctx::tabular_rules`. Collect any rules-only tabular's rules
        // before emitting, and drop them again after, so the pairing can
        // never reach an unrelated table later in the document.
        let pushed = collect_overlaid_rules(elems, ctx);
        let mut nested = String::new();
        emit_text_only(&mut nested, elems, ctx);
        ctx.tabular_rules.borrow_mut().truncate(pushed);
        out.push_str(&nested);
        return;
    }
    open_opaque(out, ctx);
    let total_h = height + depth;
    let _ = write!(
        out,
        "<span class=\"gfx\" style=\"position:relative; display:inline-block; \
         width:{width}pt; height:{total_h}pt; vertical-align:{}pt;\">\n",
        -depth,
    );
    let mut nested = String::new();
    crate::svg::emit_graphics(
        out,
        elems,
        width,
        height,
        depth,
        0.0,
        height,
        &mut |_svg, cbx, _x, _y| emit_nested_text(&mut nested, cbx, ctx),
    );
    out.push_str(&nested);
    out.push_str("</span>\n");
}

/// Whether `elem` contributes no ink of its own — a `draw-text`, or a group
/// containing only those. `Group`/`Clip` recurse so a `unite-graphics` of
/// text runs is recognised too.
fn is_pure_text(elem: &GraphicsElem) -> bool {
    match elem {
        GraphicsElem::Text { .. } => true,
        GraphicsElem::Group(inner) | GraphicsElem::Clip(_, inner) => inner.iter().all(is_pure_text),
        _ => false,
    }
}

/// Record every rules-bearing `Tabular` in this overlay on
/// [`Ctx::tabular_rules`], returning the stack depth to truncate back to.
fn collect_overlaid_rules(elems: &[GraphicsElem], ctx: &Ctx) -> usize {
    let base = ctx.tabular_rules.borrow().len();
    walk_tabulars(elems, &mut |tab| {
        if !tab.rules.is_empty() {
            ctx.tabular_rules.borrow_mut().push((
                tab.width.0,
                tab.height.0,
                tab.rules.clone(),
            ));
        }
    });
    base
}

/// Visit every `Tabular` reachable through a text-only graphics group's
/// nested boxes.
fn walk_tabulars(elems: &[GraphicsElem], f: &mut impl FnMut(&rustyfi_backend::TabularBox)) {
    for elem in elems {
        match elem {
            GraphicsElem::Text { contents, .. } => {
                for (_, bx) in contents {
                    if let PureHorzBox::Tabular(tab) = bx {
                        f(tab);
                    }
                }
            }
            GraphicsElem::Group(inner) | GraphicsElem::Clip(_, inner) => walk_tabulars(inner, f),
            _ => {}
        }
    }
}

/// The counterpart of [`is_pure_text`]: emit those runs' contents inline, in
/// document order, with no wrapper of their own.
fn emit_text_only(out: &mut String, elems: &[GraphicsElem], ctx: &Ctx) {
    for elem in elems {
        match elem {
            GraphicsElem::Text { contents, .. } => {
                for (_, cbx) in contents {
                    emit_nested_text(out, cbx, ctx);
                }
            }
            GraphicsElem::Group(inner) | GraphicsElem::Clip(_, inner) => {
                emit_text_only(out, inner, ctx)
            }
            _ => {}
        }
    }
}

/// `draw-text`'s nested boxes, rendered for the reflow backend.
///
/// They are collected into a SIDE buffer and appended after the `</svg>`,
/// never written where `svg::emit_graphics`'s callback offers them — which
/// is inside the `<svg>`'s `<g>`. The faithful backend can put them there
/// because everything it emits is an absolutely-positioned page-level
/// element; here they are `<span>`s and `<a>`s of flowing text, and an HTML
/// element inside `<svg>` outside a `<foreignObject>` is not valid markup at
/// all — the browser's parser closes the `<svg>` at the first one and the
/// rest of the drawing escapes into the document.
///
/// The consequence is that a `draw-text` run's text sits AFTER its drawing
/// rather than at its point within it. That is the documented approximation
/// this backend already made for the construct (there are no page
/// coordinates to place it at); it is now merely well-formed.
fn emit_nested_text(nested: &mut String, bx: &PureHorzBox, ctx: &Ctx) {
    emit_inline(nested, bx, ctx);
    close_run(nested, ctx);
}

/// Slice 2 (design doc §4 "Math"): MathML is not recoverable (structure is
/// flattened to positioned glyphs by `read_math`/`layout_math_value` well
/// before any box exists), so this renders the SAME honest approximation the
/// faithful backend does — each glyph as positioned text, each `rules`
/// element (fraction bar/radical) as an SVG path — bundled into ONE
/// self-contained, intrinsically-sized inline `<svg>` (the design doc's
/// "inline `<svg>` sized to the box").
///
/// Two sub-layers, both anchored at the SAME wrapper `(0,0)` top-left:
/// - **Glyphs**: native SVG `<text>` elements, positioned directly in the
///   `<svg>`'s own native (y-DOWN) coordinate space — `MathGlyph.dx`/`dy`
///   are box-local y-**up** offsets from the box's own baseline (the same
///   convention `GraphicsElem::Path` points use, confirmed by the faithful
///   writer's `ty - g.dy.0` arithmetic, `lib.rs`'s `Math` arm), so a local
///   `(dx, dy)` lands at SVG-native `(dx, height - dy)` — computed BY HAND
///   here (not via a `<g transform>` flip) specifically so `<text>` glyphs
///   are never inside a `scale(1,-1)` group, which would render them
///   MIRRORED upside-down (SVG text has no orientation-independence the way
///   a filled path does).
/// - **Rules**: [`crate::svg::emit_graphics`] reused VERBATIM (same call
///   shape as [`emit_graphics_box`]) for `rules` — these ARE orientation-
///   independent paths, so they go through the normal `<g transform>` flip
///   this helper already implements.
fn emit_math_svg(
    out: &mut String,
    width: f64,
    height: f64,
    depth: f64,
    glyphs: &[MathGlyph],
    rules: &[GraphicsElem],
    ctx: &Ctx,
) {
    if glyphs.is_empty() && rules.is_empty() {
        return;
    }
    open_opaque(out, ctx);
    let total_h = height + depth;
    let _ = write!(
        out,
        "<span class=\"math\" style=\"position:relative; display:inline-block; \
         width:{width}pt; height:{total_h}pt; vertical-align:{}pt;\">\n\
         <svg class=\"math-glyphs\" style=\"position:absolute; left:0; top:0; overflow:visible;\" \
         width=\"{width}pt\" height=\"{total_h}pt\" viewBox=\"0 0 {width} {total_h}\">\n",
        -depth,
    );
    for g in glyphs {
        let x = g.dx.0;
        let y = height - g.dy.0 - g.info.rising.0;
        let mut style = format!("font-size:{}pt;", g.info.size.0);
        if let Some(stack) = ctx.font_family_for(g.info.font) {
            style.push_str(&format!("font-family:{stack};"));
        }
        if g.info.color != Color::Gray(0.0) {
            style.push_str(&format!("fill:{};", crate::svg::css_color(g.info.color)));
        }
        let _ = write!(
            out,
            "<text x=\"{x}\" y=\"{y}\" style=\"{style}\">{}</text>\n",
            crate::escape_html(&g.text),
        );
    }
    out.push_str("</svg>\n");
    let mut nested = String::new();
    if !rules.is_empty() {
        crate::svg::emit_graphics(
            out,
            rules,
            width,
            height,
            depth,
            0.0,
            height,
            &mut |_svg, cbx, _x, _y| emit_nested_text(&mut nested, cbx, ctx),
        );
    }
    out.push_str(&nested);
    out.push_str("</span>\n");
}