PresenceEngine is an immutable, database-free snapshot of the
children's schedules answering is_present(child_id, date): a child
with NO schedule entry is present every day (the household's
always-present sibling); a scheduled child is present exactly when
the date's weekday is in the pattern for that date's cycle week
(anchor-date arithmetic via cycle_week_index — never ISO parity).
Construction validates the snapshot shape (dict keyed by the
schedule's own child_id, values are PresenceSchedules) and exposes it
read-only (MappingProxyType + __setattr__ refusal). is_present
rejects non-int child ids and non-plain dates.
Tests: the three-child fixture (two complementary rotation children,
one schedule-free) asserted for every day of a four-week span plus
spot-checked swap days; weekend/weekday-set behaviour across weeks;
construction/input rejection matrix; engine immutability. Suite:
985 passed.
Review round 1 (Codex gpt-5.6-terra, LOW): the boundary walk asserted
transitions in {(same, +1)} which even a reset/inverting
implementation could satisfy on a two-week cycle. The test now
asserts a hand-verified table of expected indices for every day
around each of the three Dec-31/Jan-1 boundaries (2019/2020/2021,
anchor 2019-01-06), so a parity bug cannot pass by coincidence.
Suite: 980 passed.
presence.cycle_week_index: ((target_date - anchor_date).days // 7) %
cycle_length_weeks — anchor-date arithmetic ONLY (D-004). Python
floor division makes pre-anchor dates walk the cycle backwards
(day -1 is the last week), never inverting; the modulo of a negative
stays non-negative, so the index is always a valid week index. The
target date passes through the model's strict plain-date parsing.
Tests: formula offsets, three-week pattern wrap, backwards walking,
day-by-day stability across three Dec-31 -> Jan-1 boundaries
including 2020 (verified 53 ISO weeks — the parity-inversion
regression), and a source guard that the module never reads ISO week
numbers. Suite: 980 passed.
Review round 1 (Codex gpt-5.6-terra, 2 MEDIUM): datetime.datetime
subclasses datetime.date and slipped past the anchor check, storing a
time component that would TypeError every later calendar comparison —
rejected explicitly now (both model classes). The frozen schedule's
pattern dict let callers inject unvalidated weekdays or drop required
weeks after construction; the validated mapping is now exposed as a
read-only MappingProxyType over frozenset weeks. Tests: datetime
rejection matrix and immutability assertions. Suite: 974 passed.
presence.py — a PURE module (no HA imports, no DB access, no timezone
logic): PresenceSchedule (child_id, cycle_length_weeks, anchor_date,
pattern mapping week index -> frozenset of present weekdays) and
PresenceOverride (child_id, inclusive start/end range, real-bool
is_present, optional note) with construction that rejects every
invalid shape up front:
- cycle length: integer 1..4 (the 4 cap mirrors schema.py's documented
CHECK); bools/floats/strings rejected.
- pattern: dict required; week indices validated as non-bool ints
covering 0..n-1 exactly (gaps and extras rejected); weekday sets
validated as ints 0..6 (bools rejected — True would silently mean
Monday; strings rejected — '02' would silently mean {0,2}); an
explicitly empty week is valid (absent all week — distinct from no
schedule, the engine's default).
- anchor/override dates: datetime.date or strict YYYY-MM-DD (strptime
round-trip; '2026-1-5' rejected).
- override range: end >= start; is_present must be a real bool;
note optional string.
- child ids: non-bool ints (SQLite binds True as 1).
Serialization: encode() emits the database's pipe-separated CSV
(sorted weekdays per week, empty segment for an absent week);
decode() derives the cycle length from the segment count (mirroring
the schema's segment-count CHECK) and validates strictly, so
decode(encode(x)) round-trips losslessly and equal patterns encode
identically. Tests: 59 (construction matrix, round-trips, encode
shapes, override coverage). Suite: 972 passed.
Joshua King