//! The terminal screen: a grid of styled cells, a cursor, and the editing
//! operations the VT parser drives.

mod links;
mod search;
mod selection;

use std::collections::VecDeque;
use std::num::NonZeroU16;

use unicode_width::UnicodeWidthChar;

pub use links::UrlHit;
use search::SearchState;

/// Maximum scrollback lines retained for the main screen.
const SCROLLBACK_CAP: usize = 10_000;

/// A cell colour: terminal default, a palette index, or direct RGB.
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
pub enum Color {
    #[default]
    Default,
    Indexed(u8),
    Rgb(u8, u8, u8),
}

/// Per-cell style flags, packed into a `u16`.
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
pub struct Flags(u16);

impl Flags {
    pub const BOLD: Self = Self(1 << 0);
    pub const DIM: Self = Self(1 << 1);
    pub const ITALIC: Self = Self(1 << 2);
    pub const BLINK: Self = Self(1 << 4);
    pub const REVERSE: Self = Self(1 << 5);
    pub const HIDDEN: Self = Self(1 << 6);
    pub const STRIKE: Self = Self(1 << 7);
    /// Trailing column of a double-width glyph; holds no character of its own.
    pub const WIDE_CONT: Self = Self(1 << 8);
    pub const OVERLINE: Self = Self(1 << 9);

    pub const fn empty() -> Self {
        Self(0)
    }

    pub const fn union(self, other: Self) -> Self {
        Self(self.0 | other.0)
    }

    pub fn contains(self, other: Self) -> bool {
        self.0 & other.0 == other.0
    }

    pub fn insert(&mut self, other: Self) {
        self.0 |= other.0;
    }

    pub fn remove(&mut self, other: Self) {
        self.0 &= !other.0;
    }
}

/// Underline style (SGR 4 / 4:x / 21).
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
pub enum Underline {
    #[default]
    None,
    Single,
    Double,
    Curly,
    Dotted,
    Dashed,
}

/// Cursor shape (DECSCUSR).
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
pub enum CursorShape {
    #[default]
    Block,
    Underline,
    Beam,
}

/// Which mouse events the application has asked to receive (DECSET 9/1000-1003).
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
pub enum MouseProtocol {
    /// No reporting; the pointer drives local selection/scroll.
    #[default]
    Off,
    /// X10 (9): button presses only.
    X10,
    /// Normal (1000): button press and release.
    Normal,
    /// Button-event (1002): press, release, and motion while a button is held.
    Button,
    /// Any-event (1003): press, release, and all pointer motion.
    Any,
}

/// How mouse events are framed on the wire (default byte form, UTF-8, or SGR).
#[derive(Clone, Copy, PartialEq, Eq, Debug, Default)]
pub enum MouseEncoding {
    /// Legacy `CSI M Cb Cx Cy`, each value a byte offset by 32 (≤ 223).
    #[default]
    X10,
    /// As X10 but coordinates above 95 are UTF-8 encoded (DECSET 1005).
    Utf8,
    /// `CSI < Cb ; Cx ; Cy M/m`, decimal and unbounded (DECSET 1006).
    Sgr,
}

/// One grid cell: a character plus its rendering style.
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct Cell {
    pub c: char,
    pub fg: Color,
    pub bg: Color,
    pub flags: Flags,
    pub underline: Underline,
    /// Underline colour; `Default` means "follow the foreground".
    pub underline_color: Color,
    /// Zero-width combining marks attached to `c`, in arrival order. `None` for
    /// the common case; the renderer stacks each over the base glyph. This is
    /// the grapheme cluster a future shaper (HarfBuzz) would consume.
    pub combining: Option<Box<str>>,
    /// OSC 8 hyperlink: a 1-based index into the grid's link table, or `None`.
    pub link: Option<NonZeroU16>,
}

impl Default for Cell {
    fn default() -> Self {
        Self {
            c: ' ',
            fg: Color::Default,
            bg: Color::Default,
            flags: Flags::empty(),
            underline: Underline::None,
            underline_color: Color::Default,
            combining: None,
            link: None,
        }
    }
}

#[derive(Clone, Copy, Debug, Default)]
struct Cursor {
    x: usize,
    y: usize,
}

/// Shell-integration prompt mark on a line (OSC 133): the start of a prompt,
/// the start of typed command input, the start of command output, or the line
/// where the command finished.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum PromptKind {
    PromptStart,
    CmdStart,
    OutputStart,
    CmdEnd,
}

/// One screen/scrollback row: its cells plus whether it soft-wrapped into the
/// next row (autowrap continuation, as opposed to a hard line break). The flag
/// is what lets resize rejoin and rewrap paragraphs.
#[derive(Clone, PartialEq, Eq, Debug)]
struct Line {
    cells: Vec<Cell>,
    wrapped: bool,
    /// OSC 133 mark attached to this (logical) line, if any.
    prompt: Option<PromptKind>,
}

impl Line {
    fn blank(cols: usize) -> Self {
        Self {
            cells: vec![Cell::default(); cols],
            wrapped: false,
            prompt: None,
        }
    }
}

/// A point in the combined scrollback+live coordinate space: `row` indexes
/// scrollback lines first (oldest at 0), then the live screen.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub struct Point {
    pub row: usize,
    pub col: usize,
}

/// The active screen plus cursor, scroll region, and current pen.
#[derive(Debug)]
pub struct Grid {
    cols: usize,
    rows: usize,
    lines: Vec<Line>,
    cursor: Cursor,
    saved: Cursor,
    /// Inclusive top/bottom rows of the scroll region.
    top: usize,
    bottom: usize,
    /// Template cell carrying the current SGR colours/flags.
    pen: Cell,
    autowrap: bool,
    origin: bool,
    insert: bool,
    /// Cursor parked past the last column, awaiting the next print to wrap.
    wrap_pending: bool,
    tabs: Vec<bool>,
    /// Saved primary screen while the alternate screen is active.
    alt_saved: Option<Vec<Line>>,
    /// Lines that have scrolled off the top of the main screen, newest last.
    scrollback: VecDeque<Line>,
    /// How many lines the viewport is scrolled back from the live bottom.
    view_offset: usize,
    cursor_shape: CursorShape,
    /// Whether the cursor shape is a blinking variant (DECSCUSR odd codes).
    cursor_blink: bool,
    cursor_visible: bool,
    /// Application cursor-keys mode (DECCKM): arrows send SS3 instead of CSI.
    app_cursor: bool,
    /// Cursor colour from OSC 12; `None` follows the cell under the cursor.
    cursor_color: Option<(u8, u8, u8)>,
    /// Active mouse selection as (anchor, head) in absolute coordinates.
    selection: Option<(Point, Point)>,
    /// Whether the selection is a rectangular block rather than linear flow.
    selection_block: bool,
    /// Bracketed paste mode (DECSET 2004): wrap pasted text in `ESC[200~`/`201~`.
    bracketed_paste: bool,
    /// Synchronized output (DECSET 2026): hold presentation while a frame is
    /// being assembled, so the screen never shows a half-drawn update.
    sync: bool,
    /// Which mouse events the application wants reported.
    mouse_protocol: MouseProtocol,
    /// Wire framing for those reports.
    mouse_encoding: MouseEncoding,
    /// Focus in/out reporting (DECSET 1004).
    focus_events: bool,
    /// Active incremental scrollback search, if any.
    search: Option<SearchState>,
    /// Characters that break a word for double-click selection.
    word_delimiters: String,
    /// History retention cap for the main screen.
    scrollback_cap: usize,
    /// Position of the last printed base cell, so a following zero-width
    /// combining mark can attach to it.
    last_base: Option<(usize, usize)>,
    /// OSC 8 hyperlink URIs; a cell's `link` is a 1-based index into this.
    links: Vec<Box<str>>,
}

fn default_tabs(cols: usize) -> Vec<bool> {
    (0..cols).map(|i| i % 8 == 0 && i != 0).collect()
}

/// Default characters that terminate a word for double-click selection (the
/// `word-delimiters` config key overrides this). `_`, `-`, `.`, `/`, `:`, `~`
/// are deliberately *not* delimiters so paths, URLs, and option flags select as
/// one unit.
const WORD_DELIMITERS: &str = " \t`!@#$%^&*()+=[]{}\\|;'\",<>?";

/// Whether `c` is part of a word (not whitespace, not in `delims`).
fn is_word(c: char, delims: &str) -> bool {
    !c.is_whitespace() && !delims.contains(c)
}

impl Grid {
    pub fn new(cols: usize, rows: usize) -> Self {
        let cols = cols.max(1);
        let rows = rows.max(1);
        Self {
            cols,
            rows,
            lines: vec![Line::blank(cols); rows],
            cursor: Cursor::default(),
            saved: Cursor::default(),
            top: 0,
            bottom: rows - 1,
            pen: Cell::default(),
            autowrap: true,
            origin: false,
            insert: false,
            wrap_pending: false,
            tabs: default_tabs(cols),
            alt_saved: None,
            scrollback: VecDeque::new(),
            view_offset: 0,
            cursor_shape: CursorShape::default(),
            cursor_blink: false,
            cursor_visible: true,
            cursor_color: None,
            app_cursor: false,
            selection: None,
            selection_block: false,
            bracketed_paste: false,
            sync: false,
            mouse_protocol: MouseProtocol::Off,
            mouse_encoding: MouseEncoding::X10,
            focus_events: false,
            search: None,
            word_delimiters: WORD_DELIMITERS.to_string(),
            scrollback_cap: SCROLLBACK_CAP,
            last_base: None,
            links: Vec::new(),
        }
    }

    /// Override the word-delimiter set; `None` keeps the built-in default.
    pub fn set_word_delimiters(&mut self, delims: Option<String>) {
        if let Some(d) = delims {
            self.word_delimiters = d;
        }
    }

    /// Set the scrollback retention cap, trimming history if it shrank.
    pub fn set_scrollback_cap(&mut self, cap: usize) {
        self.scrollback_cap = cap;
        while self.scrollback.len() > cap {
            self.scrollback.pop_front();
        }
        self.view_offset = self.view_offset.min(self.scrollback.len());
    }

    pub fn cols(&self) -> usize {
        self.cols
    }

    pub fn rows(&self) -> usize {
        self.rows
    }

    /// Resize the screen. On the main screen this reflows: soft-wrapped runs are
    /// rejoined into logical lines and rewrapped to the new width, across both
    /// scrollback and the live screen, keeping the cursor on its content. The
    /// alternate screen just clips, since its apps repaint on resize.
    pub fn resize(&mut self, cols: usize, rows: usize) {
        let cols = cols.max(1);
        let rows = rows.max(1);
        if self.alt_saved.is_some() {
            self.clip_resize(cols, rows);
        } else {
            self.reflow_resize(cols, rows);
        }
        self.cols = cols;
        self.rows = rows;
        self.top = 0;
        self.bottom = rows - 1;
        self.tabs = default_tabs(cols);
        self.cursor.x = self.cursor.x.min(cols - 1);
        self.cursor.y = self.cursor.y.min(rows - 1);
        self.wrap_pending = false;
        self.view_offset = 0;
    }

    /// Clip-resize the live screen and the saved primary (alternate screen).
    fn clip_resize(&mut self, cols: usize, rows: usize) {
        for line in &mut self.lines {
            line.cells.resize(cols, Cell::default());
        }
        self.lines.resize(rows, Line::blank(cols));
        if let Some(saved) = self.alt_saved.as_mut() {
            for line in saved.iter_mut() {
                line.cells.resize(cols, Cell::default());
            }
            saved.resize(rows, Line::blank(cols));
        }
        self.clear_selection();
        self.clear_search();
    }

    /// Reflow scrollback + live content to a new width, rewrapping soft-wrapped
    /// paragraphs and repositioning the cursor onto its character.
    fn reflow_resize(&mut self, cols: usize, rows: usize) {
        let cursor_abs = self.scrollback.len() + self.cursor.y;
        let total = self.scrollback.len() + self.lines.len();

        // 1. Rejoin soft-wrapped rows into logical lines. Track which logical
        //    line the cursor falls in and its offset within that line.
        let mut logicals: Vec<Vec<Cell>> = Vec::new();
        let mut logical_marks: Vec<Option<PromptKind>> = Vec::new();
        let mut acc: Vec<Cell> = Vec::new();
        let mut acc_mark: Option<PromptKind> = None;
        let mut cur_logical = 0usize;
        let mut cur_off = 0usize;
        for abs in 0..total {
            if abs == cursor_abs {
                cur_logical = logicals.len();
                cur_off = acc.len() + self.cursor.x;
            }
            let line = if abs < self.scrollback.len() {
                &self.scrollback[abs]
            } else {
                &self.lines[abs - self.scrollback.len()]
            };
            // The mark on the first physical row of a logical line carries over.
            if acc.is_empty() {
                acc_mark = line.prompt;
            }
            acc.extend_from_slice(&line.cells);
            if !line.wrapped {
                logicals.push(std::mem::take(&mut acc));
                logical_marks.push(acc_mark.take());
            }
        }
        if !acc.is_empty() {
            logicals.push(acc);
            logical_marks.push(acc_mark);
        }
        // Drop trailing all-blank lines (empty screen below the content), but
        // never above the cursor's line, so the cursor keeps its row.
        let last_content = logicals
            .iter()
            .rposition(|l| l.iter().any(|c| *c != Cell::default()))
            .unwrap_or(0);
        logicals.truncate(last_content.max(cur_logical) + 1);
        logical_marks.truncate(last_content.max(cur_logical) + 1);

        // 2. Rewrap each logical line to the new width, recording where the
        //    cursor lands. Trailing blanks are dropped so a hard line does not
        //    rewrap its padding onto extra rows.
        let mut new_lines: Vec<Line> = Vec::new();
        let mut new_cursor_abs = 0usize;
        let mut new_cursor_col = 0usize;
        for (li, mut logical) in logicals.into_iter().enumerate() {
            let trim = logical
                .iter()
                .rposition(|c| *c != Cell::default())
                .map_or(0, |p| p + 1);
            logical.truncate(trim);
            let first = new_lines.len();
            let chunks = logical.len().div_ceil(cols).max(1);
            for ci in 0..chunks {
                let start = ci * cols;
                let end = (start + cols).min(logical.len());
                let mut cells = logical.get(start..end).unwrap_or(&[]).to_vec();
                cells.resize(cols, Cell::default());
                new_lines.push(Line {
                    cells,
                    wrapped: ci + 1 < chunks,
                    // The mark belongs to the first physical row of the line.
                    prompt: if ci == 0 { logical_marks[li] } else { None },
                });
            }
            if li == cur_logical {
                let off = cur_off.min(logical.len());
                let chunk = (off / cols).min(chunks - 1);
                new_cursor_abs = first + chunk;
                new_cursor_col = (off - chunk * cols).min(cols - 1);
            }
        }

        // 3. The last `rows` lines are the live screen; the rest is scrollback.
        let live_start = new_lines.len().saturating_sub(rows);
        let mut scrollback: VecDeque<Line> = new_lines.drain(0..live_start).collect();
        let mut live = new_lines;
        while live.len() < rows {
            live.push(Line::blank(cols));
        }
        while scrollback.len() > self.scrollback_cap {
            scrollback.pop_front();
        }

        self.cursor.y = new_cursor_abs.saturating_sub(live_start).min(rows - 1);
        self.cursor.x = new_cursor_col;
        self.lines = live;
        self.scrollback = scrollback;
        self.clear_selection();
        self.clear_search();
    }

    pub fn cursor(&self) -> (usize, usize) {
        (self.cursor.x, self.cursor.y)
    }

    // --- pen / attributes ---

    pub fn pen_mut(&mut self) -> &mut Cell {
        &mut self.pen
    }

    pub fn reset_pen(&mut self) {
        self.pen = Cell::default();
    }

    pub fn set_autowrap(&mut self, on: bool) {
        self.autowrap = on;
    }

    pub fn set_origin(&mut self, on: bool) {
        self.origin = on;
        self.move_to(0, 0);
    }

    pub fn set_insert(&mut self, on: bool) {
        self.insert = on;
    }

    pub fn autowrap(&self) -> bool {
        self.autowrap
    }

    pub fn origin(&self) -> bool {
        self.origin
    }

    pub fn insert(&self) -> bool {
        self.insert
    }

    pub fn alt_active(&self) -> bool {
        self.alt_saved.is_some()
    }

    pub fn set_cursor_shape(&mut self, shape: CursorShape) {
        self.cursor_shape = shape;
    }

    pub fn cursor_shape(&self) -> CursorShape {
        self.cursor_shape
    }

    pub fn set_cursor_blink(&mut self, blink: bool) {
        self.cursor_blink = blink;
    }

    pub fn cursor_blink(&self) -> bool {
        self.cursor_blink
    }

    pub fn set_cursor_visible(&mut self, visible: bool) {
        self.cursor_visible = visible;
    }

    pub fn cursor_visible(&self) -> bool {
        self.cursor_visible
    }

    pub fn set_cursor_color(&mut self, color: Option<(u8, u8, u8)>) {
        self.cursor_color = color;
    }

    pub fn cursor_color(&self) -> Option<(u8, u8, u8)> {
        self.cursor_color
    }

    pub fn set_app_cursor(&mut self, on: bool) {
        self.app_cursor = on;
    }

    pub fn app_cursor(&self) -> bool {
        self.app_cursor
    }

    // --- printing ---

    /// Place a printable character at the cursor, honouring width and autowrap.
    pub fn print(&mut self, c: char) {
        let width = c.width().unwrap_or(0);
        if width == 0 {
            // A zero-width combining mark attaches to the last base cell.
            self.add_combining(c);
            return;
        }
        if self.wrap_pending {
            self.cursor.x = 0;
            self.lines[self.cursor.y].wrapped = true;
            self.line_feed();
            self.wrap_pending = false;
        }
        if width == 2 && self.cursor.x + 1 >= self.cols {
            // A double-width glyph cannot straddle the right edge: wrap first.
            if self.autowrap {
                self.cursor.x = 0;
                self.lines[self.cursor.y].wrapped = true;
                self.line_feed();
            } else {
                return;
            }
        }
        if self.insert {
            self.shift_right(width);
        }

        let (x, y) = (self.cursor.x, self.cursor.y);
        let mut cell = self.pen.clone();
        cell.c = c;
        cell.combining = None;
        cell.flags.remove(Flags::WIDE_CONT);
        self.lines[y].cells[x] = cell;
        self.last_base = Some((x, y));
        if width == 2 && x + 1 < self.cols {
            let mut cont = self.pen.clone();
            cont.c = ' ';
            cont.combining = None;
            cont.flags.insert(Flags::WIDE_CONT);
            self.lines[y].cells[x + 1] = cont;
        }

        let advance = width;
        if self.cursor.x + advance >= self.cols {
            if self.autowrap {
                self.cursor.x = self.cols - 1;
                self.wrap_pending = true;
            } else {
                self.cursor.x = self.cols - 1;
            }
        } else {
            self.cursor.x += advance;
        }
    }

    /// Attach a zero-width combining mark to the most recently printed base
    /// cell. Capped so a malicious stream of marks cannot grow a cell unbounded.
    fn add_combining(&mut self, mark: char) {
        const MAX_MARKS: usize = 8;
        let Some((x, y)) = self.last_base else {
            return;
        };
        let Some(cell) = self.lines.get_mut(y).and_then(|l| l.cells.get_mut(x)) else {
            return;
        };
        let mut s: String = cell.combining.take().map(String::from).unwrap_or_default();
        if s.chars().count() < MAX_MARKS {
            s.push(mark);
        }
        cell.combining = Some(s.into_boxed_str());
    }

    fn shift_right(&mut self, n: usize) {
        let (x, y) = (self.cursor.x, self.cursor.y);
        let end = self.cols;
        let blank = self.pen_blank();
        let row = &mut self.lines[y].cells;
        for i in (x + n..end).rev() {
            row[i] = row[i - n].clone();
        }
        for cell in &mut row[x..(x + n).min(end)] {
            *cell = blank.clone();
        }
    }

    fn pen_blank(&self) -> Cell {
        // A space carrying only the current background (back-colour erase).
        Cell {
            bg: self.pen.bg,
            ..Cell::default()
        }
    }

    // --- cursor movement ---

    fn region(&self) -> (usize, usize) {
        if self.origin {
            (self.top, self.bottom)
        } else {
            (0, self.rows - 1)
        }
    }

    pub fn move_to(&mut self, x: usize, y: usize) {
        let (rt, rb) = self.region();
        self.cursor.x = x.min(self.cols - 1);
        self.cursor.y = (y + rt).min(rb).max(rt);
        self.wrap_pending = false;
    }

    pub fn move_to_col(&mut self, x: usize) {
        self.cursor.x = x.min(self.cols - 1);
        self.wrap_pending = false;
    }

    pub fn move_to_row(&mut self, y: usize) {
        let (rt, rb) = self.region();
        self.cursor.y = (y + rt).min(rb).max(rt);
        self.wrap_pending = false;
    }

    pub fn cursor_up(&mut self, n: usize) {
        let (rt, _) = self.region();
        self.cursor.y = self.cursor.y.saturating_sub(n).max(rt);
        self.wrap_pending = false;
    }

    pub fn cursor_down(&mut self, n: usize) {
        let (_, rb) = self.region();
        self.cursor.y = (self.cursor.y + n).min(rb);
        self.wrap_pending = false;
    }

    pub fn cursor_fwd(&mut self, n: usize) {
        self.cursor.x = (self.cursor.x + n).min(self.cols - 1);
        self.wrap_pending = false;
    }

    pub fn cursor_back(&mut self, n: usize) {
        self.cursor.x = self.cursor.x.saturating_sub(n);
        self.wrap_pending = false;
    }

    pub fn save_cursor(&mut self) {
        self.saved = self.cursor;
    }

    pub fn restore_cursor(&mut self) {
        self.cursor = self.saved;
        self.cursor.x = self.cursor.x.min(self.cols - 1);
        self.cursor.y = self.cursor.y.min(self.rows - 1);
        self.wrap_pending = false;
    }

    // --- line discipline ---

    pub fn carriage_return(&mut self) {
        self.cursor.x = 0;
        self.wrap_pending = false;
    }

    pub fn backspace(&mut self) {
        self.cursor.x = self.cursor.x.saturating_sub(1);
        self.wrap_pending = false;
    }

    /// LF/VT/FF: move down one row, scrolling at the region bottom.
    pub fn line_feed(&mut self) {
        if self.cursor.y == self.bottom {
            self.scroll_up(1);
        } else if self.cursor.y < self.rows - 1 {
            self.cursor.y += 1;
        }
        self.wrap_pending = false;
    }

    /// RI: move up one row, scrolling down at the region top.
    pub fn reverse_index(&mut self) {
        if self.cursor.y == self.top {
            self.scroll_down(1);
        } else if self.cursor.y > 0 {
            self.cursor.y -= 1;
        }
        self.wrap_pending = false;
    }

    /// NEL: carriage return plus line feed.
    pub fn next_line(&mut self) {
        self.carriage_return();
        self.line_feed();
    }

    // --- tab stops ---

    pub fn tab(&mut self) {
        let mut x = self.cursor.x + 1;
        while x < self.cols && !self.tabs[x] {
            x += 1;
        }
        self.cursor.x = x.min(self.cols - 1);
        self.wrap_pending = false;
    }

    pub fn set_tab(&mut self) {
        if self.cursor.x < self.cols {
            self.tabs[self.cursor.x] = true;
        }
    }

    pub fn clear_tab(&mut self) {
        if self.cursor.x < self.cols {
            self.tabs[self.cursor.x] = false;
        }
    }

    pub fn clear_all_tabs(&mut self) {
        self.tabs.iter_mut().for_each(|t| *t = false);
    }

    // --- scrolling within the region ---

    pub fn set_scroll_region(&mut self, top: usize, bottom: usize) {
        if top < bottom && bottom < self.rows {
            self.top = top;
            self.bottom = bottom;
        } else {
            self.top = 0;
            self.bottom = self.rows - 1;
        }
        self.move_to(0, 0);
    }

    pub fn scroll_up(&mut self, n: usize) {
        let n = n.min(self.bottom - self.top + 1);
        // Lines leaving the top of the *whole* main screen become scrollback;
        // a DECSTBM region scroll (top > 0) or the alt screen does not.
        if self.top == 0 && self.alt_saved.is_none() {
            for y in 0..n {
                let line = std::mem::replace(&mut self.lines[y], Line::blank(self.cols));
                self.scrollback.push_back(line);
            }
            let mut evicted = 0;
            while self.scrollback.len() > self.scrollback_cap {
                self.scrollback.pop_front();
                evicted += 1;
            }
            if evicted > 0 {
                self.shift_selection(evicted);
                self.shift_search(evicted);
            }
            // Keep a scrolled-back viewport anchored to the same content.
            if self.view_offset > 0 {
                self.view_offset = (self.view_offset + n).min(self.scrollback.len());
            }
        }
        for y in self.top..=self.bottom {
            if y + n <= self.bottom {
                self.lines.swap(y, y + n);
            }
        }
        for y in (self.bottom + 1 - n)..=self.bottom {
            self.blank_row(y);
        }
    }

    pub fn scroll_down(&mut self, n: usize) {
        let n = n.min(self.bottom - self.top + 1);
        for y in (self.top..=self.bottom).rev() {
            if y >= self.top + n {
                self.lines.swap(y, y - n);
            }
        }
        for y in self.top..(self.top + n) {
            self.blank_row(y);
        }
    }

    fn blank_row(&mut self, y: usize) {
        let blank = self.pen_blank();
        let line = &mut self.lines[y];
        for cell in &mut line.cells {
            *cell = blank.clone();
        }
        line.wrapped = false;
    }

    // --- erase ---

    /// ED: 0=below, 1=above, 2/3=all.
    pub fn erase_display(&mut self, mode: u16) {
        let (x, y) = (self.cursor.x, self.cursor.y);
        match mode {
            0 => {
                self.erase_in_row(y, x, self.cols);
                for r in (y + 1)..self.rows {
                    self.blank_row(r);
                }
            }
            1 => {
                for r in 0..y {
                    self.blank_row(r);
                }
                self.erase_in_row(y, 0, x + 1);
            }
            _ => {
                for r in 0..self.rows {
                    self.blank_row(r);
                }
            }
        }
        self.wrap_pending = false;
    }

    /// EL: 0=right, 1=left, 2=line.
    pub fn erase_line(&mut self, mode: u16) {
        let (x, y) = (self.cursor.x, self.cursor.y);
        match mode {
            0 => self.erase_in_row(y, x, self.cols),
            1 => self.erase_in_row(y, 0, x + 1),
            _ => self.erase_in_row(y, 0, self.cols),
        }
        self.wrap_pending = false;
    }

    /// ECH: erase n characters from the cursor without moving it.
    pub fn erase_chars(&mut self, n: usize) {
        let (x, y) = (self.cursor.x, self.cursor.y);
        self.erase_in_row(y, x, (x + n).min(self.cols));
    }

    fn erase_in_row(&mut self, y: usize, from: usize, to: usize) {
        let blank = self.pen_blank();
        for cell in &mut self.lines[y].cells[from..to.min(self.cols)] {
            *cell = blank.clone();
        }
    }

    // --- intra-line editing ---

    /// ICH: insert n blanks at the cursor, shifting the rest right.
    pub fn insert_chars(&mut self, n: usize) {
        let saved = self.insert;
        self.insert = true;
        self.shift_right(n.min(self.cols));
        self.insert = saved;
    }

    /// DCH: delete n characters at the cursor, shifting the rest left.
    pub fn delete_chars(&mut self, n: usize) {
        let (x, y) = (self.cursor.x, self.cursor.y);
        let n = n.min(self.cols - x);
        let blank = self.pen_blank();
        let row = &mut self.lines[y].cells;
        for i in x..self.cols {
            row[i] = if i + n < self.cols {
                row[i + n].clone()
            } else {
                blank.clone()
            };
        }
    }

    /// IL: insert n blank lines at the cursor row, within the scroll region.
    pub fn insert_lines(&mut self, n: usize) {
        if self.cursor.y < self.top || self.cursor.y > self.bottom {
            return;
        }
        let n = n.min(self.bottom - self.cursor.y + 1);
        for y in (self.cursor.y..=self.bottom).rev() {
            if y >= self.cursor.y + n {
                self.lines.swap(y, y - n);
            }
        }
        for y in self.cursor.y..(self.cursor.y + n) {
            self.blank_row(y);
        }
    }

    /// DL: delete n lines at the cursor row, within the scroll region.
    pub fn delete_lines(&mut self, n: usize) {
        if self.cursor.y < self.top || self.cursor.y > self.bottom {
            return;
        }
        let n = n.min(self.bottom - self.cursor.y + 1);
        for y in self.cursor.y..=self.bottom {
            if y + n <= self.bottom {
                self.lines.swap(y, y + n);
            }
        }
        for y in (self.bottom + 1 - n)..=self.bottom {
            self.blank_row(y);
        }
    }

    // --- alternate screen ---

    pub fn enter_alt_screen(&mut self) {
        if self.alt_saved.is_some() {
            return;
        }
        self.view_offset = 0;
        let blank = vec![Line::blank(self.cols); self.rows];
        self.alt_saved = Some(std::mem::replace(&mut self.lines, blank));
    }

    pub fn leave_alt_screen(&mut self) {
        if let Some(main) = self.alt_saved.take() {
            self.lines = main;
        }
    }

    // --- scrollback viewport ---

    /// Scroll the viewport by `delta` lines: positive = back into history,
    /// negative = toward the live screen. No-op on the alternate screen.
    pub fn scroll_view(&mut self, delta: isize) {
        if self.alt_saved.is_some() {
            return;
        }
        let max = self.scrollback.len() as isize;
        self.view_offset = (self.view_offset as isize + delta).clamp(0, max) as usize;
    }

    pub fn scroll_to_bottom(&mut self) {
        self.view_offset = 0;
    }

    /// Whether the viewport is showing the live screen (not scrolled back).
    pub fn view_at_bottom(&self) -> bool {
        self.view_offset == 0
    }

    /// One page (a screenful) of lines, for page-scroll bindings.
    pub fn page(&self) -> usize {
        self.rows.max(1)
    }

    /// The cells shown at viewport row `y` (0 = top of the window), accounting
    /// for the scrollback offset. May differ from `cols` in width if the line
    /// predates a resize (no reflow yet), so callers must not assume length.
    pub fn view_row(&self, y: usize) -> &[Cell] {
        let start = self.scrollback.len() - self.view_offset;
        let idx = start + y;
        if idx < self.scrollback.len() {
            &self.scrollback[idx].cells
        } else {
            &self.lines[idx - self.scrollback.len()].cells
        }
    }

    // --- selection ---

    /// The absolute row currently shown at viewport row `y`.
    pub fn view_to_abs(&self, y: usize) -> usize {
        self.scrollback.len() - self.view_offset + y
    }

    /// The line at an absolute row (scrollback first, then the live screen).
    fn line_at_abs(&self, abs: usize) -> &Line {
        if abs < self.scrollback.len() {
            &self.scrollback[abs]
        } else {
            &self.lines[abs - self.scrollback.len()]
        }
    }

    /// Cells of an absolute row (scrollback first, then the live screen).
    fn abs_row(&self, row: usize) -> &[Cell] {
        if row < self.scrollback.len() {
            &self.scrollback[row].cells
        } else {
            &self.lines[row - self.scrollback.len()].cells
        }
    }

    /// Total rows across scrollback and the live screen.
    fn total_lines(&self) -> usize {
        self.scrollback.len() + self.lines.len()
    }

    /// The OSC 133 mark on an absolute row, if any.
    fn abs_prompt(&self, row: usize) -> Option<PromptKind> {
        if row < self.scrollback.len() {
            self.scrollback[row].prompt
        } else {
            self.lines
                .get(row - self.scrollback.len())
                .and_then(|l| l.prompt)
        }
    }

    // --- shell integration (OSC 133) ---

    /// Attach an OSC 133 prompt mark to the live line under the cursor.
    pub fn set_prompt_mark(&mut self, kind: PromptKind) {
        let y = self.cursor.y;
        if let Some(line) = self.lines.get_mut(y) {
            line.prompt = Some(kind);
        }
    }

    /// Scroll the viewport to the previous (`up`) or next prompt, placing that
    /// prompt line at the top of the window. No-op on the alternate screen or
    /// when there is no prompt in that direction.
    pub fn jump_prompt(&mut self, up: bool) {
        if self.alt_saved.is_some() {
            return;
        }
        let top = self.scrollback.len().saturating_sub(self.view_offset);
        let total = self.total_lines();
        let is_prompt = |k: Option<PromptKind>| k == Some(PromptKind::PromptStart);
        let target = if up {
            (0..top).rev().find(|&r| is_prompt(self.abs_prompt(r)))
        } else {
            ((top + 1)..total).find(|&r| is_prompt(self.abs_prompt(r)))
        };
        if let Some(t) = target {
            let offset = self.scrollback.len() as isize - t as isize;
            self.view_offset = offset.clamp(0, self.scrollback.len() as isize) as usize;
        }
    }

    /// Text of the most recent command's output: the rows from the last
    /// output-start (OSC 133 C) up to the command-end (D) or next prompt.
    pub fn last_command_output(&self) -> Option<String> {
        let total = self.total_lines();
        let start = (0..total)
            .rev()
            .find(|&r| self.abs_prompt(r) == Some(PromptKind::OutputStart))?;
        let mut lines: Vec<String> = Vec::new();
        for r in start..total {
            if r > start
                && matches!(
                    self.abs_prompt(r),
                    Some(PromptKind::CmdEnd | PromptKind::PromptStart)
                )
            {
                break;
            }
            lines.push(self.row_slice_text(r, 0, usize::MAX).trim_end().to_string());
        }
        // Drop trailing blank rows (e.g. the empty live screen below the output).
        while lines.last().is_some_and(|l| l.is_empty()) {
            lines.pop();
        }
        let mut out = lines.join("\n");
        out.push('\n');
        Some(out)
    }

    pub fn set_bracketed_paste(&mut self, on: bool) {
        self.bracketed_paste = on;
    }

    pub fn bracketed_paste(&self) -> bool {
        self.bracketed_paste
    }

    pub fn set_sync(&mut self, on: bool) {
        self.sync = on;
    }

    pub fn sync_active(&self) -> bool {
        self.sync
    }

    pub fn set_mouse_protocol(&mut self, protocol: MouseProtocol) {
        self.mouse_protocol = protocol;
    }

    pub fn mouse_protocol(&self) -> MouseProtocol {
        self.mouse_protocol
    }

    pub fn set_mouse_encoding(&mut self, encoding: MouseEncoding) {
        self.mouse_encoding = encoding;
    }

    pub fn mouse_encoding(&self) -> MouseEncoding {
        self.mouse_encoding
    }

    pub fn set_focus_events(&mut self, on: bool) {
        self.focus_events = on;
    }

    pub fn focus_events(&self) -> bool {
        self.focus_events
    }

    // --- inspection (logging + tests) ---

    /// The visible text of one row, trailing blanks trimmed.
    #[cfg(test)]
    pub fn row_text(&self, y: usize) -> String {
        self.lines[y]
            .cells
            .iter()
            .filter(|c| !c.flags.contains(Flags::WIDE_CONT))
            .map(|c| c.c)
            .collect::<String>()
            .trim_end()
            .to_string()
    }

    pub fn cell(&self, x: usize, y: usize) -> &Cell {
        &self.lines[y].cells[x]
    }
}

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

    #[test]
    fn prints_and_wraps() {
        let mut g = Grid::new(4, 2);
        for c in "abcde".chars() {
            g.print(c);
        }
        assert_eq!(g.row_text(0), "abcd");
        assert_eq!(g.row_text(1), "e");
        assert_eq!(g.cursor(), (1, 1));
    }

    #[test]
    fn combining_marks_attach_to_base_cell() {
        let mut g = Grid::new(8, 1);
        // "e" + COMBINING ACUTE ACCENT + "x": the mark joins the 'e' cell, the
        // 'x' lands in the next cell (the mark advanced nothing).
        for c in "e\u{0301}x".chars() {
            g.print(c);
        }
        assert_eq!(g.cell(0, 0).c, 'e');
        assert_eq!(g.cell(0, 0).combining.as_deref(), Some("\u{0301}"));
        assert_eq!(g.cell(1, 0).c, 'x');
        assert_eq!(g.cursor(), (2, 0));
        // Copied text round-trips the full grapheme cluster.
        g.start_selection(0, 0);
        g.extend_selection(0, 1);
        assert_eq!(g.selection_text().as_deref(), Some("e\u{0301}x"));
    }

    #[test]
    fn detects_urls_trimming_trailing_punctuation() {
        let mut g = Grid::new(60, 2);
        for c in "see https://example.com/p?q=1, ok".chars() {
            g.print(c);
        }
        let hits = g.visible_urls();
        assert_eq!(hits.len(), 1);
        assert_eq!(hits[0].url, "https://example.com/p?q=1");
        assert_eq!((hits[0].row, hits[0].col), (0, 4));
    }

    #[test]
    fn detects_url_across_a_soft_wrap() {
        // 20 cols: the URL wraps, but autowrap sets the wrapped flag so it rejoins.
        let mut g = Grid::new(20, 3);
        for c in "x https://example.com/averylongpath".chars() {
            g.print(c);
        }
        let hits = g.visible_urls();
        assert_eq!(hits.len(), 1);
        assert_eq!(hits[0].url, "https://example.com/averylongpath");
    }

    #[test]
    fn prompt_mark_survives_reflow() {
        let mut g = Grid::new(10, 4);
        g.set_prompt_mark(PromptKind::OutputStart); // marks line 0
        for c in "hello".chars() {
            g.print(c);
        }
        g.resize(6, 4); // rewrap to a narrower width
        // The mark followed its logical line, so the output is still found.
        assert_eq!(g.last_command_output().as_deref(), Some("hello\n"));
    }

    #[test]
    fn carriage_return_and_line_feed() {
        let mut g = Grid::new(8, 4);
        for c in "hi".chars() {
            g.print(c);
        }
        g.carriage_return();
        g.line_feed();
        for c in "yo".chars() {
            g.print(c);
        }
        assert_eq!(g.row_text(0), "hi");
        assert_eq!(g.row_text(1), "yo");
    }

    #[test]
    fn line_feed_scrolls_at_bottom() {
        let mut g = Grid::new(4, 2);
        g.print('a');
        g.next_line();
        g.print('b');
        g.next_line(); // scrolls: row0 <- "b", row1 blank
        assert_eq!(g.row_text(0), "b");
        assert_eq!(g.row_text(1), "");
    }

    #[test]
    fn erase_line_to_right() {
        let mut g = Grid::new(6, 1);
        for c in "abcdef".chars() {
            g.print(c);
        }
        g.move_to(2, 0);
        g.erase_line(0);
        assert_eq!(g.row_text(0), "ab");
    }

    #[test]
    fn delete_and_insert_chars() {
        let mut g = Grid::new(6, 1);
        for c in "abcdef".chars() {
            g.print(c);
        }
        g.move_to(1, 0);
        g.delete_chars(2);
        assert_eq!(g.row_text(0), "adef");
        g.move_to(1, 0);
        g.insert_chars(2);
        assert_eq!(g.row_text(0), "a  def");
    }

    #[test]
    fn scrollback_captures_scrolled_lines() {
        let mut g = Grid::new(8, 2);
        for c in ['1', '2', '3'] {
            g.print(c);
            g.next_line();
        }
        // Live screen: newest line on top, cleared line below.
        assert_eq!(g.view_row(0)[0].c, '3');
        assert!(g.view_at_bottom());
        // Scroll back to reveal the two captured lines.
        g.scroll_view(2);
        assert!(!g.view_at_bottom());
        assert_eq!(g.view_row(0)[0].c, '1');
        assert_eq!(g.view_row(1)[0].c, '2');
        g.scroll_to_bottom();
        assert_eq!(g.view_row(0)[0].c, '3');
    }

    #[test]
    fn wide_char_occupies_two_columns() {
        let mut g = Grid::new(6, 1);
        g.print('世');
        g.print('x');
        assert_eq!(g.cell(0, 0).c, '世');
        assert!(g.cell(1, 0).flags.contains(Flags::WIDE_CONT));
        assert_eq!(g.cell(2, 0).c, 'x');
    }

    #[test]
    fn selection_extracts_text_across_rows() {
        let mut g = Grid::new(8, 2);
        for c in "abcd".chars() {
            g.print(c);
        }
        g.carriage_return();
        g.line_feed();
        for c in "efgh".chars() {
            g.print(c);
        }
        // Select "cd" on row 0 through "ef" on row 1 (rows are live: abs 0,1).
        g.start_selection(0, 2);
        g.extend_selection(1, 1);
        assert!(g.is_selected(0, 3));
        assert!(g.is_selected(1, 0));
        assert!(!g.is_selected(1, 2));
        assert_eq!(g.selection_text().as_deref(), Some("cd\nef"));
    }

    #[test]
    fn select_word_spans_one_word() {
        let mut g = Grid::new(16, 1);
        for c in "foo bar baz".chars() {
            g.print(c);
        }
        g.select_word(0, 5); // inside "bar"
        assert_eq!(g.selection_text().as_deref(), Some("bar"));
    }

    #[test]
    fn select_word_breaks_on_delimiters_but_keeps_paths() {
        let mut g = Grid::new(32, 1);
        for c in "run /usr/bin:next".chars() {
            g.print(c);
        }
        // '/' and ':' are not delimiters, so the path selects whole.
        g.select_word(0, 7); // inside "/usr/bin:next"
        assert_eq!(g.selection_text().as_deref(), Some("/usr/bin:next"));
        // '(' is a delimiter.
        let mut g = Grid::new(16, 1);
        for c in "f(arg)".chars() {
            g.print(c);
        }
        g.select_word(0, 2); // inside "arg"
        assert_eq!(g.selection_text().as_deref(), Some("arg"));
    }

    #[test]
    fn block_selection_is_rectangular() {
        let mut g = Grid::new(8, 3);
        for line in ["abcd", "efgh", "ijkl"] {
            for c in line.chars() {
                g.print(c);
            }
            g.carriage_return();
            g.line_feed();
        }
        // A block from (row0,col1) to (row2,col2) takes columns 1..=2 each row.
        g.start_block_selection(0, 1);
        g.extend_selection(2, 2);
        assert!(g.is_selected(0, 1));
        assert!(g.is_selected(2, 2));
        assert!(!g.is_selected(1, 3));
        assert!(!g.is_selected(1, 0));
        assert_eq!(g.selection_text().as_deref(), Some("bc\nfg\njk"));
    }

    #[test]
    fn search_finds_matches_across_history() {
        let mut g = Grid::new(16, 2);
        for line in ["alpha", "beta", "ALPHA", "gamma"] {
            for c in line.chars() {
                g.print(c);
            }
            g.carriage_return();
            g.line_feed();
        }
        // Case-insensitive (no uppercase in query) matches both alphas.
        g.set_search("alpha");
        assert_eq!(g.search_count(), (2, 2)); // focus starts on the latest hit
        let spans0 = g.search_spans_on(0);
        assert_eq!(spans0, vec![(0, 4, false)]);
        // Smart case: an uppercase letter restricts to the exact-case hit.
        g.set_search("ALPHA");
        assert_eq!(g.search_count(), (1, 1));
        assert_eq!(g.search_spans_on(2), vec![(0, 4, true)]);
        // Stepping wraps and the no-match query reports zero.
        g.set_search("zzz");
        assert_eq!(g.search_count(), (0, 0));
        assert_eq!(g.search_query(), Some("zzz"));
        g.clear_search();
        assert_eq!(g.search_query(), None);
    }

    #[test]
    fn reflow_rewraps_a_wrapped_paragraph() {
        let mut g = Grid::new(4, 3);
        for c in "abcdefgh".chars() {
            g.print(c); // wraps: "abcd" | "efgh" | (cursor parked)
        }
        // Widen: the two wrapped rows rejoin into one logical line.
        g.resize(8, 3);
        assert_eq!(g.row_text(0), "abcdefgh");
        assert_eq!(g.cursor(), (7, 0)); // cursor follows the content end
        // Narrow back: it rewraps to the smaller width without losing text.
        g.resize(4, 3);
        assert_eq!(g.row_text(0), "abcd");
        assert_eq!(g.row_text(1), "efgh");
    }

    #[test]
    fn reflow_preserves_hard_breaks() {
        let mut g = Grid::new(10, 3);
        for c in "one".chars() {
            g.print(c);
        }
        g.carriage_return();
        g.line_feed();
        for c in "two".chars() {
            g.print(c);
        }
        // A hard newline must not be rejoined when the width changes.
        g.resize(6, 3);
        assert_eq!(g.row_text(0), "one");
        assert_eq!(g.row_text(1), "two");
    }

    #[test]
    fn scroll_region_limits_line_feed() {
        let mut g = Grid::new(4, 4);
        g.set_scroll_region(1, 2);
        g.move_to(0, 2); // bottom of region (origin off: absolute row 2)
        g.print('x');
        g.move_to(0, 2);
        g.line_feed(); // at region bottom: scroll [1,2] up, x moves to row 1
        assert_eq!(g.row_text(1), "x");
        assert_eq!(g.row_text(2), "");
    }
}