ExBooking

Deterministic booking logic for Elixir apps.

Installation · Quick Start · Livebooks · What It Does · Boundary · Benchmarks · Development

ExBooking is the small booking brain you put inside a product that already owns people, calendars, CRM records, payments, and workflows. Give it normalized data; it answers the hard deterministic questions: which slots are valid, whether a requested time still works, which resource should take the booking, and which events or intents the consumer app should execute next.

It has no database, no supervision tree, no provider clients, no jobs, and no clock reads. If a decision depends on the current time, the caller passes now. That makes availability, assignment, holds, cancellation, rescheduling, and calendar-data normalization easy to test and safe to replay.

What It Does

Capability	Purpose
Availability assembly	Expands wall-time rules, applies overrides and blackouts, subtracts buffered busy time, and returns sorted slots.
DST-safe scheduling	Resolves ambiguous fall-back times to the first occurrence and snaps spring-forward gaps forward.
Participant modes	Supports one-resource, collective, and capacity-aware pool booking.
Request validation	Reports all conflicts and policy failures instead of stopping at the first one.
Assignment	Picks resources with deterministic first-available, round-robin, least-recently-booked, weighted, priority, owner-first, and scorer-driven strategies.
Lifecycle decisions	Emits pure events and ordered intents for confirmation, reservation, release, reschedule, cancellation, expiry, and no-show.
Calendar interop	Normalizes a narrow dependency-free RRULE, ICS FREEBUSY, and decoded JSCalendar busy-time surface.

Installation

def deps do
  [
    {:ex_booking, "~> 0.2.0"}
  ]
end

ExBooking uses tz for timezone conversion. Configure it once in the consumer application:

config :elixir, :time_zone_database, Tz.TimeZoneDatabase

Quick Start

meeting_type = %ExBooking.MeetingType{
  id: "intro_call",
  duration_min: 30,
  slot_interval_min: 15
}

resource = %ExBooking.Resource{id: "resource_1", timezone: "Etc/UTC"}

rule = %ExBooking.AvailabilityRule{
  timezone: "Etc/UTC",
  windows: [
    %{weekday: 1, start_time: ~T[09:00:00], end_time: ~T[17:00:00]},
    %{weekday: 2, start_time: ~T[09:00:00], end_time: ~T[17:00:00]}
  ],
  lead_time_min: 60
}

{:ok, slots} =
  ExBooking.available_slots(meeting_type, [resource], [rule],
    now: ~U[2026-07-08 12:00:00Z],
    from: ~U[2026-07-13 00:00:00Z],
    until: ~U[2026-07-14 23:59:59Z]
  )

request = %ExBooking.Request{
  meeting_type_id: "intro_call",
  invitee_timezone: "America/New_York",
  slot: hd(slots),
  routing_context: %{source: "website"}
}

{:ok, decision} =
  ExBooking.decide(request, meeting_type, [resource], [rule],
    now: ~U[2026-07-08 12:00:00Z]
  )

:ok = decision.status
[%ExBooking.Event{type: :booking_confirmed}] = decision.events
[
  {:calendar_event, :create, _payload},
  {:notify, :booking_confirmation, _payload},
  {:emit, _event}
] = decision.intents

Livebooks

The Livebook notebooks are executable guides, not extra API reference pages. Start with the complete tour in your browser:

A Tour of ExBooking - Explore the whole library in one sitting: search, decide, hold, reschedule, and cancel.
Interval Algebra - Learn the half-open temporal math everything else builds on.
Schedules & DST - Turn wall time into UTC across spring-forward gaps and fall-back folds.
Availability & Slotting - Work with duration, step, grid alignment, buffers, and participant modes.
Assignment & Policy - Compare all six strategies, fairness inputs, scorers, and policy predicates.
Lifecycle & Calendar Interop - Follow decisions into events, intents, RRULE, ICS, and JSCalendar.

The notebook sources live in notebooks/.

From a local checkout, livebook server notebooks/tour.livemd — the setup cell detects the checkout and installs ExBooking from source, so the notebook always demonstrates the code you have. The run links above launch the notebooks from the latest release on HexDocs, where each notebook page also carries a "Run in Livebook" badge pinned to its release. They point at the ex-booking.hexdocs.pm host directly, because the hexdocs.pm/ex_booking redirect drops the CORS header that Livebook needs to render a preview.

Every code cell and its saved output is executed and verified by the test suite; after changing library behavior, refresh the outputs with:

mix run scripts/regen_notebook_outputs.exs

Boundary

ExBooking deliberately stops at decisions. Your application remains responsible for persistence, transactions, auth, tenancy, UI, calendar sync, notifications, CRM enrichment, routing forms, analytics, payments, retries, webhooks, and AI.

That split is the point: keep reusable booking math in one deterministic library, and keep product-specific orchestration in the product.

Calendar Data

The interop modules are intentionally small:

{:ok, intervals} =
  ExBooking.expand_rrule("FREQ=WEEKLY;COUNT=4;BYDAY=MO", dtstart, 30,
    from: from,
    until: until
  )

{:ok, busy} = ExBooking.import_ics_free_busy(ics_text)
{:ok, busy} = ExBooking.import_jscalendar_busy(decoded_jscalendar_map)

Provider auth, transport, JSON decoding, full recurrence sync, and calendar writeback belong outside this package.

Benchmarks

The benchmark suite covers interval algebra, schedule expansion, availability, validation, assignment, lifecycle decisions, and calendar-data normalizers.

mix bench --smoke   # quick run that refreshes benchmark markdown
mix bench           # full local measurement run

The generated benchmark report is included in HexDocs as the performance page.

Development

mix setup
mix test
mix check --no-retry
mix docs
mix bench --smoke

Quality gates require formatted code, no compiler warnings, strict Credo, Dialyzer, dependency audit, complete public documentation, generated docs, and at least 95% test coverage.

License

ExBooking is released under the MIT License. See LICENSE.