#![deny(unsafe_op_in_unsafe_fn)]

use crate::io;
use core::arch::asm;

pub struct Stdin;
pub struct Stdout;
pub struct Stderr;

const KCALL_DEBUG_CMD_PUT_BYTES: i64 = 2;

unsafe fn debug_call(cap_ref: u64, call_no: i64, arg1: u64, arg2: u64) -> i32 {
    let ret: u64;
    unsafe {
        asm!(
            "svc #99",
            inout("x0") cap_ref => ret,
            in("x1") call_no,
            in("x2") arg1,
            in("x3") arg2,
        );
    }

    ret as i32
}

fn print_buf(s: &[u8]) -> io::Result<usize> {
    // Corresponds to `HM_DEBUG_PUT_BYTES_LIMIT`.
    const MAX_LEN: usize = 512;
    let len = if s.len() > MAX_LEN { MAX_LEN } else { s.len() };
    let result = unsafe { debug_call(0, KCALL_DEBUG_CMD_PUT_BYTES, s.as_ptr() as u64, len as u64) };

    if result == 0 { Ok(len) } else { Err(io::Error::from(io::ErrorKind::InvalidInput)) }
}

impl Stdin {
    pub const fn new() -> Stdin {
        Stdin
    }
}

impl io::Read for Stdin {
    fn read(&mut self, _buf: &mut [u8]) -> io::Result<usize> {
        Ok(0)
    }
}

impl Stdout {
    pub const fn new() -> Stdout {
        Stdout
    }
}

impl io::Write for Stdout {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        print_buf(buf)
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

impl Stderr {
    pub const fn new() -> Stderr {
        Stderr
    }
}

impl io::Write for Stderr {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        print_buf(buf)
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

pub const STDIN_BUF_SIZE: usize = 0;

pub fn is_ebadf(err: &io::Error) -> bool {
    err.raw_os_error() == Some(libc::EBADF as i32)
}

pub fn panic_output() -> Option<impl io::Write> {
    Some(Stderr::new())
}
