#pragma once

#include <chrono>

namespace crepe {

class LoopTimer {
public:
	/**
	 * \brief Get the singleton instance of LoopTimer.
	 *
	 * \return A reference to the LoopTimer instance.
	 */
	static LoopTimer & get_instance();

	/**
	 * \brief Get the current delta time for the current frame.
	 *
	 * \return Delta time in seconds since the last frame.
	 */
	double get_delta_time() const;

	/**
	 * \brief Get the current game time.
	 *
	 * \note The current game time may vary from real-world elapsed time. It is the cumulative
	 * sum of each frame's delta time.
	 *
	 * \return Elapsed game time in seconds.
	 */
	double get_current_time() const;

	/**
	 * \brief Set the target frames per second (FPS).
	 *
	 * \param fps The desired frames rendered per second.
	 */
	void set_fps(int fps);

	/**
	 * \brief Get the current frames per second (FPS).
	 *
	 * \return Current FPS.
	 */
	int get_fps() const;

	/**
	 * \brief Get the current game scale.
	 *
	 * \return The current game scale, where 0 = paused, 1 = normal speed, and values > 1 speed
	 * up the game.
	 */
	double get_game_scale() const;

	/**
	 * \brief Set the game scale.
	 *
	 * \param game_scale The desired game scale (0 = pause, 1 = normal speed, > 1 = speed up).
	 */
	void set_game_scale(double game_scale);

private:
	friend class LoopManager;

	/**
	 * \brief Start the loop timer.
	 *
	 * Initializes the timer to begin tracking frame times.
	 */
	void start();

	/**
	 * \brief Enforce the frame rate limit.
	 *
	 * Ensures that the game loop does not exceed the target FPS by delaying frame updates as
	 * necessary.
	 */
	void enforce_frame_rate();

	/**
	 * \brief Get the fixed delta time for consistent updates.
	 *
	 * Fixed delta time is used for operations that require uniform time steps, such as physics
	 * calculations.
	 *
	 * \return Fixed delta time in seconds.
	 */
	double get_fixed_delta_time() const;

	/**
	 * \brief Get the accumulated lag in the game loop.
	 *
	 * Lag represents the difference between the target frame time and the actual frame time,
	 * useful for managing fixed update intervals.
	 *
	 * \return Accumulated lag in seconds.
	 */
	double get_lag() const;

	/**
	 * \brief Construct a new LoopTimer object.
	 *
	 * Private constructor for singleton pattern to restrict instantiation outside the class.
	 */
	LoopTimer();

	/**
	 * \brief Update the timer to the current frame.
	 *
	 * Calculates and updates the delta time for the current frame and adds it to the cumulative
	 * game time.
	 */
	void update();

	/**
	 * \brief Advance the game loop by a fixed update interval.
	 *
	 * This method progresses the game state by a consistent, fixed time step, allowing for
	 * stable updates independent of frame rate fluctuations.
	 */
	void advance_fixed_update();

private:
	//! Current frames per second
	int fps = 50;
	//! Current game scale
	double game_scale = 1;
	//! Maximum delta time in seconds to avoid large jumps
	std::chrono::duration<double> maximum_delta_time{0.25};
	//! Delta time for the current frame in seconds
	std::chrono::duration<double> delta_time{0.0};
	//! Target time per frame in seconds
	std::chrono::duration<double> frame_target_time = std::chrono::duration<double>(1.0) / fps;
	//! Fixed delta time for fixed updates in seconds
	std::chrono::duration<double> fixed_delta_time = std::chrono::duration<double>(1.0) / 50.0;
	//! Total elapsed game time in seconds
	std::chrono::duration<double> elapsed_time{0.0};
	//! Total elapsed time for fixed updates in seconds
	std::chrono::duration<double> elapsed_fixed_time{0.0};
	//! Time of the last frame
	std::chrono::steady_clock::time_point last_frame_time;
};

} // namespace crepe