Clock.hpp

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#pragma once
 
#include <atomic>
#include <chrono>
#include <cstdint>
#include <stdexcept>
#include <string>
 
namespace ecs
{
    class Clock
    {
      public:
        virtual ~Clock() = default;
        virtual std::chrono::microseconds Now() const = 0;
    };
 
    class SteadyClock : public Clock
    {
      public:
        std::chrono::microseconds Now() const override
        {
            return std::chrono::duration_cast<std::chrono::microseconds>(
                std::chrono::steady_clock::now().time_since_epoch());
        }
 
        static const SteadyClock &Instance()
        {
            static const SteadyClock instance;
            return instance;
        }
    };
 
    class ManualClock : public Clock
    {
      public:
        explicit ManualClock(std::chrono::microseconds start = std::chrono::microseconds(0))
          : count(start.count())
        {
        }
 
        std::chrono::microseconds Now() const override
        {
            return std::chrono::microseconds(this->count.load());
        }
 
        void Advance(std::chrono::microseconds delta)
        {
            if(delta.count() < 0)
            {
                throw std::runtime_error("ecs::ManualClock::Advance(): a clock cannot move backwards (" +
                                         std::to_string(delta.count()) + " us).");
            }
            this->count.fetch_add(delta.count());
        }
 
        void Set(std::chrono::microseconds value)
        {
            this->count.store(value.count());
        }
 
      private:
        std::atomic<int64_t> count;
    };
}