test.ts

import { Subject, singleshot, randomString } from "functools-kit";

declare global {
  interface Window {
    onFetchApiResponse: (requestId: string, text: string) => void;
    AndroidBinding: {
      beginFetchApi: (requestId: string, url: string, totalChunks: number) => void;
      sendFetchApiChunk: (requestId: string, chunkIndex: number, chunk: string) => void;
      endFetchApi: (requestId: string, contentLength: number) => void;
    };
  }
}

const CHUNK_SIZE = 500;

const requestWrapper = new class {

  _responseSubject = new Subject<[string, string]>();

  _listenForAnswer = singleshot(() => {
    window.onFetchApiResponse = (requestId: string, text: string) => {
      this._responseSubject.next([requestId, text]);
    }
  })

  _sendChunked = (requestId: string, path: string, body: string) => {
    const totalChunks = Math.ceil(body.length / CHUNK_SIZE);
    const contentLength = new Blob([body]).size;
    window.AndroidBinding.beginFetchApi(requestId, path, totalChunks);
    for (let i = 0; i < totalChunks; i++) {
      const chunk = body.slice(i * CHUNK_SIZE, (i + 1) * CHUNK_SIZE);
      window.AndroidBinding.sendFetchApiChunk(requestId, i, chunk);
    }
    window.AndroidBinding.endFetchApi(requestId, contentLength);
  }

  send = async (path: string, body: string) => {
    if (window.AndroidBinding?.beginFetchApi) {
      const requestId = randomString();
      this._listenForAnswer();
      this._sendChunked(requestId, path, body);
      const response = await this._responseSubject
        .filter(([id]) => id === requestId)
        .map(([, text]) => text)
        .toPromise();
      return JSON.parse(response);
    }
    const response = await fetch(path, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body,
    });
    return await response.json();
  }
}

// Использование
const payload = { foo: "bar", data: "..." };
const body = JSON.stringify(payload);
const result = await requestWrapper.send("/api/endpoint", body);