shoin 0.2.0

//! Concealment — the Obsidian live-preview model. SPEC.md §2, §5.5.
//!
//! THE INVARIANT: the active line is rendered 1:1 with its source; every other
//! line may conceal markup.
//!
//! Because the cursor only ever sits on a 1:1 line, this mapping is needed for
//! non-active lines only, and only for read-only concerns. The one direction
//! anything asks for today is SCREEN -> SOURCE (`source_col`), for mouse
//! click-to-position — the case SPEC §5.5 anticipated. Frame overlays (search
//! matches, the selection, focus dim) are applied in SOURCE coordinates before
//! `render` remaps them, so they need no mapping of their own.

use std::ops::Range;

use unicode_width::{UnicodeWidthChar, UnicodeWidthStr};

use crate::config::schema::GlyphConfig;
use crate::input::mode::Mode;
use crate::text::cursor::Cursor;

use super::indent;
use super::markdown::block::{BlockKind, Marker};
use super::markdown::inline::InlineSpan;
use super::theme::{Attrs, Color, Style, Theme};
use super::StyledSpan;

/// One display-only transformation of a source range.
#[derive(Clone, Debug, PartialEq)]
pub enum Conceal {
    /// Drop these source chars from the frame entirely.
    Hide(Range<usize>),
    /// Draw this string in place of the range. Used for glyph substitution
    /// (`- ` -> ` `, `> ` -> `▎ `) and indent guides.
    ///
    /// `style` overrides what the glyph inherits: a quote bar should wear
    /// `theme.quote_bar` and a ticked task box `theme.task_done`, not the dim
    /// marker style of the source it replaces. `None` keeps the inherited one.
    Replace {
        range: Range<usize>,
        text: String,
        style: Option<Style>,
    },
}

impl Conceal {
    pub fn range(&self) -> &Range<usize> {
        match self {
            Conceal::Hide(r) => r,
            Conceal::Replace { range, .. } => range,
        }
    }

    /// A replacement with no style of its own.
    fn plain(range: Range<usize>, text: String) -> Self {
        Conceal::Replace {
            range,
            text,
            style: None,
        }
    }
}

/// What concealment needs to know beyond the line itself: the glyphs to
/// substitute, the colors they wear, and the width a full-line rule spans.
pub struct ConcealCtx<'a> {
    pub glyphs: &'a GlyphConfig,
    pub theme: &'a Theme,
    /// The text measure in cells — a fence delimiter conceals to a rule this
    /// wide, so an entry built with it is only valid at that measure.
    pub measure: u16,
    /// Columns per indent level, for the §5.4 guides.
    pub tab_width: usize,
}

/// Built per visible, NON-ACTIVE line. Active lines have no map at all —
/// `screen_col` is the identity for them.
#[derive(Default)]
pub struct ConcealMap {
    /// Sorted by start, non-overlapping. Enforced by `build`, asserted in tests.
    pub ops: Vec<Conceal>,
}

/// The set of lines rendered raw this frame. SPEC.md §2, "The active set".
///
/// Normal/Insert/Command/Search -> the cursor's line.
/// Visual/VisualLine            -> every line the selection touches, so you
///                                 always see the exact source you are about to
///                                 operate on.
#[derive(Clone, Debug, PartialEq, Eq, Default)]
pub struct ActiveSet {
    pub start: usize,
    /// Inclusive.
    pub end: usize,
}

impl ActiveSet {
    /// No line at all: past the end of any document. Read-only mode and
    /// `--render`, where there is no cursor for a line to be revealed under.
    pub fn none() -> Self {
        ActiveSet { start: usize::MAX, end: usize::MAX }
    }

    pub fn compute(mode: &Mode, cursor: &Cursor, selection_anchor: Option<Cursor>) -> Self {
        match (mode, selection_anchor) {
            (Mode::Visual | Mode::VisualLine, Some(anchor)) => ActiveSet {
                start: anchor.line.min(cursor.line),
                end: anchor.line.max(cursor.line),
            },
            _ => ActiveSet {
                start: cursor.line,
                end: cursor.line,
            },
        }
    }

    pub fn contains(&self, line: usize) -> bool {
        line >= self.start && line <= self.end
    }
}

impl ConcealMap {
    /// Derive the conceal set from inline spans and block kind.
    ///
    /// `outer - inner` of each inline span IS the conceal set — the scanner
    /// already computed it, so there is no second parsing pass. Block-level
    /// markers (`## `, `> `, `- `) contribute `Hide` or `Replace` per §5.2.
    pub fn build(line: &str, block: &BlockKind, spans: &[InlineSpan], ctx: &ConcealCtx) -> Self {
        let chars: Vec<char> = line.chars().collect();
        let mut ops: Vec<Conceal> = Vec::new();

        block_ops(&chars, block, ctx, &mut ops);

        // Inline: the markers are exactly `outer - inner`, already computed by
        // the scanner — no second parse.
        for sp in spans {
            if sp.inner.start > sp.outer.start {
                ops.push(Conceal::Hide(sp.outer.start..sp.inner.start));
            }
            if sp.outer.end > sp.inner.end {
                ops.push(Conceal::Hide(sp.inner.end..sp.outer.end));
            }
        }

        // Sort and drop any overlap (block vs inline never overlap in practice,
        // but the invariant must hold regardless).
        ops.sort_by_key(|o| o.range().start);
        let mut clean: Vec<Conceal> = Vec::with_capacity(ops.len());
        let mut last_end = 0usize;
        for op in ops {
            if op.range().start >= last_end {
                last_end = op.range().end;
                clean.push(op);
            }
        }

        ConcealMap { ops: clean }
    }

    /// Which SOURCE column a display column maps to — mouse click-to-position,
    /// the case SPEC §5.5 anticipated. A click inside a hidden or replaced
    /// region lands on that region's source start.
    ///
    /// Takes the source line so visible characters are measured at their true
    /// width: a click past a CJK glyph or an emoji lands where it looks like it
    /// should, not one column per char.
    pub fn source_col(&self, source: &str, display_col: u16) -> usize {
        let chars: Vec<char> = source.chars().collect();
        let cell = |c: char| UnicodeWidthChar::width(c).unwrap_or(0) as u16;

        let mut disp: u16 = 0;
        let mut src = 0usize;
        // Walk the visible run before each op, then the op itself.
        for op in &self.ops {
            let r = op.range();
            while src < r.start {
                let w = cell(*chars.get(src).unwrap_or(&' '));
                if display_col < disp + w.max(1) {
                    return src;
                }
                disp += w;
                src += 1;
            }
            match op {
                Conceal::Hide(rr) => src = rr.end,
                Conceal::Replace { range, text, .. } => {
                    let w = UnicodeWidthStr::width(text.as_str()) as u16;
                    if display_col < disp + w {
                        return range.start;
                    }
                    disp += w;
                    src = range.end;
                }
            }
        }
        while src < chars.len() {
            let w = cell(chars[src]);
            if display_col < disp + w.max(1) {
                return src;
            }
            disp += w;
            src += 1;
        }
        src
    }

    /// Apply the map to a source line and its SOURCE-indexed styled spans,
    /// producing the concealed display string and spans re-indexed onto it.
    /// Replacement glyphs inherit the style of the source span they sit under.
    pub fn render(&self, source: &str, spans: &[StyledSpan]) -> (String, Vec<StyledSpan>) {
        let chars: Vec<char> = source.chars().collect();
        let style_at = |src: usize| -> Style {
            spans
                .iter()
                .find(|s| s.range.start <= src && src < s.range.end)
                .map(|s| s.style)
                .unwrap_or(Style {
                    fg: Color::None,
                    bg: Color::None,
                    attrs: Attrs::default(),
                })
        };

        let mut text = String::new();
        let mut out: Vec<StyledSpan> = Vec::new();
        let mut disp = 0usize;
        let mut push = |ch: char, style: Style, text: &mut String, disp: &mut usize| {
            text.push(ch);
            match out.last_mut() {
                Some(last) if last.style == style && last.range.end == *disp => {
                    last.range.end = *disp + 1;
                }
                _ => out.push(StyledSpan {
                    range: *disp..*disp + 1,
                    style,
                }),
            }
            *disp += 1;
        };

        let mut i = 0usize;
        let mut op_idx = 0usize;
        while i < chars.len() {
            match self.ops.get(op_idx) {
                Some(op) if op.range().start == i => {
                    match op {
                        Conceal::Hide(r) => i = r.end,
                        Conceal::Replace { range, text: s, style } => {
                            let style = style.unwrap_or_else(|| style_at(range.start));
                            for ch in s.chars() {
                                push(ch, style, &mut text, &mut disp);
                            }
                            i = range.end;
                        }
                    }
                    op_idx += 1;
                }
                _ => {
                    push(chars[i], style_at(i), &mut text, &mut disp);
                    i += 1;
                }
            }
        }
        (text, out)
    }

    /// How many cells further right the body text sits in the SOURCE than it
    /// does in the concealed form — i.e. the width the markers take back when
    /// the cursor lands on this line.
    ///
    /// `layout.stable_gutter` reserves exactly this much for the active line so
    /// its text stays in the same column as it is revealed. SPEC.md §6.
    /// Every op in the LEADING RUN counts, not just the first: a line's markers
    /// can conceal in several pieces — an indent guide, then a bullet, then a
    /// task's checkbox — and missing the later ones let the body text jump as
    /// the cursor arrived. The run ends at the first gap holding a non-blank
    /// character, which is where the body text begins.
    pub fn leading_shift(&self, source: &str) -> u16 {
        let chars: Vec<char> = source.chars().collect();
        let width_of = |c: &char| UnicodeWidthChar::width(*c).unwrap_or(0);

        let mut shift = 0usize;
        let mut src = 0usize;
        for op in &self.ops {
            let r = op.range();
            if chars[src..r.start].iter().any(|c| !c.is_whitespace()) {
                break; // body text — everything past here is not a marker
            }
            let hidden: usize = chars[r.clone()].iter().map(width_of).sum();
            let shown = match op {
                Conceal::Hide(_) => 0,
                Conceal::Replace { text, .. } => UnicodeWidthStr::width(text.as_str()),
            };
            shift += hidden.saturating_sub(shown);
            src = r.end;
        }
        shift as u16
    }

    /// The concealed display string alone, without re-styling. The render
    /// cache needs it to wrap a line; the spans come later, once the frame's
    /// overlays are known.
    pub fn display_text(&self, source: &str) -> String {
        if self.ops.is_empty() {
            return source.to_string();
        }
        let chars: Vec<char> = source.chars().collect();
        let mut text = String::with_capacity(source.len());
        let mut i = 0usize;
        let mut op_idx = 0usize;
        while i < chars.len() {
            match self.ops.get(op_idx) {
                Some(op) if op.range().start == i => {
                    match op {
                        Conceal::Hide(r) => i = r.end,
                        Conceal::Replace { range, text: s, .. } => {
                            text.push_str(s);
                            i = range.end;
                        }
                    }
                    op_idx += 1;
                }
                _ => {
                    text.push(chars[i]);
                    i += 1;
                }
            }
        }
        text
    }

}

/// The bullet a list item at this indent wears: the two glyphs alternate by
/// nesting level, the way a printed list alternates • and ◦, so a sublist reads
/// as a different rank at a glance. `depth` is the item's indent in COLUMNS.
fn bullet_for(depth: u8, ctx: &ConcealCtx) -> String {
    let level = depth as usize / ctx.tab_width.max(1);
    if level.is_multiple_of(2) {
        ctx.glyphs.bullet.clone()
    } else {
        ctx.glyphs.bullet_alt.clone()
    }
}

/// Depth-colored indent guides (SPEC §5.4): each completed indent level trades
/// its first space for the guide glyph. One char for one char, so the conceal
/// map costs nothing in width and every column downstream stays put.
///
/// The glyph carries NO style of its own — `indent::apply` has already colored
/// those columns by depth in the styled spans, and a `plain` replacement
/// inherits what it lands on. That split is the whole reason the two halves of
/// the feature can live in different modules.
///
/// Only concealed lines get the guides, like every other conceal op: the line
/// under the cursor shows its source, spaces and all.
fn indent_guide_ops(chars: &[char], block: &BlockKind, ctx: &ConcealCtx, ops: &mut Vec<Conceal>) {
    if ctx.glyphs.indent_guide.is_empty() {
        return;
    }
    let line: String = chars.iter().collect();
    for (col, _depth) in indent::guides_for(&line, block, ctx.tab_width).marks {
        // Never overwrite a tab: replacing it with a 1-cell glyph would move
        // every column after it.
        if chars.get(col) == Some(&' ') {
            ops.push(Conceal::plain(col..col + 1, ctx.glyphs.indent_guide.clone()));
        }
    }
}

/// Block-level marker concealment, at the start of the line only — except for
/// the fence delimiters, which take the whole line.
fn block_ops(chars: &[char], block: &BlockKind, ctx: &ConcealCtx, ops: &mut Vec<Conceal>) {
    let len = chars.len();
    let glyphs = ctx.glyphs;
    match block {
        // `## ` vanishes; the heading text keeps its styling.
        BlockKind::Heading(_) => {
            let mut m = chars.iter().take_while(|c| **c == '#').count();
            while m < len && (chars[m] == ' ' || chars[m] == '\t') {
                m += 1;
            }
            if m > 0 {
                ops.push(Conceal::Hide(0..m));
            }
        }
        // The `>` run becomes ONE BAR PER LEVEL, so a nested quote still reads
        // as nested instead of collapsing to a single bar.
        BlockKind::Quote(depth) => {
            let m = chars
                .iter()
                .take_while(|c| matches!(**c, ' ' | '\t' | '>'))
                .count();
            if m > 0 {
                let bars = format!("{} ", glyphs.quote_bar).repeat((*depth as usize).max(1));
                ops.push(Conceal::Replace {
                    range: 0..m,
                    text: bars,
                    style: Some(Style::fg(ctx.theme.quote_bar)),
                });
            }
        }
        // `- ` / `* ` become a real bullet — one char for one char, so the text
        // keeps its column. An ORDINAL is content, not markup ("2." says which
        // item this is), so a numbered list keeps its number. A TASK concealsr
        // its whole `- [ ] ` prefix to one checkbox, which then stands in the
        // bullet column like any other marker. The leading whitespace picks up
        // its indent guides on the way past (SPEC §5.4).
        BlockKind::ListItem { marker, checked, depth } => {
            let indent = chars.iter().take_while(|c| **c == ' ' || **c == '\t').count();
            indent_guide_ops(chars, block, ctx, ops);

            // End of the marker itself: `-`, or `12.`.
            let mut p = indent;
            match marker {
                Marker::Ordered => {
                    while p < len && chars[p].is_ascii_digit() {
                        p += 1;
                    }
                    p += 1; // the `.` or `)`
                }
                _ => p += 1,
            }
            p = p.min(len);

            // A checkbox directly after the marker, if this is a task.
            let mut q = p;
            if q < len && (chars[q] == ' ' || chars[q] == '\t') {
                q += 1;
            }
            let box_end = (q + 3 <= len && chars[q] == '[').then_some(q + 3);

            match (checked, box_end) {
                // `- [x] ` -> `☑`, marker and all. One op for the whole prefix
                // so `leading_shift` can give the columns back on the active
                // line — two ops used to leave the text jumping by two.
                (Some(done), Some(end)) => {
                    let (glyph, color) = if *done {
                        (&glyphs.task_done, ctx.theme.task_done)
                    } else {
                        (&glyphs.task_todo, ctx.theme.list_bullet)
                    };
                    // An ordered task keeps its number (and the space after it)
                    // in front of the box.
                    let mut text: String = match marker {
                        Marker::Ordered => chars[indent..q].iter().collect(),
                        _ => String::new(),
                    };
                    text.push_str(glyph);
                    ops.push(Conceal::Replace {
                        range: indent..end,
                        text,
                        style: Some(Style::fg(color)),
                    });
                }
                // A plain bullet. `bullet = ""` blanks instead — blank, never
                // dropped, or the text would sit one column left of its
                // neighbours with nothing to explain why.
                (_, _) if !matches!(marker, Marker::Ordered) && p > indent => {
                    let bullet = bullet_for(*depth, ctx);
                    if bullet.is_empty() {
                        ops.push(Conceal::plain(indent..p, " ".into()));
                    } else {
                        ops.push(Conceal::Replace {
                            range: indent..p,
                            text: bullet,
                            style: Some(Style::fg(ctx.theme.list_bullet)),
                        });
                    }
                }
                _ => {}
            }
        }
        // ``` and ~~~ conceal to a rule across the measure: the code block gets
        // a visible top and bottom without its delimiters shouting. SPEC §5.2.
        // A thematic break (`---`) is the same idea and gets the same drawing.
        BlockKind::FenceOpen(_) | BlockKind::FenceClose | BlockKind::Rule if len > 0 => {
            let color = if matches!(block, BlockKind::Rule) {
                ctx.theme.rule
            } else {
                ctx.theme.fence_bar
            };
            ops.push(Conceal::Replace {
                range: 0..len,
                text: rule(&glyphs.rule, ctx.measure),
                style: Some(Style::fg(color)),
            });
        }
        _ => {}
    }
}

/// A horizontal rule `width` cells wide, drawn from `glyph` (which may itself
/// be more than one cell).
fn rule(glyph: &str, width: u16) -> String {
    let unit = UnicodeWidthStr::width(glyph).max(1);
    glyph.repeat((width as usize / unit).max(1))
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::schema::MarkdownConfig;
    use crate::render::markdown::block::{classify, Carry};
    use crate::render::markdown::inline;

    /// Build a conceal map the way the frame will: classify the line, scan it,
    /// then derive the map.
    const MEASURE: u16 = 20;

    fn map(line: &str) -> ConcealMap {
        map_in(line, &Carry::None)
    }

    /// Build a conceal map the way the frame will: classify the line, scan it,
    /// then derive the map. `carry` sets the state entering the line, which is
    /// what tells a fence delimiter from a paragraph of backticks.
    fn map_in(line: &str, carry: &Carry) -> ConcealMap {
        let (block, _) = classify(line, carry, false);
        let spans = if block.allows_inline() {
            inline::scan(line, &MarkdownConfig::default())
        } else {
            Vec::new()
        };
        let glyphs = GlyphConfig::default();
        let theme = Theme::default();
        ConcealMap::build(
            line,
            &block,
            &spans,
            &ConcealCtx {
                glyphs: &glyphs,
                theme: &theme,
                measure: MEASURE,
                tab_width: 2,
            },
        )
    }

    /// The concealed display text, ignoring styling.
    fn shown(line: &str) -> String {
        shown_in(line, &Carry::None)
    }

    fn shown_in(line: &str, carry: &Carry) -> String {
        let styled = vec![StyledSpan {
            range: 0..line.chars().count(),
            style: Style {
                fg: Color::None,
                bg: Color::None,
                attrs: Attrs::default(),
            },
        }];
        map_in(line, carry).render(line, &styled).0
    }

    #[test]
    fn inline_markers_vanish() {
        assert_eq!(shown("a **bold** b"), "a bold b");
        assert_eq!(shown("some *italic* here"), "some italic here");
        assert_eq!(shown("call `code` now"), "call code now");
        assert_eq!(shown("a [label](http://x) b"), "a label b");
        assert_eq!(shown("a [[Wiki]] b"), "a Wiki b");
        assert_eq!(shown("tag #foo bar"), "tag foo bar");
        assert_eq!(shown(r"an escaped \* star"), "an escaped * star");
    }

    #[test]
    fn heading_marker_hidden() {
        assert_eq!(shown("## Title"), "Title");
        assert_eq!(shown("# A **bold** head"), "A bold head");
    }

    #[test]
    fn quote_becomes_bar() {
        // Default quote_bar glyph is `▎`.
        assert_eq!(shown("> quoted"), "▎ quoted");
    }

    /// A nested quote keeps its depth: one bar per level, not one bar total.
    #[test]
    fn nested_quotes_show_one_bar_per_level() {
        assert_eq!(shown("> > deep"), "▎ ▎ deep");
        assert_eq!(shown(">>> deeper"), "▎ ▎ ▎ deeper");
    }

    /// Fence delimiters conceal to a rule the width of the measure, so a code
    /// block reads as a block without its backticks shouting. SPEC §5.2.
    #[test]
    fn fence_delimiters_become_a_rule() {
        let open = shown("```rust");
        assert_eq!(UnicodeWidthStr::width(open.as_str()), MEASURE as usize);
        assert!(!open.contains('`'));
        // The closing fence needs the carry state that says we are inside one.
        let close = shown_in(
            "```",
            &Carry::InFence { fence: "```".into(), lang: None, cont: Default::default() },
        );
        assert_eq!(UnicodeWidthStr::width(close.as_str()), MEASURE as usize);
    }

    /// The bar and the box wear their own theme colors, not the dim marker
    /// style of the source characters they stand in for.
    #[test]
    fn replacement_glyphs_carry_their_own_color() {
        let theme = Theme::default();
        let styled = |line: &str| {
            let spans = vec![StyledSpan {
                range: 0..line.chars().count(),
                style: Style::fg(Color::None),
            }];
            map(line).render(line, &spans).1
        };
        assert_eq!(styled("> quoted")[0].style.fg, theme.quote_bar);
        // The tick is the line's first span now — it replaces `- [x] ` whole.
        assert_eq!(styled("- [x] done")[0].style.fg, theme.task_done);
    }

    /// A list should LOOK like a list: `- ` and `* ` become a bullet, one char
    /// for one char, so the text stays in its content column either way.
    #[test]
    fn list_marker_becomes_a_bullet() {
        assert_eq!(shown("- item"), "• item");
        assert_eq!(shown("* item"), "• item");
        assert_eq!(shown("+ item"), "• item");
        // Sub-lists alternate to the hollow bullet (helper tab_width is 2).
        assert_eq!(shown("  - nested"), "│ ◦ nested");
        assert_eq!(shown("    - deeper"), "│ │ • deeper");
        // An ordinal is content, not markup — a numbered list keeps its number.
        assert_eq!(shown("1. item"), "1. item");
        assert_eq!(shown("12) item"), "12) item");
        // A task's checkbox IS its bullet, standing in the same column.
        assert_eq!(shown("- [ ] todo"), "☐ todo");
        // The marker swap is width-preserving. (A task box is not — `[ ]` is
        // three chars for one glyph — which is how it has always rendered.)
        for line in ["- item", "  - nested", "1. item"] {
            assert_eq!(shown(line).chars().count(), line.chars().count(), "{line:?}");
        }
    }

    /// Turning the glyph off falls back to the blank, never to a shifted line.
    #[test]
    fn an_empty_bullet_glyph_still_holds_the_column() {
        let glyphs = GlyphConfig {
            bullet: String::new(),
            ..GlyphConfig::default()
        };
        let theme = Theme::default();
        let map = ConcealMap::build(
            "- item",
            &BlockKind::ListItem { depth: 0, marker: Marker::Dash, checked: None },
            &[],
            &ConcealCtx { glyphs: &glyphs, theme: &theme, measure: MEASURE, tab_width: 2 },
        );
        assert_eq!(map.display_text("- item"), "  item");
    }

    /// SPEC §5.4: each completed indent level trades its first space for the
    /// guide glyph, one char for one char (the helper's tab_width is 2).
    #[test]
    fn indent_guides_replace_a_space_per_level() {
        assert_eq!(shown("    - nested"), "│ │ • nested");
        assert_eq!(shown("  - one level"), "│ ◦ one level");
        assert_eq!(shown("- flush"), "• flush", "no indent, no guides");
        // Width is preserved exactly, which is what keeps SPEC §2 true.
        for line in ["    - nested", "  - one level"] {
            assert_eq!(shown(line).chars().count(), line.chars().count());
        }
    }

    /// A tab is one char but many columns; swapping a 1-cell glyph in for it
    /// would shift the whole line, so tab-indented lines keep their whitespace.
    #[test]
    fn indent_guides_leave_tabs_alone() {
        assert_eq!(shown("\t\t- tabbed"), "\t\t◦ tabbed");
    }

    #[test]
    fn task_checkbox_becomes_a_box_or_tick() {
        // Default glyphs are the portable ballot boxes ☐ / ☑. The box replaces
        // the WHOLE `- [ ] ` prefix, so it stands in the bullet's own column
        // and a task lines up with its plain siblings.
        assert_eq!(shown("- [ ] todo"), "☐ todo");
        assert_eq!(shown("- [x] done"), "☑ done");
        assert_eq!(shown("* [ ] starred"), "☐ starred");
        // An ordered task keeps its number in front of the box.
        assert_eq!(shown("1. [ ] first"), "1. ☐ first");
    }

    /// The reveal shift the active line has to give back: `layout.stable_gutter`
    /// draws that line this many columns left, so the body text never moves as
    /// the cursor arrives. Every leading op counts toward it.
    #[test]
    fn leading_shift_covers_the_whole_marker_run() {
        let shift = |line: &str| map(line).leading_shift(line);
        assert_eq!(shift("## Title"), 3, "`## ` is hidden outright");
        assert_eq!(shift("- item"), 0, "a bullet swaps one char for one");
        assert_eq!(shift("> quoted"), 0, "`> ` becomes a bar of the same width");
        // `- [ ] ` (5 cells) down to one box.
        assert_eq!(shift("- [ ] todo"), 4);
        // Indent guides come first and cost nothing; the task prefix still counts.
        assert_eq!(shift("  - [ ] nested"), 4);
        // The run stops at the body: an inline marker further along the line
        // does not pull the text sideways.
        assert_eq!(shift("**bold** and more"), 2);
    }

    #[test]
    fn source_col_inverts_the_display() {
        // "## Title" conceals "## " -> display "Title".
        let line = "## Title";
        let m = map(line);
        assert_eq!(m.source_col(line, 0), 3); // display 'T' -> source col 3
        assert_eq!(m.source_col(line, 1), 4); // 'i' -> 4
        // "a **bold** b" -> display "a bold b"; display col 2 = 'b' of bold.
        let line = "a **bold** b";
        let m = map(line);
        assert_eq!(m.source_col(line, 0), 0); // 'a'
        assert_eq!(m.source_col(line, 2), 4); // 'b' of bold is source col 4
    }

    /// Wide characters are measured in CELLS, so a click past a CJK glyph lands
    /// on the character it looks like it landed on.
    #[test]
    fn source_col_measures_wide_characters() {
        // "**b** 世界x": display "b 世界x" — 世 and 界 are two cells each.
        let line = "**b** 世界x";
        let m = map(line);
        assert_eq!(m.source_col(line, 0), 2); // 'b'
        assert_eq!(m.source_col(line, 2), 6); // 世 starts at display col 2
        assert_eq!(m.source_col(line, 3), 6); // its second cell is still 世
        assert_eq!(m.source_col(line, 4), 7); // 界
        assert_eq!(m.source_col(line, 6), 8); // 'x'
    }

    #[test]
    fn ops_are_sorted_and_non_overlapping() {
        let m = map("## a **b** `c` [d](e) #f");
        let mut last = 0;
        for op in &m.ops {
            assert!(op.range().start >= last, "overlap in {:?}", m.ops);
            last = op.range().end;
        }
    }
}

// The conceal map for a line is cached alongside the rest of that line's parse
// in `render::cache::RenderCache`, which keeps ONE cache instead of several
// keyed the same way. The active set does not invalidate those entries: a
// concealed and a raw line are two views of one parse, so cursor movement only
// re-picks the view (SPEC.md §9 — a caveat the earlier design missed).