bambuddy/spoolbuddy/daemon/display_control.py

"""Display brightness and screen blanking control for SpoolBuddy kiosk.

Brightness: DSI backlights are controlled via sysfs /sys/class/backlight/*/brightness.
            HDMI brightness is handled by the frontend via CSS filter.
Blanking:   swayidle is the sole authority on screen blanking (idle timeout →
            wlopm --off, touch → wlopm --on).  The daemon only *wakes* the
            display via wlopm --on when NFC/scale activity is detected — it
            never blanks.  wlopm --on is idempotent so both paths coexist
            safely.
"""

import logging
import os
import shutil
import subprocess
import time
from pathlib import Path

logger = logging.getLogger(__name__)

BACKLIGHT_BASE = Path("/sys/class/backlight")


class DisplayControl:
    def __init__(self):
        self._backlight_path = self._find_backlight()
        self._max_brightness = self._read_max_brightness()
        self._blank_timeout = 0  # seconds, 0 = disabled
        self._last_activity = time.monotonic()
        self._blanked = False
        self._wlopm_path = shutil.which("wlopm")
        self._wayland_env: dict[str, str] | None = None
        self._output = os.environ.get("SPOOLBUDDY_DISPLAY_OUTPUT", "HDMI-A-1")

        if self._backlight_path:
            logger.info("Backlight found: %s (max=%d)", self._backlight_path, self._max_brightness)
        else:
            logger.info("No DSI backlight found, brightness control via frontend CSS")

        if self._wlopm_path:
            logger.info("wlopm found at %s, HDMI wake/blank enabled", self._wlopm_path)
        else:
            logger.info("wlopm not found, HDMI wake/blank disabled")

    def _find_backlight(self) -> Path | None:
        if not BACKLIGHT_BASE.exists():
            return None
        for entry in BACKLIGHT_BASE.iterdir():
            brightness_file = entry / "brightness"
            if brightness_file.exists():
                return entry
        return None

    def _read_max_brightness(self) -> int:
        if not self._backlight_path:
            return 100
        try:
            return int((self._backlight_path / "max_brightness").read_text().strip())
        except Exception:
            return 255

    @property
    def has_backlight(self) -> bool:
        return self._backlight_path is not None

    def set_brightness(self, pct: int):
        """Set backlight brightness (0-100%). No-op if no backlight."""
        if not self._backlight_path:
            return
        pct = max(0, min(100, pct))
        value = round(self._max_brightness * pct / 100)
        try:
            (self._backlight_path / "brightness").write_text(str(value))
            logger.debug("Brightness set to %d%% (%d/%d)", pct, value, self._max_brightness)
        except PermissionError:
            logger.warning(
                "Permission denied writing to %s/brightness. Ensure spoolbuddy user is in the 'video' group.",
                self._backlight_path,
            )
        except Exception as e:
            logger.warning("Failed to set brightness: %s", e)

    def set_blank_timeout(self, seconds: int):
        """Set screen blank timeout in seconds. 0 = disabled."""
        self._blank_timeout = max(0, seconds)

    def wake(self):
        """Wake screen on activity (NFC tag, scale weight change).

        Always calls wlopm --on regardless of the daemon's internal blanked
        state, because swayidle may have blanked the screen independently and
        the daemon has no way to know.  wlopm --on is idempotent so calling it
        while the screen is already on is harmless.
        """
        self._last_activity = time.monotonic()
        self._blanked = False
        self._wlopm(on=True)

    def tick(self):
        """Called periodically from heartbeat loop. Tracks idle state internally."""
        if self._blank_timeout <= 0:
            self._blanked = False
            return
        idle = time.monotonic() - self._last_activity
        if not self._blanked and idle >= self._blank_timeout:
            self._blanked = True
            logger.debug("Screen idle timeout reached (swayidle manages blanking)")

    _WAYLAND_ENV_FILE = Path("/tmp/spoolbuddy-wayland-env")

    def _discover_wayland_env(self) -> dict[str, str] | None:
        """Discover WAYLAND_DISPLAY and XDG_RUNTIME_DIR for the kiosk session.

        The daemon runs as a systemd service outside the Wayland session, so
        these variables aren't inherited.  The kiosk idle watchdog
        (spoolbuddy-idle.sh) writes them to /tmp/spoolbuddy-wayland-env on
        startup — read that file.
        """
        if not self._WAYLAND_ENV_FILE.exists():
            return None
        try:
            env: dict[str, str] = {}
            for line in self._WAYLAND_ENV_FILE.read_text().strip().splitlines():
                if "=" in line:
                    key, value = line.split("=", 1)
                    env[key] = value
            wayland_display = env.get("WAYLAND_DISPLAY", "")
            xdg_runtime_dir = env.get("XDG_RUNTIME_DIR", "")
            if wayland_display and xdg_runtime_dir:
                return {"WAYLAND_DISPLAY": wayland_display, "XDG_RUNTIME_DIR": xdg_runtime_dir}
        except Exception as e:
            logger.warning("Failed to read %s: %s", self._WAYLAND_ENV_FILE, e)
        return None

    def _wlopm(self, on: bool) -> None:
        """Toggle HDMI output via wlopm.  No-op if wlopm is unavailable."""
        if not self._wlopm_path:
            logger.warning("wlopm not available, cannot control HDMI")
            return
        # Retry discovery each call until the Wayland socket appears — labwc
        # may start after the daemon on boot.
        if self._wayland_env is None:
            self._wayland_env = self._discover_wayland_env()
            if self._wayland_env is None:
                logger.warning("No Wayland socket found in /run/user/ (uid=%d), cannot control HDMI", os.getuid())
                return
            logger.info("Wayland session discovered: %s", self._wayland_env.get("WAYLAND_DISPLAY"))
        flag = "--on" if on else "--off"
        try:
            env = {**os.environ, **self._wayland_env}
            result = subprocess.run(
                [self._wlopm_path, flag, self._output],
                env=env,
                timeout=5,
                capture_output=True,
                text=True,
            )
            if result.returncode != 0:
                logger.warning(
                    "wlopm %s %s exit=%d: %s",
                    flag,
                    self._output,
                    result.returncode,
                    (result.stderr or result.stdout).strip(),
                )
            else:
                logger.info("wlopm %s %s OK", flag, self._output)
        except Exception as e:
            logger.warning("wlopm %s %s failed: %s", flag, self._output, e)