use std::{
	ops::{Add, Div, Mul},
	time::{Duration, Instant},
};

/// How often to update the fps interval on screen
const FPS_INTERVAL: Duration = Duration::from_millis(250);

/// How much to smooth he `delta_avg` amount (`AVG_RATIO`:1)
const AVG_RATIO: u32 = 10;

/// Keeps track of frame intervals and FPS
pub struct Timer {
	/// Last time updated
	previous: Instant,
	/// Current time
	now: Instant,
	/// Rolling delta time average
	delta_avg: Duration,
	/// Computed fps
	fps: f64,
	/// Last time the fps was updated
	fps_time: Instant,
	/// Frame count
	count: u32,
}
impl Timer {
	pub fn new() -> Self {
		let now = Instant::now();
		Self {
			previous: now,
			now,
			delta_avg: Duration::ZERO,
			fps: 0.0,
			fps_time: now,
			count: 0,
		}
	}

	pub fn update(&mut self) {
		self.previous = self.now;
		self.now = Instant::now();
		self.delta_avg = self
			.delta_avg
			.mul(AVG_RATIO)
			.add(self.delta_time())
			.div(AVG_RATIO + 1);
		if (self.now - self.fps_time) > FPS_INTERVAL {
			self.fps = 1.0 / self.delta_avg.as_secs_f64();
			self.fps_time = self.now;
		}
		self.count += 1;
	}

	pub const fn get_frame(&self) -> u32 {
		self.count
	}

	#[expect(clippy::cast_possible_truncation)]
	pub fn get_fps(&self) -> u32 {
		self.fps.ceil() as u32
	}

	pub fn delta_time(&self) -> Duration {
		self.now - self.previous
	}
}