#pragma once

#include <cstdint>

namespace Core
{
	class Timer
	{
	public:
		static const uint32_t DefaultFps = 30;

		explicit Timer(uint32_t target_fps = DefaultFps)
			: target_fps_(normalize_fps(target_fps)),
			  tick_remainder_(0),
			  frame_start_ms_(0),
			  fixed_delta_ms_(0)
		{
		}

		void begin_frame(uint32_t now_ms)
		{
			frame_start_ms_ = now_ms;
			fixed_delta_ms_ = next_tick_ms();
		}

		uint32_t target_fps() const
		{
			return target_fps_;
		}

		uint32_t fixed_delta_ms() const
		{
			return fixed_delta_ms_;
		}

		uint32_t frame_start_ms() const
		{
			return frame_start_ms_;
		}

		uint32_t remaining_frame_ms(uint32_t now_ms) const
		{
			const uint32_t elapsed_ms = now_ms - frame_start_ms_;
			return elapsed_ms < fixed_delta_ms_ ? fixed_delta_ms_ - elapsed_ms : 0u;
		}

		static bool is_supported_fps(uint32_t fps)
		{
			return fps == 30u || fps == 45u || fps == 60u;
		}

		static uint32_t normalize_fps(uint32_t fps)
		{
			return is_supported_fps(fps) ? fps : DefaultFps;
		}

	private:
		uint32_t next_tick_ms()
		{
			tick_remainder_ += 1000u;
			const uint32_t tick_ms = tick_remainder_ / target_fps_;
			tick_remainder_ %= target_fps_;
			return tick_ms;
		}

		uint32_t target_fps_;
		uint32_t tick_remainder_;
		uint32_t frame_start_ms_;
		uint32_t fixed_delta_ms_;
	};
}