import type { Db } from "@parking/db";
import type { FastifyBaseLogger } from "fastify";
import { deviceEvents, type DeviceInputEvent, type LanePresenceEvent } from "./device-events.js";
import { presenceLaneOf } from "./device-resolve.js";

// Per-lane RADAR presence for the booth's barrier lights. A vehicle-presence INPUT
// (loop/radar) shorted at an entry/exit barrier means "something is in the lane vicinity"
// BEFORE the camera confirms a vehicle. This is the SAME signal that makes the physical
// button lamp (relay 3) blink — see button-light.ts (#onInput) — so the on-screen light
// and the lamp stay in lockstep: both react to a presence edge resolved the SAME way
// (relayForPresence, on an entry/both relay). ADVISORY ONLY: it gates nothing.
//
// A radar serving an entry (or "both") barrier marks the ENTRY lane present; an exit radar
// marks EXIT. The lane is resolved via `presenceLaneOf` (direction-agnostic — unlike the
// entry-gated `relayForPresence` the one-car-one-ticket gate uses), so both lanes blink.

export class LanePresence {
  readonly #db: Db;
  readonly #logger: FastifyBaseLogger;
  /** Active presence terminals per lane, keyed `${deviceId}:${input}` (several radars may
   *  serve one lane). A lane is "present" while its set is non-empty. */
  readonly #entry = new Set<string>();
  readonly #exit = new Set<string>();
  #unsub: (() => void) | null = null;

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

  /** Subscribe to presence input edges. */
  start(): void {
    this.#unsub = deviceEvents.onInput((e) => this.#onInput(e));
  }

  /** Current snapshot (for the WS hello). */
  snapshot(): LanePresenceEvent {
    return { entry: this.#entry.size > 0, exit: this.#exit.size > 0 };
  }

  #onInput(e: DeviceInputEvent): void {
    const lane = presenceLaneOf(this.#db, e.deviceId, e.input);
    if (!lane) return; // not a presence terminal on a barrier relay
    const key = `${e.deviceId}:${e.input}`;
    const set = lane === "entry" ? this.#entry : this.#exit;
    const before = set.size > 0;
    if (e.edge === "on") set.add(key);
    else set.delete(key);
    const after = set.size > 0;
    if (before !== after) {
      this.#logger.info(`lane-presence: ${lane} -> ${after ? "present" : "clear"}`);
      deviceEvents.emitLanePresence(this.snapshot());
    }
  }

  /** Unsubscribe on shutdown. */
  stop(): void {
    this.#unsub?.();
    this.#unsub = null;
  }
}