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parking_solution/wiki/concepts/capacity-occupancy.md
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julian 5697137c52 feat(subscription): rename permit→subscription + monthly pricing
The "permit/lejet" feature is really a subscription. Full rename of the
mutable master data, plus a recurring monthly price.

- DB (migration 0004, data-preserving ALTER RENAME): permits→subscriptions,
  permit_credentials/_plates→subscription_*, sessions.permit_id→subscription_id.
- Pricing: per-subscription priceMinor + period(monthly) + currency, with a
  site default (site_config.subscription_monthly_price_minor) pre-filling the form.
- Server: subscription-flow.ts (SubscriptionFlow), routes/subscriptions.ts
  (/api/subscriptions). Web: SubscriptionManager, route, i18n (sq Abonimet/en).
- The signed ledger `permitId` payload is intentionally kept — immutable
  hash-chained history; renaming it would break verification of past events.

Deferred (wiki notes): fee collection into the ledger/shift (a shift-attributed
payment), LPR/ANPR plate source, time-of-day access windows (overnight subscriber).

Also carries the device-footer UI surface (api DeviceStatus, router mount,
i18n devices) due to shared-file overlap with the preceding footer commit.

Verified end-to-end on a fresh DB and migration on a live-DB copy (sessions
preserved). Live DB migrated. Full monorepo builds clean.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V
2026-06-18 13:15:04 +02:00

3.6 KiB
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type, tags, sources, updated, status
type tags sources updated status
concept
parking
domain
business
occupancy
2026-06-15 open

Capacity & Occupancy

How many vehicles are inside, how many spaces remain, and what happens when the lot is full.

Occupancy is a projection (like everything else)

occupancy = count(open [[parking-session|sessions]]) — an entry with no matching exit. It is a fold over the signed append-only-event-chain, never a hand-maintained counter (a counter is editable and drifts; the chain is the truth). Spaces-free = capacity − occupancy.

  • capacity is admin-set per site (and per zone/level if the lot has sections — model a zone on capacity + on the entry so multi-level is a later addition, not a rewrite).
  • Permit concurrency (maxConcurrent, see subscription) is the same kind of fold, scoped to one permit's open sessions.

Full → refuse entry + FULL sign

  • When occupancy ≥ capacity, the entry flow refuses (no vehicle_entry, no barrier open) and can drive a "FULL" sign (a relay/output, via the device adapter layer).
  • Safety/policy nuance: "full" blocks entry only — exit always works (fail-state-safety: exit fails open; never trap a vehicle). Permit holders may be allowed in past a "transient full" threshold (reserve spaces for subscribers) — an optional policy knob.
  • Counting drift is real: tailgating (two cars, one entry) and missed reads make the live count diverge from physical reality. The count is the system's occupancy; periodic ground-truth (a loop count, or the opencv-anpr-service count) reconciles it — surfaced as an anomaly, not silently corrected.

"Full" is a soft, operator-configurable policy

Refusing at capacity is the default, not an absolute. An operator may opt into valet-overcapacity — accept the car into operator custody (keys handed over, stacked beyond the marked count) instead of refusing. So the FULL gate is a policy knob (refuse vs. valet-accept), set by the operator per site. Valet is a manned-mode feature with its own custody/session shape — see valet-overcapacity (deferred).

As-built (2026-06-16)

  • Occupancy = occupancyCount (apps/server/src/occupancy.ts): a fold over the ledger — entries minus exits per identity, count those > 0. getOccupancy returns {count, capacity, free, full}.
  • Capacity is a single-row site_config table (admin-set; null = uncapped). Routes (routes/site.ts): GET /api/occupancy + GET /api/site-config (any role), PUT /api/site-config (admin; non-negative int or null).
  • FULL gate is in the transient entry flow: occupancy.full → refuse (no ticket, no vehicle_entry, no open) + signed anomaly. Permit entry is NOT gated here — subscribers are admitted past transient-full (their own maxConcurrent still applies); occupancy can read over-capacity (free negative) when permits enter a full lot, as intended.
  • UI SiteSettings: live occupancy + FULL badge (everyone); capacity editor (admin).
  • Verified: fill to cap → 3rd transient refused; permit still admitted past full; exit frees a slot; RBAC (operator can't set capacity); verifyChain ok. Physical FULL-sign relay output is deferred (needs a sign device).

Open

  • Zone/level granularity at launch vs. single capacity number.
  • Reserve-for-permits threshold (a soft transient cap below the hard capacity) — currently permits are simply ungated; a tunable threshold is the richer version.
  • Physical FULL-sign relay output (a sign-device role).
  • The valet over-capacity mode + custody model (valet-overcapacity).