#pragma once

#include <cstdint>

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 the real-world elapsed time.
	 * It is the cumulative sum of each frame's delta time.
	 *
	 * \return Elapsed game time in milliseconds.
	 */
	int get_current_time() const;

	/**
	 * \brief Set the target frames per second (FPS).
	 *
	 * \param fps The number of frames that should be 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 to avoid large jumps       
	double maximum_delta_time = 0.25;  
	//! Delta time for the current frame 
	double delta_time = 0;         
	//! Target time per frame in seconds     
	double frame_target_time = 1.0 / fps; 
	//! Fixed delta time for fixed updates
	double fixed_delta_time = 0.02; 
	//! Total elapsed game time    
	double elapsed_time = 0;    
	//! Total elapsed time for fixed updates         
	double elapsed_fixed_time = 0; 
	//! Time of the last frame     
	uint64_t last_frame_time = 0;      
};

} // namespace crepe