#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <thread>
#include <atomic>
#include <condition_variable>
#include <algorithm>

#define ASYNCIO

int main(int argc, char *argv[]) 
{
	std::string filename = (argc > 1) ? argv[1] : "test.mp4";

	std::ifstream infile(filename.c_str(), std::ios::in | std::ios::binary | std::ios::ate);
	if (infile.is_open()) {
		size_t in_file_size = static_cast<size_t>(infile.tellg());
		std::cout << "file: " << filename << " - is opened, size = " << in_file_size << " \n";
		std::vector<char> data_array(in_file_size);
		infile.seekg(0, std::ios::beg);
		std::atomic<size_t> read_pos(0);
#ifndef ASYNCIO
		infile.read(data_array.data(), in_file_size);
		read_pos = in_file_size;
		for (size_t i = 0; i < in_file_size; ++i)
			data_array[i] = data_array[i] * 2;	// process data
#else
		size_t const read_by_size = 1024 * 1024;	// 1 MB
		std::condition_variable cv_read;
		std::mutex mtx_read;
		std::thread t_read_file([&]() {
			while (read_pos < in_file_size) {
				size_t current_read_bytes = std::min(read_by_size, (size_t)in_file_size - read_pos);
				infile.read(data_array.data(), current_read_bytes);
				read_pos += current_read_bytes;
				cv_read.notify_all();
			}
			std::cout << "thread read ended \n";
		});
		size_t current_pos;
		for (current_pos = 0; current_pos < in_file_size;) {
			size_t tmp_read_pos = read_pos;
			if (tmp_read_pos > current_pos) {
				for (size_t i = current_pos; i < tmp_read_pos; ++i) {
					data_array[i] = data_array[i] * 2;	// process data
				}
			}
			else {
				for (std::unique_lock<std::mutex> lock(mtx_read); read_pos <= current_pos; cv_read.wait(lock));
			}
			current_pos = tmp_read_pos;
		}
		t_read_file.join();
		std::cout << "current_pos = " << current_pos << " \n";
#endif
		std::cout << "read_pos = " << read_pos << " \n";
	}	

	std::cout << "OK \n";
	getchar();

	return 0;
}