slot-engine

---
name: slot-engine
description: The pure `computeAvailableSlots` function — inputs, outputs, invariants, and debugging guide.
---

# Slot engine

`import { computeAvailableSlots } from "@agent-native/scheduling/core"`

## Inputs
- Event type config (duration, buffers, minimum notice, period, limits,
  slot interval)
- Schedule (timezone + weekly availability + date overrides)
- Busy intervals (UTC, aggregated from external calendars + existing
  bookings)
- Booking counts by bucket (day/week/month/year) for limit enforcement
- Time range to compute over
- Optional seats-per-slot + seats-taken map
- Viewer timezone (for limit bucketing, if it differs from the schedule)

## Output
- Array of `Slot { start: ISO, end: ISO, available: boolean, seatsRemaining?, hostEmail? }`

## Invariants

The function guarantees, in order:

1. No slot falls in the past (`now + minimumBookingNotice` is the floor).
2. No slot overlaps a busy interval (with buffers applied).
3. No slot falls outside the schedule's available intervals for that day.
4. No slot exceeds a booking limit.
5. No slot falls outside the event's period (rolling/range).
6. DST-safe: we convert to UTC using the schedule's timezone before doing
   any interval arithmetic.

## Debugging

If a slot is unexpectedly missing:
1. Check the schedule's weekly availability for that day-of-week in the
   schedule's timezone (not UTC — weekends can shift across the date line).
2. Check date overrides for that local date (empty intervals = fully
   blocked).
3. Check merged busy intervals for overlap, *including* the before/after
   buffer expansion.
4. Check booking limits: a single existing booking can close a day.
5. Check period caps: rolling periods restrict how far in the future slots
   appear.

If a slot is unexpectedly present:
1. Check that `now` is being passed correctly (defaults to `new Date()`).
2. Check that busy intervals from providers are in UTC.
3. Confirm slot interval matches what you expect (default = duration).