import type { Dataset, DatasetMetadata, DataItem, Modality } from '../types';

/**
 * A helper function to handle API errors.
 */
const handleApiError = async (response: Response) => {
  if (!response.ok) {
    let errorMessage = `API error! status: ${response.status}`;
    try {
      // First, get the response text, as it might not be JSON.
      const text = await response.text();
      try {
        // Try to parse it as JSON
        const errorData = JSON.parse(text);
        errorMessage = errorData.detail || JSON.stringify(errorData);
      } catch (e) {
        // If parsing fails, use the raw text.
        errorMessage = text || errorMessage;
      }
    } catch (e) {
      // Fallback if reading the body fails for some reason.
      // This is unlikely to be hit with the logic above.
    }
    throw new Error(errorMessage);
  }
  // Only call .json() on success to avoid "body already read" errors.
  return response.json();
};


/**
 * Returns the metadata for all available shared datasets by querying the backend.
 */
export const getSharedDatasetMetadata = async (): Promise<DatasetMetadata[]> => {
  try {
    const response = await fetch('/api/shared-dataset-metadata');
    const metadataList = await handleApiError(response);
    
    // The backend returns strings for dates, convert them to Date objects.
    return metadataList.map((meta: any) => ({
        ...meta,
        uploadDate: new Date(meta.uploadDate),
    }));
  } catch (error) {
    console.error("Failed to fetch shared dataset metadata:", error);
    // Re-throw the error so the UI layer can handle it.
    throw error;
  }
};

/**
 * Returns the full data structure for a specific shared dataset from the backend.
 * The content for each item remains null, only the URLs are provided.
 */
export const getSharedDataset = async (id: string): Promise<Dataset | null> => {
  try {
    // NOTE: The backend API endpoint for fetching the full dataset is assumed to exist.
    // It should return the full Dataset object structure based on the scanned files.
    const response = await fetch(`/api/shared-dataset?id=${id}`);
    const dataset = await handleApiError(response);
    
    // Convert date string from API to Date object
    dataset.uploadDate = new Date(dataset.uploadDate);
    
    return dataset;
  } catch (error) {
    console.error(`Failed to fetch shared dataset with id ${id}:`, error);
    // Re-throw the error so the UI layer can handle it.
    throw error;
  }
};

/**
 * Fetches the actual content of a single lazy-loaded item from the server's static files.
 * This function is used for text and mesh files. Images are loaded directly by the browser <img> tag.
 */
export const getItemContent = async (url: string): Promise<string | ArrayBuffer> => {
    const response = await fetch(url);
    if (!response.ok) {
        throw new Error(`Failed to fetch content from ${url}: ${response.statusText}`);
    }

    // Determine content type based on file extension
    if (url.endsWith('.txt')) {
        return response.text();
    } else if (url.endsWith('.stl')) {
        return response.arrayBuffer();
    } else {
        // This case is for completeness; images are usually handled by `<img>` src attribute.
        const blob = await response.blob();
        return new Promise((resolve, reject) => {
            const reader = new FileReader();
            reader.onloadend = () => resolve(reader.result as string);
            reader.onerror = reject;
            reader.readAsDataURL(blob);
        });
    }
};