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

struct Source<'a> {
    iter: core::iter::Peekable<core::slice::Iter<'a, u8>>,
}

impl<'a> From<&'a [u8]> for Source<'a> {
    fn from(value: &'a [u8]) -> Self {
        Self {
            iter: value.iter().peekable(),
        }
    }
}

#[unsafe(no_mangle)]
extern "C" fn peekc(src: *mut Source) -> u8 {
    unsafe { (*src).iter.peek().cloned().unwrap_or(&0).clone() }
}

#[unsafe(no_mangle)]
extern "C" fn getc(src: *mut Source) -> u8 {
    unsafe { (*src).iter.next().unwrap_or(&0).clone() }
}

#[test]
fn test_parse_reg() {
    let cases = [
        (&b"rax"[..], (0, 8)),
        (&b"rbx"[..], (1, 8)),
        (&b"rcx"[..], (2, 8)),
        (&b"rdx"[..], (3, 8)),
        (&b"rsp"[..], (4, 8)),
        (&b"rbp"[..], (5, 8)),
        (&b"rsi"[..], (6, 8)),
        (&b"rdi"[..], (7, 8)),
        (&b"eax"[..], (0, 4)),
        (&b"ebx"[..], (1, 4)),
        (&b"ecx"[..], (2, 4)),
        (&b"edx"[..], (3, 4)),
        (&b"esp"[..], (4, 4)),
        (&b"ebp"[..], (5, 4)),
        (&b"esi"[..], (6, 4)),
        (&b"edi"[..], (7, 4)),
        (&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"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"bx"[..], (1, 2)),
        (&b"cx"[..], (2, 2)),
        (&b"dx"[..], (3, 2)),
        (&b"sp"[..], (4, 2)),
        (&b"bp"[..], (5, 2)),
        (&b"si"[..], (6, 2)),
        (&b"di"[..], (7, 2)),
        (&b"al"[..], (0, 1)),
        (&b"bl"[..], (1, 1)),
        (&b"cl"[..], (2, 1)),
        (&b"dl"[..], (3, 1)),
        (&b"ah"[..], (0, 3)),
        (&b"bh"[..], (1, 3)),
        (&b"ch"[..], (2, 3)),
        (&b"dh"[..], (3, 3)),
        (&b"sil"[..], (6, 1)),
        (&b"dil"[..], (7, 1)),
        (&b"asd"[..], (0, 0)),
    ];

    for (text, result) in cases {
        let mut src = Source::from(text);
        unsafe {
            assert_eq!(
                parse_reg(&mut src),
                result,
                "Failed to parse '{}'",
                std::str::from_utf8(text).unwrap()
            );
        }
    }
}

#[test]
fn test_parse_gpr() {
    let cases = [
        (&b"ax"[..], (0, 2)),
        (&b"bx"[..], (1, 2)),
        (&b"cx"[..], (2, 2)),
        (&b"dx"[..], (3, 2)),
        (&b"sp"[..], (4, 2)),
        (&b"bp"[..], (5, 2)),
        (&b"si"[..], (6, 2)),
        (&b"di"[..], (7, 2)),
        (&b"al"[..], (0, 1)),
        (&b"bl"[..], (1, 1)),
        (&b"cl"[..], (2, 1)),
        (&b"dl"[..], (3, 1)),
        (&b"ah"[..], (0, 3)),
        (&b"bh"[..], (1, 3)),
        (&b"ch"[..], (2, 3)),
        (&b"dh"[..], (3, 3)),
        (&b"sil"[..], (6, 1)),
        (&b"dil"[..], (7, 1)),
        (&b"asd"[..], (0, 0)),
    ];

    for (text, result) in cases {
        let mut src = Source::from(text);
        unsafe {
            assert_eq!(
                parse_gpr(&mut src, b'r'),
                result,
                "Failed to parse '{}'",
                std::str::from_utf8(text).unwrap()
            );
        }
    }
}

enum Register {
    A = 0,
    B,
    C,
    D,
    Src,
    Dst,
    Sp,
    Bp,
    R8,
    R9,
    R10,
    R11,
    R12,
    R13,
    R14,
    R15,
}
enum RegisterSize {
    Byte = 1,
    Word = 2,
    Dword = 4,
    Qword = 8,
    HighByte = 3,
    None = 0,
}

#[repr(C)]
struct PackedRegister(u8);
impl From<PackedRegister> for Option<(Register, RegisterSize)> {
    fn from(value: PackedRegister) -> Self {
        let reg_bits = value.0 & 0x00F;
        let size_bits = (value.0 >> 4) & 0x0F;
        let size = match size_bits {
            1 => RegisterSize::Byte,
            2 => RegisterSize::Word,
            4 => RegisterSize::Dword,
            8 => RegisterSize::Qword,
            3 => RegisterSize::HighByte,
            0 => return None,
            _ => panic!("Invalid register size"),
        };

        let reg = match reg_bits {
            0 => Register::A,
            1 => Register::B,
            2 => Register::C,
            3 => Register::D,
            4 => Register::Sp,
            5 => Register::Bp,
            6 => Register::Src,
            7 => Register::Dst,
            8 => Register::R8,
            9 => Register::R9,
            10 => Register::R10,
            11 => Register::R11,
            12 => Register::R12,
            13 => Register::R13,
            14 => Register::R14,
            15 => Register::R15,
            _ => panic!("Invalid register number"),
        };

        Some((reg, size))
    }
}