import { desc, eq, ledgerEvents, sessions, tariffVersions, tariffs, type Db } from "@parking/db";
import { computeFee, type TariffStructure, type Tender } from "@parking/shared";
import type { FastifyBaseLogger } from "fastify";
import type { EventLog } from "./event-log.js";

// The PAY STATION: a customer pays for an open session BEFORE walking back to the
// car (pay-on-foot — payment is decoupled from exit). Two steps:
//   1. quote(identity)  → look up the open session, price it against the tariff in
//      force at entry, return the amount due (no side effect).
//   2. pay(identity, tender) → re-price, append a SIGNED `payment` event carrying
//      the amount, currency, tender, tariffVersionId, and graceExitMin (so the exit
//      flow can validate paid + within walk-back grace). Payment is a signed ledger
//      event, never a mutable "paid" flag — an operator can't forge or delete it.
// See wiki/concepts/tariff.md, parking-session.md.

export class NoOpenSessionError extends Error {
  constructor(identity: string) {
    super(`no open session for ${identity}`);
    this.name = "NoOpenSessionError";
  }
}
export class NoTariffError extends Error {
  constructor() {
    super("no active tariff configured");
    this.name = "NoTariffError";
  }
}

export interface Quote {
  readonly identity: string;
  readonly enteredAt: string;
  readonly amountMinor: number;
  readonly currency: string;
  readonly tariffVersionId: string;
  readonly graceExitMin: number;
}

/** One row in the booth Active Sessions list. A session is "active" while it is
 *  still open OR exited-but-within-grace — because the barrier is UNCONFIRMED, a
 *  paid/exited car is presumed possibly-still-present until grace expires. The
 *  "Open barrier" action is offered only when `paidAt != null` (no payment, no
 *  button — the no-unpaid-bypass rule). See wiki/concepts/booth-exit-flow.md. */
export interface ActiveSession {
  readonly identity: string;
  readonly source: string | null;
  readonly enteredAt: string;
  /** null while still inside; set once a vehicle_exit is signed (may still be present). */
  readonly exitedAt: string | null;
  readonly open: boolean;
  readonly paidAt: string | null;
  /** Amount owed now (open + unpaid only; null otherwise / no tariff). */
  readonly amountMinor: number | null;
  readonly currency: string | null;
  readonly withinGrace: boolean;
  readonly graceExpiresAt: string | null;
}

/** Booth session view: everything the pay/exit modal needs in one read. */
export interface SessionLookup {
  readonly identity: string;
  readonly found: boolean;
  /** Open = entered, no exit yet. */
  readonly open: boolean;
  readonly enteredAt: string | null;
  readonly exitedAt: string | null;
  /** Latest payment time, if paid. */
  readonly paidAt: string | null;
  /** Amount owed right now (the quote). Null when no session / no active tariff. */
  readonly amountMinor: number | null;
  readonly currency: string | null;
  /** True when paid AND still within the walk-back grace window. */
  readonly withinGrace: boolean;
  /** ISO time the walk-back grace expires (paidAt + graceExitMin), if paid. */
  readonly graceExpiresAt: string | null;
}

export class PayStation {
  readonly #db: Db;
  readonly #log: EventLog;
  readonly #logger: FastifyBaseLogger;

  constructor(db: Db, log: EventLog, logger: FastifyBaseLogger) {
    this.#db = db;
    this.#log = log;
    this.#logger = logger;
  }

  /** Price an open session against the tariff in force at its entry. No side effect. */
  quote(identity: string): Quote {
    const entry = this.#openEntry(identity);
    if (!entry) throw new NoOpenSessionError(identity);

    const tv = this.#tariffVersionFor(entry.occurredAt);
    if (!tv) throw new NoTariffError();
    const structure = tv.structure as unknown as TariffStructure;

    const amountMinor = computeFee(entry.occurredAt, new Date().toISOString(), structure);
    return {
      identity,
      enteredAt: entry.occurredAt,
      amountMinor,
      currency: tv.currency,
      tariffVersionId: tv.id,
      graceExitMin: structure.gracePeriodExitMin,
    };
  }

  /**
   * Take payment for a session and append the signed `payment` event. Re-quotes at
   * the moment of payment (the customer pays for time parked SO FAR). For an
   * overstay top-up the same call re-prices entry→now and the exit flow's
   * grace-window restarts from this payment. `overrideMinor` lets the operator set
   * an arbitrary amount (lost ticket / dispute) — recorded as the charged amount.
   */
  async pay(
    identity: string,
    tender: Tender,
    overrideMinor?: number,
  ): Promise<{ amountMinor: number; currency: string }> {
    const q = this.quote(identity);
    const amountMinor = overrideMinor ?? q.amountMinor;

    await this.#log.append({
      type: "payment",
      source: "manual",
      identity,
      payload: {
        sessionRef: identity,
        amountMinor,
        currency: q.currency,
        tender,
        tariffVersionId: q.tariffVersionId,
        // The exit flow reads graceExitMin off the payment to validate the
        // walk-back window without re-resolving the tariff.
        graceExitMin: q.graceExitMin,
        ...(overrideMinor != null ? { reason: "operator-set amount", quotedMinor: q.amountMinor } : {}),
      },
    });

    // Update the projection cache (rebuildable; not the source of truth).
    try {
      this.#db.update(sessions).set({ state: "paid" }).where(eq(sessions.id, identity)).run();
    } catch (err) {
      this.#logger.error(`session-cache mark-paid failed for ${identity}: ${(err as Error).message}`);
    }

    this.#logger.info(`payment ${amountMinor} ${q.currency} (${tender}) for ${identity}`);
    return { amountMinor, currency: q.currency };
  }

  /**
   * One-read session view for the booth pay/exit modal: entry/exit times, paid
   * state, amount owed now, and walk-back-grace status. Read-only — folds the
   * signed ledger (authoritative). A quote failure (no tariff) leaves amount null
   * rather than throwing, so the modal can still show the session.
   */
  lookup(identity: string): SessionLookup {
    const id = identity.trim();
    const rows = this.#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 {
        identity: id, found: false, open: false, enteredAt: null, exitedAt: null,
        paidAt: null, amountMinor: null, currency: null, withinGrace: false, graceExpiresAt: null,
      };
    }
    const exitRow = rows.find((r) => r.type === "vehicle_exit");
    const open = !exitRow;

    let paidAt: string | null = null;
    let graceExitMin: number | null = null;
    for (const r of rows) {
      if (r.type === "payment") {
        paidAt = r.occurredAt;
        const p = (r.payload ?? {}) as { graceExitMin?: number };
        if (typeof p.graceExitMin === "number") graceExitMin = p.graceExitMin;
      }
    }
    const graceExpiresAt =
      paidAt && graceExitMin != null ? new Date(Date.parse(paidAt) + graceExitMin * 60_000).toISOString() : null;
    const withinGrace = graceExpiresAt != null && Date.now() <= Date.parse(graceExpiresAt);

    // Amount owed now (best-effort; null if no tariff resolves). Only meaningful while open.
    let amountMinor: number | null = null;
    let currency: string | null = null;
    if (open) {
      try {
        const q = this.quote(id);
        amountMinor = q.amountMinor;
        currency = q.currency;
      } catch {
        /* no active tariff — leave null; modal shows session without a price */
      }
    }

    return {
      identity: id, found: true, open,
      enteredAt: entry.occurredAt, exitedAt: exitRow?.occurredAt ?? null,
      paidAt, amountMinor, currency, withinGrace, graceExpiresAt,
    };
  }

  /**
   * All ACTIVE sessions for the booth list: still-open, OR exited-but-within-grace
   * (the barrier is unconfirmed, so a paid/exited car is presumed possibly-present
   * until grace expires). One ledger scan, grouped by identity (cheaper than N
   * lookups). Sorted by entry time, newest first. Folds the SIGNED ledger
   * (authoritative — not the sessions projection cache, which can drift).
   * See wiki/concepts/booth-exit-flow.md.
   */
  activeSessions(): ActiveSession[] {
    const rows = this.#db.select().from(ledgerEvents).orderBy(ledgerEvents.index).all();

    // Group the relevant events per identity in one pass.
    type Acc = { enteredAt?: string; source: string | null; exitedAt?: string; paidAt?: string; graceExitMin?: number };
    const byId = new Map<string, Acc>();
    for (const r of rows) {
      const id = r.identity;
      if (!id) continue;
      if (r.type === "vehicle_entry") {
        const a = byId.get(id) ?? { source: r.source ?? null };
        a.enteredAt = r.occurredAt;
        a.source = r.source ?? a.source;
        byId.set(id, a);
      } else if (r.type === "vehicle_exit") {
        const a = byId.get(id);
        if (a) a.exitedAt = r.occurredAt;
      } else if (r.type === "payment") {
        const a = byId.get(id);
        if (a) {
          a.paidAt = r.occurredAt;
          const p = (r.payload ?? {}) as { graceExitMin?: number };
          if (typeof p.graceExitMin === "number") a.graceExitMin = p.graceExitMin;
        }
      }
    }

    const now = Date.now();
    const out: ActiveSession[] = [];
    for (const [identity, a] of byId) {
      if (!a.enteredAt) continue; // no entry → not a real session
      const open = a.exitedAt == null;
      const graceExpiresAt =
        a.paidAt && a.graceExitMin != null
          ? new Date(Date.parse(a.paidAt) + a.graceExitMin * 60_000).toISOString()
          : null;
      const withinGrace = graceExpiresAt != null && now <= Date.parse(graceExpiresAt);
      const paid = a.paidAt != null;

      // ACTIVE membership:
      //  - exited + within grace  → still shown (barrier unconfirmed, may be present);
      //  - exited + past grace     → presumed gone, omitted;
      //  - open + UNPAID           → always shown (a car owing money never ages out —
      //    it's genuinely still inside until it pays, however long that takes);
      //  - open + PAID + past grace → AGE-OUT (omit). A paid car whose walk-back grace
      //    lapsed has left; if no vehicle_exit was ever signed (e.g. it left via a
      //    manual barrier re-open before that path closed the session, or a historical
      //    session like T-397815c0) it would otherwise linger forever. The signed log
      //    is unchanged — this is purely a display filter. See booth-exit-flow.md.
      if (!open && !withinGrace) continue;
      if (open && paid && graceExpiresAt != null && !withinGrace) continue;

      // Amount owed now: only meaningful for an open + unpaid session.
      let amountMinor: number | null = null;
      let currency: string | null = null;
      if (open && a.paidAt == null) {
        try {
          const q = this.quote(identity);
          amountMinor = q.amountMinor;
          currency = q.currency;
        } catch {
          /* no active tariff — leave null */
        }
      }

      out.push({
        identity,
        source: a.source,
        enteredAt: a.enteredAt,
        exitedAt: a.exitedAt ?? null,
        open,
        paidAt: a.paidAt ?? null,
        amountMinor,
        currency,
        withinGrace,
        graceExpiresAt,
      });
    }

    // Newest entry first.
    out.sort((x, y) => Date.parse(y.enteredAt) - Date.parse(x.enteredAt));
    return out;
  }

  /** The vehicle_entry of an OPEN session for this identity (no later exit), or null. */
  #openEntry(identity: string) {
    const rows = this.#db
      .select()
      .from(ledgerEvents)
      .where(eq(ledgerEvents.identity, identity))
      .orderBy(ledgerEvents.index)
      .all();
    const entry = rows.find((r) => r.type === "vehicle_entry");
    if (!entry) return null;
    if (rows.some((r) => r.type === "vehicle_exit")) return null; // already closed
    return entry;
  }

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