use super::ctx::{Ctx, page_anchored};
use super::floats::{
    ObjFrame, ObjectPlacement, WrapArea, align_in, float_rect, floating, left_out_objects, place_objects, rel_exclusions, wrap_area,
};
use super::page::PageFrame;
use super::placed::Placed;
use super::table_flow::below;
use super::{
    Anchor, Arc, Block, Blocks, Border, Document, Float, FloatAlign, HashMap, ParaLayout, Paragraph, Path, Rect, StoryRef, TableFloat, TextDirection,
    Wrap, WrapText, para, table,
};

/// Cell identity is independent of optional table-style formatting.
pub(crate) enum BoxContext<'a> {
    Other,
    /// Outer cell edges relative to its text origin (not including wrap distances).
    Cell {
        text: Option<&'a para::CellText>,
        left: f32,
        right: f32,
        /// False for a turned text frame: its x axis becomes page y after rotation.
        clamp: bool,
    },
}

pub(crate) struct BoxInput<'a> {
    pub(crate) story: StoryRef,
    pub(crate) blocks: &'a Blocks,
    pub(crate) prefix: &'a [u32],
    pub(crate) width: f32,
    pub(crate) context: BoxContext<'a>,
    pub(crate) depth: usize,
    pub(crate) frame: Option<PageFrame<'a>>,
}

impl<'a> BoxInput<'a> {
    pub(crate) fn other(story: StoryRef, blocks: &'a Blocks, width: f32, depth: usize, frame: Option<PageFrame<'a>>) -> Self {
        Self { story, blocks, prefix: &[], width, context: BoxContext::Other, depth, frame }
    }

    pub(crate) fn cell(story: StoryRef, blocks: &'a Blocks, prefix: &'a [u32], width: f32, cell: Option<&'a para::CellText>, depth: usize) -> Self {
        Self { story, blocks, prefix, width, context: BoxContext::Cell { text: cell, left: 0.0, right: width, clamp: false }, depth, frame: None }
    }
}

struct ParagraphSpacing<'a> {
    index: usize,
    listed: bool,
    style: &'a str,
    contextual: bool,
    before_auto: bool,
    space_before: f32,
    allow_same_style_space: bool,
    previous_style: Option<&'a (String, bool)>,
    previous_listed: bool,
    previous_after_auto: bool,
    previous_after: &'a mut f32,
    y: &'a mut f32,
    sum_paragraph_spacing: bool,
}

struct TableBlockContext<'ctx, 'state, 'doc> {
    ctx: &'ctx mut Ctx<'doc>,
    story: StoryRef,
    table: &'state wordcraft_doc::Table,
    path: &'state [u32],
    width: f32,
    frame: Option<PageFrame<'state>>,
    in_cell: bool,
    depth: usize,
    y: &'state mut f32,
    items: &'state mut Vec<Placed>,
    exclusions: &'state mut Vec<WrapArea>,
    float_tables: &'state mut Vec<Rect>,
    table_areas: &'state mut Vec<Rect>,
    page_table_wraps: &'state mut Vec<WrapArea>,
    previous_after: &'state mut f32,
    previous_style: &'state mut Option<(String, bool)>,
}

fn paragraph_spacing(input: ParagraphSpacing<'_>) -> (bool, f32) {
    let ParagraphSpacing {
        index,
        listed,
        style,
        contextual,
        before_auto,
        space_before,
        allow_same_style_space,
        previous_style,
        previous_listed,
        previous_after_auto,
        previous_after,
        y,
        sum_paragraph_spacing,
    } = input;
    let contextual = contextual && !allow_same_style_space;
    let mut before = space_before;
    if let Some((previous, previous_contextual)) = previous_style
        && previous == style
        && !allow_same_style_space
    {
        if *previous_contextual {
            *y -= *previous_after;
            before = (before - *previous_after).max(0.0);
            *previous_after = 0.0;
        }
        if contextual {
            before = 0.0;
        }
    }
    if index > 0 && previous_listed && listed {
        if previous_after_auto {
            *y -= *previous_after;
            *previous_after = 0.0;
        }
        if before_auto {
            before = 0.0;
        }
    }
    if before_auto && index == 0 {
        before = 0.0;
    } else if index > 0 && before > 0.0 && *previous_after > 0.0 && !sum_paragraph_spacing {
        before = (before - *previous_after).max(0.0);
    }
    (contextual, before)
}

fn layout_table_block(input: TableBlockContext<'_, '_, '_>) -> bool {
    let TableBlockContext {
        ctx,
        story,
        table: t,
        path,
        width,
        frame,
        in_cell,
        depth,
        y,
        items,
        exclusions,
        float_tables,
        table_areas,
        page_table_wraps,
        previous_after,
        previous_style,
    } = input;
    if depth > 8 {
        return false;
    }
    // Page tables do not contribute to the footer text's intrinsic height.
    if frame.is_none()
        && !in_cell
        && matches!(story, StoryRef::Part(id) if ctx.doc.parts.get(&id).is_some_and(|p| p.kind == wordcraft_doc::PartKind::Footer))
        && t.props.float.is_some_and(|f| f.v_rel == Anchor::Page)
    {
        return false;
    }
    let layout = table::layout_table(ctx, story, t, path, width, depth + 1);
    let (tx, ty) = match t.props.float {
        Some(float) => {
            let legacy = if ctx.doc.settings.compat_mode < 15 { table::first_cell_left_margin(ctx, t) } else { 0.0 };
            let (rect, area) = box_float_table_rect(frame, width, *y, &layout, &float, legacy, float_tables);
            exclusions.push((area, false, None, WrapText::BothSides, true));
            float_tables.push(area);
            table_areas.push(area);
            if float.v_rel == Anchor::Page {
                page_table_wraps.push((area, false, None, WrapText::BothSides, true));
            }
            (rect.x, rect.y)
        }
        None => (layout.x, below(exclusions, *y, layout.x, layout.x + layout.width)),
    };
    let mut row_y = ty;
    for row in &layout.rows {
        for item in &row.items {
            let mut item = item.clone();
            item.translate(tx, row_y);
            items.push(item);
        }
        row_y += row.height;
    }
    if t.props.float.is_none() {
        *y = row_y;
        *previous_after = 0.0;
        *previous_style = None;
    }
    true
}

/// Lay out a block list into a free-standing box of `width` (no page breaks): table cells,
/// headers, footers, notes, text boxes. Returns items relative to (0, 0) and the height. `frame`
/// says where the box sits on its page, for floating objects positioned relative to the page or
/// its margins; without it (cells, notes, text boxes) they're positioned in the box.
pub(crate) fn layout_box(ctx: &mut Ctx, input: BoxInput<'_>) -> BoxLayout {
    let BoxInput { story, blocks, prefix, width, context, depth, frame } = input;
    // Deletions in balloons leave the body's text only: a header, note or text box keeps its own
    // inline (restored for the story around this box when it's done).
    let outer_hide = std::mem::replace(&mut ctx.hide_deleted, ctx.opts.hides_deleted(story));
    let empty_cell = para::CellText::default();
    let (in_cell, table, cell_edges) = match context {
        BoxContext::Other => (false, None, None),
        BoxContext::Cell { text, left, right, clamp } => (true, Some(text.unwrap_or(&empty_cell)), clamp.then_some((left, right))),
    };
    // Word 16.113.3: the override applies in modes 11/12/14, but not mode 15.
    let allow_same_style_space =
        in_cell && ctx.doc.settings.allow_space_of_same_style_in_table && matches!(ctx.doc.settings.compat_mode, 11 | 12 | 14);
    let mut items = Vec::new();
    // Pictures behind the text go first; `behind` counts them.
    let mut behind = 0;
    // Wrap areas of the box's floating objects.
    let mut excl: Vec<WrapArea> = Vec::new();
    // Areas of the box's floating tables, which other floating tables may have to avoid.
    let mut float_tables: Vec<Rect> = Vec::new();
    // Deepest a floating picture or shape that takes part in the text flow reaches, so the box
    // (a table cell especially) grows to hold it instead of letting it hang past the box's own
    // bottom edge (#3108). Behind-text and in-front-of-text objects don't: a page-anchored logo or
    // watermark behind a cell's text must not stretch its row (see `align_h` in table.rs).
    let mut float_objects_bottom = 0.0f32;
    let mut table_areas = Vec::new();
    let mut page_table_wraps = Vec::new();
    let mut y = 0.0f32;
    let mut prev_after = 0.0f32;
    let mut prev_after_auto = false;
    let mut prev_listed = false;
    let mut prev_style: Option<(String, bool)> = None;
    let mut last_top = 0.0f32;
    // Word has no frames in a text box: a framed paragraph there (its style's frame, usually)
    // runs with the box's text (#2357).
    let frames = !matches!(story, StoryRef::Part(id) if ctx.doc.parts.get(&id).is_some_and(|p| p.kind == wordcraft_doc::PartKind::TextBox));
    // The bottom of the last paragraph's lines.
    let mut prev_end = 0.0f32;
    for (i, b) in blocks.iter().enumerate() {
        last_top = y;
        let mut path = prefix.to_vec();
        path.push(i as u32);
        match &**b {
            Block::Para(p) => {
                let label = ctx.next_label(p);
                let listed = label.is_some();
                let mut pl = ctx.para_labelled(p, width, table, &[], label.clone());
                // A text frame (a footer's page number in a frame, say) is placed apart, like a
                // floating object, and the text after it wraps around it; it takes no room in
                // the flow.
                if let Some(fr) = pl.rp.frame.clone().filter(|_| frames) {
                    let fw = fr.w.unwrap_or_else(|| natural_width(&pl)).clamp(1.0, 1584.0);
                    let pf = if (fw - width).abs() > 0.01 { ctx.para_labelled(p, fw, table, &[], label) } else { pl };
                    let h = match fr.h {
                        Some(h) if fr.h_exact => h,
                        Some(h) => h.max(pf.height),
                        None => pf.height,
                    };
                    let float = frame_float(&fr);
                    let r = float_rect(frame, (0.0, width), y, fw, h, &float);
                    push_para(&mut items, (story, &path), &pf, (0, pf.lines.len()), (r.x, r.y), fw, Edges::own(&pf, 0, pf.lines.len()));
                    excl.extend(wrap_area(r, &float, None));
                    float_tables.push(r);
                    continue;
                }
                let (ctxl, before) = paragraph_spacing(ParagraphSpacing {
                    index: i,
                    listed,
                    style: &pl.rp.style,
                    contextual: pl.rp.contextual_spacing,
                    before_auto: pl.rp.before_auto,
                    space_before: pl.rp.space_before,
                    allow_same_style_space,
                    previous_style: prev_style.as_ref(),
                    previous_listed: prev_listed,
                    previous_after_auto: prev_after_auto,
                    previous_after: &mut prev_after,
                    y: &mut y,
                    sum_paragraph_spacing: ctx.doc.settings.sum_paragraph_spacing,
                });
                // Paragraph-relative floats start above the effective space before, as in the
                // body path. Keep text and wrap exclusions relative to the text's actual top.
                let para_top = y;
                y += if i == 0 { before } else { before.max(0.0) };
                // Floating objects anchored here: place them, then wrap the text around them.
                // One left out of the layout (hidden, or deleted in the final text) takes no room.
                let mut floats = HashMap::new();
                // A header or footer cell's floats placed on the page: no room taken in the cell.
                let mut pinned = HashMap::new();
                let left_out = left_out_objects(ctx.doc, p, table.map(|t| &t.chr), ctx.opts.show_hidden, ctx.hide_deleted);
                for (oi, o) in p.objects.iter().enumerate() {
                    let Some((w, h, float)) = floating(o) else { continue };
                    if left_out(oi) {
                        continue;
                    }
                    let h = ctx.float_height(o, w, h);
                    if let Some(pin) = ctx.pin.as_ref().filter(|pin| in_cell && pin.story == story && float.outside_cell && page_anchored(float)) {
                        let page =
                            PageFrame { sect: &pin.sect, margin_top: pin.margin_top, origin: (0.0, 0.0), number: pin.number, mirror: pin.mirror };
                        pinned.insert(oi, float_rect(Some(page), (0.0, width), para_top, w, h, float));
                        continue;
                    }
                    // Only paragraph-relative placement excludes space-before. Line anchors
                    // and frameless page/margin fallbacks retain the text-top origin.
                    let float_y = if float.v_rel == Anchor::Paragraph { para_top } else { y };
                    let mut r = float_rect(frame, (0.0, width), float_y, w, h, float);
                    // Only move an offset-positioned float when its box crosses the outer
                    // cell edge. Cell text margins and wrap distances do not move the object.
                    if let Some((left, right)) = cell_edges
                        && !float.outside_cell
                        && float.h_align.is_none()
                        && float.wrap != Wrap::InFrontOfText
                    {
                        r.x = keep_in_cell(r.x, r.w, left, right);
                    }
                    let outline = ctx.wrap_outline(o);
                    excl.extend(wrap_area(r, float, outline.as_deref().map(Vec::as_slice)));
                    floats.insert(oi, r);
                }
                let rel = rel_exclusions(&excl, 0.0, y);
                if !rel.is_empty() {
                    pl = ctx.para_labelled(p, width, table, &rel, label);
                }
                // Bordered paragraphs: room for their borders, those of a group joined in one box.
                let cell = table.map(|t| &t.para);
                let (above, below) = (joined(ctx.doc, blocks, i, i.checked_sub(1), cell), joined(ctx.doc, blocks, i, Some(i + 1), cell));
                let mut edges = Edges::own(&pl, 0, pl.lines.len());
                if above {
                    edges.top = 0.0;
                }
                if below {
                    edges.bottom = 0.0;
                }
                let lead = pl.lines.first().map_or(0.0, |l| l.top.max(0.0)) + edges.top;
                if above {
                    edges.up = (y + lead - prev_end).max(0.0);
                }
                prev_end = push_para(&mut items, (story, &path), &pl, (0, pl.lines.len()), (0.0, y + lead), width, edges);
                // Pictures, shapes and text boxes: drawn, their areas and text boxes' text.
                if !p.objects.is_empty() {
                    let at = ObjFrame {
                        page: frame,
                        col: (0.0, width),
                        para_y: para_top,
                        table_chr: table.map(|t| &t.chr),
                        pinned: Some(&pinned),
                        late: None,
                    };
                    let (back, front) = place_objects(
                        ctx,
                        &ObjectPlacement {
                            story,
                            path: &path,
                            p,
                            pl: &pl,
                            lines: (0, pl.lines.len()),
                            origin: (0.0, y + lead),
                            at: &at,
                            floats: &floats,
                            depth,
                        },
                    );
                    for placed in back.iter().chain(front.iter()) {
                        if let Placed::Object { rect, spin, wrap, .. } = placed
                            && !matches!(wrap, Wrap::Inline | Wrap::BehindText | Wrap::InFrontOfText)
                        {
                            float_objects_bottom = float_objects_bottom.max(spin.bounds(*rect).bottom());
                        }
                    }
                    let at = behind.min(items.len());
                    behind += back.len();
                    items.splice(at..at, back);
                    items.extend(front);
                }
                // Automatic space after: none after the last paragraph of a cell or box.
                let after = if pl.rp.after_auto && i + 1 == blocks.len() { 0.0 } else { pl.rp.space_after };
                y += edges.top + pl.height + edges.bottom + after;
                prev_after = after;
                prev_after_auto = pl.rp.after_auto;
                prev_listed = listed;
                prev_style = Some((pl.rp.style.clone(), ctxl));
            }
            Block::Table(t) => {
                if !layout_table_block(TableBlockContext {
                    ctx,
                    story,
                    table: t,
                    path: &path,
                    width,
                    frame,
                    in_cell,
                    depth,
                    y: &mut y,
                    items: &mut items,
                    exclusions: &mut excl,
                    float_tables: &mut float_tables,
                    table_areas: &mut table_areas,
                    page_table_wraps: &mut page_table_wraps,
                    previous_after: &mut prev_after,
                    previous_style: &mut prev_style,
                }) {
                    continue;
                }
            }
        }
    }
    let floats_bottom = float_tables.iter().map(|r| r.bottom()).fold(float_objects_bottom, f32::max);
    ctx.hide_deleted = outer_hide;
    BoxLayout { items, height: y.max(0.0), floats_bottom, last_top: last_top.max(0.0), table_areas, page_table_wraps }
}

/// The width a text frame without one takes: its widest line, with the paragraph's indents.
fn natural_width(pl: &ParaLayout) -> f32 {
    let widest = (0..pl.lines.len())
        .filter_map(|li| {
            let l = pl.lines.get(li)?;
            Some((pl.x_of(li, l.stop)? - pl.x_of(li, l.start)?).abs())
        })
        .fold(0.0f32, f32::max);
    widest + pl.rp.indent_left.max(0.0) + pl.rp.indent_right.max(0.0)
}

/// A text frame's placement as a floating object's (`w:framePr` → anchors, alignment, wrap).
fn frame_float(fr: &wordcraft_doc::props::TextFrame) -> Float {
    let anchor = |a: &str, text: Anchor| match a {
        "page" => Anchor::Page,
        "margin" => Anchor::Margin,
        _ => text,
    };
    let align = |a: Option<&str>| match a {
        Some("left" | "top") => Some(FloatAlign::Start),
        Some("center") => Some(FloatAlign::Center),
        Some("right" | "bottom") => Some(FloatAlign::End),
        Some("inside") => Some(FloatAlign::Inside),
        Some("outside") => Some(FloatAlign::Outside),
        _ => None,
    };
    Float {
        wrap: match fr.wrap.as_str() {
            "notBeside" => Wrap::TopAndBottom,
            "none" => Wrap::InFrontOfText,
            "tight" => Wrap::Tight,
            "through" => Wrap::Through,
            _ => Wrap::Square,
        },
        h_rel: anchor(&fr.h_anchor, Anchor::Column),
        v_rel: anchor(&fr.v_anchor, Anchor::Paragraph),
        x: fr.x,
        y: fr.y,
        h_align: align(fr.x_align.as_deref()),
        v_align: align(fr.y_align.as_deref()),
        dist: fr.h_space,
        dist_top: fr.v_space,
        dist_bottom: fr.v_space,
        ..Default::default()
    }
}

/// A laid-out box: items relative to its top-left, the height of its text flow, where its
/// floating tables end (a table cell grows to hold them) and where its last block starts (the
/// height without it).
pub(crate) struct BoxLayout {
    pub(crate) items: Vec<Placed>,
    pub(crate) table_areas: Vec<Rect>,
    pub(crate) page_table_wraps: Vec<WrapArea>,
    pub(crate) height: f32,
    pub(crate) floats_bottom: f32,
    pub(crate) last_top: f32,
}

/// Where floating table `tl` goes in a box `width` wide whose next paragraph starts at `y`, and
/// the area text keeps clear of. Positions relative to the page or its margins need the box's
/// `frame`; without one (a table cell) they're relative to the box.
fn box_float_table_rect(
    frame: Option<PageFrame>,
    width: f32,
    y: f32,
    tl: &table::TableLayout,
    f: &TableFloat,
    legacy: f32,
    float_tables: &[Rect],
) -> (Rect, Rect) {
    let h = tl.rows.iter().map(|r| r.height).sum::<f32>().clamp(0.0, 100_000.0);
    let w = tl.width.clamp(1.0, 100_000.0);
    // Across, as laid out before an even page is mirrored (see `float_rect`).
    let page_x = |fr: &PageFrame| {
        let (left, _, shift) = fr.sides();
        match f.h_rel {
            Anchor::Page => Some((-shift, fr.sect.page_w)),
            Anchor::Margin => Some((left - shift, fr.sect.text_width())),
            _ => None,
        }
    };
    let page_y = |fr: &PageFrame| {
        let s = fr.sect;
        match f.v_rel {
            Anchor::Page => Some((0.0, s.page_h)),
            Anchor::Margin => {
                let mut reference = s.clone();
                reference.margin_top = fr.margin_top.unwrap_or(s.margin_top);
                Some((reference.margin_top, reference.text_height()))
            }
            _ => None,
        }
    };
    let h_area = frame.and_then(|fr| page_x(&fr).map(|(a, e)| (a - fr.origin.0, e))).unwrap_or((0.0, width));
    // In a cell an offset from the page or margin has nothing to measure from: the table stands
    // where the text is.
    let (v_area, y_off) = match frame.and_then(|fr| page_y(&fr).map(|(a, e)| (a - fr.origin.1, e))) {
        Some(area) => (area, f.y),
        None if matches!(f.v_rel, Anchor::Page | Anchor::Margin) => ((y, 0.0), 0.0),
        None => ((y, 0.0), f.y),
    };
    // Nor is there an area to align in: the table starts where the text is.
    let v_align = if frame.is_none() && matches!(f.v_rel, Anchor::Page | Anchor::Margin) { None } else { f.v_align };
    let x = align_in(h_area, f.x, w, PageFrame::h_align(frame.as_ref(), f.h_align)) - if f.h_align.is_none() { legacy } else { 0.0 };
    let r = clear_of_float_tables(Rect::new(x, align_in(v_area, y_off, h, v_align), w, h), f, legacy, h_area.0, float_tables);
    let [dl, dt, dr, db] = f.dist_from_text();
    (r, r.inset(-dl, -dt, -dr, -db))
}

/// Floating table `f` at `r`, moved below the floating tables in its way when it may not
/// overlap them. In Word 2013+ layout one placed by an offset keeps its distance from the text's
/// left edge (`text_left`).
pub(crate) fn clear_of_float_tables(mut r: Rect, f: &TableFloat, legacy: f32, text_left: f32, others: &[Rect]) -> Rect {
    let [dl, dt, dr, db] = f.dist_from_text();
    let keeps_text_distance = legacy == 0.0 && f.h_align.is_none() && f.x >= 0.0 && matches!(f.h_rel, Anchor::Margin | Anchor::Column);
    for _ in 0..64 {
        let area = r.inset(-dl, -dt, -dr, -db);
        let Some(below) = others.iter().filter(|o| !f.overlap && o.intersects(&area)).map(|o| o.bottom()).reduce(f32::max) else { break };
        r.y = below + dt;
        if keeps_text_distance {
            r.x = r.x.max(text_left + dl);
        }
    }
    r
}

/// Keep a float's box within the outer cell edges, relative to the cell's text origin.
/// Offsets that fit are unchanged, including those inside the text margins. Wrap distances
/// affect surrounding text only. An oversized object starts at the outer left edge.
pub(crate) fn keep_in_cell(x: f32, w: f32, left: f32, right: f32) -> f32 {
    let left = if left.is_finite() { left } else { 0.0 };
    let end = right - w;
    if !end.is_finite() || end <= left {
        return left;
    }
    // max/min also place a non-finite offset at a finite edge without panicking.
    x.max(left).min(end)
}

/// A text box's default internal margins (Word's: 0.1" left/right, 0.05" top/bottom); a box's
/// own come from its [`wordcraft_doc::TextBody`].
#[cfg(test)]
pub(crate) const BOX_INSET_X: f32 = 7.2;

#[cfg(test)]
pub(crate) const BOX_INSET_Y: f32 = 3.6;

/// Keep what fits in a box `height` tall (items relative to its top): lines that don't fit are
/// dropped (whole lines; a line that only partly fits too) and so is anything starting below.
/// The first line always stays, so even a tiny box shows the start of its text.
pub(crate) fn fit_box(items: Vec<Placed>, height: f32) -> Vec<Placed> {
    let limit = height + 0.5;
    let mut out = Vec::with_capacity(items.len());
    let mut kept_line = false;
    for it in items {
        if let Some(r) = it.turned_bounds() {
            // Turned text (in a table cell) stays whole.
            if r.y < limit {
                out.push(it);
            }
            continue;
        }
        match it {
            Placed::Lines { story, path, para, l0, l1, x, y, turn } => {
                let Some(first) = para.lines.get(l0) else { continue };
                let mut end = l0;
                for k in l0..l1 {
                    let Some(l) = para.lines.get(k) else { break };
                    if y + (l.top - first.top) + l.height > limit && kept_line {
                        break;
                    }
                    end = k + 1;
                    kept_line = true;
                }
                if end > l0 {
                    out.push(Placed::Lines { story, path, para, l0, l1: end, x, y, turn });
                }
            }
            Placed::Fill { rect, color } if rect.y < limit => {
                out.push(Placed::Fill { rect: Rect::new(rect.x, rect.y, rect.w, rect.h.min(limit - rect.y)), color });
            }
            Placed::Rule { x0, y0, x1, y1, border } if y0.min(y1) < limit => {
                out.push(Placed::Rule { x0, y0: y0.min(limit), x1, y1: y1.min(limit), border });
            }
            Placed::Image { rect, .. }
            | Placed::Shape { rect, .. }
            | Placed::Graphic { rect, .. }
            | Placed::Clip { rect, .. }
            | Placed::Cell { rect, .. }
            | Placed::Object { rect, .. }
                if rect.y < limit =>
            {
                out.push(it);
            }
            _ => {}
        }
    }
    out
}

/// Word joins neighbouring paragraphs with the same borders and indents into one box: the top
/// border goes above the first of them only, the bottom one below the last, and the shading and
/// side borders run on through the space between them (`table`: the cell's paragraph properties).
fn border_group(doc: &Document, a: &Paragraph, b: &Paragraph, table: Option<&wordcraft_doc::props::ParaProps>) -> bool {
    let (a, b) = (doc.styles.resolve_para_in(&a.props, table), doc.styles.resolve_para_in(&b.props, table));
    a.borders.is_some() && a.borders == b.borders && a.indent_left == b.indent_left && a.indent_right == b.indent_right
}

/// Whether paragraph `i` of `blocks` and the one at `j` are of one border group.
pub(crate) fn joined(doc: &Document, blocks: &Blocks, i: usize, j: Option<usize>, table: Option<&wordcraft_doc::props::ParaProps>) -> bool {
    match (blocks.get(i).map(|b| &**b), j.and_then(|j| blocks.get(j)).map(|b| &**b)) {
        (Some(Block::Para(a)), Some(Block::Para(b))) => border_group(doc, a, b, table),
        _ => false,
    }
}

/// The room a paragraph's top or bottom border takes in the text flow: its distance from the
/// text plus its width (Word).
fn border_room(b: Option<Border>) -> f32 {
    b.filter(Border::is_visible).map_or(0.0, |b| {
        let extent = b.space + b.width;
        if extent.is_finite() { extent.max(0.0) } else { 0.0 }
    })
}

/// How a piece of a paragraph meets the paragraphs around it: the room taken by its top and
/// bottom borders (0: none drawn there — the paragraph goes on from or into one of its border
/// group, or it is split there) and how far its shading and side borders reach up to join the
/// paragraph above in its group.
#[derive(Clone, Copy, Default)]
pub(crate) struct Edges {
    pub(crate) top: f32,
    pub(crate) bottom: f32,
    pub(crate) up: f32,
}

impl Edges {
    /// A paragraph on its own: its top and bottom borders at its ends.
    pub(crate) fn own(pl: &ParaLayout, l0: usize, l1: usize) -> Edges {
        let b = pl.rp.borders.unwrap_or_default();
        Edges { top: if l0 == 0 { border_room(b.top) } else { 0.0 }, bottom: if l1 >= pl.lines.len() { border_room(b.bottom) } else { 0.0 }, up: 0.0 }
    }
}

/// Paragraph lines plus their shading and borders; returns the bottom of the lines. The
/// shading fills the box out to the borders, the room they take included (Word).
pub(crate) fn push_para(
    items: &mut Vec<Placed>,
    (story, path): (StoryRef, &[u32]),
    pl: &Arc<ParaLayout>,
    (l0, l1): (usize, usize),
    (x, y): (f32, f32),
    width: f32,
    e: Edges,
) -> f32 {
    let (Some(first), Some(last)) = (pl.lines.get(l0), l1.checked_sub(1).and_then(|k| pl.lines.get(k))) else {
        return y;
    };
    let h = last.top + last.height - first.top;
    // Indents are logical: a right-to-left paragraph's start indent (and hanging indent) is on the right.
    let start = pl.rp.indent_left.min(pl.rp.indent_left + pl.rp.indent_first);
    let (li, ri) = if pl.rp.bidi { (pl.rp.indent_right, start) } else { (start, pl.rp.indent_right) };
    let left = x + li;
    let right = x + width - ri;
    let (top, bottom) = (y - e.top - e.up, y + h + e.bottom);
    // The outer edges of the side borders.
    let sides = pl.rp.borders.unwrap_or_default();
    let (lx, rx) = (left - border_room(sides.left), right + border_room(sides.right));
    if let Some(c) = pl.rp.shading {
        let pad = pl.rp.borders.as_ref().map(|b| b.left.map(|l| l.space).unwrap_or(4.0)).unwrap_or(0.0);
        let (sl, sr) = (lx.min(left - pad), rx.max(right + pad));
        items.push(Placed::Fill { rect: Rect::new(sl, top, sr - sl, bottom - top), color: c });
    }
    items.push(Placed::Lines { story, path: Path(path.to_vec()), para: pl.clone(), l0, l1, x, y, turn: TextDirection::Horizontal });
    if let Some(b) = &pl.rp.borders {
        // All four lines lie beyond their distance from the text; top and bottom reach the corners.
        if let Some(t) = b.top.filter(|t| e.top > 0.0 && t.is_visible()) {
            let ty = y - t.space - t.width / 2.0;
            items.push(Placed::Rule { x0: lx, y0: ty, x1: rx, y1: ty, border: t });
        }
        if let Some(t) = b.bottom.filter(|t| e.bottom > 0.0 && t.is_visible()) {
            let by = y + h + t.space + t.width / 2.0;
            items.push(Placed::Rule { x0: lx, y0: by, x1: rx, y1: by, border: t });
        }
        if let Some(t) = b.left.filter(Border::is_visible) {
            let bx = lx + t.width / 2.0;
            items.push(Placed::Rule { x0: bx, y0: top, x1: bx, y1: bottom, border: t });
        }
        if let Some(t) = b.right.filter(Border::is_visible) {
            let bx = rx - t.width / 2.0;
            items.push(Placed::Rule { x0: bx, y0: top, x1: bx, y1: bottom, border: t });
        }
    }
    y + h
}