import { and, eq, laneDevices, ledgerEvents, permitCredentials, permitPlates, permits, sessions, type Db } from "@parking/db";
import { registry, type AccessControlDevice } from "@parking/devices";
import type { FastifyBaseLogger } from "fastify";
import type { DeviceReadEvent, ReadOutcome } from "./device-events.js";
import type { EventLog } from "./event-log.js";

// PERMIT flow: a subscriber identified by card/QR/plate enters/exits without paying.
// Reached from the read dispatcher when a read matches a permit (not an open ticket).
// See wiki/entities/permit.md.
//
// Two optional, independent bindings:
//   - car-count: `maxConcurrent` (default 1, null = unbound) — how many of the
//     permit's cars may be inside at once; enforced over the session projection.
//   - plate: optional `plates[]` — when set, a matching plate is an accepted identity
//     too (card/QR OR plate). When unset, any car may use the permit's card/QR.
//
// Direction is inferred from session state for THAT car (the read credential value
// is the per-car session key): no open session → ENTRY; open session → EXIT. So a
// fleet permit can have several cars in at once, each its own session, and
// anti-passback falls out (a second "entry" on a car already in becomes its exit).

export interface PermitMatch {
  readonly permitId: string;
  /** The specific credential/plate value read — the per-car session key. */
  readonly carKey: string;
  readonly via: "card" | "qr" | "plate";
}

export class PermitFlow {
  readonly #db: Db;
  readonly #log: EventLog;
  readonly #logger: FastifyBaseLogger;
  readonly #inFlight = new Set<string>();

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

  /** Resolve a read to a permit (by card/QR credential, or by a bound plate), or null. */
  match(e: DeviceReadEvent): PermitMatch | null {
    // Card / QR / generic credential value.
    const cred = this.#db
      .select()
      .from(permitCredentials)
      .where(eq(permitCredentials.value, e.value))
      .get();
    if (cred) {
      return { permitId: cred.permitId, carKey: e.value, via: cred.kind === "qr" ? "qr" : "card" };
    }
    // Plate binding: a read plate that matches a permit's bound plate is an identity.
    if (e.kind === "plate") {
      const plate = this.#db.select().from(permitPlates).where(eq(permitPlates.plate, e.value)).get();
      if (plate) return { permitId: plate.permitId, carKey: e.value, via: "plate" };
    }
    return null;
  }

  /** Run the permit entry/exit for a matched read at a lane. */
  async run(lane: number, e: DeviceReadEvent, m: PermitMatch): Promise<ReadOutcome> {
    const key = `${m.permitId}:${m.carKey}`;
    if (this.#inFlight.has(key)) return { accepted: false, reason: "duplicate read in flight" };
    this.#inFlight.add(key);
    try {
      return await this.#run(lane, e, m);
    } catch (err) {
      this.#logger.error(`permit-flow failed (lane ${lane}): ${(err as Error).message}`);
      return { accepted: false, reason: (err as Error).message };
    } finally {
      this.#inFlight.delete(key);
    }
  }

  async #run(lane: number, e: DeviceReadEvent, m: PermitMatch): Promise<ReadOutcome> {
    const permit = this.#db.select().from(permits).where(eq(permits.id, m.permitId)).get();
    if (!permit) return { accepted: false, reason: "permit not found" };

    // Validity: active + within the coverage window.
    const now = new Date().toISOString();
    const invalid =
      permit.status !== "active" ||
      (permit.validFrom != null && now < permit.validFrom) ||
      (permit.validTo != null && now > permit.validTo);
    if (invalid) {
      const reason = `permit ${permit.status}/out-of-window`;
      await this.#reject(lane, m, reason);
      return { accepted: false, reason };
    }

    const carOpen = this.#carHasOpenSession(m.carKey);

    if (carOpen) {
      // EXIT: this car is already inside → the read is its exit.
      await this.#log.append({
        type: "vehicle_exit",
        lane,
        direction: "exit",
        source: m.via === "plate" ? "lpr" : m.via === "qr" ? "qr" : "wiegand",
        identity: m.carKey,
        payload: { sessionRef: m.carKey, permitId: m.permitId },
      });
      await this.#open(lane, m.carKey, "permit exit");
      this.#closeCache(m.carKey);
      return { accepted: true, direction: "exit" };
    }

    // ENTRY: enforce the car-count binding (maxConcurrent), then sign + open.
    if (permit.maxConcurrent != null) {
      const open = this.#permitOpenCount(m.permitId);
      if (open >= permit.maxConcurrent) {
        const reason = `permit at capacity (${open}/${permit.maxConcurrent} cars in)`;
        await this.#reject(lane, m, reason);
        return { accepted: false, direction: "entry", reason };
      }
    }

    await this.#log.append({
      type: "vehicle_entry",
      lane,
      direction: "entry",
      source: m.via === "plate" ? "lpr" : m.via === "qr" ? "qr" : "wiegand",
      identity: m.carKey,
      // No ticket, no fee — the permit IS the authorization. Recorded for audit.
      payload: { sessionRef: m.carKey, permitId: m.permitId, permit: true },
      occurredAt: now,
    });
    await this.#open(lane, m.carKey, "permit entry");
    try {
      this.#db
        .insert(sessions)
        .values({ id: m.carKey, lane, identity: m.carKey, source: m.via === "plate" ? "lpr" : "wiegand", permitId: m.permitId, enteredAt: now, state: "open" })
        .run();
    } catch (err) {
      this.#logger.error(`session-cache insert failed for ${m.carKey}: ${(err as Error).message}`);
    }
    return { accepted: true, direction: "entry" };
  }

  /** Does this specific car (credential value) have an open session right now? */
  #carHasOpenSession(carKey: string): boolean {
    const rows = this.#db
      .select()
      .from(ledgerEvents)
      .where(eq(ledgerEvents.identity, carKey))
      .orderBy(ledgerEvents.index)
      .all();
    const entries = rows.filter((r) => r.type === "vehicle_entry").length;
    const exits = rows.filter((r) => r.type === "vehicle_exit").length;
    return entries > exits;
  }

  /** How many of this permit's cars are inside right now (fold over the ledger). */
  #permitOpenCount(permitId: string): number {
    const rows = this.#db
      .select()
      .from(ledgerEvents)
      .where(and(eq(ledgerEvents.type, "vehicle_entry")))
      .all()
      .filter((r) => (r.payload as { permitId?: string } | null)?.permitId === permitId);
    let open = 0;
    for (const entry of rows) {
      if (!this.#carHasOpenSession(entry.identity ?? "")) continue;
      open += 1;
    }
    return open;
  }

  async #reject(lane: number, m: PermitMatch, reason: string): Promise<void> {
    await this.#log.append({
      type: "anomaly",
      lane,
      identity: m.carKey,
      payload: { reason: `permit refused — ${reason}`, permitId: m.permitId, permitRefused: true },
    });
    this.#logger.warn(`permit refused (lane ${lane}, ${m.carKey}): ${reason}`);
  }

  async #open(lane: number, carKey: string, what: string): Promise<void> {
    const access = await this.#access(lane);
    if (access) await access.pulseOpen(1);
    else this.#logger.warn(`${what} signed for ${carKey} but lane ${lane} has no access device`);
  }

  #closeCache(carKey: string): void {
    try {
      this.#db.update(sessions).set({ exitedAt: new Date().toISOString(), state: "closed" }).where(eq(sessions.id, carKey)).run();
    } catch (err) {
      this.#logger.error(`session-cache close failed for ${carKey}: ${(err as Error).message}`);
    }
  }

  async #access(lane: number): Promise<AccessControlDevice | null> {
    const row = await this.#db
      .select()
      .from(laneDevices)
      .where(and(eq(laneDevices.category, "access"), eq(laneDevices.lane, lane)))
      .get();
    if (!row || !row.enabled) return null;
    const driver = registry.get(row.driverId);
    if (!driver) return null;
    try {
      return driver.create(row.config as never) as AccessControlDevice;
    } catch {
      return null;
    }
  }
}