// Public entry point for the optional generative ("ask your lectures") layer.
//
// `./engineImpl` is resolved by Metro to engineImpl.web.ts or
// engineImpl.native.ts by platform extension; the base engineImpl.ts re-export
// (web) is what TypeScript resolves for typechecking. Consumers call
// getGenerationEngine() and stay platform-agnostic.
//
// IMPORTANT: relative imports only inside src/lib (vitest has no '@/*' alias).

import type { CloudConfig, GenerationEngine } from './engine';
import { createCloudEngine } from './cloud';
import { webllm } from './engineImpl';

/**
 * An engine that does nothing useful — represents "no generation backend here".
 * isAvailable() is always false; generate()/loadModel() throw. Callers should
 * check isAvailable() and fall back to the search-only path (no fake answers).
 */
export const noneEngine: GenerationEngine = {
  kind: 'none',
  label: 'No model',
  async isAvailable(): Promise<boolean> {
    return false;
  },
  async loadModel(): Promise<void> {
    throw new Error('No generation engine is available.');
  },
  isLoaded(): boolean {
    return false;
  },
  async generate(): Promise<string> {
    throw new Error('No generation engine is available.');
  },
};

/**
 * Pick the generation engine.
 *
 * - If a cloud config WITH an apiKey is given, use the BYO-key cloud engine.
 * - Otherwise return the platform on-device (webllm) engine. On a device without
 *   WebGPU (web) or on native, that engine's isAvailable() resolves false, which
 *   is how the "none" state is represented in practice — callers MUST check
 *   isAvailable() before loading/generating, and fall back to search-only.
 */
export function getGenerationEngine(cloud?: CloudConfig): GenerationEngine {
  if (cloud?.apiKey) return createCloudEngine(cloud);
  return webllm;
}

export { createCloudEngine, webllm };
export * from './engine';