server/imageLoader.ts

import type {DescribeRequestBody, DetectRequestBody} from './types.js';

export async function resolveImagePayload(
  body: DetectRequestBody | DescribeRequestBody,
): Promise<{imageBase64: string; mimeType: string}> {
  if (body.image_base64) {
    const base64 = body.image_base64.replace(/^data:[^;]+;base64,/, '');
    return {
      imageBase64: base64,
      mimeType: body.image_type ?? 'image/jpeg',
    };
  }

  if (body.image_url) {
    const response = await fetch(body.image_url);
    if (!response.ok) {
      throw new Error(`Failed to fetch image_url (${response.status})`);
    }

    const buffer = Buffer.from(await response.arrayBuffer());
    const mimeType =
      response.headers.get('content-type')?.split(';')[0]?.trim() ??
      body.image_type ??
      'image/jpeg';

    return {
      imageBase64: buffer.toString('base64'),
      mimeType,
    };
  }

  throw new Error('Provide image_url or image_base64');
}