edamame 0.1.6

//! Per-frame table layout snapshots plus the row/column-button rendering behind mouse-driven
//! reorder, resize, and delete.
//!
//! There is deliberately **no** standalone `StatefulWidget` for tables: the rendered lines keep
//! flowing through `ParsedDoc`'s pre-rendered line list, so scroll, wrap, and cell-scoped raw
//! reveal work unchanged.  What lives here is the mouse-facing half — [`build_snapshots`] scans the
//! visible lines, [`hit_test`](TableLayoutSnapshot::hit_test) maps a click onto one, and
//! [`paint_handles`] overlays the glyphs after the line-render pass.
//!
//! Snapshots are stored on the `RenderedViewState` so the next frame's mouse handling can hit-test
//! against them.

use std::ops::Range;

use ratatui::buffer::Buffer as TuiBuf;
use ratatui::layout::Rect;
use ratatui::style::Style;

use crate::config::Theme;
use crate::document::row_map::{self, TablePart};
use crate::editor::{table_edit_ops, EditorState};
use crate::markdown::table_layout;

/// Reorder-handle glyph, for both row-reorder (in the external left gutter) and column-reorder
/// (centered on each column's top border cell).  The "dot grip" convention reads as "drag me".
pub const REORDER_HANDLE_GLYPH: char = '⠿';
/// Highlights the destination separator during a row-handle drag; the heavier weight reads against
/// the table's standard `─`.
pub const DROP_ROW_GLYPH: char = '━';
/// Column-drag counterpart, reading against the standard `│` border.
pub const DROP_COL_GLYPH: char = '┃';
/// Column-resize glyph, painted on each interior `│` of the header row as a visible target;
/// clicks anywhere within the border's `±1` tolerance still resize.
pub const COLUMN_RESIZE_GLYPH: char = '⇔';
/// Delete-handle glyph, painted on the outer right `│` for each data row and on the bottom border
/// for each column.  A click deletes outright; undo restores.  Gated by `config.table.show_buttons`
/// like the other handles.
pub const DELETE_HANDLE_GLYPH: char = '✕';

/// Rows preceding the first data row (header, then alignment), so data row `i` is at
/// `HEADER_ROWS + i`.
pub const HEADER_ROWS: usize = 2;

/// Per-frame snapshot of one visible table's layout.  Every coordinate is in terminal cells
/// relative to the document area's origin, and valid only for the frame it was built on.
#[derive(Debug, Clone)]
pub struct TableLayoutSnapshot {
    /// Byte offset of this table's first row in the source buffer.
    pub table_byte_start: usize,
    /// Byte offset just past the last newline of the final row.
    pub table_byte_end: usize,
    /// Number of columns (`info.col_count`).
    pub col_count: usize,
    /// Number of TableInfo rows (header + alignment + data).
    pub row_count: usize,
    /// Per-column cell ranges inside a row's content area: `start` is just after the opening `│`,
    /// `end` is the closing `│` itself.
    pub col_ranges: Vec<Range<u16>>,
    /// Per-data-row vertical ranges; `row_ranges[i]` spans `info.rows[HEADER_ROWS + i]`.  Only
    /// data rows carry a drag handle, so the header and alignment rows are skipped.
    pub row_ranges: Vec<Range<u16>>,
    /// Where the `⠿` row-reorder glyph is painted: ON the outer left `│`, overlaying the border for
    /// each data row, wherever the table sits (top-level, or behind a quote's bar or an item's
    /// indent), as `✕` does on the right.  `None` when handles are disabled.
    pub row_handle_col: Option<u16>,
    /// The `┌─┬─┐` top border, carrying one column-reorder glyph per column.  `None` when handles
    /// are disabled or the border scrolled off.
    pub top_border_row: Option<u16>,
    /// The header row, carrying the `⇔` resize glyphs.  `None` when it scrolled off.
    pub header_row: Option<u16>,
    /// Where the `✕` row-delete glyph is painted: ON the outer right `│`, overlaying the border
    /// for each data row.  Resize on a data row therefore shifts to one cell inside the border;
    /// non-data rows have no delete hit and still fall through to `ColumnBorder`.
    pub delete_row_handle_col: Option<u16>,
    /// The `└─┴─┘` bottom border, carrying the column-delete glyphs.  `None` when handles are
    /// disabled or the border scrolled off.
    pub bottom_border_row: Option<u16>,
}

/// What a `(col, row)` click lands on inside a table.  Every `row_idx` is a **TableInfo** row
/// index (`HEADER_ROWS + data_index`).
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TableHit {
    /// Click inside a data cell's content area.
    Cell { row_idx: usize, col_idx: usize },
    /// Click on a vertical `│` border; `col_idx` is `0..=col_count`, with 0 and `col_count` the
    /// outer borders.  Only the interior ones drive resize.
    ColumnBorder { col_idx: usize },
    /// Click on the `≡` row-drag glyph next to a data row.
    RowHandle { row_idx: usize },
    /// Click on the `⇔` column-drag glyph above a column.
    ColumnHandle { col_idx: usize },
    /// Click on the `✕` row-delete glyph.  `row_idx` is ≥ `HEADER_ROWS`: header and alignment
    /// can't be deleted, so that border cell stays a resize target on those rows.
    DeleteRowHandle { row_idx: usize },
    /// Click on the `✕` column-delete glyph.  Only emitted when the table has more than one
    /// column.
    DeleteColumnHandle { col_idx: usize },
}

impl TableLayoutSnapshot {
    /// `TableInfo` row index of the data row nearest `row`, or `None` outside the data-row band.
    ///
    /// Consecutive `row_ranges` entries are separated by a one-row gap (the `├─┼─┤` rule, or the
    /// blank stripe line), and a strict range test answered `None` on every one — which made
    /// grabbing the `⠿` handle a coin flip and stalled the drop indicator mid-crossing.  Snapping
    /// to the nearest row closes the gaps.  The band stops at the separators bounding the first and
    /// last data rows, so the header stays un-grabbable and a pointer leaving the table below stops
    /// moving the hover.
    pub fn data_row_at_y(&self, row: u16) -> Option<usize> {
        let first = self.row_ranges.first()?;
        let last = self.row_ranges.last()?;
        if row < first.start.saturating_sub(1) || row > last.end {
            return None;
        }
        let idx = self
            .row_ranges
            .iter()
            .enumerate()
            .min_by_key(|(_, r)| range_distance(r, row))
            .map(|(i, _)| i)?;
        Some(HEADER_ROWS + idx)
    }

    /// 0-indexed column nearest `col`, or `None` outside the table's horizontal extent.  Same
    /// snapping rationale as [`Self::data_row_at_y`]: the `│` / `┬` vertices between `col_ranges`
    /// entries are exactly where a user aiming at a column handle tends to press.
    pub fn column_at_x(&self, col: u16) -> Option<usize> {
        let first = self.col_ranges.first()?;
        let last = self.col_ranges.last()?;
        if col < first.start.saturating_sub(1) || col > last.end {
            return None;
        }
        self.col_ranges
            .iter()
            .enumerate()
            .min_by_key(|(_, r)| range_distance(r, col))
            .map(|(i, _)| i)
    }

    /// Hit-test document-area-relative `(col, row)` against this snapshot.
    ///
    /// Precedence: delete handle → row handle → column handle → column border → cell.  Delete wins
    /// over `ColumnBorder` because the row-delete glyph sits ON the outer right `│`; resize on a
    /// data row stays reachable one cell either side, and non-data rows have no delete hit at all.
    /// Borders are hit within `±1` of their `│` column.
    pub fn hit_test(&self, col: u16, row: u16) -> Option<TableHit> {
        // Checked before ColumnBorder so the `✕` cell wins over the right border's ±1 window.
        if let Some(handle_col) = self.delete_row_handle_col {
            if col == handle_col {
                for (i, y_range) in self.row_ranges.iter().enumerate() {
                    if row >= y_range.start && row < y_range.end {
                        return Some(TableHit::DeleteRowHandle {
                            row_idx: HEADER_ROWS + i,
                        });
                    }
                }
            }
        }

        // Deliberately ±1 of the glyph rather than the column's whole width: this is the one
        // destructive hit on the border rows, so aiming at a border must not drop a column.
        if let Some(bot_y) = self.bottom_border_row {
            if row == bot_y {
                for (c, x_range) in self.col_ranges.iter().enumerate() {
                    if let Some(glyph_x) = column_glyph_x(x_range) {
                        if col.abs_diff(glyph_x) <= 1 {
                            return Some(TableHit::DeleteColumnHandle { col_idx: c });
                        }
                    }
                }
            }
        }

        // Anywhere across the data rows' vertical band, separators included.
        if let Some(handle_col) = self.row_handle_col {
            if col == handle_col {
                if let Some(row_idx) = self.data_row_at_y(row) {
                    return Some(TableHit::RowHandle { row_idx });
                }
            }
        }

        // A `┬` vertex resolves to the adjacent column: clicking exactly on one would otherwise
        // miss the handle and silently start a resize.
        if let Some(top_y) = self.top_border_row {
            if row == top_y {
                if let Some(col_idx) = self.column_at_x(col) {
                    return Some(TableHit::ColumnHandle { col_idx });
                }
            }
        }

        // Within ±1 of a `│`, provided the row is part of the table.  The header's `⇔` glyph is
        // just a highlighted sub-region of this same area.
        if self.row_count > 0 && self.row_on_table(row) {
            if let Some(first) = self.col_ranges.first() {
                let left_border = first.start.saturating_sub(1);
                if col.abs_diff(left_border) <= 1 {
                    return Some(TableHit::ColumnBorder { col_idx: 0 });
                }
            }
            for (c, x_range) in self.col_ranges.iter().enumerate() {
                let border_col = x_range.end;
                if col.abs_diff(border_col) <= 1 {
                    return Some(TableHit::ColumnBorder { col_idx: c + 1 });
                }
            }
        }

        // Data cell.
        for (i, y_range) in self.row_ranges.iter().enumerate() {
            if row >= y_range.start && row < y_range.end {
                for (c, x_range) in self.col_ranges.iter().enumerate() {
                    if col >= x_range.start && col < x_range.end {
                        return Some(TableHit::Cell {
                            row_idx: HEADER_ROWS + i,
                            col_idx: c,
                        });
                    }
                }
            }
        }
        None
    }

    fn row_on_table(&self, row: u16) -> bool {
        let first_y = self
            .top_border_row
            .or_else(|| self.row_ranges.first().map(|r| r.start.saturating_sub(2)))
            .unwrap_or(0);
        let last_y = self
            .row_ranges
            .last()
            .map(|r| r.end + 1) // include the bottom border
            .unwrap_or(first_y);
        row >= first_y && row <= last_y
    }
}

/// Distance from `v` to `range` (0 when inside), for snapping a pointer that landed on one of the
/// box-drawing cells between two ranges.
fn range_distance(range: &Range<u16>, v: u16) -> u16 {
    if v < range.start {
        range.start - v
    } else if v >= range.end {
        v - range.end + 1
    } else {
        0
    }
}

/// Center of a column's content span — where its border-cell glyph is painted.  Shared by
/// `paint_handles` and the column-delete hit-test so the glyph and the live cell can't drift apart.
fn column_glyph_x(x_range: &Range<u16>) -> Option<u16> {
    if x_range.end <= x_range.start {
        return None;
    }
    Some(x_range.start + (x_range.end - x_range.start) / 2)
}

/// Per-frame instruction for `paint_drop_indicator`.  The caller distills `mouse_ops::DragTarget`
/// into one of these so the UI layer doesn't import the editor-side enum.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum DropIndicator {
    /// Row drag: highlight the separator that would receive the drop — above `hover_row_idx` when
    /// dropping upward, below when downward, as derived from `src_row_idx`.
    Row {
        table_byte_start: usize,
        src_row_idx: usize,
        hover_row_idx: usize,
    },
    /// Column drag; same drop-side semantics as `Row`.
    Column {
        table_byte_start: usize,
        src_col_idx: usize,
        hover_col_idx: usize,
    },
    /// Resize guideline at the pointer's X.  Driven only by `tests/ui.rs` today; the live
    /// column-border drag paints through a different path.
    #[allow(dead_code)]
    ColumnBorder { table_byte_start: usize, x: u16 },
}

// ── Snapshot construction ───────────────────────────────────────────────────

/// Refresh `snapshots` in place when the cache key (`scroll`, `area`, `parsed_version`,
/// `show_handles`) changed, mirroring the image and link snapshot caches.  `show_handles` is part
/// of the key because it changes the snapshot contents.
pub fn build_snapshots_cached(
    state: &EditorState,
    area: Rect,
    show_handles: bool,
    snapshots: &mut Vec<TableLayoutSnapshot>,
    cache_key: &mut Option<(usize, Rect, u64, bool)>,
) {
    let key = (state.scroll, area, state.parsed_version, show_handles);
    if *cache_key == Some(key) {
        return;
    }
    *snapshots = build_snapshots(state, area, show_handles);
    *cache_key = Some(key);
}

/// Build a snapshot for every table fully or partially on screen.
///
/// `show_handles` controls whether snapshots carry the handle coordinates, and therefore whether
/// hit-testing classifies clicks on those cells as handle hits.
pub fn build_snapshots(
    state: &EditorState,
    area: Rect,
    show_handles: bool,
) -> Vec<TableLayoutSnapshot> {
    let mut out: Vec<TableLayoutSnapshot> = Vec::new();
    if area.height == 0 {
        return out;
    }
    let lines = &state.parsed.lines;
    let total = lines.len();
    let width = area.width as usize;

    let (mut virtual_idx, mut first_sub_row) =
        state.rendered_line_at_visual_row(state.scroll, width);
    let mut vis_y: usize = 0;
    let height = area.height as usize;

    // The open snapshot stays open through border / separator rows so a multi-row table merges
    // into one snapshot; it closes only when the rendered line leaves the table.
    let mut open_table: Option<TableLayoutSnapshot> = None;
    // The source line of the open snapshot's table's header.
    let mut open_table_line: Option<usize> = None;
    // Per-data-row span accumulator: opened by a row's first `DataRow` sub-line, extended by its
    // continuations, pushed onto `snap.row_ranges` when a separator closes the row.
    let mut current_data_row_y: Option<(usize, Range<u16>)> = None;
    // The block last read, its first rendered line, and its rows' table parts with the header
    // lines made absolute: one read per block, not per line.
    let mut block_parts: Option<(usize, usize, row_map::TableParts)> = None;

    while vis_y < height && virtual_idx < total {
        let Some(line) = lines.get(virtual_idx) else {
            break;
        };
        let full_rows_used = state
            .parsed
            .visual_rows_for_line_at(virtual_idx, width)
            .max(1);
        let rows_used = full_rows_used.saturating_sub(first_sub_row).max(1);

        // Which table this rendered line belongs to, at any depth, by the parse's row origins:
        // the source line of its header, and the part it draws.
        let mut part: Option<(usize, TablePart)> = None;
        if let Some(block) = state.parsed.source_map.block_for_rendered_line(virtual_idx) {
            if block_parts.as_ref().is_none_or(|(b, ..)| *b != block) {
                let map = &state.parsed.source_map;
                let first_line = map
                    .original_range_for_block(block)
                    .map_or(0, |r| state.parsed.byte_to_line(r.start));
                let mut parts = row_map::table_parts(&state.parsed, block);
                for (header, _) in parts.iter_mut().flatten() {
                    *header += first_line;
                }
                block_parts = Some((block, map.rendered_lines_for_block(block).start, parts));
            }
            if let Some((_, first_row, parts)) = block_parts.as_ref() {
                part = parts
                    .get(virtual_idx.saturating_sub(*first_row))
                    .copied()
                    .flatten();
            }
        }
        let current_table = part.map(|(header, _)| header);
        let sub_kind = part.map(|(_, p)| p);

        // Close the open snapshot if we've moved off its table.
        if current_table != open_table_line {
            if let Some(mut prev) = open_table.take() {
                if let Some((_, range)) = current_data_row_y.take() {
                    prev.row_ranges.push(range);
                }
                out.push(prev);
            }
            open_table_line = None;
            current_data_row_y = None;
        }

        if let Some(header_line) = current_table {
            // Open a new snapshot if we aren't already tracking this table.
            if open_table.is_none() {
                // By line: the parse's bytes drift from the buffer's while an in-line edit
                // defers the re-parse, its lines don't.
                let rope = state.buffer.rope();
                let line = header_line.min(rope.len_lines());
                if let Some(info) = table_edit_ops::locate_table(state, rope.line_to_byte(line)) {
                    open_table = Some(TableLayoutSnapshot {
                        table_byte_start: info.start,
                        table_byte_end: info.end,
                        col_count: info.col_count,
                        row_count: info.rows.len(),
                        col_ranges: Vec::new(),
                        row_ranges: Vec::new(),
                        row_handle_col: None,
                        top_border_row: None,
                        header_row: None,
                        delete_row_handle_col: None,
                        bottom_border_row: None,
                    });
                    open_table_line = Some(header_line);
                }
            }

            if let Some(snap) = open_table.as_mut() {
                // Fill col_ranges from the first row carrying `│` characters.  Screen
                // geometry, so pipe *cells*: a wide glyph to the left takes two.
                if snap.col_ranges.is_empty() {
                    let pipes = table_layout::rendered_pipe_cells(line);
                    if pipes.len() == snap.col_count + 1 {
                        for i in 0..snap.col_count {
                            let start = pipes[i] as u16 + 1;
                            let end = pipes[i + 1] as u16;
                            snap.col_ranges.push(Range { start, end });
                        }
                    }
                }

                let y = vis_y as u16;
                let y_end = y + rows_used as u16;

                match sub_kind {
                    Some(TablePart::TopBorder) => {
                        if show_handles && snap.top_border_row.is_none() {
                            snap.top_border_row = Some(y);
                        }
                    }
                    Some(TablePart::Header { sub: 0 }) => {
                        // Anchor the column-resize glyph row on the header's first sub-line.
                        if show_handles && snap.header_row.is_none() {
                            snap.header_row = Some(y);
                        }
                    }
                    Some(TablePart::Header { .. }) => {
                        // A wrapped header's continuation lines anchor nothing new.
                    }
                    Some(TablePart::HeavyRule)
                    | Some(TablePart::Separator)
                    | Some(TablePart::BottomBorder) => {
                        // A separator closes the current data row's span.
                        if let Some((_, range)) = current_data_row_y.take() {
                            snap.row_ranges.push(range);
                        }
                        if matches!(sub_kind, Some(TablePart::BottomBorder))
                            && show_handles
                            && snap.bottom_border_row.is_none()
                            && snap.col_count > 1
                        {
                            // A single-column table can't lose its last column.
                            snap.bottom_border_row = Some(y);
                        }
                    }
                    Some(TablePart::DataRow { row, .. }) => match current_data_row_y.as_mut() {
                        Some((existing_row, range)) if *existing_row == row => {
                            range.end = y_end;
                        }
                        _ => {
                            if let Some((_, prev_range)) = current_data_row_y.take() {
                                snap.row_ranges.push(prev_range);
                            }
                            current_data_row_y = Some((row, y..y_end));
                        }
                    },
                    None => {}
                }

                // ON the outer left `│`.
                if show_handles && snap.row_handle_col.is_none() && !snap.col_ranges.is_empty() {
                    snap.row_handle_col = Some(snap.col_ranges[0].start.saturating_sub(1));
                }
                // ON the outer right `│`, overlaying the border for each data row; `hit_test`
                // checks delete before `ColumnBorder`, so non-data rows still resize here.
                if show_handles
                    && snap.delete_row_handle_col.is_none()
                    && !snap.col_ranges.is_empty()
                {
                    let outer_right = snap.col_ranges.last().unwrap().end;
                    snap.delete_row_handle_col = Some(outer_right);
                }
            }
        }

        vis_y += rows_used;
        virtual_idx += 1;
        first_sub_row = 0;
    }

    if let Some(mut prev) = open_table.take() {
        if let Some((_, range)) = current_data_row_y.take() {
            prev.row_ranges.push(range);
        }
        out.push(prev);
    }
    out
}

// ── Handle rendering ────────────────────────────────────────────────────────

/// Overlay the row/column-button glyphs on top of already-rendered table lines.
///
/// `cursor_table_start` limits painting to the table the cursor is inside; `None` paints on every
/// visible table (used by tests).
pub fn paint_handles(
    snapshots: &[TableLayoutSnapshot],
    area: Rect,
    buf: &mut TuiBuf,
    theme: &Theme,
    cursor_table_start: Option<usize>,
) {
    // Reorder and resize glyphs share the interactive accent; delete uses the louder
    // `table_handle_delete` so the destructive affordance stands out.
    let move_style: Style = theme.table_handle;
    let delete_style: Style = theme.table_handle_delete;
    for snap in snapshots {
        if let Some(start) = cursor_table_start {
            if snap.table_byte_start != start {
                continue;
            }
        } else {
            // No cursor table — skip painting handles entirely.
            return;
        }
        // One glyph per logical data row, at its first sub-line: one per wrapped sub-line reads
        // as noise, and the hit-test covers the row's full y-range anyway.
        if let Some(col) = snap.row_handle_col {
            if col < area.width {
                for y_range in &snap.row_ranges {
                    let y = y_range.start;
                    if y < area.height {
                        if let Some(cell) = buf.cell_mut((area.x + col, area.y + y)) {
                            cell.set_char(REORDER_HANDLE_GLYPH);
                            cell.set_style(move_style);
                        }
                    }
                }
            }
        }

        // Centered within each column's content span, so they overlay the `─` and leave the
        // `┌`/`┬` corners intact.
        if let Some(y) = snap.top_border_row {
            if y < area.height {
                for x_range in &snap.col_ranges {
                    let Some(x) = column_glyph_x(x_range) else {
                        continue;
                    };
                    if x < area.width {
                        if let Some(cell) = buf.cell_mut((area.x + x, area.y + y)) {
                            cell.set_char(REORDER_HANDLE_GLYPH);
                            cell.set_style(move_style);
                        }
                    }
                }
            }
        }

        // Every interior border plus the rightmost outer one (which resizes the last column).
        // Not the leftmost: there is no column to its left.
        if let Some(y) = snap.header_row {
            if y < area.height {
                for x_range in &snap.col_ranges {
                    let border_x = x_range.end;
                    if border_x < area.width {
                        if let Some(cell) = buf.cell_mut((area.x + border_x, area.y + y)) {
                            cell.set_char(COLUMN_RESIZE_GLYPH);
                            cell.set_style(move_style);
                        }
                    }
                }
            }
        }

        // One per data row, at its first sub-line, like the reorder gutter.  `row_ranges` only
        // tracks data rows, so the undeletable header and alignment rows are skipped for free.
        if let Some(col) = snap.delete_row_handle_col {
            if col < area.width {
                for y_range in &snap.row_ranges {
                    let y = y_range.start;
                    if y < area.height {
                        if let Some(cell) = buf.cell_mut((area.x + col, area.y + y)) {
                            cell.set_char(DELETE_HANDLE_GLYPH);
                            cell.set_style(delete_style);
                        }
                    }
                }
            }
        }

        // Mirrors the column-reorder glyphs on the top border.  `bottom_border_row` is `None` for
        // a single-column table, so nothing paints there.
        if let Some(y) = snap.bottom_border_row {
            if y < area.height {
                for x_range in &snap.col_ranges {
                    let Some(x) = column_glyph_x(x_range) else {
                        continue;
                    };
                    if x < area.width {
                        if let Some(cell) = buf.cell_mut((area.x + x, area.y + y)) {
                            cell.set_char(DELETE_HANDLE_GLYPH);
                            cell.set_style(delete_style);
                        }
                    }
                }
            }
        }
    }
}

// ── Drop-indicator painter ──────────────────────────────────────────────────

/// Highlight every valid drop separator for an in-progress drag — the hover target at the bright
/// accent, the other candidates dimmer.  Runs after `paint_handles` so it overlays the border
/// glyphs.  No-op when no snapshot matches the indicator's table.
pub fn paint_drop_indicator(
    snapshots: &[TableLayoutSnapshot],
    indicator: &DropIndicator,
    area: Rect,
    buf: &mut TuiBuf,
    theme: &Theme,
) {
    let active_style: Style = theme.table_drop_indicator;
    let candidate_style: Style = theme.table_drop_target;
    match *indicator {
        DropIndicator::Row {
            table_byte_start,
            src_row_idx,
            hover_row_idx,
        } => {
            let Some(snap) = snapshots
                .iter()
                .find(|s| s.table_byte_start == table_byte_start)
            else {
                return;
            };
            if src_row_idx < 2 || snap.row_ranges.is_empty() {
                return;
            }
            // The separator on the side of the hover row matching the drag direction.
            let active_y = active_row_drop_y(snap, src_row_idx, hover_row_idx);

            // Paint every valid drop dimly so the user sees the full set.  The two separators
            // bounding the source row are excluded — dropping there is a no-op.
            let src_data_idx = src_row_idx - 2;
            let Some(first) = snap.col_ranges.first() else {
                return;
            };
            let Some(last) = snap.col_ranges.last() else {
                return;
            };
            let x_start = first.start.saturating_sub(1);
            let x_end = last.end;
            let x_max = area.width;
            for (i, y_range) in snap.row_ranges.iter().enumerate() {
                // Separator above this data row.
                let above = y_range.start.saturating_sub(1);
                // Separator below this data row.
                let below = y_range.end;
                for &y in &[above, below] {
                    if y >= area.height {
                        continue;
                    }
                    // A drop on the source row's own separators is a no-op.
                    if (i == src_data_idx && (y == above || y == below))
                        || (i + 1 == src_data_idx && y == below)
                        || (i == src_data_idx + 1 && y == above)
                    {
                        continue;
                    }
                    let style = if Some(y) == active_y {
                        active_style
                    } else {
                        candidate_style
                    };
                    paint_horizontal_drop(
                        buf,
                        area.x + x_start,
                        area.x + x_end,
                        area.x + x_max,
                        area.y + y,
                        style,
                    );
                }
            }
        }
        DropIndicator::Column {
            table_byte_start,
            src_col_idx,
            hover_col_idx,
        } => {
            let Some(snap) = snapshots
                .iter()
                .find(|s| s.table_byte_start == table_byte_start)
            else {
                return;
            };
            if snap.col_ranges.is_empty() {
                return;
            }
            let active_x = active_column_drop_x(snap, src_col_idx, hover_col_idx);
            // Vertical span shared across every candidate.
            let y_top = snap
                .top_border_row
                .or_else(|| snap.row_ranges.first().map(|r| r.start.saturating_sub(2)))
                .unwrap_or(0);
            let y_bot = snap
                .row_ranges
                .last()
                .map(|r| r.end)
                .unwrap_or(area.height.saturating_sub(1));
            let y_max = area.height;
            // Every border is a candidate except the two flanking the source column.
            let mut borders: Vec<u16> = Vec::with_capacity(snap.col_ranges.len() + 1);
            if let Some(first) = snap.col_ranges.first() {
                borders.push(first.start.saturating_sub(1));
            }
            for r in &snap.col_ranges {
                borders.push(r.end);
            }
            for (i, &x) in borders.iter().enumerate() {
                if x >= area.width {
                    continue;
                }
                // Skip borders adjacent to the source column.
                if i == src_col_idx || i == src_col_idx + 1 {
                    continue;
                }
                let style = if Some(x) == active_x {
                    active_style
                } else {
                    candidate_style
                };
                paint_vertical_drop(
                    buf,
                    area.y + y_top,
                    area.y + y_bot,
                    area.y + y_max,
                    area.x + x,
                    style,
                );
            }
        }
        DropIndicator::ColumnBorder {
            table_byte_start,
            x,
        } => {
            let Some(snap) = snapshots
                .iter()
                .find(|s| s.table_byte_start == table_byte_start)
            else {
                return;
            };
            if x >= area.width {
                return;
            }
            let y_top = snap
                .top_border_row
                .or_else(|| snap.row_ranges.first().map(|r| r.start.saturating_sub(2)))
                .unwrap_or(0);
            let y_bot = snap
                .row_ranges
                .last()
                .map(|r| r.end)
                .unwrap_or(area.height.saturating_sub(1));
            let y_max = area.height;
            for y in y_top..=y_bot {
                if y >= y_max {
                    break;
                }
                if let Some(cell) = buf.cell_mut((area.x + x, area.y + y)) {
                    cell.set_char(DROP_COL_GLYPH);
                    cell.set_style(active_style);
                }
            }
        }
    }
}

/// Y of the active drop separator for a row drag; `None` over the source row itself.
fn active_row_drop_y(
    snap: &TableLayoutSnapshot,
    src_row_idx: usize,
    hover_row_idx: usize,
) -> Option<u16> {
    if hover_row_idx < 2 || hover_row_idx == src_row_idx {
        return None;
    }
    let data_idx = hover_row_idx - 2;
    let y_range = snap.row_ranges.get(data_idx)?;
    if src_row_idx > hover_row_idx {
        Some(y_range.start.saturating_sub(1))
    } else {
        Some(y_range.end)
    }
}

/// X of the active drop separator for a column drag; `None` on the source column.
fn active_column_drop_x(
    snap: &TableLayoutSnapshot,
    src_col_idx: usize,
    hover_col_idx: usize,
) -> Option<u16> {
    if hover_col_idx == src_col_idx {
        return None;
    }
    if src_col_idx > hover_col_idx {
        snap.col_ranges
            .get(hover_col_idx)
            .map(|r| r.start.saturating_sub(1))
    } else {
        snap.col_ranges.get(hover_col_idx).map(|r| r.end)
    }
}

/// Heavy horizontal rule across `[x_start, x_end]` at row `y`, clipped at `x_max`.
fn paint_horizontal_drop(
    buf: &mut TuiBuf,
    x_start: u16,
    x_end: u16,
    x_max: u16,
    y: u16,
    style: Style,
) {
    for x in x_start..=x_end {
        if x >= x_max {
            break;
        }
        if let Some(cell) = buf.cell_mut((x, y)) {
            cell.set_char(DROP_ROW_GLYPH);
            cell.set_style(style);
        }
    }
}

/// Heavy vertical rule down `[y_top, y_bot]` at column `x`, clipped at `y_max`.
fn paint_vertical_drop(buf: &mut TuiBuf, y_top: u16, y_bot: u16, y_max: u16, x: u16, style: Style) {
    for y in y_top..=y_bot {
        if y >= y_max {
            break;
        }
        if let Some(cell) = buf.cell_mut((x, y)) {
            cell.set_char(DROP_COL_GLYPH);
            cell.set_style(style);
        }
    }
}

// ── Tests ───────────────────────────────────────────────────────────────────

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

    fn snap(col_ranges: Vec<Range<u16>>, row_ranges: Vec<Range<u16>>) -> TableLayoutSnapshot {
        TableLayoutSnapshot {
            table_byte_start: 0,
            table_byte_end: 100,
            col_count: col_ranges.len(),
            row_count: HEADER_ROWS + row_ranges.len(),
            col_ranges,
            row_ranges,
            row_handle_col: None,
            top_border_row: None,
            header_row: None,
            delete_row_handle_col: None,
            bottom_border_row: None,
        }
    }

    #[test]
    fn hit_test_returns_cell_for_click_in_content() {
        let s = snap(vec![1..4, 5..8], vec![3..4, 4..5]);
        let hit = s.hit_test(2, 3).unwrap();
        assert_eq!(
            hit,
            TableHit::Cell {
                row_idx: 2,
                col_idx: 0
            }
        );
    }

    #[test]
    fn hit_test_returns_border_for_click_on_pipe() {
        let s = snap(vec![1..4, 5..8], vec![3..4, 4..5]);
        // Interior border sits at col_ranges[0].end == 4.
        let hit = s.hit_test(4, 3).unwrap();
        assert_eq!(hit, TableHit::ColumnBorder { col_idx: 1 });
    }

    #[test]
    fn hit_test_border_tolerates_one_cell_miss() {
        // Col 5 is both within the border's ±1 window and `col_ranges[1].start`; borders win.
        let s = snap(vec![1..4, 5..8], vec![3..4, 4..5]);
        let hit = s.hit_test(5, 3).unwrap();
        assert!(matches!(
            hit,
            TableHit::ColumnBorder { col_idx: 1 } | TableHit::Cell { col_idx: 1, .. }
        ));
    }

    #[test]
    fn hit_test_row_handle_when_handles_enabled() {
        let mut s = snap(vec![5..8], vec![3..4]);
        s.row_handle_col = Some(2);
        let hit = s.hit_test(2, 3).unwrap();
        assert_eq!(hit, TableHit::RowHandle { row_idx: 2 });
    }

    #[test]
    fn hit_test_column_handle_when_handles_enabled() {
        let mut s = snap(vec![5..8, 9..12], vec![3..4]);
        s.top_border_row = Some(1);
        let hit = s.hit_test(6, 1).unwrap();
        assert_eq!(hit, TableHit::ColumnHandle { col_idx: 0 });
    }

    #[test]
    fn hit_test_border_in_header_row_when_resize_glyphs_on() {
        // Header at y=2, interior border at col_ranges[0].end=8.
        let mut s = snap(vec![5..8, 9..12], vec![3..4]);
        s.top_border_row = Some(1);
        s.header_row = Some(2);
        let hit = s.hit_test(8, 2).unwrap();
        assert_eq!(hit, TableHit::ColumnBorder { col_idx: 1 });
    }

    /// Regression: a gutter click on the separator between two data rows used to classify as
    /// nothing, which made grabbing the `⠿` handle a coin flip.
    #[test]
    fn hit_test_row_handle_covers_the_separator_between_rows() {
        let mut s = snap(vec![5..8], vec![3..4, 5..6]);
        s.row_handle_col = Some(2);
        // y=4 is the separator between data row 0 (y=3) and row 1 (y=5).
        assert_eq!(s.hit_test(2, 4), Some(TableHit::RowHandle { row_idx: 2 }));
        // The bounding separators count too.
        assert_eq!(s.hit_test(2, 2), Some(TableHit::RowHandle { row_idx: 2 }));
        assert_eq!(s.hit_test(2, 6), Some(TableHit::RowHandle { row_idx: 3 }));
        // …but the header / alignment rows above the band do not.
        assert_eq!(s.hit_test(2, 1), None);
    }

    /// A `┬` vertex — where a user aiming at a column handle tends to press — must resolve to an
    /// adjacent column, not fall through to `ColumnBorder` and silently start a resize.
    #[test]
    fn hit_test_column_handle_covers_the_border_vertices() {
        let mut s = snap(vec![5..8, 9..12], vec![3..4]);
        s.top_border_row = Some(1);
        // `┌` at x=4, `┬` at x=8, `┐` at x=12.
        assert_eq!(
            s.hit_test(4, 1),
            Some(TableHit::ColumnHandle { col_idx: 0 })
        );
        assert_eq!(
            s.hit_test(8, 1),
            Some(TableHit::ColumnHandle { col_idx: 0 })
        );
        assert_eq!(
            s.hit_test(12, 1),
            Some(TableHit::ColumnHandle { col_idx: 1 })
        );
        // Past the right edge the handle band ends and the border's ±1 window takes over.
        assert_eq!(
            s.hit_test(13, 1),
            Some(TableHit::ColumnBorder { col_idx: 2 })
        );
    }

    /// The destructive `✕` gets a glyph ±1 hitbox, not the column's whole width, so the bottom
    /// border stays usable as a resize target.
    #[test]
    fn hit_test_column_delete_is_scoped_to_the_glyph() {
        let mut s = snap(vec![1..8, 9..16], vec![3..4]);
        s.bottom_border_row = Some(5);
        // Glyph centre of column 0 is x = 1 + 7/2 = 4.
        assert_eq!(
            s.hit_test(4, 5),
            Some(TableHit::DeleteColumnHandle { col_idx: 0 })
        );
        assert_eq!(
            s.hit_test(5, 5),
            Some(TableHit::DeleteColumnHandle { col_idx: 0 })
        );
        // Well away from the glyph: the interior border resizes.
        assert_eq!(
            s.hit_test(8, 5),
            Some(TableHit::ColumnBorder { col_idx: 1 })
        );
    }

    #[test]
    fn hit_test_returns_none_outside_any_region() {
        let s = snap(vec![1..4, 5..8], vec![3..4]);
        assert!(s.hit_test(100, 100).is_none());
    }

    #[test]
    fn hit_test_returns_delete_row_handle_when_handle_set() {
        // The delete column sits ON the outer right `│`, so a data-row click there deletes while
        // the header / alignment rows fall through to ColumnBorder.
        let mut s = snap(vec![1..4, 5..8], vec![3..4, 4..5]);
        s.delete_row_handle_col = Some(8);
        let hit = s.hit_test(8, 3).unwrap();
        assert_eq!(hit, TableHit::DeleteRowHandle { row_idx: 2 });
        let hit = s.hit_test(8, 4).unwrap();
        assert_eq!(hit, TableHit::DeleteRowHandle { row_idx: 3 });
    }

    /// With `✕` painted ON the right border, the cell just inside it is the data-row resize
    /// target, via the `ColumnBorder ±1` tolerance.
    #[test]
    fn hit_test_cell_just_inside_right_border_still_resizes() {
        let mut s = snap(vec![1..4, 5..8], vec![3..4]);
        s.delete_row_handle_col = Some(8); // same as last.end
                                           // x=7 is one cell inside the right `│` at x=8 — within the ColumnBorder ±1 window.
        let hit = s.hit_test(7, 3).unwrap();
        assert_eq!(hit, TableHit::ColumnBorder { col_idx: 2 });
    }

    /// On a non-data row the delete glyph's x has no `row_range` match, so the click falls
    /// through to `ColumnBorder` and the right column stays resizable.
    #[test]
    fn hit_test_right_border_on_non_data_row_still_resizes() {
        let mut s = snap(vec![1..4, 5..8], vec![5..6]); // single data row at y=5
        s.delete_row_handle_col = Some(8);
        // y=3 is in the header / alignment region, outside `row_ranges`.
        assert_eq!(
            s.hit_test(8, 3),
            Some(TableHit::ColumnBorder { col_idx: 2 })
        );
    }

    /// What `config.table.show_buttons = false` guarantees: with no delete handle the right border
    /// on a data row is a plain `ColumnBorder`.
    #[test]
    fn hit_test_falls_through_when_delete_handles_disabled() {
        let s = snap(vec![1..4, 5..8], vec![3..4]);
        assert_eq!(
            s.hit_test(8, 3),
            Some(TableHit::ColumnBorder { col_idx: 2 })
        );
    }

    #[test]
    fn hit_test_returns_delete_column_handle_on_bottom_border() {
        let mut s = snap(vec![1..4, 5..8], vec![3..4]);
        s.bottom_border_row = Some(5);
        let hit = s.hit_test(2, 5).unwrap();
        assert_eq!(hit, TableHit::DeleteColumnHandle { col_idx: 0 });
        let hit = s.hit_test(6, 5).unwrap();
        assert_eq!(hit, TableHit::DeleteColumnHandle { col_idx: 1 });
    }

    /// `row_ranges` tracks only data rows, so the delete check can't fire outside one.
    #[test]
    fn hit_test_delete_row_handle_skips_header_and_alignment() {
        let mut s = snap(vec![1..4, 5..8], vec![5..6]); // single data row at y=5
        s.delete_row_handle_col = Some(8);
        // The contract: y=2 gives ColumnBorder, not DeleteRowHandle.
        assert_ne!(
            s.hit_test(8, 2),
            Some(TableHit::DeleteRowHandle { row_idx: 2 })
        );
    }

    /// An unchanged cache key must leave `snapshots` untouched.
    #[test]
    fn build_snapshots_cached_reuses_output_when_key_matches() {
        use crate::config::Theme;
        use crate::document::Buffer;
        use crate::editor::EditorState;

        let theme: &'static Theme = Box::leak(Box::new(Theme::default()));
        let src = "| a | b |\n|---|---|\n| 1 | 2 |\n";
        let state = EditorState::new(Buffer::from_str(src), theme);
        let area = Rect::new(0, 0, 40, 10);

        let mut snapshots: Vec<TableLayoutSnapshot> = Vec::new();
        let mut key: Option<(usize, Rect, u64, bool)> = None;
        build_snapshots_cached(&state, area, false, &mut snapshots, &mut key);
        let first_len = snapshots.len();
        assert!(first_len > 0, "expected at least one snapshot");

        // Tag the snapshots so a rebuild is detectable.
        snapshots[0].col_count = 999;
        build_snapshots_cached(&state, area, false, &mut snapshots, &mut key);
        assert_eq!(
            snapshots[0].col_count, 999,
            "snapshots must not be rebuilt when cache key matches",
        );

        // Changing show_handles busts the cache.
        build_snapshots_cached(&state, area, true, &mut snapshots, &mut key);
        assert_ne!(
            snapshots[0].col_count, 999,
            "snapshots must be rebuilt when show_handles changes",
        );
    }
}