path: root/main.zig

const std = @import("std");
const vaxis = @import("vaxis");
const ghostty_vt = @import("ghostty-vt");
const Term = @import("term.zig");

extern "c" fn forkpty(
    amaster: *c_int,
    name: ?[*:0]u8,
    termp: ?*const anyopaque,
    winp: ?*const std.posix.winsize,
) c_int;

// execv, not execvp: no PATH search means no malloc in the child, so it's
// async-signal-safe and survives being forked from a multithreaded process.
extern "c" fn execv(
    path: [*:0]const u8,
    argv: [*:null]const ?[*:0]const u8,
) c_int;

extern "c" fn _exit(status: c_int) noreturn;

// basic file navigation
// basic shell io
// acme-style layout: columns split horizontally, windows stacked in each column.
// * /home/goblin/05-genizah/plan9port/src/cmd/acme
// right click and enter on lines to open files at specified lines

const PtyRead = struct { id: usize, bytes: []u8 };

pub const Command = struct {
    prev: ?*Command = null,
    pub var value: union(enum) {
        close,
        ping,
        nop,
        quit,
        tick,
        key_press: vaxis.Key,
        pty_read: PtyRead,
        pty_eof: usize,
        winsize: vaxis.Winsize,
        mouse: vaxis.Mouse,
    } = .nop;
};

const Loop = vaxis.Loop(@TypeOf(Command.value));

// layout constants
const GUTTER: u16 = 2; // left gutter: box (top) + scrollbar (below) per pane
const BOX_H: u16 = 1; // rows of the drag/rearrange box; scrollbar starts below it
const MINW: u16 = 10; // min pane width  (cells)
const MINH: u16 = 3; // min pane height (cells)
const MAX_TERMS: usize = 16;
const MAX_COLS: usize = 6;

const Rect = struct { x: u16, y: u16, w: u16, h: u16 };

// acme model: columns own X (col_weight), windows own Y (Term.vweight). The
// per-column ordered list `col_terms[c][0..col_n[c]]` is the source of truth.
const Layout = struct {
    ncol: usize,
    col_weight: [MAX_COLS]f32,
    col_terms: [MAX_COLS][MAX_TERMS]usize,
    col_n: [MAX_COLS]usize,
};

const Drag = union(enum) {
    none,
    border_v: struct { left_col: usize, cur_x: u16 },
    border_h: struct { col: usize, top_idx: usize, cur_y: u16 },
    move: struct { id: usize, cur_x: u16, cur_y: u16 },
    select: struct { id: usize, button: Button },
};

// mouse button driving a selection; also indexes Term.sel / SEL_BG / SEL_FG.
const Button = enum { left, middle, right };

// highlight colors per button (left, middle, right)
const SEL_BG = [3]u8{ 4, 2, 5 }; // blue, green, magenta
const SEL_FG = [3]u8{ 7, 0, 7 }; // readable text on the highlight

fn fork_pty(argv: [:0]const u8, ws: std.posix.winsize) std.Io.File {
    var master: c_int = undefined;
    const pid = forkpty(&master, null, null, &ws);
    if (pid == 0) {
        const child_argv = [_:null]?[*:0]const u8{ argv.ptr, null };
        _ = execv(argv.ptr, &child_argv);
        _exit(127);
    }
    return .{ .handle = master, .flags = .{ .nonblocking = false } };
}

// TIOCSWINSZ: set the pty size; the kernel raises SIGWINCH in the child so it
// (and anything running in it) reflows to the new grid.
fn pty_set_size(pty: std.Io.File, rows: u16, cols: u16) void {
    const ws: std.posix.winsize = .{ .row = rows, .col = cols, .xpixel = 0, .ypixel = 0 };
    _ = std.posix.system.ioctl(pty.handle, std.posix.T.IOCSWINSZ, @intFromPtr(&ws));
}

// One reader task per terminal. Tags each chunk with the terminal's slot id so
// the main loop knows which emulator to feed; posts pty_eof when the shell exits.
fn readPty(io: std.Io, gpa: std.mem.Allocator, pty: std.Io.File, id: usize, loop: *Loop) anyerror!void {
    var read_buf: [0x1000]u8 = undefined;
    var reader = pty.readerStreaming(io, &read_buf);
    while (true) {
        var buf: [0x1000]u8 = undefined;
        var vec = [_][]u8{&buf};
        const n = reader.interface.readVec(&vec) catch break;
        if (n == 0) break;
        const bytes = try gpa.dupe(u8, buf[0..n]);
        loop.postEvent(.{ .pty_read = .{ .id = id, .bytes = bytes } }) catch {
            gpa.free(bytes);
            break;
        };
    }
    loop.postEvent(.{ .pty_eof = id }) catch {};
}

// fork the pty + boot the emulator. Forking is the dangerous part in a
// multithreaded process, so this does NOT start the reader task (no new
// threads) — call startReader once the term is wired in.
fn forkTerm(gpa: std.mem.Allocator, init_cols: u16, init_rows: u16) !*Term {
    const pty = fork_pty("/usr/bin/bash", .{ .row = init_rows, .col = init_cols, .xpixel = 0, .ypixel = 0 });
    const t = try gpa.create(Term);
    errdefer gpa.destroy(t);
    t.* = .{
        .pty = pty,
        .term = try ghostty_vt.Terminal.init(gpa, .{ .cols = init_cols, .rows = init_rows }),
        .stream = undefined,
        .reader = .{ .any_future = null, .result = {} }, // no-op until startReader
        .cols = init_cols,
        .rows = init_rows,
    };
    t.stream = t.term.vtStream();
    return t;
}

fn startReader(io: std.Io, gpa: std.mem.Allocator, loop: *Loop, t: *Term, id: usize) !void {
    t.reader = try io.concurrent(readPty, .{ io, gpa, t.pty, id, loop });
}

// ---- layout surgery over the per-column ordered lists ----

fn layoutFindTerm(l: *const Layout, id: usize) ?struct { col: usize, idx: usize } {
    var c: usize = 0;
    while (c < l.ncol) : (c += 1) {
        var k: usize = 0;
        while (k < l.col_n[c]) : (k += 1) {
            if (l.col_terms[c][k] == id) return .{ .col = c, .idx = k };
        }
    }
    return null;
}

fn layoutRemove(l: *Layout, id: usize) void {
    const f = layoutFindTerm(l, id) orelse return;
    const c = f.col;
    var k = f.idx;
    while (k + 1 < l.col_n[c]) : (k += 1) l.col_terms[c][k] = l.col_terms[c][k + 1];
    l.col_n[c] -= 1;
    if (l.col_n[c] == 0) {
        var j = c;
        while (j + 1 < l.ncol) : (j += 1) {
            l.col_terms[j] = l.col_terms[j + 1];
            l.col_n[j] = l.col_n[j + 1];
            l.col_weight[j] = l.col_weight[j + 1];
        }
        l.ncol -= 1;
    }
}

fn layoutInsert(l: *Layout, c: usize, idx: usize, id: usize) void {
    var k = l.col_n[c];
    while (k > idx) : (k -= 1) l.col_terms[c][k] = l.col_terms[c][k - 1];
    l.col_terms[c][idx] = id;
    l.col_n[c] += 1;
}

fn layoutAppendColumn(l: *Layout, id: usize) void {
    if (l.ncol >= MAX_COLS) return;
    const c = l.ncol;
    l.col_weight[c] = 1;
    l.col_terms[c][0] = id;
    l.col_n[c] = 1;
    l.ncol += 1;
}

// Tile the screen: columns by col_weight, then each column's windows by vweight.
// Last column/window absorbs rounding so the tiling always fills the screen.
// `out_*` written for every live term and live column.
fn computeGeom(
    l: *const Layout,
    terms: *const [MAX_TERMS]?*Term,
    sw: u16,
    sh: u16,
    rects: *[MAX_TERMS]Rect,
    col_x: *[MAX_COLS]u16,
    col_w: *[MAX_COLS]u16,
) void {
    if (l.ncol == 0) return;
    var wsum: f32 = 0;
    for (0..l.ncol) |c| wsum += l.col_weight[c];
    if (wsum <= 0) wsum = 1;
    const sep_cols: u16 = @intCast(l.ncol - 1);
    const avail_w: u16 = sw -| sep_cols;

    var x: u16 = 0;
    for (0..l.ncol) |c| {
        const last = (c + 1 == l.ncol);
        const cw: u16 = if (last) (sw -| x) else @max(1, @as(u16, @intFromFloat(@round(@as(f32, @floatFromInt(avail_w)) * l.col_weight[c] / wsum))));
        col_x[c] = x;
        col_w[c] = cw;

        const n = l.col_n[c];
        var vsum: f32 = 0;
        for (0..n) |k| {
            if (terms[l.col_terms[c][k]]) |t| vsum += t.vweight;
        }
        if (vsum <= 0) vsum = 1;
        const sep_rows: u16 = if (n > 0) @intCast(n - 1) else 0;
        const avail_h: u16 = sh -| sep_rows;

        var y: u16 = 0;
        for (0..n) |k| {
            const id = l.col_terms[c][k];
            const t = terms[id] orelse continue;
            const lastk = (k + 1 == n);
            const ch: u16 = if (lastk) (sh -| y) else @max(1, @as(u16, @intFromFloat(@round(@as(f32, @floatFromInt(avail_h)) * t.vweight / vsum))));
            rects[id] = .{ .x = x, .y = y, .w = cw, .h = ch };
            y +|= ch + 1;
        }
        x +|= cw + 1;
    }
}

// `alloc` must be a per-frame arena, NOT freed before vx.render(): vaxis is a
// retained renderer and stores each cell's grapheme as a *slice* into the text
// we hand it, so plainString has to outlive the render call.
fn renderPane(root: vaxis.Window, alloc: std.mem.Allocator, t: *Term, r: Rect, active: bool) !void {
    if (r.w <= GUTTER or r.h == 0) return;

    // text
    const text = root.child(.{ .x_off = r.x + GUTTER, .y_off = r.y, .width = r.w - GUTTER, .height = r.h });
    text.clear();
    const tty_str = try t.term.plainString(alloc);
    const off: i32 = @intCast(t.term.screens.active.pages.scrollbar().offset);
    var it = std.mem.splitAny(u8, tty_str, "\n");
    var i: u16 = 0;
    while (it.next()) |line| : (i += 1) {
        _ = text.printSegment(.{ .text = line }, .{ .row_offset = i });
    }

    // recolor selected cells, one pass per button — later buttons win on overlap.
    // only while actively dragging; a released selection is no longer drawn.
    for (t.sel, 0..) |sl, b| {
        if (sl.state != .dragging) continue;
        const r0 = @min(sl.r0, sl.r1);
        const r1 = @max(sl.r0, sl.r1);
        const c0 = @max(0, @min(sl.c0, sl.c1));
        const c1 = @max(0, @max(sl.c0, sl.c1));
        var row: u16 = 0;
        while (row < r.h) : (row += 1) {
            const j = @as(i32, row) + off;
            if (j < r0 or j > r1) continue;
            var col: i32 = c0;
            while (col <= c1 and col < @as(i32, r.w - GUTTER)) : (col += 1) {
                const cc: u16 = @intCast(col);
                if (text.readCell(cc, row)) |cell| {
                    var nc = cell;
                    nc.default = false; // else vaxis ignores the style on cleared cells
                    nc.style.bg = .{ .index = SEL_BG[b] };
                    nc.style.fg = .{ .index = SEL_FG[b] };
                    text.writeCell(cc, row, nc);
                }
            }
        }
    }
    if (active) text.showCursor(t.term.screens.active.cursor.x, t.term.screens.active.cursor.y);

    // gutter: box (the drag/rearrange handle) on top, scrollbar below
    const gut = root.child(.{ .x_off = r.x, .y_off = r.y, .width = GUTTER, .height = r.h });
    const box_bg: u8 = if (active) 4 else 8;
    var bx: u16 = 0;
    while (bx < GUTTER) : (bx += 1) {
        var by: u16 = 0;
        while (by < BOX_H) : (by += 1)
            gut.writeCell(bx, by, .{ .char = .{ .grapheme = " " }, .style = .{ .bg = .{ .index = box_bg } } });
    }
    const sb = t.term.screens.active.pages.scrollbar();
    const track_h: usize = if (r.h > BOX_H) r.h - BOX_H else 0;
    if (track_h > 0) {
        const total: usize = if (sb.total == 0) 1 else sb.total;
        const pos = (track_h * sb.offset) / total;
        const len = @max(1, (track_h * sb.len) / total);
        var gy: usize = 0;
        while (gy < track_h) : (gy += 1) {
            const thumb = gy >= pos and gy < pos + len;
            const st_bg: u8 = if (thumb) 6 else 8;
            var cx: u16 = 0;
            while (cx < GUTTER) : (cx += 1)
                gut.writeCell(cx, @intCast(BOX_H + gy), .{ .char = .{ .grapheme = " " }, .style = .{ .bg = .{ .index = st_bg } } });
        }
    }
}

pub fn main(init: std.process.Init) !void {
    const io = init.io;
    const gpa = init.gpa;

    var screen_w: u16 = 80;
    var screen_h: u16 = 24;
    var resize_count: usize = 0;

    // per-frame scratch for plainString; reset (not freed) after each render so
    // the retained vaxis screen can keep referencing it through vx.render().
    var frame_arena: std.heap.ArenaAllocator = .init(gpa);
    defer frame_arena.deinit();
    var ov_buf: [128]u8 = undefined; // overlay text; must outlive each vx.render()

    var tty_buf: [0x10000]u8 = undefined;
    var tty = try vaxis.Tty.init(io, &tty_buf);

    var vx = try vaxis.init(io, gpa, init.environ_map, .{});
    defer vx.deinit(gpa, tty.writer());

    try vx.setMouseMode(tty.writer(), true);
    try vx.enterAltScreen(tty.writer());
    defer vx.exitAltScreen(tty.writer()) catch {};

    // ---- terminals + layout ----
    var terms: [MAX_TERMS]?*Term = @splat(null);
    defer for (&terms) |*slot| {
        if (slot.*) |t| {
            t.deinit(io, gpa);
            gpa.destroy(t);
            slot.* = null;
        }
    };

    var layout: Layout = .{
        .ncol = 0,
        .col_weight = @splat(1),
        .col_terms = undefined,
        .col_n = @splat(0),
    };

    // Fork the initial terminals BEFORE starting any io worker thread. forkpty
    // from a multithreaded process can leave the child wedged before exec; doing
    // it while still single-threaded avoids that. (initial: two columns, the
    // left one split into two windows.)
    terms[0] = try forkTerm(gpa, screen_w, screen_h);
    terms[1] = try forkTerm(gpa, screen_w, screen_h);
    terms[2] = try forkTerm(gpa, screen_w, screen_h);
    layout.ncol = 2;
    layout.col_n[0] = 2;
    layout.col_terms[0][0] = 0;
    layout.col_terms[0][1] = 1;
    layout.col_n[1] = 1;
    layout.col_terms[1][0] = 2;
    var active: usize = 0;

    var loop: Loop = .init(io, &tty, &vx);
    try loop.start();
    defer loop.stop();
    try loop.installResizeHandler();

    // now safe to spawn the per-terminal reader tasks (no forking here)
    for (&terms, 0..) |*slot, id| {
        if (slot.*) |t| try startReader(io, gpa, &loop, t, id);
    }

    var rects: [MAX_TERMS]Rect = undefined;
    var col_x: [MAX_COLS]u16 = undefined;
    var col_w: [MAX_COLS]u16 = undefined;
    computeGeom(&layout, &terms, screen_w, screen_h, &rects, &col_x, &col_w);

    var drag: Drag = .none;

    while (true) {
        const event = try loop.nextEvent();
        switch (event) {
            .mouse => |mouse| {
                const mcol: u16 = if (mouse.col < 0) 0 else @min(@as(u16, @intCast(mouse.col)), screen_w -| 1);
                const mrow: u16 = if (mouse.row < 0) 0 else @min(@as(u16, @intCast(mouse.row)), screen_h -| 1);

                // which pane is under the cursor (if any)
                const hovered: ?usize = for (terms, 0..) |slot, i| {
                    if (slot == null) continue;
                    const r = rects[i];
                    if (mcol >= r.x and mcol < r.x + r.w and mrow >= r.y and mrow < r.y + r.h) break i;
                } else null;

                if (mouse.button == .wheel_down) {
                    if (hovered) |id| terms[id].?.term.screens.active.scroll(.{ .delta_row = 1 });
                } else if (mouse.button == .wheel_up) {
                    if (hovered) |id| terms[id].?.term.screens.active.scroll(.{ .delta_row = -1 });
                } else if (mouse.type == .press and mouse.button == .left) {
                    var handled = false;

                    // vertical separator (between columns)?
                    var c: usize = 0;
                    while (c + 1 < layout.ncol and !handled) : (c += 1) {
                        if (mcol == col_x[c] + col_w[c]) {
                            drag = .{ .border_v = .{ .left_col = c, .cur_x = mcol } };
                            handled = true;
                        }
                    }

                    // horizontal separator (between stacked windows)?
                    if (!handled) {
                        var cc: usize = 0;
                        outer: while (cc < layout.ncol) : (cc += 1) {
                            if (mcol < col_x[cc] or mcol >= col_x[cc] + col_w[cc]) continue;
                            var k: usize = 0;
                            while (k + 1 < layout.col_n[cc]) : (k += 1) {
                                const id = layout.col_terms[cc][k];
                                const r = rects[id];
                                if (mrow == r.y + r.h) {
                                    drag = .{ .border_h = .{ .col = cc, .top_idx = k, .cur_y = mrow } };
                                    handled = true;
                                    break :outer;
                                }
                            }
                        }
                    }

                    // inside a pane?
                    if (!handled) {
                        if (hovered) |id| {
                            const r = rects[id];
                            const in_gutter = mcol < r.x + GUTTER;
                            if (in_gutter and mrow < r.y + BOX_H) {
                                drag = .{ .move = .{ .id = id, .cur_x = mcol, .cur_y = mrow } };
                            } else if (in_gutter) {
                                active = id;
                                if (terms[id]) |t| {
                                    const local: i16 = @intCast(@as(i32, mrow) - @as(i32, r.y + BOX_H));
                                    t.term.screens.active.scroll(.{ .delta_row = -local });
                                }
                            } else {
                                active = id;
                                if (terms[id]) |t| {
                                    const textx = r.x + GUTTER;
                                    const off: i32 = @intCast(t.term.screens.active.pages.scrollbar().offset);
                                    t.sel[@intFromEnum(Button.left)] = .{
                                        .state = .dragging,
                                        .c0 = @as(i32, mcol) - @as(i32, textx),
                                        .r0 = (@as(i32, mrow) - @as(i32, r.y)) + off,
                                        .c1 = @as(i32, mcol) - @as(i32, textx),
                                        .r1 = (@as(i32, mrow) - @as(i32, r.y)) + off,
                                    };
                                    drag = .{ .select = .{ .id = id, .button = .left } };
                                }
                            }
                        }
                    }
                } else if (mouse.type == .press and (mouse.button == .middle or mouse.button == .right)) {
                    // middle/right select text too (own state + color), text area only
                    const b: Button = if (mouse.button == .middle) .middle else .right;
                    if (hovered) |id| {
                        const r = rects[id];
                        if (mcol >= r.x + GUTTER) {
                            active = id;
                            if (terms[id]) |t| {
                                const textx = r.x + GUTTER;
                                const off: i32 = @intCast(t.term.screens.active.pages.scrollbar().offset);
                                t.sel[@intFromEnum(b)] = .{
                                    .state = .dragging,
                                    .c0 = @as(i32, mcol) - @as(i32, textx),
                                    .r0 = (@as(i32, mrow) - @as(i32, r.y)) + off,
                                    .c1 = @as(i32, mcol) - @as(i32, textx),
                                    .r1 = (@as(i32, mrow) - @as(i32, r.y)) + off,
                                };
                                drag = .{ .select = .{ .id = id, .button = b } };
                            }
                        }
                    }
                } else if (mouse.type == .drag) {
                    switch (drag) {
                        .border_v => |*d| {
                            const c = d.left_col;
                            if (c + 1 < layout.ncol) {
                                const lo = col_x[c] + MINW;
                                const hi = col_x[c] +| col_w[c] +| col_w[c + 1] -| MINW;
                                d.cur_x = if (lo <= hi) std.math.clamp(mcol, lo, hi) else mcol;
                            } else d.cur_x = mcol;
                        },
                        .border_h => |*d| {
                            const cc = d.col;
                            const k = d.top_idx;
                            if (k + 1 < layout.col_n[cc]) {
                                const a = layout.col_terms[cc][k];
                                const b = layout.col_terms[cc][k + 1];
                                const lo = rects[a].y + MINH;
                                const hi = rects[a].y +| rects[a].h +| rects[b].h -| MINH;
                                d.cur_y = if (lo <= hi) std.math.clamp(mrow, lo, hi) else mrow;
                            } else d.cur_y = mrow;
                        },
                        .move => |*d| {
                            d.cur_x = mcol;
                            d.cur_y = mrow;
                        },
                        .select => |s| {
                            if (terms[s.id]) |t| {
                                const r = rects[s.id];
                                const textx = r.x + GUTTER;
                                const off: i32 = @intCast(t.term.screens.active.pages.scrollbar().offset);
                                t.sel[@intFromEnum(s.button)].c1 = @as(i32, mcol) - @as(i32, textx);
                                t.sel[@intFromEnum(s.button)].r1 = (@as(i32, mrow) - @as(i32, r.y)) + off;
                            }
                        },
                        .none => {},
                    }
                } else if (mouse.type == .release) {
                    switch (drag) {
                        .border_v => |d| {
                            const c = d.left_col;
                            if (c + 1 < layout.ncol) {
                                const combined: f32 = @floatFromInt(col_w[c] + col_w[c + 1]);
                                var nl: f32 = @floatFromInt(d.cur_x -| col_x[c]);
                                const minw: f32 = MINW;
                                nl = std.math.clamp(nl, minw, @max(minw, combined - minw));
                                const pair = layout.col_weight[c] + layout.col_weight[c + 1];
                                layout.col_weight[c] = pair * (nl / combined);
                                layout.col_weight[c + 1] = pair - layout.col_weight[c];
                            }
                        },
                        .border_h => |d| {
                            const c = d.col;
                            const k = d.top_idx;
                            if (k + 1 < layout.col_n[c]) {
                                const a = layout.col_terms[c][k];
                                const b = layout.col_terms[c][k + 1];
                                if (terms[a]) |ta| if (terms[b]) |tb| {
                                    const combined: f32 = @floatFromInt(rects[a].h + rects[b].h);
                                    var nt: f32 = @floatFromInt(d.cur_y -| rects[a].y);
                                    const minh: f32 = MINH;
                                    nt = std.math.clamp(nt, minh, @max(minh, combined - minh));
                                    const pair = ta.vweight + tb.vweight;
                                    ta.vweight = pair * (nt / combined);
                                    tb.vweight = pair - ta.vweight;
                                };
                            }
                        },
                        .move => |d| moveTerm(&layout, &rects, &col_x, &col_w, d.id, d.cur_x, d.cur_y),
                        .select => |s| {
                            if (terms[s.id]) |t| {
                                t.sel[@intFromEnum(s.button)].state = .done;
                                if (selectionText(gpa, t, t.sel[@intFromEnum(s.button)])) |txt| {
                                    defer gpa.free(txt);
                                    onSelect(s.button, txt);
                                } else |_| {}
                            }
                        },
                        .none => {},
                    }
                    drag = .none;
                }
            },
            .key_press => |key| {
                if (key.matches('c', .{ .ctrl = true })) break;

                if (terms[active]) |at| {
                    if (key.matches('n', .{ .alt = true })) {
                        // new terminal below the active one, in its column.
                        // ponytail: forks from the now-multithreaded process;
                        // execv (not execvp) keeps the child async-signal-safe.
                        const free_slot: ?usize = for (terms, 0..) |s, i| {
                            if (s == null) break i;
                        } else null;
                        if (free_slot) |slot| {
                            if (forkTerm(gpa, screen_w, screen_h)) |nt| {
                                terms[slot] = nt;
                                startReader(io, gpa, &loop, nt, slot) catch {};
                                const f = layoutFindTerm(&layout, active).?;
                                layoutInsert(&layout, f.col, f.idx + 1, slot);
                                active = slot;
                            } else |_| {}
                        }
                    } else if (key.matches('c', .{ .alt = true })) {
                        // move active terminal into a fresh column
                        const f = layoutFindTerm(&layout, active).?;
                        if (layout.ncol < MAX_COLS and layout.col_n[f.col] > 1) {
                            layoutRemove(&layout, active);
                            layoutAppendColumn(&layout, active);
                        }
                    } else if (key.matches('d', .{ .ctrl = true })) {
                        at.term.screens.active.scroll(.{ .delta_row = 15 });
                    } else if (key.matches('u', .{ .ctrl = true })) {
                        at.term.screens.active.scroll(.{ .delta_row = -15 });
                    } else {
                        const bytes: ?[]const u8 = if (key.text) |text| text else switch (key.codepoint) {
                            vaxis.Key.enter => "\r",
                            vaxis.Key.backspace => "\x7f",
                            vaxis.Key.tab => "\t",
                            vaxis.Key.escape => "\x1b",
                            vaxis.Key.up => "\x1b[A",
                            vaxis.Key.down => "\x1b[B",
                            vaxis.Key.right => "\x1b[C",
                            vaxis.Key.left => "\x1b[D",
                            else => null,
                        };
                        if (bytes) |b| {
                            // raw write straight to the pty master; a fresh
                            // File.Writer per keystroke doesn't reliably flush.
                            var off: usize = 0;
                            while (off < b.len) {
                                const rc = std.os.linux.write(at.pty.handle, b[off..].ptr, b.len - off);
                                switch (std.posix.errno(rc)) {
                                    .SUCCESS => off += @intCast(rc),
                                    .INTR => {},
                                    else => break,
                                }
                            }
                        }
                    }
                }
            },
            .pty_read => |pr| {
                defer gpa.free(pr.bytes);
                if (terms[pr.id]) |t| t.stream.nextSlice(pr.bytes);
            },
            .pty_eof => |id| {
                if (terms[id]) |t| {
                    layoutRemove(&layout, id);
                    t.deinit(io, gpa);
                    gpa.destroy(t);
                    terms[id] = null;
                    // refocus the first surviving terminal; quit if none remain.
                    if (active == id) active = for (terms, 0..) |s, i| {
                        if (s != null) break i;
                    } else break;
                }
            },
            .winsize => |ws| {
                resize_count += 1;
                screen_w = ws.cols;
                screen_h = ws.rows;
                try vx.resize(gpa, tty.writer(), ws);
            },
            .quit => break,
            else => {},
        }

        // recompute geometry from the (possibly mutated) layout, then push any
        // grid-size change to each emulator + pty. Weights only change on a drag
        // *release*, so mid-drag the rects are unchanged and nothing resizes.
        computeGeom(&layout, &terms, screen_w, screen_h, &rects, &col_x, &col_w);
        for (&terms, 0..) |*slot, id| {
            if (slot.*) |t| {
                const r = rects[id];
                const cols = @max(1, r.w -| GUTTER);
                const rows = @max(1, r.h);
                if (cols != t.cols or rows != t.rows) {
                    t.term.resize(gpa, cols, rows) catch {};
                    pty_set_size(t.pty, rows, cols);
                    t.cols = cols;
                    t.rows = rows;
                }
            }
        }

        // ---- render ----
        const win = vx.window();
        win.clear();

        for (&terms, 0..) |*slot, id| {
            if (slot.*) |t| try renderPane(win, frame_arena.allocator(), t, rects[id], id == active);
        }

        // separators (the grips signal that borders are draggable)
        for (0..layout.ncol) |c| {
            if (c + 1 < layout.ncol) {
                const sx = col_x[c] + col_w[c];
                const mid = screen_h / 2;
                var ry: u16 = 0;
                while (ry < screen_h) : (ry += 1) {
                    const g: []const u8 = if (ry == mid) "⇔" else "│";
                    win.writeCell(sx, ry, .{ .char = .{ .grapheme = g }, .style = .{ .fg = .{ .index = 5 } } });
                }
            }
            const n = layout.col_n[c];
            var k: usize = 0;
            while (k + 1 < n) : (k += 1) {
                const r = rects[layout.col_terms[c][k]];
                const sy = r.y + r.h;
                const midx = col_x[c] + col_w[c] / 2;
                var rx: u16 = col_x[c];
                while (rx < col_x[c] + col_w[c]) : (rx += 1) {
                    const g: []const u8 = if (rx == midx) "⇕" else "─";
                    win.writeCell(rx, sy, .{ .char = .{ .grapheme = g }, .style = .{ .fg = .{ .index = 5 } } });
                }
            }
        }

        // dashed preview while dragging; commit happens on release.
        switch (drag) {
            .border_v => |d| {
                var ry: u16 = 0;
                while (ry < screen_h) : (ry += 1)
                    win.writeCell(d.cur_x, ry, .{ .char = .{ .grapheme = "╎" }, .style = .{ .fg = .{ .index = 3 } } });
            },
            .border_h => |d| {
                const c = d.col;
                var rx: u16 = col_x[c];
                while (rx < col_x[c] + col_w[c]) : (rx += 1)
                    win.writeCell(rx, d.cur_y, .{ .char = .{ .grapheme = "╌" }, .style = .{ .fg = .{ .index = 3 } } });
            },
            .move => |d| {
                // insertion indicator: dashed line at cur_y across the target column
                var tc: usize = if (layout.ncol > 0) layout.ncol - 1 else 0;
                for (0..layout.ncol) |c| {
                    if (d.cur_x >= col_x[c] and d.cur_x < col_x[c] + col_w[c]) {
                        tc = c;
                        break;
                    }
                }
                var rx: u16 = col_x[tc];
                while (rx < col_x[tc] + col_w[tc]) : (rx += 1)
                    win.writeCell(rx, d.cur_y, .{ .char = .{ .grapheme = "╌" }, .style = .{ .fg = .{ .index = 2 } } });
                win.writeCell(d.cur_x, d.cur_y, .{ .char = .{ .grapheme = "▌" }, .style = .{ .fg = .{ .index = 2 } } });
            },
            else => {},
        }

        // debug overlay: a small virtual-text box drawn last, on top of everything.
        // ov_buf lives across vx.render() — vaxis keeps slices into it (retained).
        if (terms[active]) |at| {
            var nlive: usize = 0;
            for (terms) |slot| {
                if (slot != null) nlive += 1;
            }
            const sb = at.term.screens.active.pages.scrollbar();
            const s = std.fmt.bufPrint(
                &ov_buf,
                "pardes  resizes={d}\nterms {d}  cols {d}\nactive #{d}  {d}x{d}\nscroll {d}/{d}",
                .{ resize_count, nlive, layout.ncol, active, at.cols, at.rows, sb.offset, sb.total },
            ) catch "";
            const ow: u16 = 26;
            const oh: u16 = 6;
            const ox: u16 = if (screen_w > ow) screen_w - ow else 0;
            const ov = win.child(.{ .x_off = ox, .y_off = 0, .width = ow, .height = oh, .border = .{ .where = .all } });
            ov.fill(.{ .char = .{ .grapheme = " " }, .style = .{ .bg = .{ .index = 0 } } });
            _ = ov.printSegment(.{ .text = s, .style = .{ .fg = .{ .index = 3 } } }, .{});
        }

        try vx.render(tty.writer());
        _ = frame_arena.reset(.retain_capacity);
    }
}

// On box-drag release: drop the window into the column under cur_x at the
// vertical slot picked by cur_y (acme's coldragwin, minus the live retile).
fn moveTerm(
    l: *Layout,
    rects: *const [MAX_TERMS]Rect,
    col_x: *const [MAX_COLS]u16,
    col_w: *const [MAX_COLS]u16,
    id: usize,
    cur_x: u16,
    cur_y: u16,
) void {
    const src = layoutFindTerm(l, id) orelse return;
    // target column under cur_x (last column absorbs anything past the right edge)
    var tc: usize = if (l.ncol > 0) l.ncol - 1 else 0;
    for (0..l.ncol) |c| {
        if (cur_x >= col_x[c] and cur_x < col_x[c] + col_w[c]) {
            tc = c;
            break;
        }
    }

    // insertion index in the target column, ignoring the moving window itself
    var ti: usize = 0;
    var k: usize = 0;
    while (k < l.col_n[tc]) : (k += 1) {
        const cid = l.col_terms[tc][k];
        if (cid == id) continue;
        const rr = rects[cid];
        if (cur_y < rr.y + rr.h / 2) break;
        ti += 1;
    }

    const src_solo = l.col_n[src.col] == 1;
    if (tc == src.col and src_solo) return; // dragging the only window of its column: nothing to do

    layoutRemove(l, id);
    if (src_solo and src.col < tc) tc -= 1; // removing src dropped a column to our left
    if (tc >= l.ncol) tc = l.ncol - 1;
    if (ti > l.col_n[tc]) ti = l.col_n[tc];
    layoutInsert(l, tc, ti, id);
}

// Build the block-selected text, newline-joined per row; caller frees.
fn selectionText(gpa: std.mem.Allocator, t: *Term, sl: Term.Sel) ![]u8 {
    const off: i32 = @intCast(t.term.screens.active.pages.scrollbar().offset);
    const r0 = @min(sl.r0, sl.r1);
    const r1 = @max(sl.r0, sl.r1);
    const c0: usize = @intCast(@max(0, @min(sl.c0, sl.c1)));
    const c1: usize = @intCast(@max(0, @max(sl.c0, sl.c1)));
    const ps = try t.term.plainString(gpa);
    defer gpa.free(ps);
    var out: std.ArrayList(u8) = .empty;
    errdefer out.deinit(gpa);
    var it = std.mem.splitAny(u8, ps, "\n");
    var i: i32 = 0;
    var first = true;
    while (it.next()) |line| : (i += 1) {
        const j = i + off;
        if (j < r0 or j > r1) continue;
        if (!first) try out.append(gpa, '\n');
        first = false;
        const b0 = @min(c0, line.len);
        const b1 = @min(c1 + 1, line.len);
        try out.appendSlice(gpa, line[b0..b1]);
    }
    return out.toOwnedSlice(gpa);
}

// Empty selection callback; receives the button and the selected text slice.
// Fill in per-button behaviour later (acme: left=snarf, middle=execute, right=look).
fn onSelect(button: Button, text: []const u8) void {
    _ = button;
    _ = text;
}