//! Represents the renderer thread logic. The renderer thread is able to
//! be woken up to render.
pub const Thread = @This();

const std = @import("std");
const builtin = @import("builtin");
const global = @import("../global.zig");
const xev = global.xev;
const crash = @import("../crash/main.zig");
const internal_os = @import("../os/main.zig");
const rendererpkg = @import("../renderer.zig");
const apprt = @import("../apprt.zig");
const configpkg = @import("../config.zig");
const terminalpkg = @import("../terminal/main.zig");
const BlockingQueue = @import("../datastruct/main.zig").BlockingQueue;
const App = @import("../App.zig");

const Allocator = std.mem.Allocator;
const log = std.log.scoped(.renderer_thread);

const CURSOR_BLINK_INTERVAL = 600;

/// Whether calls to `drawFrame` must be done from the app thread.
///
/// The type used for sending messages to the IO thread. For now this is
/// hardcoded with a capacity. We can make this a comptime parameter in
/// the future if we want it configurable.
pub const Mailbox = BlockingQueue(rendererpkg.Message, 64);

/// Allocator used for some state
alloc: std.mem.Allocator,

/// The main event loop for the application. The user data of this loop
/// is always the allocator used to create the loop. This is a convenience
/// so that users of the loop always have an allocator.
loop: xev.Loop,

/// This can be used to wake up the renderer and force a render safely from
/// any thread.
wakeup: xev.Async,
wakeup_c: xev.Completion = .{},

/// This can be used to stop the renderer on the next loop iteration.
stop: xev.Async,
stop_c: xev.Completion = .{},

/// The timer used for animations (custom shaders, Kitty graphics).
/// Normal rendering is driven by wakeup messages instead.
render_h: xev.Timer,
render_c: xev.Completion = .{},
render_c_cancel: xev.Completion = .{},

/// The kind of work the currently scheduled animation wake needs,
/// stored when the timer is armed.
animation_wake: rendererpkg.Renderer.AnimationWake.Kind = .draw,

/// This async is used to force a draw immediately. This does not
/// coalesce like the wakeup does.
draw_now: xev.Async,
draw_now_c: xev.Completion = .{},

/// The timer used for cursor blinking
cursor_h: xev.Timer,
cursor_c: xev.Completion = .{},
cursor_c_cancel: xev.Completion = .{},

/// Incremental scrollback compression scheduling.
compression: Compression = undefined,

/// The surface we're rendering to.
surface: *apprt.Surface,

/// The underlying renderer implementation.
renderer: *rendererpkg.Renderer,

/// Pointer to the shared state that is used to generate the final render.
state: *rendererpkg.State,

/// The mailbox that can be used to send this thread messages. Note
/// this is a blocking queue so if it is full you will get errors (or block).
mailbox: *Mailbox,

/// Mailbox to send messages to the app thread
app_mailbox: App.Mailbox,

/// Configuration we need derived from the main config.
config: DerivedConfig,

flags: packed struct {
    /// This is true when a blinking cursor should be visible and false
    /// when it should not be visible. This is toggled on a timer by the
    /// thread automatically.
    cursor_blink_visible: bool = false,

    /// This is true when the inspector is active.
    has_inspector: bool = false,

    /// This is true when the view is visible. This is used to determine
    /// if we should be rendering or not.
    visible: bool = true,

    /// This is true when the view is focused. This defaults to true
    /// and it is up to the apprt to set the correct value.
    focused: bool = true,
} = .{},

pub const DerivedConfig = struct {
    scrollback_compression: bool,

    pub fn init(config: *const configpkg.Config) DerivedConfig {
        return .{
            .scrollback_compression = config.@"scrollback-compression",
        };
    }
};

/// Initialize the thread. This does not START the thread. This only sets
/// up all the internal state necessary prior to starting the thread. It
/// is up to the caller to start the thread with the threadMain entrypoint.
pub fn init(
    alloc: Allocator,
    config: *const configpkg.Config,
    surface: *apprt.Surface,
    renderer_impl: *rendererpkg.Renderer,
    state: *rendererpkg.State,
    app_mailbox: App.Mailbox,
) !Thread {
    // Create our event loop.
    var loop = try xev.Loop.init(.{});
    errdefer loop.deinit();

    // This async handle is used to "wake up" the renderer and force a render.
    var wakeup_h = try xev.Async.init();
    errdefer wakeup_h.deinit();

    // This async handle is used to stop the loop and force the thread to end.
    var stop_h = try xev.Async.init();
    errdefer stop_h.deinit();

    // The primary timer for rendering.
    var render_h = try xev.Timer.init();
    errdefer render_h.deinit();

    // Draw now async, see comments.
    var draw_now = try xev.Async.init();
    errdefer draw_now.deinit();

    // Setup a timer for blinking the cursor
    var cursor_timer = try xev.Timer.init();
    errdefer cursor_timer.deinit();

    // The mailbox for messaging this thread
    var mailbox = try Mailbox.create(alloc);
    errdefer mailbox.destroy(alloc);

    var result: Thread = .{
        .alloc = alloc,
        .config = .init(config),
        .loop = loop,
        .wakeup = wakeup_h,
        .stop = stop_h,
        .render_h = render_h,
        .draw_now = draw_now,
        .cursor_h = cursor_timer,
        .surface = surface,
        .renderer = renderer_impl,
        .state = state,
        .mailbox = mailbox,
        .app_mailbox = app_mailbox,
    };

    // Only enable compression if we have it enabled... save some
    // minor resources.
    if (comptime terminalpkg.compression_enabled) {
        result.compression = try .init();
    }

    return result;
}

/// Clean up the thread. This is only safe to call once the thread
/// completes executing; the caller must join prior to this.
pub fn deinit(self: *Thread) void {
    self.stop.deinit();
    self.wakeup.deinit();
    self.render_h.deinit();
    self.draw_now.deinit();
    self.cursor_h.deinit();
    if (comptime terminalpkg.compression_enabled)
        self.compression.deinit();
    self.loop.deinit();

    // Nothing can possibly access the mailbox anymore, destroy it.
    self.mailbox.destroy(self.alloc);
}

/// The main entrypoint for the thread.
pub fn threadMain(self: *Thread) void {
    // Call child function so we can use errors...
    self.threadMain_() catch |err| {
        // In the future, we should expose this on the thread struct.
        log.warn("error in renderer err={}", .{err});
    };
}

fn threadMain_(self: *Thread) !void {
    defer log.debug("renderer thread exited", .{});

    // Right now, on Darwin, `std.Thread.setName` can only name the current
    // thread, and we have no way to get the current thread from within it,
    // so instead we use this code to name the thread instead.
    if (builtin.os.tag.isDarwin()) {
        internal_os.macos.pthread_setname_np(&"renderer".*);
    }

    // Setup our crash metadata
    crash.sentry.thread_state = .{
        .type = .renderer,
        .surface = self.renderer.surface_mailbox.surface,
    };
    defer crash.sentry.thread_state = null;

    // Setup our thread QoS
    self.setQosClass();

    // Run our loop start/end callbacks if the renderer cares.
    const has_loop = @hasDecl(rendererpkg.Renderer, "loopEnter");
    if (has_loop) try self.renderer.loopEnter(self);
    defer if (has_loop) self.renderer.loopExit();

    // Run our thread start/end callbacks. This is important because some
    // renderers have to do per-thread setup. For example, OpenGL has to set
    // some thread-local state since that is how it works.
    try self.renderer.threadEnter(self.surface);
    defer self.renderer.threadExit();

    // Start the async handlers
    self.wakeup.wait(&self.loop, &self.wakeup_c, Thread, self, wakeupCallback);
    self.stop.wait(&self.loop, &self.stop_c, Thread, self, stopCallback);
    self.draw_now.wait(&self.loop, &self.draw_now_c, Thread, self, drawNowCallback);

    // Send an initial wakeup message so that we render right away.
    try self.wakeup.notify();

    // Start blinking the cursor.
    self.cursor_h.run(
        &self.loop,
        &self.cursor_c,
        cursorBlinkInterval(),
        Thread,
        self,
        cursorTimerCallback,
    );

    // Arm the animation timer in case the renderer already needs
    // animation wakes (e.g. custom shaders loaded at startup).
    self.armAnimationTimer();

    // Run
    log.debug("starting renderer thread", .{});
    defer log.debug("starting renderer thread shutdown", .{});
    _ = try self.loop.run(.until_done);
}

fn setQosClass(self: *const Thread) void {
    // Thread QoS classes are only relevant on macOS.
    if (comptime !builtin.target.os.tag.isDarwin()) return;

    const class: internal_os.macos.QosClass = class: {
        // If we aren't visible (our view is fully occluded) then we
        // always drop our rendering priority down because it's just
        // mostly wasted work.
        //
        // The renderer itself should be doing this as well (for example
        // Metal will stop our DisplayLink) but this also helps with
        // general forced updates and CPU usage i.e. a rebuild cells call.
        if (!self.flags.visible) break :class .utility;

        // If we're not focused, but we're visible, then we set a higher
        // than default priority because framerates still matter but it isn't
        // as important as when we're focused.
        if (!self.flags.focused) break :class .user_initiated;

        // We are focused and visible, we are the definition of user interactive.
        break :class .user_interactive;
    };

    if (internal_os.macos.setQosClass(class)) {
        log.debug("thread QoS class set class={}", .{class});
    } else |err| {
        log.warn("error setting QoS class err={}", .{err});
    }
}

/// Drain the mailbox.
fn drainMailbox(self: *Thread) !void {
    // There's probably a more elegant way to do this...
    //
    // This is effectively an @autoreleasepool{} block, which we need in
    // order to ensure that autoreleased objects are properly released.
    const pool = if (builtin.os.tag.isDarwin())
        @import("objc").AutoreleasePool.init()
    else
        void;
    defer if (builtin.os.tag.isDarwin()) pool.deinit();

    while (self.mailbox.pop(global.io())) |message| {
        log.debug("mailbox message={}", .{message});
        switch (message) {
            .crash => @panic("crash request, crashing intentionally"),

            .visible => |v| visible: {
                // If our state didn't change we do nothing.
                if (self.flags.visible == v) break :visible;

                // Set our visible state
                self.flags.visible = v;

                // Visibility affects our QoS class
                self.setQosClass();

                // If we became visible then we immediately rebuild cells
                // (renderCallback skips updateFrame while invisible) and
                // draw. Going through renderCallback also reschedules
                // any Kitty graphics animation wakeup that lapsed
                // while we were invisible.
                if (v) _ = renderCallback(self, undefined, undefined, {});

                // Notify the renderer so it can update any state.
                self.renderer.setVisible(v);

                // Note that we're explicitly today not stopping any
                // cursor timers, draw timers, etc. These things have very
                // little resource cost and properly maintaining their active
                // state across different transitions is going to be bug-prone,
                // so its easier to just let them keep firing and have them
                // check the visible state themselves to control their behavior.
            },

            .focus => |v| focus: {
                // If our state didn't change we do nothing.
                if (self.flags.focused == v) break :focus;

                // Set our state
                self.flags.focused = v;

                // Focus affects our QoS class
                self.setQosClass();

                // Set it on the renderer
                try self.renderer.setFocus(v);

                // Focus gates custom shader animation, so re-arm
                // the animation timer for the new state.
                self.armAnimationTimer();

                if (!v) {
                    // If we're not focused, then we stop the cursor blink
                    if (self.cursor_c.state() == .active and
                        self.cursor_c_cancel.state() == .dead)
                    {
                        self.cursor_h.cancel(
                            &self.loop,
                            &self.cursor_c,
                            &self.cursor_c_cancel,
                            void,
                            null,
                            cursorCancelCallback,
                        );
                    }
                } else {
                    // If we're focused, we immediately show the cursor again
                    // and then restart the timer.
                    if (self.cursor_c.state() != .active) {
                        self.flags.cursor_blink_visible = true;
                        self.cursor_h.run(
                            &self.loop,
                            &self.cursor_c,
                            cursorBlinkInterval(),
                            Thread,
                            self,
                            cursorTimerCallback,
                        );
                    }
                }
            },

            .reset_cursor_blink => {
                self.flags.cursor_blink_visible = true;
                if (self.cursor_c.state() == .active) {
                    self.cursor_h.reset(
                        &self.loop,
                        &self.cursor_c,
                        &self.cursor_c_cancel,
                        cursorBlinkInterval(),
                        Thread,
                        self,
                        cursorTimerCallback,
                    );
                }
            },

            .font_grid => |grid| {
                self.renderer.setFontGrid(grid.grid);
                grid.set.deref(grid.old_key);
            },

            .resize => |v| self.renderer.setScreenSize(v),

            .change_config => |config| {
                defer config.alloc.destroy(config.thread);
                defer config.alloc.destroy(config.impl);
                try self.changeConfig(config.thread);
                try self.renderer.changeConfig(config.impl);

                // The config affects what animation wakes the
                // renderer needs (custom shaders, animation mode).
                self.armAnimationTimer();
            },

            .search_viewport_matches => |v| {
                // Note we don't free the new value because we expect our
                // allocators to match.
                if (self.renderer.search_matches) |*m| m.arena.deinit();
                self.renderer.search_matches = v;
                self.renderer.search_matches_dirty = true;
            },

            .search_selected_match => |v| {
                // Note we don't free the new value because we expect our
                // allocators to match.
                if (self.renderer.search_selected_match) |*m| m.arena.deinit();
                self.renderer.search_selected_match = v;
                self.renderer.search_matches_dirty = true;
            },

            .inspector => |v| {
                self.flags.has_inspector = v;
            },

            .macos_display_id => |v| {
                if (@hasDecl(rendererpkg.Renderer, "setMacOSDisplayID")) {
                    try self.renderer.setMacOSDisplayID(v, &self.draw_now);
                }
            },
        }
    }
}

fn changeConfig(self: *Thread, config: *const DerivedConfig) !void {
    // A newly enabled scheduler must reconsider existing history even when no
    // terminal activity occurred while compression was disabled.
    if (comptime terminalpkg.compression_enabled) {
        if (!self.config.scrollback_compression and
            config.scrollback_compression)
        {
            self.compression.activity = null;
        }
    }

    self.config = config.*;
}

/// Trigger a draw. This will not update frame data or anything, it will
/// just trigger a draw/paint.
fn drawFrame(self: *Thread, now: bool) void {
    // If we're invisible, we do not draw.
    if (!self.flags.visible) return;

    // If the renderer is managing a vsync on its own, we only draw
    // when we're forced to via `now`.
    if (!now and self.renderer.hasVsync()) return;

    if (apprt.must_draw_from_app_thread) {
        _ = self.app_mailbox.push(
            .{ .redraw_surface = self.surface },
            .{ .instant = {} },
        );
    } else {
        self.renderer.drawFrame(false) catch |err|
            log.warn("error drawing err={}", .{err});
    }
}

fn wakeupCallback(
    self_: ?*Thread,
    _: *xev.Loop,
    _: *xev.Completion,
    r: xev.Async.WaitError!void,
) xev.CallbackAction {
    _ = r catch |err| {
        log.err("error in wakeup err={}", .{err});
        return .rearm;
    };

    const t = self_.?;

    // When we wake up, we check the mailbox. Mailbox producers should
    // wake up our thread after publishing.
    t.drainMailbox() catch |err|
        log.err("error draining mailbox err={}", .{err});

    // Render immediately
    _ = renderCallback(t, undefined, undefined, {});

    // PageList mutations maintain their own compression dirty state. Checking
    // it here covers output, resize, and viewport scrolling uniformly.
    t.compression.wake(t);

    // The below is not used anymore but if we ever want to introduce
    // a configuration to introduce a delay to coalesce renders, we can
    // use this.
    //
    // // If the timer is already active then we don't have to do anything.
    // if (t.render_c.state() == .active) return .rearm;
    //
    // // Timer is not active, let's start it
    // t.render_h.run(
    //     &t.loop,
    //     &t.render_c,
    //     10,
    //     Thread,
    //     t,
    //     renderCallback,
    // );

    return .rearm;
}

fn drawNowCallback(
    self_: ?*Thread,
    _: *xev.Loop,
    _: *xev.Completion,
    r: xev.Async.WaitError!void,
) xev.CallbackAction {
    _ = r catch |err| {
        log.err("error in draw now err={}", .{err});
        return .rearm;
    };

    // Draw immediately
    const t = self_.?;
    t.drawFrame(true);

    return .rearm;
}

fn renderCallback(
    self_: ?*Thread,
    _: *xev.Loop,
    _: *xev.Completion,
    r: xev.Timer.RunError!void,
) xev.CallbackAction {
    _ = r catch |err| switch (err) {
        // Sent when a scheduled animation wakeup is superseded by a
        // newer one (Timer.reset cancels the pending run). Nothing to
        // do; the replacement timer carries on.
        error.Canceled => return .disarm,
        else => unreachable,
    };
    const t: *Thread = self_ orelse {
        // This shouldn't happen so we log it.
        log.warn("render callback fired without data set", .{});
        return .disarm;
    };

    // If we're not visible there's no point spending CPU rebuilding cells —
    // we'll catch up when the .visible mailbox message flips us back on.
    // Kitty graphics animations pause with us and resume on visibility.
    if (!t.flags.visible) return .disarm;

    // Update our frame data
    t.renderer.updateFrame(
        t.state,
        t.flags.cursor_blink_visible,
    ) catch |err|
        log.warn("error rendering err={}", .{err});

    // Draw
    t.drawFrame(false);

    // Schedule the next animation wake, if the renderer needs one.
    t.armAnimationTimer();

    return .disarm;
}

/// Schedule the animation timer for the renderer's next animation
/// wake, if it needs one.
///
/// This is called after every frame update or animation draw and
/// whenever the wake inputs change (focus, config, visibility
/// regain). Resetting a pending timer is always safe: every call
/// recomputes the wake, so the deadline only ever moves toward the
/// actual next wake.
fn armAnimationTimer(self: *Thread) void {
    const wake = self.renderer.animationWake() orelse return;
    self.animation_wake = wake.kind;
    self.render_h.reset(
        &self.loop,
        &self.render_c,
        &self.render_c_cancel,
        wake.delay_ms,
        Thread,
        self,
        animationTimerCallback,
    );
}

fn animationTimerCallback(
    self_: ?*Thread,
    _: *xev.Loop,
    _: *xev.Completion,
    r: xev.Timer.RunError!void,
) xev.CallbackAction {
    _ = r catch |err| switch (err) {
        // Sent when a scheduled animation wake is superseded by a
        // newer one (Timer.reset cancels the pending run). Nothing to
        // do; the replacement timer carries on.
        error.Canceled => return .disarm,
        else => unreachable,
    };
    const t: *Thread = self_ orelse {
        // This shouldn't happen so we log it.
        log.warn("animation callback fired without data set", .{});
        return .disarm;
    };

    // Animations pause entirely while we're invisible; the .visible
    // mailbox message re-arms us when we can be seen again.
    if (!t.flags.visible) return .disarm;

    switch (t.animation_wake) {
        // Frame data must be updated (a Kitty animation frame is
        // due). renderCallback updates, draws, and re-arms us.
        .update => return renderCallback(
            t,
            undefined,
            undefined,
            {},
        ),

        // A redraw alone suffices (custom shader time uniform).
        // Draw calls don't update from the terminal state so they
        // are much cheaper than a frame update.
        .draw => {
            t.drawFrame(false);
            t.armAnimationTimer();
            return .disarm;
        },
    }
}

fn cursorTimerCallback(
    self_: ?*Thread,
    _: *xev.Loop,
    _: *xev.Completion,
    r: xev.Timer.RunError!void,
) xev.CallbackAction {
    _ = r catch |err| switch (err) {
        // This is sent when our timer is canceled. That's fine.
        error.Canceled => return .disarm,

        else => {
            log.warn("error in cursor timer callback err={}", .{err});
            unreachable;
        },
    };

    const t: *Thread = self_ orelse {
        // This shouldn't happen so we log it.
        log.warn("render callback fired without data set", .{});
        return .disarm;
    };

    t.flags.cursor_blink_visible = !t.flags.cursor_blink_visible;
    t.wakeup.notify() catch {};

    t.cursor_h.run(
        &t.loop,
        &t.cursor_c,
        cursorBlinkInterval(),
        Thread,
        t,
        cursorTimerCallback,
    );
    return .disarm;
}

fn cursorCancelCallback(
    _: ?*void,
    _: *xev.Loop,
    _: *xev.Completion,
    r: xev.Timer.CancelError!void,
) xev.CallbackAction {
    // This makes it easier to work across platforms where different platforms
    // support different sets of errors, so we just unify it.
    const CancelError = xev.Timer.CancelError || error{
        Canceled,
        NotFound,
        Unexpected,
    };

    _ = r catch |err| switch (@as(CancelError, @errorCast(err))) {
        error.Canceled => {}, // success
        error.NotFound => {}, // completed before it could cancel
        else => {
            log.warn("error in cursor cancel callback err={}", .{err});
            unreachable;
        },
    };

    return .disarm;
}

// fn prepFrameCallback(h: *libuv.Prepare) void {
//     _ = h;
//
//     tracy.frameMark();
// }

fn stopCallback(
    self_: ?*Thread,
    _: *xev.Loop,
    _: *xev.Completion,
    r: xev.Async.WaitError!void,
) xev.CallbackAction {
    _ = r catch unreachable;
    self_.?.loop.stop();
    return .disarm;
}

/// Returns the interval for the blinking cursor in milliseconds.
fn cursorBlinkInterval() u64 {
    if (std.valgrind.runningOnValgrind() > 0) {
        // If we're running under Valgrind, the cursor blink adds enough
        // churn that it makes some stalls annoying unless you're on a
        // super powerful computer, so we delay it.
        //
        // This is a hack, we should change some of our cursor timer
        // logic to be more efficient:
        // https://github.com/ghostty-org/ghostty/issues/8003
        return CURSOR_BLINK_INTERVAL * 5;
    }

    return CURSOR_BLINK_INTERVAL;
}

/// Schedules incremental terminal compression after renderer activity stops.
///
/// This owns all renderer-specific compression state. The terminal decides
/// when compression-relevant activity changes and performs the actual work;
/// the renderer only provides idle scheduling and avoids waiting for the
/// terminal lock.
const Compression = struct {
    const idle_interval = 250;
    const step_interval = 1;

    timer: xev.Timer,
    completion: xev.Completion = .{},
    reset_completion: xev.Completion = .{},
    activity: ?u64 = null,

    fn init() !Compression {
        return .{ .timer = try xev.Timer.init() };
    }

    fn deinit(self: *Compression) void {
        self.timer.deinit();
    }

    /// Start or postpone compression after a renderer wake.
    fn wake(self: *Compression, thread: *Thread) void {
        // If we have no compression then don't do anything.
        if (comptime !terminalpkg.compression_enabled) return;
        if (!thread.config.scrollback_compression) return;

        // PageList activity, rather than a generic renderer wake, restarts the
        // idle interval. In particular, the inspector wakes the renderer every
        // frame without changing terminal contents and must not starve this
        // timer indefinitely.
        if (thread.state.mutex.tryLock()) {
            defer thread.state.mutex.unlock(global.io());
            const activity = thread.state.terminal.compressionActivity();
            if (self.activity == activity) return;
            self.activity = activity;
        } else if (self.completion.state() == .active) {
            // Contention doesn't prove that compression-relevant activity
            // changed. Keep an existing deadline so frequent inspector frames
            // cannot postpone compression forever. The timer rechecks both the
            // activity token and lock availability before doing any work.
            return;
        }

        // Contention may mean parsing is active. Scheduling is a harmless
        // false positive when no compression work is actually pending, but is
        // necessary when no timer is already active.
        self.schedule(thread, idle_interval);
    }

    /// Start the one-shot timer, or move its deadline if it is already active.
    fn schedule(self: *Compression, thread: *Thread, delay_ms: u64) void {
        self.timer.reset(
            &thread.loop,
            &self.completion,
            &self.reset_completion,
            delay_ms,
            Thread,
            thread,
            timerCallback,
        );
    }

    fn timerCallback(
        thread_: ?*Thread,
        _: *xev.Loop,
        _: *xev.Completion,
        result: xev.Timer.RunError!void,
    ) xev.CallbackAction {
        _ = result catch |err| switch (err) {
            error.Canceled => return .disarm,
            else => {
                log.warn("error in compression timer err={}", .{err});
                return .disarm;
            },
        };

        const thread = thread_ orelse return .disarm;
        const self = &thread.compression;

        if (self.step(thread)) |delay| self.schedule(thread, delay);
        return .disarm;
    }

    /// Try one bounded step without waiting for the terminal lock. The return
    /// value is the delay before another attempt, or null when work is done.
    fn step(self: *Compression, thread: *Thread) ?u64 {
        if (!thread.config.scrollback_compression) return null;

        const state = thread.state;
        if (!state.mutex.tryLock()) return idle_interval;
        defer state.mutex.unlock(global.io());

        const activity = state.terminal.compressionActivity();
        if (self.activity != activity) {
            self.activity = activity;
            return idle_interval;
        }

        return switch (state.terminal.compress(.incremental)) {
            .pending => step_interval,
            .unsupported,
            .complete,
            => null,
        };
    }
};