//! Internals for `RawFd`
use super::*;
use std::num::NonZeroU32;

/// Used for the base of valid file descriptors for non-null optimisation.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Copy, PartialOrd, Ord)]
#[repr(transparent)]
pub(super) struct NonNegativeI32(NonZeroU32);

const RANGE_MASK: u32 = u32::MAX >> 1;
const NEG_FLAG: u32 = !RANGE_MASK;

#[inline(always)] 
const fn is_negative(val: i32) -> bool
{
    ((val as u32) & NEG_FLAG) != 0
}

impl NonNegativeI32
{
    #[inline] 
    pub fn new_or_else<F: FnOnce() -> Self>(raw: i32, f: F) -> Self
    {
	Self::new(raw).unwrap_or_else(f)
    }
    #[inline] 
    pub fn new_or(raw: i32, or: Self) -> Self
    {
	Self::new(raw).unwrap_or(or)
    }
    #[inline]
    pub const fn new_or_panic(raw: i32) -> Self
    {
	#[inline(never)]
	#[cold]
	const fn _panic_negative() -> !
	{
	    panic!("Negative integer passed to asserting panic")
	}
	match Self::new(raw) {
	    Some(v) => v,
	    None => _panic_negative()
	}
    }
    #[inline] 
    pub const fn new(raw: i32) -> Option<Self>
    {
	if is_negative(raw) {
	    None
	} else {
	    Some(Self(unsafe {NonZeroU32::new_unchecked(raw as u32 | NEG_FLAG)}))
	}
    }

    #[inline] 
    pub const fn get(self) -> i32
    {
	(self.0.get() & RANGE_MASK) as i32
    }

    #[inline] 
    pub const unsafe fn new_unchecked(raw: i32) -> Self
    {
	Self(NonZeroU32::new_unchecked(raw as u32 | NEG_FLAG))
    }
}

impl PartialOrd<i32> for NonNegativeI32
{
    #[inline] 
    fn partial_cmp(&self, other: &i32) -> Option<std::cmp::Ordering> {
	self.get().partial_cmp(other)
    }
}
impl PartialEq<i32> for NonNegativeI32
{
    #[inline] 
    fn eq(&self, other: &i32) -> bool
    {
	self.get().eq(other)
    }
}

impl PartialEq<NonNegativeI32> for i32
{
    #[inline] 
    fn eq(&self, other: &NonNegativeI32) -> bool
    {
	self.eq(&other.get())
    }
}

impl PartialOrd<NonNegativeI32> for i32
{
    #[inline] 
    fn partial_cmp(&self, other: &NonNegativeI32) -> Option<std::cmp::Ordering> {
	self.partial_cmp(&other.get())
    }
}

impl From<NonNegativeI32> for i32
{
    #[inline] 
    fn from(from: NonNegativeI32) -> Self
    {
	from.get()
    }
}

impl From<i32> for NonNegativeI32
{
    // Convenience `From` impl (panicking) 
    #[inline(always)] 
    fn from(from: i32) -> Self
    {
	Self::new_or_panic(from)
    }
}