import { desc, eq, siteConfig, subscriptionPlans, tariffVersions, tariffs, type Db } from "@parking/db";
import {
  computeFee,
  minutesOutsideWindow,
  outOfWindowGap,
  type PlanTimeframes,
  type SubscriptionPlan,
  type TariffStructure,
} from "@parking/shared";

// Subscription TIME-WINDOW → TARIFF BRIDGE. A plan may restrict WHEN a subscriber may be
// parked (e.g. weekday 20:00→08:00, weekend all-day). A scan OUTSIDE the window is NOT
// refused — the out-of-window minutes are charged at the normal TRANSIENT tariff:
//   - early ENTRY: arrival → window-open is owed (deferred; collected at exit).
//   - late EXIT:   window-close → departure is owed (exit is GATED until paid).
// Only plans WITH timeframes trigger any charge; a 24/7 plan never does. The gap math is
// pure + tz-aware (outOfWindowGap in @parking/shared); pricing reuses computeFee (the same
// engine transient stays use). See wiki/entities/subscription.md ("tariff bridge").

const DEFAULT_TZ = "Europe/Tirane";

/** A computed out-of-window charge: the gap, what it costs, and the tariff version used
 *  (recorded so it reprices identically — like every transient payment). */
export interface WindowCharge {
  readonly amountMinor: number;
  readonly gapStart: string;
  readonly gapEnd: string;
  readonly minutes: number;
  readonly currency: string;
  readonly tariffVersionId: string;
}

/** The plan VERSION that priced a subscription's sale (by planVersionId), or null. The
 *  timeframes are read from THIS version so a later plan edit can't retroactively change
 *  an existing subscriber's window rules. */
export function planVersionById(db: Db, planVersionId: string | null): SubscriptionPlan | null {
  if (!planVersionId) return null;
  const row = db.select().from(subscriptionPlans).where(eq(subscriptionPlans.id, planVersionId)).get();
  return row ? (row as unknown as SubscriptionPlan) : null;
}

/** The site IANA timezone (falls back to the project default). */
export function siteTz(db: Db): string {
  const cfg = db.select().from(siteConfig).where(eq(siteConfig.id, 1)).get();
  return cfg?.timezone && cfg.timezone.length > 0 ? cfg.timezone : DEFAULT_TZ;
}

/** The active site tariff version in force at `at` (latest effectiveFrom ≤ at), or null. */
function tariffVersionAt(db: Db, at: string) {
  const tariff = db.select().from(tariffs).where(eq(tariffs.scope, "site")).get();
  if (!tariff) return null;
  const versions = db
    .select()
    .from(tariffVersions)
    .where(eq(tariffVersions.tariffId, tariff.id))
    .orderBy(desc(tariffVersions.effectiveFrom))
    .all();
  return versions.find((v) => v.effectiveFrom <= at) ?? null;
}

/**
 * Compute the out-of-window charge for a subscriber scan at `atISO`, or null when there
 * is nothing to charge (no plan timeframes, in-window, weekend all-day, within grace, or
 * no tariff configured). `edge` = "entry" (early) or "exit" (late). The gap is priced as
 * a fresh transient stay of that duration (computeFee over [gapStart, gapEnd]).
 */
export function windowCharge(
  db: Db,
  planVersionId: string | null,
  atISO: string,
  edge: "entry" | "exit",
): WindowCharge | null {
  const plan = planVersionById(db, planVersionId);
  const timeframes = (plan?.timeframes ?? null) as PlanTimeframes | null;
  if (!timeframes) return null; // 24/7 plan (or comp sub) — never a time charge.

  const tz = timeframes.tz || siteTz(db);
  const gap = outOfWindowGap(timeframes, tz, atISO, edge);
  if (!gap) return null; // in-window / all-day / within grace.

  const tv = tariffVersionAt(db, gap.start);
  if (!tv) return null; // no tariff to price against — can't charge (don't trap).
  const structure = tv.structure as unknown as TariffStructure;
  const amountMinor = computeFee(gap.start, gap.end, structure);
  if (amountMinor <= 0) return null;

  return {
    amountMinor,
    gapStart: gap.start,
    gapEnd: gap.end,
    minutes: gap.minutes,
    currency: tv.currency,
    tariffVersionId: tv.id,
  };
}

/**
 * The TOTAL out-of-window charge a subscriber owes for an OPEN occurrence, computed over
 * the whole stay `[enteredAt, nowISO)` in ONE shot (not entry-gap + exit-gap, which
 * double-counts and lets the exit gap reach back to a previous day's close). Sums the
 * minutes parked outside the plan's allowed window and prices them as a single transient
 * stay of that duration — so the tariff's increments + daily cap apply correctly. Returns
 * null when the plan has no timeframes / nothing is owed / no tariff to price against.
 */
export function windowOwedBetween(
  db: Db,
  planVersionId: string | null,
  enteredAtISO: string,
  nowISO: string,
): { amountMinor: number; minutes: number; currency: string; tariffVersionId: string } | null {
  const plan = planVersionById(db, planVersionId);
  const timeframes = (plan?.timeframes ?? null) as PlanTimeframes | null;
  if (!timeframes) return null;

  const tz = timeframes.tz || siteTz(db);
  const minutes = minutesOutsideWindow(timeframes, tz, enteredAtISO, nowISO);
  if (minutes <= 0) return null;

  // Price the out-of-window duration as a transient stay (entry→entry+minutes), against
  // the tariff in force at entry — reproducible, and the daily cap applies.
  const tv = tariffVersionAt(db, enteredAtISO);
  if (!tv) return null;
  const structure = tv.structure as unknown as TariffStructure;
  const end = new Date(Date.parse(enteredAtISO) + minutes * 60_000).toISOString();
  const amountMinor = computeFee(enteredAtISO, end, structure);
  if (amountMinor <= 0) return null;

  return { amountMinor, minutes, currency: tv.currency, tariffVersionId: tv.id };
}