/**
 * v2.6 — AgentPool (Phase 0 scaffold).
 *
 * Lazy get-or-create registry of `AgentBackend` instances keyed by
 * `${sessionId}:${agent}`. Phase 0 ships the skeleton only: an in-memory Map,
 * lookup / register / health, and clean disposal wired to the server's onClose.
 * Spawning lands in Phase 1/2; nothing populates the map yet.
 *
 * Spec: openspec/changes/v2-6-persistent-agent-sessions/design.md §2.
 */
import type { AgentBackend } from './agent-backend.js';

export class AgentPool {
  private readonly backends = new Map<string, AgentBackend>();

  private key(sessionId: string, agent: string): string {
    return `${sessionId}:${agent}`;
  }

  /** Map lookup only. Spawning is Phase 1/2 — never creates here. */
  get(sessionId: string, agent: string): AgentBackend | undefined {
    return this.backends.get(this.key(sessionId, agent));
  }

  /** Store a backend instance for this (session, agent). */
  register(sessionId: string, agent: string, backend: AgentBackend): void {
    this.backends.set(this.key(sessionId, agent), backend);
  }

  /** Summary for the health endpoint. */
  health(): { size: number } {
    return { size: this.backends.size };
  }

  /** Dispose every backend and clear the map. Tolerates throwing backends. */
  async dispose(): Promise<void> {
    const entries = [...this.backends.values()];
    this.backends.clear();
    await Promise.allSettled(entries.map((b) => b.dispose()));
  }
}

/** Single shared instance — referenced only by the server's onClose hook in Phase 0. */
export const agentPool = new AgentPool();