HDR Toggle for Gnome - can be assigned to shortcut and run via gjs

hdr-toggle.js

#!/usr/bin/gjs
const {GLib, Gio} = imports.gi;

const BUS_NAME = 'org.gnome.Mutter.DisplayConfig';
const BUS_PATH = '/org/gnome/Mutter/DisplayConfig';

const ColorMode = {SDR: 0, HDR: 1};
const PERSISTENT = 2;

const connection = Gio.bus_get_sync(Gio.BusType.SESSION, null);

const dbusCall = (method, params) =>
    connection.call_sync(
        BUS_NAME, BUS_PATH, BUS_NAME,
        method, params, null,
        Gio.DBusCallFlags.NONE, -1, null
    );

const notify = message => {
    Gio.Subprocess.new(
        ['notify-send', '-a', 'HDR Toggle', message],
        Gio.SubprocessFlags.NONE
    );
};

// recursiveUnpack unwraps the values inside Mutter's a{sv} dictionaries.
const [serial, monitors, displayLayouts, topLevelProps] =
    dbusCall('GetCurrentState', null).recursiveUnpack();

// Mode tuples contain the ID at index 0 and properties at index 6.
const monitorsByConnector = new Map(monitors.map(([[connector], modes, props]) => {
    const modeId = modes.find(mode => mode[6]['is-current'] === true)?.[0] ?? modes[0]?.[0];
    return [connector, {
        modeId,
        colorMode: props['color-mode'] ?? ColorMode.SDR,
        hdrCapable: (props['supported-color-modes'] ?? []).includes(ColorMode.HDR),
        underscanning: props['underscanning'],
    }];
}));

const monitorsWithoutMode = [...monitorsByConnector]
    .filter(([, monitor]) => monitor.modeId == null)
    .map(([connector]) => connector);

if (monitorsWithoutMode.length > 0) {
    notify(`Could not determine a display mode for: ${monitorsWithoutMode.join(', ')}`);
    imports.system.exit(1);
}

const hdrMonitors = [...monitorsByConnector.values()].filter(monitor => monitor.hdrCapable === true);

if (hdrMonitors.length === 0) {
    notify('No HDR-capable monitors.');
    imports.system.exit(1);
}

// Any non-SDR mode (including mode 2) counts as HDR being on.
const targetColorMode = hdrMonitors.some(monitor => monitor.colorMode === ColorMode.SDR)
    ? ColorMode.HDR
    : ColorMode.SDR;

// ApplyMonitorsConfig takes per-monitor properties, unlike GetCurrentState.
const updatedLayouts = displayLayouts.map(([x, y, scale, transform, primary, displays]) =>
    [x, y, scale, transform, primary, displays.map(([connector]) => {
        const monitor = monitorsByConnector.get(connector);
        const props = {};
        if (monitor.underscanning !== undefined) {
            props['underscanning'] = new GLib.Variant('b', monitor.underscanning);
        }
        if (monitor.hdrCapable === true) {
            props['color-mode'] = new GLib.Variant('u', targetColorMode);
        }
        return [connector, monitor.modeId, props];
    })]
);

const applyProps = {};
if (topLevelProps['layout-mode'] !== undefined) {
    applyProps['layout-mode'] = new GLib.Variant('u', topLevelProps['layout-mode']);
}

dbusCall('ApplyMonitorsConfig',
    new GLib.Variant('(uua(iiduba(ssa{sv}))a{sv})', [serial, PERSISTENT, updatedLayouts, applyProps])
);

const nightLight = new Gio.Settings({schema_id: 'org.gnome.settings-daemon.plugins.color'});
const stateDir = GLib.get_user_state_dir();
const nightLightMarker = GLib.build_filenamev([stateDir, 'hdr-toggle-night-light']);

if (targetColorMode === ColorMode.HDR && nightLight.get_boolean('night-light-enabled') === true) {
    GLib.mkdir_with_parents(stateDir, 0o700);
    GLib.file_set_contents(nightLightMarker, '');
    nightLight.set_boolean('night-light-enabled', false);
} else if (targetColorMode === ColorMode.SDR &&
    GLib.file_test(nightLightMarker, GLib.FileTest.EXISTS) === true) {
    if (nightLight.set_boolean('night-light-enabled', true) === true) {
        GLib.unlink(nightLightMarker);
    }
}

notify(`HDR ${targetColorMode === ColorMode.HDR ? 'enabled' : 'disabled'}`);