unsafe extern "C" {
    // unsafe fn parse_gpr(src: *mut Source, prefix: u8) -> (u64, u64);
    // unsafe fn parse_reg(src: *mut Source) -> (u64, u64);

    unsafe fn try_parse_reg() -> (usize, Register);

    #[link_name = "buf"]
    static mut BUF: [u8; 0x100];
}

#[repr(C)]
#[derive(Debug, PartialEq, Eq)]
struct Register {
    size: u32,
    num: u32,
}

impl Register {
    fn new(num: u32, size: u32) -> Self {
        Self {
            num,
            size: size.ilog2(),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn write_to_buf(b: &[u8]) {
        assert!(b.len() <= 0x100, "Buffer overflow");
        unsafe {
            core::ptr::copy_nonoverlapping(b.as_ptr(), (&raw mut BUF).cast(), b.len());
        }
    }

    #[test]
    fn parse_reg() {
        let cases = [
            (&b"rax"[..], (0, 8)),
            (&b"rcx"[..], (1, 8)),
            (&b"rdx"[..], (2, 8)),
            (&b"rbx"[..], (3, 8)),
            (&b"rsp"[..], (4, 8)),
            (&b"rbp"[..], (5, 8)),
            (&b"rsi"[..], (6, 8)),
            (&b"rdi"[..], (7, 8)),
            (&b"r8"[..], (8, 8)),
            (&b"r9"[..], (9, 8)),
            (&b"r10"[..], (10, 8)),
            (&b"r11"[..], (11, 8)),
            (&b"r12"[..], (12, 8)),
            (&b"r13"[..], (13, 8)),
            (&b"r14"[..], (14, 8)),
            (&b"r15"[..], (15, 8)),
            (&b"rip"[..], (!0, 8)),
            (&b"eax"[..], (0, 4)),
            (&b"ecx"[..], (1, 4)),
            (&b"edx"[..], (2, 4)),
            (&b"ebx"[..], (3, 4)),
            (&b"esp"[..], (4, 4)),
            (&b"ebp"[..], (5, 4)),
            (&b"esi"[..], (6, 4)),
            (&b"edi"[..], (7, 4)),
            (&b"r8d"[..], (8, 4)),
            (&b"r9d"[..], (9, 4)),
            (&b"r10d"[..], (10, 4)),
            (&b"r11d"[..], (11, 4)),
            (&b"r12d"[..], (12, 4)),
            (&b"r13d"[..], (13, 4)),
            (&b"r14d"[..], (14, 4)),
            (&b"r15d"[..], (15, 4)),
            (&b"r8w"[..], (8, 2)),
            (&b"r9w"[..], (9, 2)),
            (&b"r10w"[..], (10, 2)),
            (&b"r11w"[..], (11, 2)),
            (&b"r12w"[..], (12, 2)),
            (&b"r13w"[..], (13, 2)),
            (&b"r14w"[..], (14, 2)),
            (&b"r15w"[..], (15, 2)),
            (&b"r8b"[..], (8, 1)),
            (&b"r9b"[..], (9, 1)),
            (&b"r10b"[..], (10, 1)),
            (&b"r11b"[..], (11, 1)),
            (&b"r12b"[..], (12, 1)),
            (&b"r13b"[..], (13, 1)),
            (&b"r14b"[..], (14, 1)),
            (&b"r15b"[..], (15, 1)),
            (&b"ax"[..], (0, 2)),
            (&b"cx"[..], (1, 2)),
            (&b"dx"[..], (2, 2)),
            (&b"bx"[..], (3, 2)),
            (&b"sp"[..], (4, 2)),
            (&b"bp"[..], (5, 2)),
            (&b"si"[..], (6, 2)),
            (&b"di"[..], (7, 2)),
            (&b"al"[..], (0, 1)),
            (&b"cl"[..], (1, 1)),
            (&b"dl"[..], (2, 1)),
            (&b"bl"[..], (3, 1)),
            (&b"spl"[..], (4, 1)),
            (&b"bpl"[..], (5, 1)),
            (&b"sil"[..], (6, 1)),
            (&b"dil"[..], (7, 1)),
        ];

        for (text, (reg, size)) in cases {
            write_to_buf(text);
            let (n, result) = unsafe { try_parse_reg() };
            assert_eq!(
                result,
                Register::new(reg, size),
                "Failed to parse '{}' n={n}",
                std::str::from_utf8(text).unwrap()
            );
        }
    }
}