diet-guard/CLAUDE.md

CLAUDE.md — diet_guard

What this does

A log-to-unlock gate: every ~30 minutes, diet-guard-gate.timer runs diet-guard-gate.service, which checks whether a meal slot (08:00, 12:00, 16:00, 20:00) has elapsed without a logged meal. If so, it opens a fullscreen Tk window that blocks the desktop until the user logs what they ate (with autocomplete from a local food-name "bank", optionally seeded from Open Food Facts via requests). It also tracks a daily calorie/macro budget, sealed at init time and tamper-resistant via chattr +i.

See docs/design.md for the original feature spec (meal-slot timing logic, the Tue/Wed/Thu "filled most of the day" catch-up rule, multi-item meals).

Scheduling

diet-guard-gate.timer — wall-clock OnCalendar=*-*-* *:00/30:00, Persistent=true. Deliberately wall-clock rather than boot-relative: an earlier boot-relative timer interacted badly with fullscreen games grabbing keyboard/mouse input around the same point in their session, so this is pinned to the clock instead of "N minutes after boot/login."

diet-guard-gate.service is Type=oneshot, fires every tick, and exits 0 immediately if no lock is due — cheap enough to run that often. It needs DISPLAY/XAUTHORITY because it opens a Tk window; see the inline comments in the unit file for why XAUTHORITY is pinned explicitly (a Persistent=true catch-up run at session start can beat the display manager writing ~/.Xauthority) and why a real fix lives in Python (wait_for_display()) rather than in the unit file.

Production dependency installation — read this before adding any dependency

diet-guard-gate.service runs /usr/bin/python directly — not a venv. Any new non-stdlib dependency (this package itself, gatelock, requests, anything added later) must be installed into system Python's user site-packages, the same place python-kasa already lives:

/usr/bin/python3 -m pip install --user --break-system-packages -e .

install.sh already does this. If you add a dependency and only install it into a dev venv, the production service will silently fail with ModuleNotFoundError on its next tick — this exact gap caused a 3-day diet_guard production outage (2026-06-19 to 2026-06-22) when gatelock was added but only pip install-ed into .venv. Always verify against /usr/bin/python3 -c "import <new_dep>", not just the dev venv, before considering a dependency change done.

Operational gotchas

• The budget file is sealed immutable. ~/.local/share/diet_guard/.budget gets chattr +i after init (see install.sh step 5). This is the actual tamper-resistance mechanism — the budget can't be casually edited to "make room" once locked. To intentionally change it: sudo chattr -i the file, re-run python -m diet_guard init, then re-lock.
• Biometrics are used once and discarded. init asks for biometrics to compute the daily budget, then the only persisted output is the computed budget number — never the biometrics themselves.
• State lives entirely under ~/.local/share/diet_guard/ — no cross-repo file coupling (unlike wake_alarm, which reads ~/screen-locker/screen_locker/workout_log.json). Safe to reason about in isolation.

Commands

• Run tests: python -m pytest diet_guard/tests/ --cov=diet_guard --cov-branch --cov-fail-under=100
• Lint: pre-commit run --all-files
• Test the lock manually (safe, closeable): python -m diet_guard gate --demo
• Install for production: bash install.sh

Do NOT

• Don't relax the meal-slot/macro logic without re-reading docs/design.md — the Tue/Wed/Thu catch-up rule and multi-item meal summing are deliberate, not accidental complexity.
• Don't add a dependency without doing the production install-path check above.
• Don't remove the chattr +i step from install.sh — it's the actual enforcement mechanism, not a formality.