use std::{sync::LazyLock, time::Instant};
static TIME_START: LazyLock<Instant> = LazyLock::new(Instant::now);

pub fn get_micros() -> u64 {
    TIME_START.elapsed().as_micros() as u64
}

#[derive(Default)]
pub struct Timestep {
    current_time_us: u64,
    accumulator: f32,
    time_micros: u64,
    ticks: u32,
    speed: f32,
    pub alpha: f32,
    delta: f32,
    loopnum: u8,
}

impl Timestep {
    pub fn new() -> Timestep {
        let mut timestep = Timestep {
            speed: 1.0,
            ..Default::default()
        };

        timestep.reset();
        timestep
    }

    fn calculate_alpha(&mut self) {
        self.alpha = (self.accumulator / self.delta).clamp(0.0, 1.0);
    }

    pub fn set_tps(&mut self, tps: f32) {
        self.delta = 1000.0 / tps;
    }

    pub fn reset(&mut self) {
        self.current_time_us = get_micros();
        self.accumulator = 0.0;
    }

    pub fn on_tick(&mut self) -> bool {
        let newtime = get_micros();
        let frametime = newtime - self.current_time_us;
        self.time_micros += frametime;
        self.current_time_us = newtime;
        self.accumulator += frametime as f32 * self.speed / 1000.0;
        self.calculate_alpha();

        if self.accumulator >= self.delta {
            self.accumulator -= self.delta;
            self.loopnum += 1;
            self.ticks += 1;

            if self.loopnum > 5 {
                // cannot keep up!
                self.loopnum = 0;
                self.accumulator = 0.0;
                return false;
            }

            true
        } else {
            self.loopnum = 0;
            false
        }
    }
}