import { randomUUID } from 'node:crypto';

import type { DropTarget } from '../config.js';
import { TooManyUploadsError, UploadSessionNotFoundError } from '../errors.js';

/** Un upload fragmenté en cours : morceaux écrits dans `partPath`, finalisé en `finalPath`. */
export interface UploadSession {
  id: string;
  target: DropTarget;
  /** Nom de fichier annoncé par le client (pour les notifications). */
  originalName: string;
  /** Nom simple, ou chemin relatif `dossier/sous/fichier.ext` (mode dossier). */
  storedName: string;
  mimeType: string;
  partPath: string;
  finalPath: string;
  totalSize: number;
  chunkSize: number;
  chunkCount: number;
  received: Set<number>;
  lastActivity: number;
}

export type NewUploadSession = Omit<UploadSession, 'id' | 'received' | 'lastActivity'>;

const IDLE_TTL_MS = 30 * 60_000;
const SWEEP_INTERVAL_MS = 60_000;
const MAX_SESSIONS = 100;

export interface UploadSessionStore {
  create(input: NewUploadSession): UploadSession;
  /** Récupère et rafraîchit la session ; lève `UploadSessionNotFoundError` si absente. */
  use(id: string): UploadSession;
  remove(id: string): UploadSession | undefined;
  stop(): void;
}

/**
 * Registre en mémoire des uploads fragmentés. Les sessions inactives depuis plus
 * de 30 min sont purgées et `onExpire` est appelé (pour supprimer le `.part`).
 */
export function createUploadSessionStore(
  onExpire: (session: UploadSession) => void,
): UploadSessionStore {
  const sessions = new Map<string, UploadSession>();

  const timer = setInterval(() => {
    const now = Date.now();
    for (const session of sessions.values()) {
      if (now - session.lastActivity > IDLE_TTL_MS) {
        sessions.delete(session.id);
        onExpire(session);
      }
    }
  }, SWEEP_INTERVAL_MS);
  timer.unref();

  return {
    create(input: NewUploadSession): UploadSession {
      if (sessions.size >= MAX_SESSIONS) {
        throw new TooManyUploadsError();
      }
      const session: UploadSession = {
        ...input,
        id: randomUUID(),
        received: new Set<number>(),
        lastActivity: Date.now(),
      };
      sessions.set(session.id, session);
      return session;
    },

    use(id: string): UploadSession {
      const session = sessions.get(id);
      if (session === undefined) {
        throw new UploadSessionNotFoundError();
      }
      session.lastActivity = Date.now();
      return session;
    },

    remove(id: string): UploadSession | undefined {
      const session = sessions.get(id);
      sessions.delete(id);
      return session;
    },

    stop(): void {
      clearInterval(timer);
    },
  };
}