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use core::cmp::Ordering;

use crate::config::CLOCK_FREQ;
use crate::sbi::set_timer;
use crate::sync::UPIntrFreeCell;
use crate::task::{wakeup_task, TaskControlBlock};
use alloc::collections::BinaryHeap;
use alloc::sync::Arc;
use lazy_static::*;
use riscv::register::time;

const TICKS_PER_SEC: usize = 100;
const MSEC_PER_SEC: usize = 1000;

pub fn get_time() -> usize {
    time::read()
}

pub fn get_time_ms() -> usize {
    time::read() / (CLOCK_FREQ / MSEC_PER_SEC)
}

pub fn set_next_trigger() {
    set_timer(get_time() + CLOCK_FREQ / TICKS_PER_SEC);
}

pub struct TimerCondVar {
    pub expire_ms: usize,
    pub task: Arc<TaskControlBlock>,
}

impl PartialEq for TimerCondVar {
    fn eq(&self, other: &Self) -> bool {
        self.expire_ms == other.expire_ms
    }
}
impl Eq for TimerCondVar {}
impl PartialOrd for TimerCondVar {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        let a = -(self.expire_ms as isize);
        let b = -(other.expire_ms as isize);
        Some(a.cmp(&b))
    }
}

impl Ord for TimerCondVar {
    fn cmp(&self, other: &Self) -> Ordering {
        self.partial_cmp(other).unwrap()
    }
}

lazy_static! {
    static ref TIMERS: UPIntrFreeCell<BinaryHeap<TimerCondVar>> =
        unsafe { UPIntrFreeCell::new(BinaryHeap::<TimerCondVar>::new()) };
}

pub fn add_timer(expire_ms: usize, task: Arc<TaskControlBlock>) {
    let mut timers = TIMERS.exclusive_access();
    timers.push(TimerCondVar { expire_ms, task });
}

pub fn check_timer() {
    let current_ms = get_time_ms();
    TIMERS.exclusive_session(|timers| {
        while let Some(timer) = timers.peek() {
            if timer.expire_ms <= current_ms {
                wakeup_task(Arc::clone(&timer.task));
                timers.pop();
            } else {
                break;
            }
        }
    });
}