C# (.NET)

static readonly string ApiKey = "your_api_key";
static readonly string BaseUrl = "https://api.flimpa.com/api/v1";
static readonly HttpClient client = new HttpClient();

using System;
using System.IO;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;

class Program
{
    static readonly string ApiKey = "your_api_key";
    static readonly string BaseUrl = "https://api.flimpa.com/api/v1";
    static readonly HttpClient client = new HttpClient();

    static async Task Main()
    {
        // 1. Create Task (Upload)
        using var form = new MultipartFormDataContent();
        form.Add(new StringContent("compress-pdf"), "operation");
        
        using var fileStream = File.OpenRead("input.pdf");
        form.Add(new StreamContent(fileStream), "file", "input.pdf");

        client.DefaultRequestHeaders.Add("X-API-Key", ApiKey);
        var createRes = await client.PostAsync($"{BaseUrl}/tasks", form);
        
        if (!createRes.IsSuccessStatusCode) {
            var errorBody = await createRes.Content.ReadAsStringAsync();
            var errorData = JsonDocument.Parse(errorBody).RootElement;
            throw new Exception($"Failed to create task: {errorData.GetProperty("error").GetString()} ({errorData.GetProperty("code").GetString()})");
        }

        var createBody = await createRes.Content.ReadAsStringAsync();
        var taskData = JsonDocument.Parse(createBody).RootElement;
        var taskId = taskData.GetProperty("taskId").GetString();
        var accessToken = taskData.GetProperty("accessToken").GetString();

        // 2. Poll Status
        int delay = 1000;
        client.DefaultRequestHeaders.Clear();
        client.DefaultRequestHeaders.Add("X-Task-Access-Token", accessToken);

        while (true)
        {
            var statusRes = await client.GetStringAsync($"{BaseUrl}/tasks/{taskId}");
            var statusData = JsonDocument.Parse(statusRes).RootElement;
            var status = statusData.GetProperty("status").GetString();

            if (status == "COMPLETED") break;
            if (status == "FAILED") {
                throw new Exception($"Task failed: {statusData.GetProperty("error").GetString()} ({statusData.GetProperty("code").GetString()})");
            }

            await Task.Delay(delay);
            delay = Math.Min(delay * 2, 10000);
        }

        // 3. Download Result
        var downloadRes = await client.GetAsync($"{BaseUrl}/tasks/{taskId}/download");
        downloadRes.EnsureSuccessStatusCode();
        
        using var fs = new FileStream("output.pdf", FileMode.Create);
        await downloadRes.Content.CopyToAsync(fs);
        
        Console.WriteLine("Success!");
    }
}