import { and, desc, deviceEvents, eq, type Db } from "@parking/db";

// READ-TIME plate resolution. A recognized licence plate is ADVISORY evidence — it
// lives in the unsigned, prunable `device_events` (kind="read") stream written by the
// ANPR-on-snapshot path (snapshot.ts → recognizePlate), keyed to the session `identity`.
// It is deliberately NOT on the signed ledger (a fuzzy camera read must never become a
// signed fact). To SHOW it next to a feed event or an active session we resolve it here,
// at serialize time, the same way subscriber names are resolved (see event-enrich.ts).
//
// Preference: an ENTRY read over an exit read (the plate as it arrived identifies the
// session); within a direction, the newest read wins. Returns the plate text only —
// confidence/region detail stays on the snapshot review panel, not the at-a-glance feed.

/** The best advisory plate observed for a session, for display. */
export interface PlateView {
  readonly plate: string;
  readonly confidence: number | null;
  readonly direction: "entry" | "exit" | null;
}

interface ReadDetail {
  identity?: string;
  plate?: string;
  confidence?: number;
  direction?: string;
}

/** Best plate for one identity, or null. Prefers an entry read, then the newest read. */
export function plateForIdentity(db: Db, identity: string): PlateView | null {
  const rows = db
    .select({ detail: deviceEvents.detail })
    .from(deviceEvents)
    .where(and(eq(deviceEvents.category, "camera"), eq(deviceEvents.kind, "read")))
    .orderBy(desc(deviceEvents.occurredAt))
    .all();
  return pickBest(rows.map((r) => (r.detail ?? {}) as ReadDetail), identity);
}

/** Resolve plates for MANY identities in one device_events scan (used by the active-
 *  sessions list and the feed page, which each carry tens–hundreds of rows). */
export function platesForIdentities(db: Db, identities: Iterable<string>): Map<string, PlateView> {
  const want = new Set(identities);
  const out = new Map<string, PlateView>();
  if (want.size === 0) return out;
  // Newest first so the first acceptable read per (identity,direction) is the freshest.
  const rows = db
    .select({ detail: deviceEvents.detail })
    .from(deviceEvents)
    .where(and(eq(deviceEvents.category, "camera"), eq(deviceEvents.kind, "read")))
    .orderBy(desc(deviceEvents.occurredAt))
    .all();
  const byId = new Map<string, ReadDetail[]>();
  for (const r of rows) {
    const d = (r.detail ?? {}) as ReadDetail;
    if (!d.identity || !d.plate || !want.has(d.identity)) continue;
    let list = byId.get(d.identity);
    if (!list) byId.set(d.identity, (list = []));
    list.push(d);
  }
  for (const [id, reads] of byId) {
    const best = pickBest(reads, id);
    if (best) out.set(id, best);
  }
  return out;
}

/** Pick the best read for `identity` from a NEWEST-FIRST list: an entry read beats an
 *  exit read; otherwise the first (newest) acceptable read wins. */
function pickBest(reads: ReadDetail[], identity: string): PlateView | null {
  let fallback: ReadDetail | null = null;
  for (const d of reads) {
    if (d.identity !== identity || !d.plate) continue;
    if (d.direction === "entry") return toView(d);
    if (!fallback) fallback = d;
  }
  return fallback ? toView(fallback) : null;
}

function toView(d: ReadDetail): PlateView {
  return {
    plate: d.plate!.trim().toUpperCase(),
    confidence: typeof d.confidence === "number" ? d.confidence : null,
    direction: d.direction === "entry" || d.direction === "exit" ? d.direction : null,
  };
}