//! The message row: messages and statuses a pane shows between its body and
//! its tagline, how each line falls in, lingers and dissolves, the notices
//! built from them every frame, and the log of everything said.
const pardes = @import("pardes.zig");
const memory = @import("memory.zig");
const std = @import("std");
const layout = @import("layout.zig");
const animation = @import("animation.zig");
const ctlfs = @import("ninep/tree.zig");
const panes = @import("panes.zig");
const CellStyle = @import("surface.zig").CellStyle;
const Surface = @import("surface.zig").Surface;
const limits = memory.limits;
const config = @import("config.zig");
const platform = pardes.platform;
const Pane = panes.Pane;
const MAX_PANES = pardes.MAX_PANES;
const BOX_H = pardes.BOX_H;
const Key = pardes.Key;
const Rect = layout.Rect;
const Pardes = pardes.Pardes;

const Messages = @This();

/// The message-row log: a fixed ring, never allocated, never grown. See
/// `logMessage` and the `Messages` builtin.
log: [limits.message_log]LoggedMessage = @splat(.{}),
/// Next slot to write. `len` saturates at the ring's size.
head: usize = 0,
len: usize = 0,

pub const LoggedMessage = struct {
    pub const cap = 256;
    text: [cap]u8 = undefined,
    len: u16 = 0,
    /// The serial of the pane that said it, or 0 for none in particular. A
    /// serial, not a slot: slots are reused, so an old line would name
    /// whichever pane took the slot since.
    serial: u32 = 0,
    /// How many times in a row. Saturating: a key held down against the same
    /// refusal is one event, not four hundred.
    repeats: u16 = 0,

    pub fn slice(m: *const LoggedMessage) []const u8 {
        return m.text[0..m.len];
    }
};

/// `SPC` plus the chord keys typed so far, spaced out the way the help
/// index spells a leader path.
fn leaderText(p: *const Pardes, buf: *[16]u8) []const u8 {
    buf.* = @splat(' ');
    @memcpy(buf[0..3], "SPC");
    var at: usize = 3;
    for (p.leader_keys[0..p.leader_n]) |ch| {
        if (at + 2 > buf.len) break;
        buf[at + 1] = ch;
        at += 2;
    }
    return buf[0..at];
}

/// How wide a notice chip is, in grid columns: its own text plus a blank
/// cell either side. A notice is an OVERLAY over the body's top rows, not
/// a row taken from them, so it is sized to its message and never to the
/// pane. Counted in GRID columns rather than scaled into the tagline face
/// it is drawn in, because the canonical grid is what a terminal client
/// draws and a chip narrower than its own text there would clip it; the
/// tagline face simply leaves a little more room inside the chip.
pub fn noticeCols(p: *const Pardes, text: []const u8, limit: u16) u16 {
    _ = p;
    if (limit == 0) return 0;
    return @intCast(std.math.clamp(panes.File.displayWidth(text) + 2, 1, @as(usize, limit)));
}

const Printed = struct { left: u16, dropped: usize };

/// Prints `text` flush with the right edge of the band, and answers the
/// column it started at so a cursor can follow it. Text wider than the
/// band loses its HEAD: the end is the part that says something -- a
/// path's file name, an error's reason -- and `dropped` is how many
/// columns of it went.
pub fn printRight(s: *Surface, x: u16, row: u16, w: u16, text: []const u8, style: CellStyle) Printed {
    const width = panes.File.displayWidth(text);
    if (width <= w) {
        const left: u16 = @intCast(x + w - width);
        _ = s.print(left, row, @intCast(width), text, style);
        return .{ .left = left, .dropped = 0 };
    }
    // Whole glyphs only: a cut inside a wide one would leave the rest a
    // column too wide and clip its LAST glyph instead of the first.
    var dropped = width - w;
    var start = panes.File.rawAtDisplay(text, dropped);
    if (panes.File.rawDisplayCol(text, start) < dropped) {
        dropped += 1;
        start = panes.File.rawAtDisplay(text, dropped);
    }
    const left: u16 = @intCast(x + w - (width - dropped));
    _ = s.print(left, row, @intCast(width - dropped), text[start..], style);
    return .{ .left = left, .dropped = dropped };
}

pub const Message = struct {
    const libc = std.c;
    const Tm = extern struct {
        sec: c_int,
        min: c_int,
        hour: c_int,
        mday: c_int,
        mon: c_int,
        year: c_int,
        wday: c_int,
        yday: c_int,
        isdst: c_int,
        gmtoff: c_long,
        zone: ?[*:0]const u8,
    };
    extern "c" fn localtime_r(timep: *const libc.time_t, result: *Tm) ?*Tm;

    pub fn body(text: []const u8) []const u8 {
        if (text.len < 10) return text;
        if (text[2] != ':' or text[5] != ':' or text[8] != ' ' or text[9] != ' ') return text;
        for ([_]usize{ 0, 1, 3, 4, 6, 7 }) |i| {
            if (!std.ascii.isDigit(text[i]) and text[i] != '-') return text;
        }
        return text[10..];
    }

    pub fn stamp(buf: []u8, verb: []const u8, subject: []const u8) []const u8 {
        var clock: [8]u8 = "--:--:--".*;
        const notime = if (libc.getenv("PARDES_NOTIME")) |v| std.mem.span(v).len != 0 else false;
        if (!notime) {
            var ts: libc.timespec = undefined;
            _ = libc.clock_gettime(.REALTIME, &ts);
            const secs: libc.time_t = ts.sec;
            var tm: Tm = undefined;
            if (localtime_r(&secs, &tm) != null) {
                _ = std.fmt.bufPrint(&clock, "{d:0>2}:{d:0>2}:{d:0>2}", .{
                    @as(u32, @intCast(tm.hour)),
                    @as(u32, @intCast(tm.min)),
                    @as(u32, @intCast(tm.sec)),
                }) catch {};
            }
        }
        const head = std.fmt.bufPrint(buf, "{s}  {s} ", .{ &clock, verb }) catch return buf[0..0];
        const room = buf.len - head.len;
        const tail = if (subject.len <= room) subject else subject[subject.len - room ..];
        @memcpy(buf[head.len..][0..tail.len], tail);
        return buf[0 .. head.len + tail.len];
    }
};

/// A status updates the message line in place (a progress count does not
/// pile up); a message is an event, and stacks.
pub fn setStatus(p: *Pardes, id: usize, text: []const u8) void {
    showMessage(p, id, text, false);
}

pub fn setMessage(p: *Pardes, id: usize, text: []const u8) void {
    logMessage(p, id, text);
    showMessage(p, id, text, true);
}

fn showMessage(p: *Pardes, id: usize, text: []const u8, stack: bool) void {
    if (id >= MAX_PANES) return;
    const pane = p.panes[id] orelse return;
    // One row of printable text: a language server's multi-line report
    // reads as one line, and the cut never leaves half a glyph behind.
    var n: usize = @min(text.len, pane.msg.len);
    if (n < text.len) {
        while (n > 0 and text[n] & 0xC0 == 0x80) n -= 1;
    }
    const same = pane.msg_len == n and for (text[0..n], pane.msg[0..n]) |c, have| {
        if ((if (c < 0x20 or c == 0x7f) ' ' else c) != have) break false;
    } else true;
    // A new event moves the line on screen up the stack, where it keeps
    // its own timing, and falls in below it.
    // Only an event stacks on an event: an announcement or a status
    // stands in for whatever comes next.
    if (stack and pane.msg_len > 0 and !same and !pane.msg_announcement and !pane.msg_status)
        pane.pushOlderMessage();
    if (pane.msg_len == 0) pane.msg_slot = pane.freeMessageSlot();
    pane.msg_announcement = false;
    pane.msg_sent = false;
    pane.msg_status = !stack;
    const arrives = pane.msg_len == 0 or pane.msg_life.phase == .leaving;
    for (text[0..n], pane.msg[0..n]) |c, *cell| cell.* = if (c < 0x20 or c == 0x7f) ' ' else c;
    pane.msg_len = @intCast(n);
    pane.msg_said_ms = nowMs();
    p.needs_frame = true;
    if (arrives) {
        pane.msg_life = .{ .phase = if (p.settings.message_animation and n > 0) .entering else .shown };
    } else if (pane.msg_life.phase == .lingering or
        (pane.msg_life.phase == .entering and !p.settings.message_animation))
    {
        // The same line again, or a status update: fresh, so it stays.
        pane.msg_life = .{};
    } else {
        pane.msg_life.dismissed = false;
    }
}

fn nowMs() i64 {
    if (comptime !pardes.hosted) return 0;
    var ts: std.c.timespec = undefined;
    if (std.c.clock_gettime(.MONOTONIC, &ts) != 0) return 0;
    return @as(i64, ts.sec) * 1000 + @divTrunc(@as(i64, ts.nsec), 1_000_000);
}

/// With no frontend attached no input dismisses a message, and a detached
/// session's /screen and messages kept what was said an hour ago: each
/// pane's lines go once its newest has been up `message_linger_ms`, on the
/// clock, checked as the core is stepped and by the detached session's loop
/// between steps -- not as a 9P request is served, since a read is answered
/// while a step is out and must change nothing.
/// ponytail: a pane's older lines go with its newest, not each on its own
/// clock; the render pipeline's clock will give every line its own.
pub fn expireUnattended(p: *Pardes) void {
    if (!p.unattended) return;
    const now = nowMs();
    for (p.panes) |slot| {
        const pane = slot orelse continue;
        if (pane.msg_len == 0 and pane.msg_older_len == 0) continue;
        if (now - pane.msg_said_ms < p.settings.message_linger_ms) continue;
        pane.msg_len = 0;
        pane.msg_life = .{};
        pane.msg_older_len = 0;
        p.needs_frame = true;
    }
}

/// The key or click that used to clear the message row now starts each
/// line's exit: it stays `message_linger_ms`, then dissolves. A line
/// already on its way out keeps its own timing.
pub fn dismissMessage(p: *Pardes, pane: *Pane) void {
    if (pane.msg_len > 0 and dismissLine(p, &pane.msg_life)) {
        pane.msg_len = 0;
        pane.msg_life = .{};
    }
    var i: usize = 0;
    while (i < pane.msg_older_len) {
        if (dismissLine(p, &pane.msg_older[i].life)) pane.removeOlderMessage(i) else i += 1;
    }
}

/// Start one line's exit; true when it is gone at once (no linger, no
/// animation).
fn dismissLine(p: *const Pardes, life: *Pane.MessageLife) bool {
    switch (life.phase) {
        .lingering, .leaving => return false,
        // A falling line lands first, then lingers -- unless falling was
        // just turned off, and nothing will land it.
        .entering => if (p.settings.message_animation) {
            life.dismissed = true;
            return false;
        },
        .shown => {},
    }
    life.frame = 0;
    if (p.settings.message_linger_ms > 0) {
        life.phase = .lingering;
    } else if (p.settings.message_animation) {
        life.phase = .leaving;
    } else return true;
    return false;
}

/// One animation frame of every message line. Each one that moves owes
/// a frame, the one that finishes included: a tick asks for none itself.
pub fn advanceMessages(p: *Pardes) void {
    for (p.panes) |slot| {
        const pane = slot orelse continue;
        if (pane.msg_len > 0 and pane.msg_life.phase != .shown) {
            p.needs_frame = true;
            if (advanceLine(p, &pane.msg_life)) {
                pane.msg_len = 0;
                pane.msg_life = .{};
            }
        }
        var i: usize = 0;
        while (i < pane.msg_older_len) {
            if (pane.msg_older[i].life.phase != .shown) p.needs_frame = true;
            if (advanceLine(p, &pane.msg_older[i].life)) pane.removeOlderMessage(i) else i += 1;
        }
    }
}

/// One frame of one line's life; true once it has left.
fn advanceLine(p: *const Pardes, life: *Pane.MessageLife) bool {
    if (life.phase == .shown) return false;
    life.frame +|= 1;
    switch (life.phase) {
        .shown => {},
        .entering => if (life.frame >= messageFrames(p.settings.message_fall_ms)) {
            life.* = .{ .phase = if (life.dismissed) .lingering else .shown };
        },
        .lingering => if (life.frame >= messageFrames(p.settings.message_linger_ms)) {
            if (!p.settings.message_animation) return true;
            life.* = .{ .phase = .leaving };
        },
        .leaving => if (life.frame >= messageFrames(p.settings.message_dissolve_ms)) return true,
    }
    return false;
}

/// Move every lingering message line `frames` along its linger at once:
/// how `advance` jumps a wait instead of stepping it frame by frame.
pub fn holdMessages(p: *Pardes, frames: u64) void {
    const n: u16 = @intCast(@min(frames, std.math.maxInt(u16)));
    for (p.panes) |slot| {
        const pane = slot orelse continue;
        if (pane.msg_len > 0 and pane.msg_life.phase == .lingering) pane.msg_life.frame +|= n;
        for (pane.msg_older[0..pane.msg_older_len]) |*line| {
            if (line.life.phase == .lingering) line.life.frame +|= n;
        }
    }
}

/// Frames until this pane's message lines next change: 1 while a line
/// falls in or dissolves, the rest of its linger while one only waits, null
/// when every line just shows.
pub fn messageWake(p: *const Pardes, pane: *const Pane) ?u64 {
    var soonest: ?u64 = null;
    const linger = messageFrames(p.settings.message_linger_ms);
    for (0..@as(usize, pane.msg_older_len) + 1) |i| {
        const life = if (i < pane.msg_older_len) pane.msg_older[i].life else if (pane.msg_len > 0) pane.msg_life else continue;
        const frames: u64 = switch (life.phase) {
            .shown => continue,
            .entering, .leaving => 1,
            .lingering => @max(1, linger -| life.frame),
        };
        soonest = if (soonest) |n| @min(n, frames) else frames;
    }
    return soonest;
}

/// How present a message is (1 = fully) and how far above its row it
/// still is (rows): a fall that decelerates into place with its colour
/// arriving ahead of it, and a dissolve.
pub const MessageMotion = struct { alpha: f32 = 1, slide: f32 = 0 };

/// Animation frames a message timing lasts; at least one.
pub fn messageFrames(ms: u16) u16 {
    return @intCast(@max(1, (@as(u32, ms) + animation.frame_ms - 1) / animation.frame_ms));
}

pub fn messageMotion(p: *const Pardes, life: Pane.MessageLife) MessageMotion {
    const fall_frames = messageFrames(p.settings.message_fall_ms);
    const dissolve_frames = messageFrames(p.settings.message_dissolve_ms);
    return switch (life.phase) {
        .shown, .lingering => .{ .alpha = 1, .slide = 0 },
        .entering => blk: {
            const t = @as(f32, @floatFromInt(@min(life.frame, fall_frames))) / @as(f32, @floatFromInt(fall_frames));
            // Out of the gate fast and easing into its row (a cubic
            // ease-out), so it is there the moment it is said and the
            // last frames only settle it. No overshoot: at a row's height
            // and a dozen frames, a follow-through is a pixel or two that
            // reads as a jitter, not a bounce.
            // The drop follows the Motion flavour (its wind-up, overshoot
            // and all) over the fall's length.
            const left = 1 - animation.Motion.of(p.settings.motion).ease(t);
            // The colour leads the motion: solid by half way, so what
            // lands is already legible rather than still fading up.
            const faded = 1 - @min(1, 2 * t);
            // And never behind it, however fast the flavour leaves.
            break :blk .{ .alpha = @max(1 - faded * faded, std.math.clamp(1 - left, 0, 1)), .slide = -left };
        },
        .leaving => blk: {
            // Counted to its last frame rather than past it, so that frame
            // shows it gone and it never blinks out from part way.
            const last = @max(1, dissolve_frames - 1);
            const t = @as(f32, @floatFromInt(@min(life.frame, last))) / @as(f32, @floatFromInt(last));
            // An exit eases in: still readable for a beat, then away
            // faster and faster. It stays where it is -- the lines
            // stacked around it do not move either.
            break :blk .{ .alpha = 1 - t * t, .slide = 0 };
        },
    };
}

/// What notice band `i` says. The grid pass and the band layers both
/// read it here, so a terminal and a pixel shell show the same line.
pub fn noticeText(p: *const Pardes, pane: *const Pane, i: usize, leader_buf: *[16]u8) []const u8 {
    return switch (pane.notices.kinds[i]) {
        .message => pane.msg[0..pane.msg_len],
        .older => pane.msg_older[pane.notices.index[i]].slice(),
        .leader => leaderText(p, leader_buf),
        .prompt => pane.promptText() orelse "",
    };
}

/// The life of the message line notice `i` shows, if it shows one.
pub fn noticeLife(pane: *const Pane, i: usize) ?Pane.MessageLife {
    return switch (pane.notices.kinds[i]) {
        .message => pane.msg_life,
        .older => pane.msg_older[pane.notices.index[i]].life,
        .leader, .prompt => null,
    };
}

pub fn blendRgb(from: [3]u8, to: [3]u8, amount: f32) [3]u8 {
    var out: [3]u8 = undefined;
    for (&out, from, to) |*o, a, b| {
        const af: f32 = @floatFromInt(a);
        const bf: f32 = @floatFromInt(b);
        o.* = @intFromFloat(@round(bf + (af - bf) * std.math.clamp(amount, 0, 1)));
    }
    return out;
}

fn logMessage(p: *Pardes, id: usize, text: []const u8) void {
    if (text.len == 0) return;
    const serial: u32 = if (p.fs.session_write) 0 else if (id < MAX_PANES) if (p.panes[id]) |pane| pane.serial else 0 else 0;
    const kept = text[0..@min(text.len, LoggedMessage.cap)];
    // /log hears every one: a client that retried and failed the same way
    // is waiting on that second line. Only the +Messages view collapses.
    ctlfs.events.noteMessage(p, serial, kept);
    if (p.messages.len > 0) {
        const last = &p.messages.log[(p.messages.head + limits.message_log - 1) % limits.message_log];
        if (last.serial == serial and
            std.mem.eql(u8, Message.body(last.slice()), Message.body(kept)))
        {
            // The NEWEST wording wins, so the row carries the latest clock
            // rather than the moment the run started.
            last.len = @intCast(kept.len);
            @memcpy(last.text[0..last.len], kept);
            last.repeats +|= 1;
            return;
        }
    }
    const slot = &p.messages.log[p.messages.head];
    slot.len = @intCast(kept.len);
    @memcpy(slot.text[0..slot.len], kept);
    slot.serial = serial;
    slot.repeats = 1;
    p.messages.head = (p.messages.head + 1) % limits.message_log;
    p.messages.len = @min(p.messages.len + 1, limits.message_log);
}

/// The log oldest-first, which is reading order.
pub fn messageLog(m: *const Messages, i: usize) ?*const LoggedMessage {
    if (i >= m.len) return null;
    const first = (m.head + limits.message_log - m.len) % limits.message_log;
    return &m.log[(first + i) % limits.message_log];
}

/// `<operation>: <the error in words>`: FileNotFound reads "file not found".
/// What a route that would open a pane says when every slot is taken.
/// "no space": 9ns's word for ENOSPC (it has none for ENFILE).
pub const no_pane_slots = "no space for a pane: {d} max";

pub fn reportError(p: *Pardes, id: usize, operation: []const u8, err: anyerror) void {
    var buf: [256]u8 = undefined;
    var w = std.Io.Writer.fixed(&buf);
    w.print("{s}: ", .{operation}) catch {};
    // Every route that opens a pane says the cap the same way.
    if (err == error.NoPaneSlots) {
        w.print(no_pane_slots, .{pardes.MAX_PANES}) catch {};
        // A 9P look or exec that would open the pane fails with it too.
        p.fs.no_pane_slot = true;
        @memcpy(p.fs.ename[0..w.buffered().len], w.buffered());
        p.fs.no_pane_slot_len = @intCast(w.buffered().len);
        return reportFailure(p, id, w.buffered());
    }
    for (@errorName(err), 0..) |c, i| {
        if (std.ascii.isUpper(c) and i > 0) w.writeByte(' ') catch break;
        w.writeByte(std.ascii.toLower(c)) catch break;
    }
    reportFailure(p, id, w.buffered());
}

/// The longest start of `text` that fits `max` bytes and ends between
/// words (or, with no space to cut at, between characters).
pub fn clip(text: []const u8, max: usize) []const u8 {
    if (text.len <= max) return text;
    if (std.mem.lastIndexOfScalar(u8, text[0 .. max + 1], ' ')) |sp| return text[0..sp];
    var n = max;
    while (n > 0 and text[n] & 0xC0 == 0x80) n -= 1;
    return text[0..n];
}

/// reportError with the words already chosen.
pub fn reportFailure(p: *Pardes, id: usize, text: []const u8) void {
    // A builtin a ctl write runs: its first error is also the write's, cut
    // between words.
    if (p.fs.no_prompt and p.fs.failure_len == 0) {
        const kept = if (text.len > p.fs.failure.len) clip(text, p.fs.failure.len - 3) else text;
        @memcpy(p.fs.failure[0..kept.len], kept);
        var n = kept.len;
        if (kept.len < text.len) {
            @memcpy(p.fs.failure[n..][0..3], "...");
            n += 3;
        }
        p.fs.failure_len = @intCast(n);
    }
    setMessage(p, id, text);
}

test "an error reads as words and a failure is cut between them" {
    try std.testing.expectEqualStrings("go", clip("go haskell", 4));
    try std.testing.expectEqualStrings("go haskell", clip("go haskell", 10));
    try std.testing.expectEqualStrings("\u{e9}", clip("\u{e9}\u{e9}", 3));
}

/// The one place that decides which transient lines a pane is showing and
/// in what order. Everything downstream reads the answer: the body layer
/// so it does not paint under them, and the paint pass so it can stack
/// them instead of letting the last one win the row.
pub fn collectNotices(p: *Pardes, pane: *Pane, r: Rect, id: usize) void {
    pane.notices.len = 0;
    if (r.w <= config.GUTTER or r.h <= pane.tag_rows) return;
    // Oldest message line on top, so lines already up do not move when a
    // new one lands under them; when rows run out the oldest go first.
    for (pane.msg_older[0..pane.msg_older_len], 0..) |line, i| pane.notices.pushAt(.older, @intCast(i), line.slot);
    if (pane.msg_len > 0) pane.notices.pushAt(.message, 0, pane.msg_slot);
    if (id == p.active and p.leader_on) pane.notices.push(.leader);
    if (pane.promptText()) |text| if (text.len > 0) pane.notices.push(.prompt);
    // A pane only has so many rows to give. When they do not all fit the
    // LAST ones survive, because the prompt is last and it is the one
    // carrying the cursor: a prompt you cannot see is a prompt you type
    // into blind. A two-row pane spends its only body row on one notice,
    // which is what the single shared row used to do anyway.
    const room: u8 = @intCast(@min(@as(u16, Pane.Notices.max), r.h - pane.tag_rows));
    const n = &pane.notices;
    if (n.span() <= room) return;
    // Too short for the gaps: close them up in screen order, and if even
    // that does not fit, the top bands go.
    var i: usize = 1;
    while (i < n.len) : (i += 1) {
        var j = i;
        while (j > 0 and n.row[j - 1] > n.row[j]) : (j -= 1) {
            std.mem.swap(Pane.Notices.Kind, &n.kinds[j - 1], &n.kinds[j]);
            std.mem.swap(u8, &n.index[j - 1], &n.index[j]);
            std.mem.swap(u8, &n.row[j - 1], &n.row[j]);
        }
    }
    const drop = n.len -| room;
    for (0..n.len - drop) |k| {
        n.kinds[k] = n.kinds[k + drop];
        n.index[k] = n.index[k + drop];
        n.row[k] = @intCast(k);
    }
    n.len -= @intCast(drop);
}

test "the message log keeps what the row forgets, and collapses repeats" {
    const gpa = std.testing.allocator;
    const p = try Pardes.init(gpa, .{ .tty_only = true, .cols = 100, .rows = 30 });
    defer p.deinit();

    setMessage(p, 0, "14:32:07  saved /x.zig");
    setMessage(p, 0, "14:32:09  saved /x.zig"); // same event, later clock
    setMessage(p, 0, "save: AccessDenied");

    try std.testing.expectEqual(@as(usize, 2), p.messages.len);
    const first = p.messages.messageLog(0).?;
    try std.testing.expectEqual(@as(u16, 2), first.repeats);
    // ...and the NEWEST wording is what survives, so the row carries the last
    // time it happened rather than the first.
    try std.testing.expectEqualStrings("14:32:09  saved /x.zig", first.slice());
    try std.testing.expectEqualStrings("save: AccessDenied", p.messages.messageLog(1).?.slice());
    try std.testing.expect(p.messages.messageLog(2) == null);

    // The same text from a DIFFERENT pane is a different event: one pane's
    // failure must not be recorded as another's.
    p.newScratchBelow(0);
    const other = p.active;
    setMessage(p, other, "save: AccessDenied");
    try std.testing.expectEqual(@as(usize, 3), p.messages.len);
    try std.testing.expectEqual(p.panes[other].?.serial, p.messages.messageLog(2).?.serial);

    // Progress is NOT logged: it arrives several times a second for a whole
    // index and would push everything else out (`setStatus`).
    setStatus(p, 0, "14:32:10  lsp rust-analyzer: Indexing 47%");
    try std.testing.expectEqual(@as(usize, 3), p.messages.len);

    // The ring wraps rather than grows, and still reads oldest-first.
    for (0..limits.message_log + 5) |i| {
        var buf: [32]u8 = undefined;
        setMessage(p, 0, std.fmt.bufPrint(&buf, "line {d}", .{i}) catch unreachable);
    }
    try std.testing.expectEqual(@as(usize, limits.message_log), p.messages.len);
    try std.testing.expectEqualStrings("line 5", p.messages.messageLog(0).?.slice());
    var last_buf: [32]u8 = undefined;
    const want_last = std.fmt.bufPrint(&last_buf, "line {d}", .{limits.message_log + 4}) catch unreachable;
    try std.testing.expectEqualStrings(want_last, p.messages.messageLog(limits.message_log - 1).?.slice());
}

test "Msg writes the transient row by hand, bare or with text, and input ends it" {
    const p = try Pardes.init(std.testing.allocator, .{ .shells = 3, .cols = 100, .rows = 30 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    const row = struct {
        fn of(pp: *Pardes, i: usize) []const u8 {
            const pane = pp.panes[i].?;
            return pane.msg[0..pane.msg_len];
        }
    }.of;

    // the whole tail, spaces and all: the row is a sentence, not a word
    try std.testing.expect(p.executeBuiltinLine(2, "Msg saved /etc/hosts"));
    try std.testing.expectEqualStrings("saved /etc/hosts", row(p, 2));
    // ...on the pane that ran it, and nowhere else
    try std.testing.expectEqualStrings("", row(p, 0));

    // Bare, it reports ITSELF through reportError — the `<operation>: <error in words>`
    // every failed save and refused Look arrives in.
    try std.testing.expect(p.executeBuiltinLine(2, "Msg"));
    try std.testing.expectEqualStrings("Msg: no message", row(p, 2));

    // Input starts its exit: it lingers, dissolves, and is gone.
    p.update(.{ .key = .{ .cp = Key.escape } });
    try std.testing.expectEqualStrings("Msg: no message", row(p, 2));
    for (0..200) |_| p.update(.tick);
    try std.testing.expectEqualStrings("", row(p, 2));
    // ...and with neither linger nor animation it is as old as your last input.
    try std.testing.expect(p.executeBuiltinLine(2, "MessageAnimation off"));
    try std.testing.expect(p.executeBuiltinLine(2, "MessageLinger 0"));
    try std.testing.expect(p.executeBuiltinLine(2, "Msg gone"));
    p.update(.{ .key = .{ .cp = 'h' } });
    try std.testing.expectEqualStrings("", row(p, 2));

    // Longer than the row's buffer is CUT, never refused and never overrun:
    // this word is the only way to reach that boundary without a 300-byte path.
    var long: [600]u8 = @splat('x');
    var line: [608]u8 = undefined;
    const cmd = try std.fmt.bufPrint(&line, "Msg {s}", .{&long});
    try std.testing.expect(p.executeBuiltinLine(2, cmd));
    try std.testing.expectEqual(p.panes[2].?.msg.len, row(p, 2).len);
}

test "with no frontend attached a message goes once it has lingered, on the clock" {
    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true });
    defer p.deinit();
    const pane = p.panes[p.active].?;
    p.setMessage(p.active, "said");
    p.setMessage(p.active, "said again");
    // Attached: it waits for input, however long.
    pane.msg_said_ms -= 60_000;
    p.update(.tick);
    try std.testing.expect(pane.msg_len > 0);
    // Detached with nobody attached: past its linger it is gone, and the
    // line above it with it.
    p.unattended = true;
    // A read served meanwhile changes nothing; the session's loop expires.
    _ = p.serveFs(.{ .tag = 1, .op = .read, .node = @intFromEnum(ctlfs.TopFile.index), .size = 64 });
    try std.testing.expect(pane.msg_len > 0);
    expireUnattended(p);
    try std.testing.expectEqual(@as(u16, 0), pane.msg_len);
    try std.testing.expectEqual(@as(u8, 0), pane.msg_older_len);
    // A fresh one stays until its linger is up.
    p.setMessage(p.active, "fresh");
    p.update(.tick);
    try std.testing.expect(pane.msg_len > 0);
}

test "a message falls in, lingers past the input that dismisses it, and dissolves" {
    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true, .cols = 80, .rows = 24 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    const pane = p.panes[p.active].?;
    try std.testing.expect(p.settings.message_animation);
    // Crisp: the flavour whose drop leaves at full speed and lands without
    // passing its row (the others are the Motion tests').
    p.settings.motion = .crisp;
    try std.testing.expect(p.executeBuiltinLine(p.active, "MessageLinger 160"));
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg hello"));
    try std.testing.expectEqual(Pane.MessagePhase.entering, pane.msg_life.phase);
    try std.testing.expect(p.animationActive());
    // An ease-out fall: starts a whole row up and unseen, covers most of the
    // way at once and settles into its row, landing exactly on it without
    // passing it. Its colour is whole by half way.
    const start = messageMotion(p, pane.msg_life);
    try std.testing.expectEqual(@as(f32, -1), start.slide);
    try std.testing.expectEqual(@as(f32, 0), start.alpha);
    const fall = messageFrames(p.settings.message_fall_ms);
    var last = start;
    var first_step: f32 = 0;
    var last_step: f32 = 0;
    for (0..fall) |frame| {
        p.needs_frame = false;
        p.update(.tick);
        // Every tick that moves it owes a frame, the landing one included.
        try std.testing.expect(p.needs_frame);
        const now = messageMotion(p, pane.msg_life);
        try std.testing.expect(now.slide >= last.slide and now.slide <= 0);
        try std.testing.expect(now.alpha >= last.alpha);
        if (frame == 0) first_step = now.slide - last.slide;
        // Never slower to colour up than to arrive, and solid by half way.
        try std.testing.expect(now.alpha >= 1 + now.slide);
        if (2 * (frame + 1) >= fall) try std.testing.expectEqual(@as(f32, 1), now.alpha);
        last_step = now.slide - last.slide;
        last = now;
    }
    try std.testing.expect(first_step > 4 * last_step);
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
    try std.testing.expectEqual(@as(f32, 0), messageMotion(p, pane.msg_life).slide);
    try std.testing.expect(!p.animationActive());
    // Shown until input, like always; the same line again does not re-enter.
    for (0..100) |_| p.update(.tick);
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg hello"));
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
    // Input (a key that announces nothing): 160 ms of lingering (ten frames), unaffected by more input...
    p.update(.{ .key = .{ .cp = 'h' } });
    try std.testing.expectEqual(Pane.MessagePhase.lingering, pane.msg_life.phase);
    for (0..9) |_| {
        p.update(.tick);
        p.update(.{ .key = .{ .cp = 'h' } });
    }
    try std.testing.expectEqual(Pane.MessagePhase.lingering, pane.msg_life.phase);
    p.update(.tick);
    // ...then an ease-in dissolve: it lets go slowly and goes faster and
    // faster, in place, its last frame showing it gone.
    try std.testing.expectEqual(Pane.MessagePhase.leaving, pane.msg_life.phase);
    const dissolve = messageFrames(p.settings.message_dissolve_ms);
    var alpha: f32 = 1;
    var first_drop: f32 = 0;
    var last_drop: f32 = 0;
    for (0..dissolve) |frame| {
        const now = messageMotion(p, pane.msg_life);
        try std.testing.expect(now.alpha <= alpha);
        try std.testing.expectEqual(@as(f32, 0), now.slide);
        if (frame == 1) first_drop = alpha - now.alpha;
        last_drop = alpha - now.alpha;
        alpha = now.alpha;
        p.needs_frame = false;
        p.update(.tick);
    }
    try std.testing.expectEqual(@as(f32, 0), alpha);
    try std.testing.expect(first_drop > 0 and first_drop < last_drop);
    try std.testing.expectEqual(@as(u16, 0), pane.msg_len);
    try std.testing.expect(!p.animationActive());
    // The tick that clears it still owes the frame that shows it gone.
    try std.testing.expect(p.needs_frame);

    // Dismissed mid-fall: it lands, then lingers.
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg again"));
    try std.testing.expectEqual(Pane.MessagePhase.entering, pane.msg_life.phase);
    p.update(.tick);
    p.update(.{ .key = .{ .cp = 'h' } });
    try std.testing.expectEqual(Pane.MessagePhase.entering, pane.msg_life.phase);
    for (0..messageFrames(p.settings.message_fall_ms)) |_| p.update(.tick);
    try std.testing.expectEqual(Pane.MessagePhase.lingering, pane.msg_life.phase);
    // Shown again while lingering: fresh, so it stays; a status update to a
    // line on screen swaps its text in place instead of falling again.
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg again"));
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
    setStatus(p, p.active, "progress 50%");
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
    try std.testing.expectEqualStrings("progress 50%", pane.msg[0..pane.msg_len]);
    try std.testing.expectEqual(@as(u8, 0), pane.msg_older_len);
    // The fall and the dissolve are timings of their own, in milliseconds.
    try std.testing.expect(p.executeBuiltinLine(p.active, "MessageFall 48"));
    try std.testing.expect(p.executeBuiltinLine(p.active, "MessageDissolve 0"));
    try std.testing.expectEqual(@as(u16, 3), messageFrames(p.settings.message_fall_ms));
    try std.testing.expectEqual(@as(u16, 1), messageFrames(p.settings.message_dissolve_ms));
    // The Config report reads back as configuration.
    try std.testing.expect(p.executeBuiltinLine(p.active, "MessageAnimation"));
    try std.testing.expect(!p.settings.message_animation);
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg plain"));
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
}

test "messages stack, oldest on top, each on its own timing" {
    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true, .cols = 80, .rows = 24 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    const pane = p.panes[p.active].?;
    try std.testing.expect(p.executeBuiltinLine(p.active, "Verbose off"));
    try std.testing.expect(p.executeBuiltinLine(p.active, "MessageLinger 160"));
    // `Verbose off` announced itself before it took effect.
    pane.msg_len = 0;
    pane.msg_life = .{};
    const fall = messageFrames(p.settings.message_fall_ms);
    setMessage(p, p.active, "first");
    for (0..fall) |_| p.update(.tick);
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
    // A second message stacks under the first instead of replacing it.
    setMessage(p, p.active, "second");
    try std.testing.expectEqual(@as(u8, 1), pane.msg_older_len);
    try std.testing.expectEqualStrings("first", pane.msg_older[0].slice());
    try std.testing.expectEqualStrings("second", pane.msg[0..pane.msg_len]);
    try std.testing.expectEqual(Pane.MessagePhase.entering, pane.msg_life.phase);
    collectNotices(p, pane, p.rects[p.active], p.active);
    try std.testing.expectEqual(Pane.Notices.Kind.older, pane.notices.kinds[0]);
    try std.testing.expectEqual(Pane.Notices.Kind.message, pane.notices.kinds[1]);
    // One key dismisses both, but each runs its own clock: the first starts
    // lingering now, the second only once it has landed.
    p.update(.{ .key = .{ .cp = 'h' } });
    try std.testing.expectEqual(Pane.MessagePhase.lingering, pane.msg_older[0].life.phase);
    try std.testing.expectEqual(Pane.MessagePhase.entering, pane.msg_life.phase);
    const linger = messageFrames(p.settings.message_linger_ms);
    const dissolve = messageFrames(p.settings.message_dissolve_ms);
    for (0..linger + dissolve) |_| p.update(.tick);
    // The first is gone; the second, a fall later, is still dissolving.
    try std.testing.expectEqual(@as(u8, 0), pane.msg_older_len);
    try std.testing.expectEqualStrings("second", pane.msg[0..pane.msg_len]);
    try std.testing.expectEqual(Pane.MessagePhase.leaving, pane.msg_life.phase);
    for (0..fall) |_| p.update(.tick);
    try std.testing.expectEqual(@as(u16, 0), pane.msg_len);
    try std.testing.expect(!p.animationActive());
    // A status ticking in place does not pile up.
    setStatus(p, p.active, "lsp 10%");
    setStatus(p, p.active, "lsp 20%");
    try std.testing.expectEqual(@as(u8, 0), pane.msg_older_len);
    // Lines keep their rows: when the top one leaves, the one under it does
    // not move up, and the next message fills the gap instead.
    setMessage(p, p.active, "top");
    setMessage(p, p.active, "under");
    try std.testing.expectEqual(@as(u8, 0), pane.msg_older[0].slot);
    try std.testing.expectEqual(@as(u8, 1), pane.msg_slot);
    pane.removeOlderMessage(0);
    collectNotices(p, pane, p.rects[p.active], p.active);
    try std.testing.expectEqual(@as(u8, 1), pane.notices.row[0]);
    try std.testing.expectEqual(@as(u8, 2), pane.notices.span());
    setMessage(p, p.active, "fills");
    try std.testing.expectEqual(@as(u8, 0), pane.msg_slot);
    try std.testing.expectEqual(@as(u8, 1), pane.msg_older[0].slot);
    // The stack keeps the newest few.
    for ([_][]const u8{ "a", "b", "c", "d", "e" }) |text| setMessage(p, p.active, text);
    try std.testing.expectEqual(@as(u8, Pane.message_stack), pane.msg_older_len);
    try std.testing.expectEqualStrings("b", pane.msg_older[0].slice());
    try std.testing.expectEqualStrings("e", pane.msg[0..pane.msg_len]);
}

test "a builtin announces itself on the message row, and Verbose silences it" {
    if (platform == .web) return;
    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true, .cols = 80, .rows = 24 });
    defer p.deinit();
    const pane = p.panes[p.active].?;

    p.sync();
    try std.testing.expect(p.settings.verbose);
    // Wrap, not Collapse: a builtin that folds its own pane away leaves no row
    // for its announcement, which is correct and not what this is testing.
    try std.testing.expect(p.executeBuiltinLine(p.active, "Wrap"));
    try std.testing.expectEqualStrings("Wrap", pane.msg[0..pane.msg_len]);
    // A value it does not take is said, in place of the announcement.
    const wrapped = p.settings.wrap;
    try std.testing.expect(p.executeBuiltinLine(p.active, "Wrap maybe"));
    try std.testing.expectEqualStrings("Wrap: takes on or off", pane.msg[0..pane.msg_len]);
    try std.testing.expectEqual(wrapped, p.settings.wrap);

    // The notice list is what the paint pass reads, so the announcement has to
    // reach it, not just the buffer.
    collectNotices(p, pane, p.rects[p.active], p.active);
    try std.testing.expect(pane.notices.len > 0);
    try std.testing.expectEqual(Pane.Notices.Kind.message, pane.notices.kinds[0]);

    // ...and it is carried as a tagline band, not a body row: that is what
    // gives it the tagline's height, its small font and its border.
    var frame = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer frame.deinit();
    _ = try p.render(frame.allocator());
    const r = p.rects[p.active];
    const band = for (p.surface.tagLayers()) |*layer| {
        if (layer.rows != 0 and layer.kind == .notice) break layer;
    } else return error.NoNoticeBand;
    try std.testing.expectEqual(@as(u16, 1), band.viewport.h);
    try std.testing.expectEqual(if (p.settings.tag_bottom) r.y else r.y + BOX_H, band.viewport.y);
    // Right aligned: the text ends at the band's right edge.
    const line = band.cells[0..band.cols];
    var last: usize = line.len;
    while (last > 0 and line[last - 1].grapheme()[0] == ' ') last -= 1;
    try std.testing.expect(last > 0);
    try std.testing.expect(line[0].grapheme()[0] == ' ');

    // Msg owns the row itself, so it does not announce over its own text.
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg hello"));
    try std.testing.expectEqualStrings("hello", pane.msg[0..pane.msg_len]);

    pane.msg_len = 0;
    p.settings.verbose = false;
    try std.testing.expect(p.executeBuiltinLine(p.active, "Wrap"));
    try std.testing.expectEqual(@as(u16, 0), pane.msg_len);
}

test "notices stack over the body's top rows without moving them" {
    if (platform == .web) return;
    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true, .cols = 80, .rows = 24 });
    defer p.deinit();
    const id = p.active;
    const pane = p.panes[id].?;
    p.sync();
    var frame = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer frame.deinit();

    const r = p.rects[id];
    const top = p.bodyTop(pane, r);

    // A message and a leader prefix at once: two chips, in the order
    // collectNotices chose, each one row tall and each one row further down.
    try std.testing.expect(p.executeBuiltinLine(id, "Msg first"));
    p.leader_on = true;
    p.leader_n = 0;
    _ = frame.reset(.retain_capacity);
    _ = try p.render(frame.allocator());
    try std.testing.expectEqual(@as(u8, 2), pane.notices.len);
    // An overlay, not a reservation: the body still starts where it did.
    try std.testing.expectEqual(top, p.bodyTop(pane, r));

    var seen: usize = 0;
    for (p.surface.tagLayers()) |*layer| {
        if (layer.rows == 0 or layer.kind != .notice) continue;
        try std.testing.expectEqual(@as(u16, 1), layer.viewport.h);
        // Sized to its own message, right up against the pane's right edge --
        // not the width of the pane.
        try std.testing.expectEqual(r.x + r.w, layer.viewport.x + layer.viewport.w);
        try std.testing.expect(layer.viewport.w < r.w - config.GUTTER);
        try std.testing.expect(layer.viewport.y == top or layer.viewport.y == top + 1);
        try std.testing.expectEqual(pane.notices.left[layer.viewport.y - top], layer.viewport.x);
        seen += 1;
    }
    try std.testing.expectEqual(@as(usize, 2), seen);
    // "first" is longer than "SPC", so its chip is wider.
    try std.testing.expect(pane.notices.left[0] < pane.notices.left[1]);

    // Gone with the notices: no stale chip left behind.
    p.leader_on = false;
    pane.msg_len = 0;
    _ = frame.reset(.retain_capacity);
    _ = try p.render(frame.allocator());
    for (p.surface.tagLayers()) |*layer|
        try std.testing.expect(layer.rows == 0 or layer.kind != .notice);
}

test "an idle core wants no wake and a lingering message sleeps to its linger's end" {
    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true, .cols = 80, .rows = 24 });
    defer p.deinit();
    while (p.nextEffect()) |_| {}
    const frame = animation.frame_ns;
    p.advance(1_000_000);
    try std.testing.expectEqual(@as(?u64, null), p.nextWake());
    const pane = p.panes[p.active].?;
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg hello"));
    // Falling in: a frame from now.
    try std.testing.expectEqual(@as(?u64, p.stepped_ns + frame), p.nextWake());
    const fall = messageFrames(p.settings.message_fall_ms);
    p.advance(p.stepped_ns + fall * frame);
    try std.testing.expectEqual(Pane.MessagePhase.shown, pane.msg_life.phase);
    try std.testing.expectEqual(@as(?u64, null), p.nextWake());
    // A key starts the 800 ms linger: the core sleeps to its end, not a
    // frame at a time, and the frames it jumps draw nothing.
    p.update(.{ .key = .{ .cp = 'x' } });
    try std.testing.expectEqual(Pane.MessagePhase.lingering, pane.msg_life.phase);
    const linger = messageFrames(p.settings.message_linger_ms);
    const due = p.stepped_ns + linger * frame;
    try std.testing.expectEqual(@as(?u64, due), p.nextWake());
    p.needs_frame = false;
    p.advance(due - frame);
    try std.testing.expectEqual(@as(?u64, due), p.nextWake());
    try std.testing.expectEqual(Pane.MessagePhase.lingering, pane.msg_life.phase);
    p.advance(due);
    try std.testing.expectEqual(Pane.MessagePhase.leaving, pane.msg_life.phase);
    try std.testing.expectEqual(@as(?u64, due + frame), p.nextWake());
    p.advance(due + 10 * std.time.ns_per_s);
    try std.testing.expectEqual(@as(usize, 0), pane.msg_len);
    try std.testing.expectEqual(@as(?u64, null), p.nextWake());

    // A long linger ends when it says, jumped in one step, not stretched by
    // the cap on catching up with moving frames.
    try std.testing.expect(p.executeBuiltinLine(p.active, "MessageLinger 5000"));
    try std.testing.expect(p.executeBuiltinLine(p.active, "Msg again"));
    p.advance(p.stepped_ns + fall * frame);
    p.update(.{ .key = .{ .cp = 'x' } });
    const long_due = p.stepped_ns + messageFrames(5000) * frame;
    try std.testing.expectEqual(@as(?u64, long_due), p.nextWake());
    p.advance(long_due);
    try std.testing.expectEqual(Pane.MessagePhase.leaving, pane.msg_life.phase);
}