autostore/cpp17/lib/src/infrastructure/http/HttpOrderService.cpp

/**
 * HTTP-based order service implementation with retry logic and
 * connection pooling
 *
 * FLOW OVERVIEW:
 * 1. orderItem() validates input and enqueues order request
 * 2. Background worker thread processes queue sequentially (FIFO)
 * 3. Failed requests are retried with exponential backoff (1s, 2s, 4s...)
 * 4. HTTP clients are cached per host and auto-cleaned when unused
 * 5. Service shuts down gracefully, completing queued orders
 *
 * IMPORTANT LIMITATIONS:
 * - Uses single worker thread - retries of failed requests will block
 * processing of new orders until retry delay expires
 * - Not suitable for time-critical operations due to sequential processing
 * - Designed for fire-and-forget order notifications, not real-time
 * transactions
 */

#include "HttpOrderService.h"
#include "autostore/Version.h"
#include <httplib.h>
#include <stdexcept>
#include <regex>
#include <thread>
#include <queue>
#include <mutex>
#include <condition_variable>
#include <atomic>
#include <chrono>
#include <memory>
#include <unordered_map>

namespace nxl::autostore::infrastructure {

namespace {

constexpr int MAX_RETRIES = 3;
constexpr int CONNECTION_TIMEOUT_SECONDS = 5;
constexpr int READ_TIMEOUT_SECONDS = 5;
constexpr int WRITE_TIMEOUT_SECONDS = 5;
constexpr char CONTENT_TYPE_JSON[] = "application/json";

std::pair<std::string, std::string> parseUrl(const std::string& url)
{
  static const std::regex url_regex(
    R"(^(https?:\/\/)?([^\/:]+)(?::(\d+))?(\/[^\?]*)?(\?.*)?$)");

  std::smatch matches;
  if (!std::regex_match(url, matches, url_regex) || matches.size() < 5) {
    throw std::runtime_error("Invalid URL format: " + url);
  }

  std::string host = matches[2].str();
  std::string port = matches[3].str();
  std::string path = matches[4].str();
  std::string query = matches[5].str();

  if (!port.empty()) {
    host += ":" + port;
  }

  if (path.empty()) {
    path = "/";
  }

  path += query;
  return {host, path};
}

std::string createOrderPayload(const domain::Item& item)
{
  // Escape JSON special characters in strings
  auto escapeJson = [](const std::string& str) {
    std::string escaped;
    escaped.reserve(str.size() + 10); // Reserve extra space for escapes

    for (char c : str) {
      switch (c) {
        case '"':
          escaped += "\\\"";
          break;
        case '\\':
          escaped += "\\\\";
          break;
        case '\b':
          escaped += "\\b";
          break;
        case '\f':
          escaped += "\\f";
          break;
        case '\n':
          escaped += "\\n";
          break;
        case '\r':
          escaped += "\\r";
          break;
        case '\t':
          escaped += "\\t";
          break;
        default:
          escaped += c;
          break;
      }
    }
    return escaped;
  };

  return R"({"itemName": ")" + escapeJson(item.name) + R"(", "itemId": ")"
         + escapeJson(item.id) + "\"}";
}

} // namespace

struct OrderRequest
{
  std::string url;
  std::string payload;
  int retryCount = 0;
  std::chrono::system_clock::time_point nextAttemptTime;

  OrderRequest() = default;
  OrderRequest(std::string url, std::string payload, int rc = 0,
               std::chrono::system_clock::time_point nat =
                 std::chrono::system_clock::now())
    : url{std::move(url)}, payload{std::move(payload)}, retryCount{rc},
      nextAttemptTime(nat)
  {}
};

class HttpOrderService::Impl
{
public:
  explicit Impl(ILoggerPtr logger)
    : log{std::move(logger)}, shutdownRequested{false}
  {
    if (!log) {
      throw std::invalid_argument("Logger cannot be null");
    }

    userAgent = "Autostore/" + nxl::getVersionString();
    workerThread = std::thread(&Impl::processQueue, this);
  }

  ~Impl()
  {
    shutdown();
    if (workerThread.joinable()) {
      workerThread.join();
    }
  }

  void enqueueOrder(const std::string& url, std::string payload)
  {
    {
      std::lock_guard<std::mutex> lock(queueMutex);
      if (shutdownRequested) {
        throw std::runtime_error(
          "Service is shutting down, cannot enqueue new orders");
      }
      orderQueue.emplace(url, std::move(payload));
    }
    queueCondition.notify_one();
  }

private:
  void shutdown()
  {
    {
      std::lock_guard<std::mutex> lock(queueMutex);
      shutdownRequested = true;
    }
    queueCondition.notify_one();
  }

  bool shouldShutdown() const
  {
    return shutdownRequested && orderQueue.empty();
  }

  bool isRequestReady(const OrderRequest& request) const
  {
    return request.nextAttemptTime <= std::chrono::system_clock::now();
  }

  void processQueue()
  {
    while (true) {
      std::unique_lock<std::mutex> lock(queueMutex);

      // Wait for orders or shutdown signal
      queueCondition.wait(
        lock, [this] { return !orderQueue.empty() || shutdownRequested; });

      if (shouldShutdown()) {
        break;
      }

      if (orderQueue.empty()) {
        continue;
      }

      // Check if the front request is ready to be processed
      if (!isRequestReady(orderQueue.front())) {
        // Wait until the next attempt time
        auto waitTime =
          orderQueue.front().nextAttemptTime - std::chrono::system_clock::now();
        if (waitTime > std::chrono::milliseconds(0)) {
          queueCondition.wait_for(lock, waitTime);
        }
        continue;
      }

      // Extract request for processing
      OrderRequest request = std::move(orderQueue.front());
      orderQueue.pop();

      // Release lock before processing to avoid blocking other operations
      lock.unlock();

      processRequest(request);
    }
  }

  void processRequest(OrderRequest& request)
  {
    try {
      sendPostRequest(request.url, request.payload);
      log->i("Order request sent successfully to: %s", request.url.c_str());
    } catch (const std::exception& e) {
      log->e("Failed to send order request to %s: %s", request.url.c_str(),
             e.what());
      handleFailedRequest(request);
    }
  }

  void handleFailedRequest(OrderRequest& request)
  {
    if (request.retryCount < MAX_RETRIES) {
      request.retryCount++;
      // Exponential backoff: 1s, 2s, 4s, 8s...
      auto delay = std::chrono::seconds(1 << (request.retryCount - 1));
      request.nextAttemptTime = std::chrono::system_clock::now() + delay;

      log->w("Retrying order request to %s (attempt %d/%d) in %ld seconds",
             request.url.c_str(), request.retryCount, MAX_RETRIES,
             delay.count());

      {
        std::lock_guard<std::mutex> lock(queueMutex);
        if (!shutdownRequested) {
          orderQueue.push(std::move(request));
        }
      }
      queueCondition.notify_one();
    } else {
      log->e("Max retries exceeded for order request to: %s",
             request.url.c_str());
    }
  }

  std::shared_ptr<httplib::Client> getOrCreateClient(const std::string& host)
  {
    std::lock_guard<std::mutex> lock(clientsMutex);

    auto it = clients.find(host);
    if (it != clients.end()) {
      // Check if client is still valid
      auto client = it->second.lock();
      if (client) {
        return client;
      } else {
        // Remove expired weak_ptr
        clients.erase(it);
      }
    }

    // Create new client
    auto client = std::make_shared<httplib::Client>(host);
    configureClient(*client);
    clients[host] = client;
    return client;
  }

  void configureClient(httplib::Client& client)
  {
    client.set_connection_timeout(CONNECTION_TIMEOUT_SECONDS, 0);
    client.set_read_timeout(READ_TIMEOUT_SECONDS, 0);
    client.set_write_timeout(WRITE_TIMEOUT_SECONDS, 0);

    // Enable keep-alive for better performance
    client.set_keep_alive(true);

    // Set reasonable limits
    client.set_compress(true);
  }

  void sendPostRequest(const std::string& url, const std::string& payload)
  {
    auto [host, path] = parseUrl(url);
    auto client = getOrCreateClient(host);

    httplib::Headers headers = {{"Content-Type", CONTENT_TYPE_JSON},
                                {"User-Agent", userAgent},
                                {"Accept", CONTENT_TYPE_JSON}};

    log->i("Sending POST request to: %s%s", host.c_str(), path.c_str());
    log->v(1, "Payload: %s", payload.c_str());

    auto res = client->Post(path, headers, payload, CONTENT_TYPE_JSON);

    if (!res) {
      throw std::runtime_error("Failed to connect to: " + host);
    }

    log->v(2, "Response status: %d", res->status);
    log->v(3, "Response body: %s", res->body.c_str());

    if (res->status < 200 || res->status >= 300) {
      std::string error_msg =
        "HTTP request failed with status: " + std::to_string(res->status)
        + " for URL: " + url;
      if (!res->body.empty()) {
        error_msg += " Response: " + res->body;
      }
      throw std::runtime_error(error_msg);
    }
  }

  ILoggerPtr log;
  std::queue<OrderRequest> orderQueue;
  std::mutex queueMutex;
  std::condition_variable queueCondition;
  std::thread workerThread;
  std::atomic<bool> shutdownRequested;

  // Use weak_ptr to allow automatic cleanup of unused clients
  std::unordered_map<std::string, std::weak_ptr<httplib::Client>> clients;
  std::mutex clientsMutex;
  std::string userAgent;
};

HttpOrderService::HttpOrderService(ILoggerPtr logger)
  : impl{std::make_unique<Impl>(std::move(logger))}
{}

HttpOrderService::~HttpOrderService() = default;

void HttpOrderService::orderItem(const domain::Item& item)
{
  if (item.orderUrl.empty()) {
    throw std::runtime_error("Order URL is empty for item: " + item.name);
  }

  if (item.orderUrl.find("://") == std::string::npos) {
    throw std::runtime_error("Invalid URL format for item: " + item.name
                             + " (missing protocol)");
  }

  std::string payload = createOrderPayload(item);
  impl->enqueueOrder(item.orderUrl, std::move(payload));
}

} // namespace nxl::autostore::infrastructure