1 files changed, 123 insertions, 0 deletions
diff --git a/include/cru/base/Timer.h b/include/cru/base/Timer.h
new file mode 100644
index 00000000..80929f17
--- /dev/null
+++ b/include/cru/base/Timer.h
@@ -0,0 +1,123 @@
+#pragma once
+
+#include "Base.h"
+#include "Exception.h"
+
+#include <algorithm>
+#include <chrono>
+#include <list>
+#include <mutex>
+#include <optional>
+#include <ranges>
+
+namespace cru {
+template <typename D>
+class TimerRegistry : public Object2 {
+ private:
+  struct TimerData {
+    int id;
+    D data;
+    std::chrono::steady_clock::time_point created;
+    std::chrono::steady_clock::time_point last_check;
+    std::chrono::milliseconds interval;
+    bool repeat;
+
+    TimerData(int id, std::chrono::milliseconds interval, bool repeat,
+              std::chrono::steady_clock::time_point created, D data)
+        : id(id),
+          created(created),
+          last_check(created),
+          interval(interval),
+          repeat(repeat),
+          data(std::move(data)) {}
+
+    std::chrono::milliseconds NextTimeout(
+        std::chrono::steady_clock::time_point now) const {
+      return std::chrono::duration_cast<std::chrono::milliseconds>(
+          interval - (now - created) % interval);
+    }
+
+    bool Update(std::chrono::steady_clock::time_point now) {
+      auto next_trigger =
+          last_check - (last_check - created) % interval + interval;
+      if (now >= next_trigger) {
+        last_check = next_trigger;
+        return true;
+      } else {
+        last_check = now;
+        return false;
+      }
+    }
+  };
+
+ public:
+  struct UpdateResult {
+    int id;
+    D data;
+
+    bool operator==(const UpdateResult&) const = default;
+  };
+
+ public:
+  TimerRegistry() : next_id_(1) {}
+
+  int Add(D data, std::chrono::milliseconds interval, bool repeat,
+          std::chrono::steady_clock::time_point created =
+              std::chrono::steady_clock::now()) {
+    if (interval < std::chrono::milliseconds::zero()) {
+      throw Exception("Timer interval can't be negative.");
+    }
+    if (repeat && interval == std::chrono::milliseconds::zero()) {
+      throw Exception("Repeat timer interval can't be 0.");
+    }
+
+    std::unique_lock lock(mutex_);
+    auto id = next_id_++;
+    timers_.emplace_back(id, interval, repeat, created, std::move(data));
+    return id;
+  }
+
+  void Remove(int id) {
+    std::unique_lock lock(mutex_);
+    timers_.remove_if([id](const TimerData& timer) { return timer.id == id; });
+  }
+
+  /**
+   * Returns 0 if there is no timer.
+   */
+  std::chrono::milliseconds NextTimeout(
+      std::chrono::steady_clock::time_point now) {
+    std::unique_lock lock(mutex_);
+
+    if (timers_.empty()) return std::chrono::milliseconds::zero();
+
+    return std::ranges::min(
+        timers_ | std::views::transform([now](const TimerData& timer) {
+          return timer.NextTimeout(now);
+        }));
+  }
+
+  std::optional<UpdateResult> Update(
+      std::chrono::steady_clock::time_point new_time) {
+    std::unique_lock lock(mutex_);
+    for (auto iter = timers_.begin(); iter != timers_.end(); ++iter) {
+      auto& timer = *iter;
+      if (timer.Update(new_time)) {
+        if (timer.repeat) {
+          return UpdateResult{timer.id, timer.data};
+        } else {
+          D data(std::move(timer.data));
+          timers_.erase(iter);  // We will return, so it's safe to erase here.
+          return UpdateResult{timer.id, std::move(data)};
+        }
+      }
+    }
+    return std::nullopt;
+  }
+
+ private:
+  std::mutex mutex_;
+  int next_id_;
+  std::list<TimerData> timers_;
+};
+}  // namespace cru