parking_solution/apps/server/src/routes/tariffs.ts

import { randomUUID } from "node:crypto";
import type { FastifyInstance } from "fastify";
import { desc, eq, ledgerEvents, siteConfig, tariffVersions, tariffs, type Db } from "@parking/db";
import {
  computeFee,
  isTariffV2,
  priceSession,
  validateTariffStructure,
  type SessionPayment,
  type TariffStructure,
} from "@parking/shared";
import { requirePermission } from "../auth.js";

/** Default site timezone for wall-clock tariff windows when none is configured. */
const DEFAULT_TZ = "Europe/Tirane";

// Tariff composer API — the admin builds + edits the rate card at runtime. Tariffs
// are EFFECTIVE-DATED IMMUTABLE VERSIONS: editing publishes a new version, never
// mutates one; a session reprices against the version in force at its entry, and
// the `payment` event records the tariffVersionId. "One active tariff per site" for
// now (a single `tariffs` row, lazily created). See wiki/concepts/tariff.md.

interface PublishBody {
  currency: string;
  structure: TariffStructure;
  /** When this version takes effect (ISO-8601). Defaults to now. */
  effectiveFrom?: string;
}

const SITE_TARIFF_NAME = "Site tariff";

/** Body for POST /api/tariff/simulate — price a hypothetical session, no ledger write.
 *  Provide a structure source (one of): `tariffVersionId`, inline `structure`, or
 *  neither (uses the active version). */
interface SimulateBody {
  enteredAt: string; // ISO-8601
  asOf: string; // ISO-8601 (the "now"/exit instant being simulated)
  payments?: SessionPayment[]; // hypothetical payment history (latest grants grace)
  category?: string;
  tariffVersionId?: string;
  structure?: TariffStructure;
  currency?: string;
}

export async function tariffRoutes(app: FastifyInstance, db: Db): Promise<void> {
  // Reading the rate card (pay station / operator UI needs it).
  const readGuard = requirePermission("tariff:read");
  // Publishing a new version changes what customers are charged.
  const writeGuard = requirePermission("tariff:update");

  // The single site tariff row, created on first read/publish.
  function ensureSiteTariff(): string {
    const existing = db.select().from(tariffs).where(eq(tariffs.scope, "site")).get();
    if (existing) return existing.id;
    const id = randomUUID();
    db.insert(tariffs).values({ id, scope: "site", name: SITE_TARIFF_NAME }).run();
    return id;
  }

  // Current state: the active (latest-effective, ≤ now) version + the full history.
  app.get("/api/tariff", { preHandler: readGuard }, async () => {
    const tariffId = ensureSiteTariff();
    const versions = db
      .select()
      .from(tariffVersions)
      .where(eq(tariffVersions.tariffId, tariffId))
      .orderBy(desc(tariffVersions.effectiveFrom))
      .all();
    const now = new Date().toISOString();
    const active = versions.find((v) => v.effectiveFrom <= now) ?? null;
    return { tariffId, active, versions };
  });

  // Publish a new immutable version. Validates the structure first — a malformed
  // rate card can never be published (the fee calc + the chain depend on it).
  app.post<{ Body: PublishBody }>(
    "/api/tariff/versions",
    { preHandler: writeGuard },
    async (req, reply) => {
      const { currency, structure, effectiveFrom } = req.body ?? ({} as PublishBody);
      if (!currency || typeof currency !== "string" || currency.length < 3) {
        return reply.code(400).send({ error: "currency (ISO 4217) required" });
      }
      // For a windowed (V2) structure, stamp the wall-clock timezone from SITE config
      // (not the client) BEFORE validating — so the frozen tz is authoritative and the
      // validation that requires tz passes. A V1 (bare) structure is left untouched.
      let toStore: TariffStructure = structure;
      if (structure && isTariffV2(structure)) {
        const cfg = db.select().from(siteConfig).where(eq(siteConfig.id, 1)).get();
        const tz = cfg?.timezone && cfg.timezone.length > 0 ? cfg.timezone : DEFAULT_TZ;
        toStore = { ...structure, tz };
      }

      const problems = validateTariffStructure(toStore);
      if (problems.length) {
        return reply.code(400).send({ error: "invalid tariff structure", problems });
      }

      // effectiveFrom must NOT be in the past. A version is selected by
      // "latest effectiveFrom <= entry time", so a backdated effectiveFrom would
      // retroactively reprice already-entered sessions — exactly the immutability
      // the versioning exists to prevent (wiki/concepts/tariff.md). So we forbid
      // backdating: a new version applies only from publish (now) forward; a future
      // effectiveFrom (scheduling a price change) is allowed. A small skew tolerance
      // absorbs client/server clock drift + request round-trip. Once a car has
      // entered, no later publish can reprice it (no effectiveFrom can predate it).
      const now = Date.now();
      const SKEW_MS = 60_000; // 1 min: clock skew + round-trip slack
      let effective = new Date().toISOString();
      if (effectiveFrom != null) {
        const t = Date.parse(effectiveFrom);
        if (Number.isNaN(t)) {
          return reply.code(400).send({ error: "effectiveFrom must be a valid ISO-8601 timestamp" });
        }
        if (t < now - SKEW_MS) {
          return reply.code(400).send({
            error: "effectiveFrom cannot be in the past — backdating a tariff would retroactively reprice entered sessions",
          });
        }
        effective = new Date(t).toISOString();
      }

      const tariffId = ensureSiteTariff();
      const id = randomUUID();
      const row = {
        id,
        tariffId,
        effectiveFrom: effective,
        currency,
        structure: toStore as unknown as Record<string, unknown>,
        createdBy: req.user?.username ?? null,
      };
      db.insert(tariffVersions).values(row).run();
      return reply.code(201).send(row);
    },
  );

  // --- Tariff Lab (simulator) -------------------------------------------------
  // Price a HYPOTHETICAL session at arbitrary times against any tariff version —
  // pure, no ledger writes. Lets an admin test rates "in time" (overnight windows,
  // daily caps, overstay) in seconds instead of waiting hours. Also used to quote a
  // customer dispute on-site. tariff:read (admins always have it). See tariff.md.
  app.post<{ Body: SimulateBody }>("/api/tariff/simulate", { preHandler: readGuard }, async (req, reply) => {
    const b = req.body ?? ({} as SimulateBody);
    if (!b.enteredAt || !b.asOf) {
      return reply.code(400).send({ error: "enteredAt and asOf (ISO-8601) required" });
    }
    if (!(Date.parse(b.enteredAt) <= Date.parse(b.asOf))) {
      return reply.code(400).send({ error: "asOf must be at or after enteredAt" });
    }

    // Resolve the structure: an explicit version id, or the active version, or an
    // inline structure (preview unpublished edits). A version carries its currency.
    let structure: TariffStructure | undefined = b.structure;
    let currency = b.currency ?? null;
    if (b.tariffVersionId) {
      const v = db.select().from(tariffVersions).where(eq(tariffVersions.id, b.tariffVersionId)).get();
      if (!v) return reply.code(404).send({ error: "tariff version not found" });
      structure = v.structure as unknown as TariffStructure;
      currency = v.currency;
    } else if (!structure) {
      const tariffId = ensureSiteTariff();
      const nowIso = new Date().toISOString();
      const active =
        db
          .select()
          .from(tariffVersions)
          .where(eq(tariffVersions.tariffId, tariffId))
          .orderBy(desc(tariffVersions.effectiveFrom))
          .all()
          .find((v) => v.effectiveFrom <= nowIso) ?? null;
      if (!active) return reply.code(404).send({ error: "no active tariff to simulate against" });
      structure = active.structure as unknown as TariffStructure;
      currency = active.currency;
    }

    const problems = validateTariffStructure(structure);
    if (problems.length) return reply.code(400).send({ error: "invalid tariff structure", problems });

    const payments = Array.isArray(b.payments) ? b.payments : [];
    const pricing = priceSession(b.enteredAt, b.asOf, structure, payments, b.category);

    // A duration curve from entry: handy to SEE where the cap flattens / windows shift.
    const SAMPLES_MIN = [30, 60, 120, 180, 360, 720, 1440, 2880, 4320];
    const enteredMs = Date.parse(b.enteredAt);
    const curve = SAMPLES_MIN.map((min) => ({
      minutes: min,
      amountMinor: computeFee(b.enteredAt, new Date(enteredMs + min * 60_000).toISOString(), structure!, b.category),
    }));

    return { currency, pricing, curve, gracePeriodExitMin: structure.gracePeriodExitMin };
  });

  // Prefill the lab from a REAL session: fold its ledger into entry + payments so the
  // admin can re-evaluate an actual ticket (e.g. an overstay) at any chosen `asOf`.
  app.get<{ Params: { identity: string } }>(
    "/api/tariff/simulate/session/:identity",
    { preHandler: readGuard },
    async (req, reply) => {
      const id = (req.params.identity ?? "").trim();
      if (!id) return reply.code(400).send({ error: "identity required" });
      const rows = db
        .select()
        .from(ledgerEvents)
        .where(eq(ledgerEvents.identity, id))
        .orderBy(ledgerEvents.index)
        .all();
      const entry = rows.find((r) => r.type === "vehicle_entry");
      if (!entry) return reply.code(404).send({ error: "no session for identity" });
      const payments: { paidAt: string; graceExitMin: number | null }[] = [];
      for (const r of rows) {
        if (r.type !== "payment") continue;
        const g = (r.payload as { graceExitMin?: number } | null)?.graceExitMin;
        payments.push({ paidAt: r.occurredAt, graceExitMin: typeof g === "number" ? g : null });
      }
      const exit = rows.find((r) => r.type === "vehicle_exit");
      const category = (entry.payload as { category?: string } | null)?.category ?? null;
      return {
        identity: id,
        enteredAt: entry.occurredAt,
        exitedAt: exit?.occurredAt ?? null,
        payments,
        category,
        // The version frozen at entry — the rate card this session actually keeps.
        tariffVersionId: tariffVersionIdFor(entry.occurredAt),
      };
    },
  );

  /** The tariff version in force at a given instant (latest effectiveFrom ≤ when). */
  function tariffVersionIdFor(whenIso: string): string | null {
    const tariffId = ensureSiteTariff();
    const v =
      db
        .select()
        .from(tariffVersions)
        .where(eq(tariffVersions.tariffId, tariffId))
        .orderBy(desc(tariffVersions.effectiveFrom))
        .all()
        .find((row) => row.effectiveFrom <= whenIso) ?? null;
    return v?.id ?? null;
  }
}