export interface SendResult {
  result: string;
  costUsd: number;
  turns: number;
  /** Optional channel-level signal for transports with richer UI than plain text. */
  signal?: "provider_down";
  /** DB message ID for delivery status tracking (only set for agent replies) */
  messageId?: number;
  /** Validated object, when the engine was opened with an `outputSchema`. */
  structured?: unknown;
}

export type StreamCallback = (textSoFar: string) => void;
export type ActivityCallback = (status: string) => void;

export interface SendCallbacks {
  onStream?: StreamCallback;
  onActivity?: ActivityCallback;
}

export interface ChatEngine {
  sessionId: string | null;
  room: string;
  send(
    userMessage: string,
    callbacks?: SendCallbacks,
    attachments?: import("./attachment").Attachment[],
  ): Promise<SendResult>;
  close(): Promise<void>;
}

export interface EngineOptions {
  room: string;
  channel: string;
  /** true = resume latest session, or pass a specific session ID */
  resume: boolean | string;
  mcpServers?: Record<string, unknown>;
  employee?: string;
  agent?: string;
  job?: string;
  /** Watch channel behavior — injected into system prompt for watch-mode engines. */
  watchBehavior?: { channel: string; behavior: string };
  /** JSON Schema the final answer must satisfy, enforced by whichever backend runs. */
  outputSchema?: Record<string, unknown>;
}