Availability & Scheduling

The availability engine turns a subject's working hours (minus the time they're already busy) into open booking slots. It is pure, core, and reusable by any feature that needs "who is free when" — bookings is one consumer.

Schedules

A subject has one schedule (Schedule / data/schedule_class.php, table sch_schedules) — it is the subject's availability and the timezone anchor for their windows.

sch_subject_type / sch_subject_id — the owning CalendarSubject, unique together (one schedule per subject).
sch_timezone — the IANA timezone the windows are defined in.

Schedule::for_subject(CalendarSubject) and Schedule::get_or_create_for_subject(CalendarSubject) load (or seed) the row.

Weekly windows (ScheduleWindow, scw_schedule_windows): scw_day_of_week (0=Sunday…6=Saturday), scw_start_time/scw_end_time (PostgreSQL time). End must be after start; windows do not cross midnight (enter an overnight span as two windows on adjacent days).

Date overrides (ScheduleOverride, sco_schedule_overrides): sco_date plus nullable sco_start_time/sco_end_time. If any override rows exist for a date, they replace the weekly windows for that date — a single row with null start/end means fully unavailable; rows with times are that date's windows.

The wall-clock-time exception

Unlike every other time in the database (UTC), scw_*_time / sco_*_time are wall-clock times in the schedule's timezone, not UTC instants — "9am Monday" must survive DST transitions. The slot generator converts wall-clock windows to UTC instants per concrete date.

SlotGenerator

includes/scheduling/SlotGenerator.php — pure computation, no HTTP/DB, unit-testable.

SlotGenerator::generate(array $params) → list of ['start'=>UTC, 'end'=>UTC]. Params: timezone, windows, overrides, range (UTC), duration_minutes, increment_minutes, buffer_before_minutes, buffer_after_minutes, min_notice_minutes, busy (the busy projection), optional now_utc.
SlotGenerator::availableIntervals(array $params) → merged free intervals (windows minus busy), for previews.
SlotGenerator::forSchedule($schedule, $start, $end, $opts, $busy) → loads a Schedule's windows/overrides and generates slots; the caller supplies the busy projection.

Algorithm: expand weekly windows over the concrete dates (applying overrides, converting wall-clock → UTC per date), pad busy blocks by the buffers, then anchor the increment grid to each availability window's start and emit a duration-long slot at each grid point that stays inside the window, clears the padded busy regions, and passes the min-notice and range filters. Window-anchored (not busy-anchored) start times keep slots on a predictable grid.

Per-period caps (max bookings/day/week) are not the generator's job — the bookings layer counts its own bookings and suppresses slots on capped days, bounded in the schedule's timezone.

Availability editor

/profile/bookings/availability (a bookings-plugin view over the core models) edits the subject's single schedule: weekly windows, date overrides, and timezone. It previews the resulting open availability (green) against existing commitments using the calendar_grid component, fed by /api/v1/action/availability_preview.

Calendar UI components

Two universal HTML5 + vanilla-JS component types in views/components/, rendered viewer-local from UTC data:

calendar_grid — month/week views of timed items. ComponentRenderer::render(null, 'calendar_grid', ['items'=>[...], 'view'=>'month', 'feed_url'=>'...', 'initial_date'=>'Y-m-d']). With feed_url it fetches {items:[...]} per range and pages client-side. Emits a calendardayclick event (date) for click-to-create.
slot_picker — booking time picker: mini-month + the selected day's times + a viewer-timezone selector (auto-detected, overridable). Loads UTC slots from slots_url ({slots:[{start,end}]}) and writes the chosen UTC slot start into a hidden field; emits a slotchosen event.

Data layer

sch_schedules, scw_schedule_windows, sco_schedule_overrides, and cal_entries are core data-model classes. Schedule and CalendarEntry carry a polymorphic owner — (subject_type, subject_id) rather than a usr_users FK — so each defines a hand-written owner-or-staff authenticate_read/write() keyed on subject_id.