use crate::callback::Identity0Consumer;
use crate::futures;
use crate::result::TockResult;
use crate::syscalls;
use core::cell::Cell;
use core::mem;

const DRIVER_NUMBER: usize = 0x40001;

mod command_nr {
    pub const REQUEST_RNG: usize = 1;
}

mod subscribe_nr {
    pub const BUFFER_FILLED: usize = 0;
}

mod allow_nr {
    pub const SHARE_BUFFER: usize = 0;
}

#[non_exhaustive]
pub struct RngDriver;

impl RngDriver {
    pub async fn fill_buffer(&mut self, buf: &mut [u8]) -> TockResult<()> {
        let buf_len = buf.len();
        let shared_memory = syscalls::allow(DRIVER_NUMBER, allow_nr::SHARE_BUFFER, buf)?;
        let is_filled = Cell::new(false);
        let mut is_filled_alarm = || is_filled.set(true);
        let subscription = syscalls::subscribe::<Identity0Consumer, _>(
            DRIVER_NUMBER,
            subscribe_nr::BUFFER_FILLED,
            &mut is_filled_alarm,
        )?;
        syscalls::command(DRIVER_NUMBER, command_nr::REQUEST_RNG, buf_len, 0)?;
        futures::wait_until(|| is_filled.get()).await;
        mem::drop(subscription);
        mem::drop(shared_memory);
        Ok(())
    }
}