import { randomInt } from "node:crypto";
import { eq, sessions, siteConfig, type Db, type DeviceRow } from "@parking/db";
import {
  NoPrinterAvailableError,
  printWithFailover,
  registry,
  type AccessControlDevice,
  type PrinterDevice,
  type PrinterInstance,
  type TicketData,
  type TicketHeader,
} from "@parking/devices";
import type { FastifyBaseLogger } from "fastify";
import type { DeviceInputEvent } from "./device-events.js";
import { getOccupancy } from "./occupancy.js";
import type { EventLog } from "./event-log.js";
import { devicesByDirection, relayForButton, type ResolvedRelay } from "./device-resolve.js";
import { snapshotAsync } from "./snapshot.js";

// The transient ENTRY flow: a button press → print a ticket → sign a vehicle_entry
// → open the barrier. The button is wired into an access controller's input; the
// admin maps that input terminal to a relay (config.relays[].button), so a press
// resolves to exactly the entry relay it should open. See entry-exit-points.md.
//
// Two invariants from the threat model + safety analysis:
//   1. SIGNED BEFORE OPEN — the vehicle_entry is appended to the signed ledger
//      BEFORE pulseOpen fires; an open with no matching signed event is the fraud
//      signal (wiki/concepts/append-only-event-chain.md).
//   2. HOLD ON PRINT FAILURE — a transient with no ticket can't pay on exit, so if
//      all printers are down we do NOT open. We sign an `anomaly` (attempt, ticket
//      unprinted) and leave the barrier closed; the operator handles the held car.
//      Crucially, NO vehicle_entry is written in that case — we never record an
//      "entered" event for a car that didn't get in (decision 2026-06-15).
//
// Ordering: print → (ok) sign vehicle_entry → pulseOpen → snapshot → cache session.
//                   (fail) sign anomaly, stop.

export class EntryFlow {
  readonly #db: Db;
  readonly #log: EventLog;
  readonly #logger: FastifyBaseLogger;
  /** Guard against double-fire from the same physical press (on edge only). */
  readonly #inFlight = new Set<string>();

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

  /** Handle a device input edge. Acts only on the rising ("on") edge of an entry
   *  button — an input terminal mapped to an entry relay on its controller. */
  async onInput(e: DeviceInputEvent): Promise<void> {
    if (e.edge !== "on") return; // release edge is just telemetry

    // The firing device must be an access controller, and the pressed input terminal
    // must map to an ENTRY (or both) relay — that's an entry button. Anything else
    // (reader/printer edge, exit-only relay's input) is not a transient-entry trigger.
    const resolved = relayForButton(this.#db, e.deviceId, e.input);
    if (!resolved) return;

    const key = `${e.deviceId}:${e.input}`;
    if (this.#inFlight.has(key)) return; // ignore re-fire while one is processing
    this.#inFlight.add(key);
    try {
      await this.#runEntry(resolved);
    } catch (err) {
      this.#logger.error(`entry-flow failed: ${(err as Error).message}`);
    } finally {
      this.#inFlight.delete(key);
    }
  }

  async #runEntry(resolved: ResolvedRelay): Promise<void> {
    // CAPACITY GATE (transient only). When the lot is full, refuse transient entry:
    // no ticket, no vehicle_entry, no open — sign an anomaly. Permit holders are NOT
    // gated here (their flow ignores site-full; their own maxConcurrent applies), so
    // subscribers aren't locked out. "Full" is a soft policy seam for valet over-
    // capacity later. See wiki/concepts/capacity-occupancy.md.
    const occ = getOccupancy(this.#db);
    if (occ.full) {
      await this.#log.append({
        type: "anomaly",
        payload: { reason: `transient entry refused — lot full (${occ.count}/${occ.capacity})`, entryRefused: true, full: true },
      });
      this.#logger.warn(`transient entry REFUSED: full (${occ.count}/${occ.capacity})`);
      return;
    }

    const ticketId = newTicketId();
    const issuedAt = new Date().toISOString();
    const printers = this.#loadPrinters();

    // 1. PRINT FIRST. The ticket is the transient's session key — no ticket, no entry.
    const ticket: TicketData = { ticketId, issuedAt, header: this.#ticketHeader() };
    try {
      const printedBy = await printWithFailover(printers, "entry-dispenser", (d: PrinterDevice) =>
        d.printTicket(ticket),
      );
      this.#logger.info(`entry ticket ${ticketId} printed on ${printedBy}`);
    } catch (err) {
      // HOLD: do not open, do not record a vehicle_entry. Sign an anomaly so the
      // failed attempt is in the tamper-evident record for the operator.
      const reason =
        err instanceof NoPrinterAvailableError ? err.message : (err as Error).message;
      await this.#log.append({
        type: "anomaly",
        identity: ticketId,
        payload: { reason: `entry held — ticket not printed: ${reason}`, ticketPrinted: false },
      });
      this.#logger.warn(`entry HELD: ${reason} (barrier NOT opened)`);
      return;
    }

    // 2. SIGN the vehicle_entry — BEFORE the relay fires (the core invariant).
    await this.#log.append({
      type: "vehicle_entry",
      direction: "entry",
      source: "ticket",
      identity: ticketId,
      payload: { sessionRef: ticketId, ticketPrinted: true },
      occurredAt: issuedAt,
    });

    // 3. OPEN the resolved entry barrier (intent only; the barrier owns the close).
    const access = this.#buildAccess(resolved.controller);
    if (access) await access.pulseOpen(resolved.relay);
    else this.#logger.warn(`entry signed for ${ticketId} but the entry relay won't build`);

    // 3b. SNAPSHOT — fire the entry camera(s), never awaited (evidence, not a gate;
    //     a camera failure must not delay or block the already-open barrier).
    void snapshotAsync({
      db: this.#db,
      direction: "entry",
      identity: ticketId,
      logger: this.#logger,
    }).catch((err) => this.#logger.error(`entry snapshot error: ${(err as Error).message}`));

    // 4. Update the session projection cache (rebuildable from the ledger; this is
    //    just a fast read-model, never the source of truth).
    try {
      this.#db
        .insert(sessions)
        .values({ id: ticketId, identity: ticketId, source: "ticket", enteredAt: issuedAt, state: "open" })
        .run();
    } catch (err) {
      // Cache miss is non-fatal — the ledger is authoritative and the projection
      // can be rebuilt. Log it; don't fail the (already-open) entry.
      this.#logger.error(`session-cache insert failed for ${ticketId}: ${(err as Error).message}`);
    }
  }

  /** Build a live access adapter from a resolved controller row, or null. */
  #buildAccess(row: DeviceRow): AccessControlDevice | null {
    const driver = registry.get(row.driverId);
    if (!driver) return null;
    try {
      return driver.create(row.config as never) as AccessControlDevice;
    } catch {
      return null;
    }
  }

  /** Build live ENTRY printer instances (for failover selection). */
  #loadPrinters(): PrinterInstance[] {
    const rows = devicesByDirection(this.#db, "printer", "entry"); // already enabled-filtered
    const out: PrinterInstance[] = [];
    for (const row of rows) {
      const driver = registry.get(row.driverId);
      if (!driver) continue;
      const cfg = row.config as Record<string, unknown>;
      const role = cfg.role === "booth-receipt" ? "booth-receipt" : "entry-dispenser";
      try {
        out.push({
          id: row.id,
          role,
          failoverRank: typeof cfg.failoverRank === "number" ? cfg.failoverRank : 0,
          device: driver.create(cfg as never) as PrinterDevice,
        });
      } catch {
        // skip a printer whose config won't build
      }
    }
    return out;
  }

  /** Park identity for the ticket header, from site_config (all fields optional;
   *  the driver prints only what's set). See wiki/concepts/site-metadata.md. */
  #ticketHeader(): TicketHeader | undefined {
    const row = this.#db.select().from(siteConfig).where(eq(siteConfig.id, 1)).get();
    if (!row) return undefined;
    return {
      parkName: row.parkName,
      operatorName: row.operatorName,
      nius: row.nius,
      address: row.address,
      phone: row.phone,
    };
  }
}

/**
 * Opaque, unguessable transient ticket id (wiki/concepts/ticket-encoding.md).
 *
 * Format: 13 digits = 12 cryptographically-random digits + 1 trailing Luhn check
 * digit. All-numeric so the booth can read it on ANY legacy 1D barcode scanner and
 * an operator can hand-key it if every reader is down. RANDOM (not sequential): the
 * id must stay unguessable so an attacker can't iterate to claim a cheaper session
 * — the anti-fraud property the wiki settles. 12 random digits = 10^12 space, so
 * collisions are negligible at lot scale; the unique constraints on
 * ledger_events.index / sessions.id are the backstop. The Luhn digit lets a manual
 * entry reject a typo (validateTicketCode) instead of failing as "session not found".
 */
function newTicketId(): string {
  let body = "";
  for (let i = 0; i < 12; i += 1) body += String(randomInt(10));
  return body + luhnCheckDigit(body);
}

/** The Luhn (mod-10) check digit for an all-digit string. */
function luhnCheckDigit(digits: string): string {
  let sum = 0;
  // Walk right-to-left; the check digit sits at position 0 from the right, so the
  // last body digit is an "even" position that gets doubled.
  let double = true;
  for (let i = digits.length - 1; i >= 0; i -= 1) {
    let d = digits.charCodeAt(i) - 48;
    if (double) {
      d *= 2;
      if (d > 9) d -= 9;
    }
    sum += d;
    double = !double;
  }
  return String((10 - (sum % 10)) % 10);
}

/**
 * True if `code` is a well-formed ticket code: all digits and a valid Luhn checksum.
 * Lets a manual-entry path (operator types the code off the ticket when readers are
 * down) reject a typo up front. A scanned/looked-up id that predates this format
 * (e.g. legacy `T-<uuid>`) won't pass — callers should only gate MANUAL entry on it,
 * never reject an id that already exists in the ledger. See ticket-encoding.md.
 */
export function validateTicketCode(code: string): boolean {
  if (!/^\d{13}$/.test(code)) return false;
  const body = code.slice(0, 12);
  return luhnCheckDigit(body) === code[12];
}