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

use super::{Direction, Opcode};

use consts::*;

/// Compose an opcode from its component parts.

pub(super) const fn compose_opcode(

    dir: Direction,

    group: Opcode,

    num: Opcode,

    size: Opcode,

) -> Opcode {

    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: Opcode = 8;

const GROUP_BITS: Opcode = 8;

const NUM_SHIFT: Opcode = 0;

const GROUP_SHIFT: Opcode = NUM_SHIFT + NUM_BITS;

const SIZE_SHIFT: Opcode = GROUP_SHIFT + GROUP_BITS;

const DIR_SHIFT: Opcode = SIZE_SHIFT + SIZE_BITS;

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

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

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

const DIR_MASK: Opcode = (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::Opcode;

    pub(super) const NONE: Opcode = 0;

    pub(super) const READ: Opcode = 2;

    pub(super) const WRITE: Opcode = 1;

    pub(super) const SIZE_BITS: Opcode = 14;

    pub(super) const DIR_BITS: Opcode = 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::Opcode;

    pub(super) const NONE: Opcode = 1;

    pub(super) const READ: Opcode = 2;

    pub(super) const WRITE: Opcode = 4;

    pub(super) const SIZE_BITS: Opcode = 13;

    pub(super) const DIR_BITS: Opcode = 3;

}

#[cfg(test)]

mod tests {

    #[allow(unused_imports)]

    use super::*;

    #[cfg(all(linux_raw_dep, not(any(

    // These have no ioctl opcodes defined in linux_raw_sys so we 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 Opcode,

                15,

                size_of::<c_uint>() as Opcode

            ),

            linux_raw_sys::ioctl::USBDEVFS_CLAIMINTERFACE as Opcode

        );

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

        assert_eq!(

            compose_opcode(

                Direction::Write,

                b'v' as Opcode,

                2,

                size_of::<c_long>() as Opcode

            ),

            linux_raw_sys::ioctl::FS_IOC_SETVERSION as Opcode

        );

    }

}