parking_solution/packages/shared/src/index.ts

// Shared types and utilities across the parking system.
//
// The domain is offline-first and threat-model driven. The central integrity
// primitive is an append-only, hash-chained, ATECC608-signed event log: entry
// and exit events are never edited or deleted — a "void" is itself an appended
// event. See wiki/concepts/append-only-event-chain.md.

export type Role = "admin" | "operator" | "cashier" | "readonly";

export type Direction = "entry" | "exit";

/** What kind of identity source produced a read. */
export type IdentitySource = "wiegand" | "lpr" | "qr" | "ticket" | "manual";

/**
 * A signed business-LEDGER event. Records are never mutated; corrections are new
 * events. `prevHash` chains each event to the previous one; `signature` is the
 * ATECC608 signature over the canonical contents (which INCLUDE `payload`).
 * Distinct from device telemetry — see wiki/decisions/event-streams-split.md.
 */
export interface LedgerEvent {
  readonly id: string;
  readonly index: number;
  readonly type: LedgerEventType;
  readonly direction: Direction | null;
  readonly lane: number;
  readonly source: IdentitySource | null;
  /** Card number, plate, ticket id, etc. — depends on `source`. */
  readonly identity: string | null;
  /** Type-specific business data (amount, tariffVersionId, sessionRef…). Signed. */
  readonly payload: LedgerPayload | null;
  readonly occurredAt: string; // ISO-8601
  /** Hash of the previous event in the chain (hex). Null only for genesis. */
  readonly prevHash: string | null;
  /** ATECC608 signature over the canonical event payload (hex). */
  readonly signature: string;
  /** Which signer/key produced `signature` (verifiable across a signer swap). */
  readonly keyId: string;
}

/** Business/accountability events that live in the SIGNED, hash-chained ledger. */
export type LedgerEventType =
  | "vehicle_entry"
  | "vehicle_exit"
  | "payment"
  | "void"
  // Witness-grade: a host-commanded open, and an independently-observed open
  // (loop/sensor) — reconciled against each other.
  | "barrier_open_command"
  | "barrier_open_observed"
  // Manned-mode shift boundary: an operator takes over (shift_open) / hands over
  // with a takings summary (shift_z_report). See wiki/concepts/shift.md.
  | "shift_open"
  | "shift_z_report"
  | "anomaly";

/** How money was tendered (for payment events + the shift Z-report). */
export type Tender = "cash" | "card";

/**
 * Type-specific data carried on a ledger event's `payload`. All amounts are
 * integer minor units in the named currency — never floats. Fields are optional
 * because they're event-type-specific; the producer fills what applies.
 */
export interface LedgerPayload {
  /** The parking_session this event concerns (entry/exit/payment/void). */
  readonly sessionRef?: string;
  /** payment: amount in minor units, its currency, and how it was tendered. */
  readonly amountMinor?: number;
  readonly currency?: string;
  readonly tender?: Tender;
  /** payment: which tariff_version priced it (reproducible repricing). */
  readonly tariffVersionId?: string;
  /** payment: gross/discount/net split when a validation applied. */
  readonly grossMinor?: number;
  readonly discountMinor?: number;
  /** FX-ready, deferred: rate applied (null/absent now). See open-questions #8. */
  readonly fxRate?: number | null;
  /** void / anomaly / override: a human/machine reason code. */
  readonly reason?: string;
  /** plate/vehicle from the vision service (advisory). */
  readonly plate?: string;
  readonly plateConfidence?: number;
  /** Free-form for forward-compat without a schema change. */
  readonly [k: string]: unknown;
}

/** Operational device telemetry — UNSIGNED, prunable. NOT the ledger. */
export type DeviceEventKind = "input" | "relay" | "status" | "read" | "snapshot";

/**
 * The composable rate card stored in a tariff_version.structure. Pure data the
 * fee function interprets — no rates in code. Stepped duration blocks + caps/grace;
 * a flat rate is just one block. See wiki/concepts/tariff.md.
 */
export interface TariffStructure {
  /** Free if exited within this (drop-off/turnaround). */
  readonly gracePeriodEntryMin: number;
  /** Billing granularity; partial increments round UP. */
  readonly incrementMin: number;
  /** Consumed in order as duration accrues; last block may be open-ended. */
  readonly blocks: readonly TariffBlock[];
  /** Cap per rolling 24h (null = no cap). */
  readonly dailyCapMinor: number | null;
  /** Flat charge when there's no entry id (admin may override at the moment). */
  readonly lostTicketMinor: number;
  /** Pay-on-foot walk-back window: minutes after payment to reach the car. */
  readonly gracePeriodExitMin: number;
  /** How an overstay top-up is charged. "reprice" = recompute(entry→now) − paid. */
  readonly overstay: "reprice";
}

export interface TariffBlock {
  /** Upper bound of this block in minutes; null = open-ended (thereafter). */
  readonly uptoMin: number | null;
  readonly priceMinorPerIncrement: number;
}

/**
 * Compute the parking fee (integer minor units) for a stay, from a TariffStructure.
 * PURE + deterministic + offline — the pay station calls it with asOf = now; the
 * result is fixed into a signed `payment` event, so it must be reproducible.
 *
 * Algorithm (wiki/concepts/tariff.md): round duration UP to incrementMin; free if
 * within entry grace; else walk the stay one rolling-24h segment at a time, charging
 * each increment at its block's rate (blocks consumed in order by cumulative minutes),
 * capping each segment at dailyCapMinor. Times are ISO-8601; bad input → 0 (caller
 * validates the tariff exists first).
 */
export function computeFee(
  enteredAt: string,
  asOf: string,
  tariff: TariffStructure,
): number {
  const ms = Date.parse(asOf) - Date.parse(enteredAt);
  if (!Number.isFinite(ms) || ms <= 0) return 0;
  const rawMinutes = ms / 60_000;
  // Grace uses the RAW duration (a 10-min stay is free even if the increment is
  // 60 min — otherwise rounding-up would defeat the grace window).
  if (rawMinutes <= tariff.gracePeriodEntryMin) return 0;
  const inc = Math.max(1, tariff.incrementMin);
  const minutes = Math.ceil(rawMinutes / inc) * inc; // round UP to the increment

  const DAY = 24 * 60;
  let total = 0;
  for (let segStart = 0; segStart < minutes; segStart += DAY) {
    const segEnd = Math.min(segStart + DAY, minutes);
    let segFee = 0;
    // The block ladder RESETS each rolling-24h day: `within` is minutes elapsed
    // WITHIN this day, so day 2 starts at the first block again (decision 2026-06-15).
    for (let within = 0; segStart + within < segEnd; within += inc) {
      segFee += rateAt(tariff.blocks, within);
    }
    if (tariff.dailyCapMinor != null) segFee = Math.min(segFee, tariff.dailyCapMinor);
    total += segFee;
  }
  return total;
}

/**
 * Validate an admin-authored tariff structure. Returns [] if valid, else a list
 * of human-readable problems. Pure — used by the composer route (and any caller)
 * so a malformed rate card can never be published. See wiki/concepts/tariff.md.
 */
export function validateTariffStructure(s: unknown): string[] {
  const errs: string[] = [];
  if (!s || typeof s !== "object") return ["structure must be an object"];
  const t = s as Partial<TariffStructure>;

  const nonNegInt = (v: unknown, label: string) => {
    if (typeof v !== "number" || !Number.isInteger(v) || v < 0) errs.push(`${label} must be a non-negative integer`);
  };
  nonNegInt(t.gracePeriodEntryMin, "gracePeriodEntryMin");
  nonNegInt(t.gracePeriodExitMin, "gracePeriodExitMin");
  nonNegInt(t.lostTicketMinor, "lostTicketMinor");
  if (typeof t.incrementMin !== "number" || !Number.isInteger(t.incrementMin) || t.incrementMin < 1) {
    errs.push("incrementMin must be a positive integer");
  }
  if (t.dailyCapMinor != null) nonNegInt(t.dailyCapMinor, "dailyCapMinor");
  if (t.overstay !== "reprice") errs.push('overstay must be "reprice"');

  if (!Array.isArray(t.blocks) || t.blocks.length === 0) {
    errs.push("blocks must be a non-empty array");
  } else {
    let prevBound = 0;
    t.blocks.forEach((b, i) => {
      const last = i === t.blocks!.length - 1;
      nonNegInt(b?.priceMinorPerIncrement, `blocks[${i}].priceMinorPerIncrement`);
      if (b?.uptoMin == null) {
        if (!last) errs.push(`blocks[${i}] is open-ended (uptoMin null) but not last`);
      } else {
        if (typeof b.uptoMin !== "number" || !Number.isInteger(b.uptoMin) || b.uptoMin <= prevBound) {
          errs.push(`blocks[${i}].uptoMin must be an integer greater than the previous block's bound (${prevBound})`);
        } else {
          prevBound = b.uptoMin;
        }
      }
    });
  }
  return errs;
}

/** Price of the increment that starts at `cumulativeMin` — the block whose range
 *  [prevUpto, uptoMin) contains it; the open-ended (uptoMin=null) block catches the rest. */
function rateAt(blocks: readonly TariffBlock[], cumulativeMin: number): number {
  let prev = 0;
  for (const b of blocks) {
    if (b.uptoMin == null || cumulativeMin < b.uptoMin) return b.priceMinorPerIncrement;
    prev = b.uptoMin;
    void prev;
  }
  // No open-ended block and past the last bound: charge the last block's rate.
  return blocks.length ? blocks[blocks.length - 1]!.priceMinorPerIncrement : 0;
}

export const ROLES: readonly Role[] = [
  "admin",
  "operator",
  "cashier",
  "readonly",
] as const;

/**
 * Signs the canonical bytes of an event for the append-only chain. This is the
 * abstraction over the [[atecc608]] secure element: the real, non-extractable
 * hardware key is ONE implementation. Whether the chip is wired is still
 * open-question #6, so the server ships a software signer in the meantime —
 * same interface, swappable with no business-logic change (the device-adapter
 * philosophy applied to signing). See wiki/concepts/append-only-event-chain.md.
 *
 * IMPORTANT: a software signer makes the chain self-consistent and detectably
 * tamper-evident, but NOT unforgeable by someone who owns the machine — only the
 * ATECC608 provides that. Don't conflate the two.
 */
export interface Signer {
  /** Stable id of the signer/key (e.g. "sw-hmac-v1", "atecc608-slot0"). Stored
   *  alongside events so verification knows which key to check against. */
  readonly keyId: string;
  /** Sign the canonical payload; returns a hex signature. */
  sign(payload: string): string;
  /** Verify a signature over the payload (software signers can; the ATECC608
   *  verifies via its public key). */
  verify(payload: string, signature: string): boolean;
}