att_menu/services/Brightness.qml

pragma Singleton

import Quickshell
import Quickshell.Io
import QtQuick
import qs.config

// The display backlight, driven through brightnessctl.
//
// Writing to /sys/class/backlight needs privileges a session usually does not
// have, so the write goes through brightnessctl, which asks logind when it
// cannot open the file itself. Reads do not: actual_brightness is world
// readable, so the current value comes straight off sysfs rather than from a
// process spawned every couple of seconds.
//
// sysfs attributes do not raise inotify events, so `refresh()` is polled by
// whoever is displaying the value — only the controls panel, and only while it
// is on screen. Nothing here runs with the panel closed.
Singleton {
    id: root

    // Device name as brightnessctl knows it, e.g. "intel_backlight", or "" on a
    // machine with no backlight — a desktop, or a laptop whose panel is not
    // controllable. Without one there is no brightness row.
    property string device: ""
    property int max: 0
    property int current: 0

    readonly property bool available: Config.showBrightness && root.device !== "" && root.max > 0

    readonly property real value: root.max > 0 ? root.current / root.max : 0

    // Never all the way off: a backlight at zero is indistinguishable from a
    // broken panel, and on most laptops the only way back is the hardware key.
    readonly property int minimum: Math.max(1, Math.round(root.max * Config.minBrightness))

    // What was last asked for, and whether a request landed while the previous
    // one was still in flight. Dragging the slider produces far more requests
    // than brightnessctl can service, so they coalesce onto the newest.
    property int pending: 0
    property bool queued: false

    function set(fraction: real): void {
        if (!root.available)
            return;

        const raw = Math.max(root.minimum, Math.min(root.max, Math.round(fraction * root.max)));
        if (raw === root.current && !write.running)
            return;

        // Optimistic, like the keyboard button: the slider has to track the
        // finger, not the process. The next refresh overwrites this with what
        // the hardware actually did.
        root.current = raw;
        root.pending = raw;

        if (write.running)
            root.queued = true;
        else
            root.dispatch();
    }

    function step(delta: real): void {
        root.set(root.value + delta);
    }

    function dispatch(): void {
        write.command = ["brightnessctl", "-m", "-q", "-c", "backlight", "-d", root.device, "set", String(root.pending)];
        write.running = true;
    }

    function refresh(): void {
        // A write in flight is the newer truth: sysfs still holds the value the
        // drag has already moved past.
        if (root.available && !write.running && !root.queued)
            actual.reload();
    }

    // `brightnessctl -m` prints one CSV line per device:
    //   device,class,current,percent,max
    function parseInfo(text: string): void {
        const fields = text.trim().split("\n")[0].split(",");
        if (fields.length < 5)
            return;

        const max = parseInt(fields[4]);
        if (!(max > 0))
            return;

        root.device = fields[0];
        root.max = max;
        root.current = parseInt(fields[2]) || 0;
    }

    Process {
        id: write
    }

    // Guarded by `command -v` so a machine without brightnessctl gets a quiet
    // "no backlight" rather than a failed spawn on every start.
    Process {
        running: Config.showBrightness

        command: ["sh", "-c", "command -v brightnessctl >/dev/null 2>&1 && brightnessctl -m -c backlight || true"]

        stdout: StdioCollector {
            onStreamFinished: root.parseInfo(this.text)
        }
    }

    // actual_brightness, not brightness: what the hardware settled on, which is
    // also what the hardware keys move.
    FileView {
        id: actual

        path: root.available ? `/sys/class/backlight/${root.device}/actual_brightness` : ""
        printErrors: false

        onLoaded: {
            if (write.running || root.queued)
                return;

            const value = parseInt(this.text());
            if (value >= 0)
                root.current = value;
        }
    }

    Connections {
        target: write

        function onExited(exitCode: int, exitStatus: int): void {
            if (root.queued) {
                root.queued = false;
                root.dispatch();
                return;
            }

            // What the hardware settled on, which is the value the next step
            // has to count from — and, when the write was refused (no logind,
            // or a device that will not take the value), the number that goes
            // back under the slider.
            actual.reload();
        }
    }
}