#![no_std]
#![no_main]

use core::fmt::Write;

fn exit(code: i32) -> ! {
    unsafe {
        core::arch::asm!(
            "li a7, 93",
            "ecall",
            in("a0") code,
            options(noreturn),
        );
    }
}

fn write(fd: i32, data: &[u8]) -> isize {
    let mut out;
    unsafe {
        core::arch::asm!(
            "li a7, 64",
            "ecall",
            in("a0") fd,
            in("a1") data.as_ptr(),
            in("a2") data.len(),
            lateout("a0") out,
            out("a7") _,
        )
    }
    out
}

fn read(fd: i32, buf: &mut [u8]) -> isize {
    let mut out;
    unsafe {
        core::arch::asm!(
            "li a7, 63",
            "ecall",
            in("a0") fd,
            in("a1") buf.as_mut_ptr(),
            in("a2") buf.len(),
            lateout("a0") out,
            out("a7") _,
        )
    }
    out
}

struct Stderr;

impl core::fmt::Write for Stderr {
    fn write_str(&mut self, s: &str) -> core::fmt::Result {
        let ret = write(2, s.as_bytes());
        if ret < 0 {
            Err(core::fmt::Error)
        } else {
            Ok(())
        }
    }
}

macro_rules! eprintln {
    ($($tt:tt)*) => {
        writeln!(Stderr, $($tt)*).unwrap();
    };
}
macro_rules! eprint {
    ($($tt:tt)*) => {
        write!(Stderr, $($tt)*).unwrap();
    };
}

#[panic_handler]
fn handle(info: &core::panic::PanicInfo<'_>) -> ! {
    let _ = writeln!(Stderr, "panicked: {}", info.message());
    unsafe { core::arch::asm!("unimp", options(noreturn)) }
}

fn input() -> u64 {
    eprint!("enter a number: ");

    loop {
        let mut buf = [0; 10];
        let len = read(0, &mut buf);
        let buf = &buf[..(len as usize)];
        let n = str::from_utf8(buf).unwrap().trim();
        match n.parse::<u64>() {
            Ok(v) => return v,
            Err(_) => {
                eprint!("not a valid number, try again: ");
            }
        }
    }
}


#[no_mangle]
fn _start() -> ! {
    let random_number = 45;

    let num = core::sync::atomic::AtomicI32::new(0);
    num.swap(10, core::sync::atomic::Ordering::SeqCst);

    loop {
        let n = input();
        if n == random_number {
            eprintln!("correct!");
            break;
        } else if n < random_number {
            eprintln!("random number is greater");
        } else {
            eprintln!("random number is smaller");
        }
    }

    exit(0);
}