[feat] add background and manual update checks

apps/desktop/src/version_checker/update_checker.cpp

@@ -0,0 +1,84 @@
+#include "update_checker.h"
+
+#include <algorithm>
+#include <utility>
+
+#include "rd_log.h"
+
+namespace crossdesk {
+using namespace std::chrono_literals;
+
+UpdateChecker::UpdateChecker(std::string current_version, Fetch fetch)
+    : current_version_(std::move(current_version)), fetch_(std::move(fetch)) {}
+
+UpdateChecker::~UpdateChecker() { Stop(); }
+
+bool UpdateChecker::RequestCheck(TimePoint now) {
+  if (stopped_ || pending_.valid()) {
+    return false;
+  }
+  try {
+    pending_ = std::async(std::launch::async, fetch_);
+    status_ = Status::Checking;
+    return true;
+  } catch (const std::exception& error) {
+    LOG_WARN("Could not start update check: {}", error.what());
+    ScheduleRetry(now);
+    return false;
+  }
+}
+
+bool UpdateChecker::Poll(TimePoint now) {
+  if (stopped_) {
+    return false;
+  }
+  if (!pending_.valid()) {
+    if (now >= next_check_) {
+      RequestCheck(now);
+    }
+    return false;
+  }
+  if (pending_.wait_for(0ms) != std::future_status::ready) {
+    return false;
+  }
+
+  std::optional<VersionInfo> result;
+  try {
+    result = pending_.get();
+  } catch (const std::exception& error) {
+    LOG_WARN("Update check failed: {}", error.what());
+  } catch (...) {
+    LOG_WARN("Update check failed with an unknown error");
+  }
+  if (!result) {
+    ScheduleRetry(now);
+    return true;
+  }
+  latest_ = std::move(result);
+  update_available_ =
+      IsNewerVersionWithMetadata(current_version_, latest_->version,
+                                 latest_->release_date, latest_->patch);
+  status_ = update_available_ ? Status::Available : Status::UpToDate;
+  failures_ = 0;
+  next_check_ = now + 6h;
+  return true;
+}
+
+void UpdateChecker::ScheduleRetry(TimePoint now) {
+  constexpr std::chrono::minutes delays[] = {5min, 30min, 60min};
+  next_check_ = now + delays[std::min(failures_, 2u)];
+  failures_ = std::min(failures_ + 1, 3u);
+  status_ = Status::Failed;
+}
+
+void UpdateChecker::Stop() {
+  stopped_ = true;
+  // Join before application/logging teardown. The HTTP client uses finite
+  // connection/read/write and overall request timeouts; no worker is detached.
+  if (pending_.valid()) {
+    pending_.wait();
+    pending_ = {};
+  }
+}
+
+}  // namespace crossdesk