import { Platform } from 'expo-modules-core';

import { DocumentPickerAsset, DocumentPickerOptions, DocumentPickerResult } from './types';

export default {
  async getDocumentAsync({
    type = '*/*',
    multiple = false,
    base64 = false,
  }: DocumentPickerOptions): Promise<DocumentPickerResult> {
    // SSR guard
    if (!Platform.isDOMAvailable) {
      return { canceled: true, assets: null };
    }

    const input = document.createElement('input');
    input.style.display = 'none';
    input.setAttribute('type', 'file');
    input.setAttribute('accept', Array.isArray(type) ? type.join(',') : type);
    input.setAttribute('id', String(Math.random()));
    if (multiple) {
      input.setAttribute('multiple', 'multiple');
    }

    document.body.appendChild(input);

    return new Promise((resolve, reject) => {
      input.addEventListener('change', async () => {
        if (input.files) {
          const results: Promise<DocumentPickerAsset>[] = [];
          for (let i = 0; i < input.files.length; i++) {
            results.push(readFileAsync(input.files[i], base64));
          }
          try {
            const assets = await Promise.all(results);
            resolve({ canceled: false, assets, output: input.files });
          } catch (e) {
            reject(e);
          }
        } else {
          resolve({ canceled: true, assets: null });
        }

        document.body.removeChild(input);
      });

      input.addEventListener('cancel', () => {
        resolve({ canceled: true, assets: null });
      });

      const event = new MouseEvent('click');
      input.dispatchEvent(event);
    });
  },
};

function readFileAsync(targetFile: File, base64: boolean = true): Promise<DocumentPickerAsset> {
  return new Promise((resolve, reject) => {
    const mimeType = targetFile.type;
    if (!base64) {
      resolve({
        uri: URL.createObjectURL(targetFile),
        mimeType,
        name: targetFile.name,
        lastModified: targetFile.lastModified,
        size: targetFile.size,
        file: targetFile,
      });
      return;
    }
    const reader = new FileReader();
    reader.onerror = () => {
      reject(new Error(`Failed to read the selected media because the operation failed.`));
    };
    reader.onload = ({ target }) => {
      const base64 = (target as any).result;
      resolve({
        uri: URL.createObjectURL(targetFile),
        base64,
        mimeType,
        name: targetFile.name,
        lastModified: targetFile.lastModified,
        size: targetFile.size,
        file: targetFile,
      });
    };

    // Read in the image file as a binary string.
    reader.readAsDataURL(targetFile);
  });
}