//! `ioctl` opcode behavior for Linux platforms.

use super::{Direction, RawOpcode};

use consts::*;

/// Compose an opcode from its component parts.

pub(super) const fn compose_opcode(

    dir: Direction,

    group: RawOpcode,

    num: RawOpcode,

    size: RawOpcode,

) -> RawOpcode {

    macro_rules! mask_and_shift {

        ($val:expr, $shift:expr, $mask:expr) => {{

            ($val & $mask) << $shift

        }};

    }

    let dir = match dir {

        Direction::None => NONE,

        Direction::Read => READ,

        Direction::Write => WRITE,

        Direction::ReadWrite => READ | WRITE,

    };

    mask_and_shift!(group, GROUP_SHIFT, GROUP_MASK)

        | mask_and_shift!(num, NUM_SHIFT, NUM_MASK)

        | mask_and_shift!(size, SIZE_SHIFT, SIZE_MASK)

        | mask_and_shift!(dir, DIR_SHIFT, DIR_MASK)

}

const NUM_BITS: RawOpcode = 8;

const GROUP_BITS: RawOpcode = 8;

const NUM_SHIFT: RawOpcode = 0;

const GROUP_SHIFT: RawOpcode = NUM_SHIFT + NUM_BITS;

const SIZE_SHIFT: RawOpcode = GROUP_SHIFT + GROUP_BITS;

const DIR_SHIFT: RawOpcode = SIZE_SHIFT + SIZE_BITS;

const NUM_MASK: RawOpcode = (1 << NUM_BITS) - 1;

const GROUP_MASK: RawOpcode = (1 << GROUP_BITS) - 1;

const SIZE_MASK: RawOpcode = (1 << SIZE_BITS) - 1;

const DIR_MASK: RawOpcode = (1 << DIR_BITS) - 1;

#[cfg(any(

    target_arch = "x86",

    target_arch = "arm",

    target_arch = "s390x",

    target_arch = "x86_64",

    target_arch = "aarch64",

    target_arch = "riscv32",

    target_arch = "riscv64",

    target_arch = "loongarch64",

    target_arch = "csky"

))]

mod consts {

    use super::RawOpcode;

    pub(super) const NONE: RawOpcode = 0;

    pub(super) const READ: RawOpcode = 2;

    pub(super) const WRITE: RawOpcode = 1;

    pub(super) const SIZE_BITS: RawOpcode = 14;

    pub(super) const DIR_BITS: RawOpcode = 2;

}

#[cfg(any(

    target_arch = "mips",

    target_arch = "mips32r6",

    target_arch = "mips64",

    target_arch = "mips64r6",

    target_arch = "powerpc",

    target_arch = "powerpc64",

    target_arch = "sparc",

    target_arch = "sparc64"

))]

mod consts {

    use super::RawOpcode;

    pub(super) const NONE: RawOpcode = 1;

    pub(super) const READ: RawOpcode = 2;

    pub(super) const WRITE: RawOpcode = 4;

    pub(super) const SIZE_BITS: RawOpcode = 13;

    pub(super) const DIR_BITS: RawOpcode = 3;

}

#[cfg(not(any(

    // These have no ioctl opcodes defined in linux_raw_sys

    // so can't use that as a known-good value for this test.

    target_arch = "sparc",

    target_arch = "sparc64"

)))]

#[test]

fn check_known_opcodes() {

    use crate::backend::c::{c_long, c_uint};

    use core::mem::size_of;

    // _IOR('U', 15, unsigned int)

    assert_eq!(

        compose_opcode(

            Direction::Read,

            b'U' as RawOpcode,

            15,

            size_of::<c_uint>() as RawOpcode

        ),

        linux_raw_sys::ioctl::USBDEVFS_CLAIMINTERFACE as RawOpcode

    );

    // _IOW('v', 2, long)

    assert_eq!(

        compose_opcode(

            Direction::Write,

            b'v' as RawOpcode,

            2,

            size_of::<c_long>() as RawOpcode

        ),

        linux_raw_sys::ioctl::FS_IOC_SETVERSION as RawOpcode

    );

}