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//!Conversions from bytes.
//!
//!# Usage
//!
//!```rust
//!use lazy_bytes_cast::from::{bytes_cast};
//!
//!fn main() {
//!    let bytes = vec![127, 150, 152, 0];
//!
//!    if let Some(int) = bytes_cast::<u32>(&bytes) {
//!        println!("bytes={}", int);
//!    } else {
//!        println!("Couldn't extract integer from bytes");
//!    }
//!}
//!```

use core::{marker, mem, ptr};

use crate::to::ToBytesCast;

///Unsafe version of `bytes_cast`
///
///# Note:
///
///This function is able to convert only to types that implements `marker::Copy`
///
///# Parameters:
///
///* `bytes` - slice of bytes to convert.
///
///# Result:
///
///* `T` - Converted data.
pub unsafe fn bytes_cast_lazy<T: marker::Copy>(bytes: &[u8]) -> T {
    let len = mem::size_of::<T>();

    let mut result: T = mem::uninitialized();
    ptr::copy_nonoverlapping(bytes.as_ptr(), &mut result as *mut _ as *mut u8, len);

    result
}

///Converts slice of bytes to an integer.
///
///# Note:
///
///To be safe this function allows conversion only to types that implements `ToBytesCast`.
///
///# Parameters:
///
///* `bytes` - slice of bytes to convert
///
///# Result:
///
///* `None` - Insufficient amount of bytes for cast.
pub fn bytes_cast<T: ToBytesCast>(bytes: &[u8]) -> Option<T> {
    let len = mem::size_of::<T>();

    if bytes.len() < len {
        None
    }
    else {
        unsafe {
            Some(bytes_cast_lazy(bytes))
        }
    }
}

///Provides casting from bytes slice.
///
///If you're absolutely hate to bother yourself by checking Result.
///
///Feel free to just use `bytes_cast_lazy`
pub unsafe trait FromBytesCast<T: ToBytesCast> {
    ///Performs cast to integer.
    fn cast_to(&self) -> Option<T>;
}

#[cfg(feature = "std")]
unsafe impl<T: ToBytesCast> FromBytesCast<T> for Vec<u8> {
    #[inline]
    fn cast_to(&self) -> Option<T> {
        bytes_cast(self)
    }
}

unsafe impl<T: ToBytesCast> FromBytesCast<T> for [u8] {
    #[inline]
    fn cast_to(&self) -> Option<T> {
        bytes_cast(self)
    }
}

unsafe impl<'a, T: ToBytesCast> FromBytesCast<T> for &'a[u8] {
    #[inline]
    fn cast_to(&self) -> Option<T> {
        bytes_cast(*self)
    }
}

///Provides casting from fixed size arrays to integers
///
///Supposed to be safe without wrapping into `Result`.
///
///Besides isn't it bothersome to unwrap perfectly safe cast from bytes array? ;)
pub unsafe trait FromBytesCastLazy<T: ToBytesCast> {
    ///Performs cast to integer.
    fn cast_to(&self) -> T;
}

macro_rules! impl_from_traits_arr
{
    ($([$t:ty; $size:expr]), +) => {
        $(
            unsafe impl FromBytesCastLazy<$t> for [u8; $size] {
                #[inline]
                fn cast_to(&self) -> $t {
                    unsafe {
                        bytes_cast_lazy(self)
                    }
                }
            }
        )+
    };
}

impl_from_traits_arr!(
    [u32; 4], [i32; 4], [f32; 4],
    [u64; 8], [i64; 8], [f64; 8],
    [i128; 16], [u128; 16],
    [u16; 2], [i16; 2]
);

#[cfg(target_pointer_width = "64")]
impl_from_traits_arr!([usize; 8], [isize; 8]);

#[cfg(target_pointer_width = "32")]
impl_from_traits_arr!([usize; 4], [isize; 4]);

macro_rules! impl_from_traits_tuple4
{
    ($($t:ty),+) => {
        $(
            unsafe impl FromBytesCastLazy<$t> for (u8, u8, u8, u8) {
                #[inline]
                fn cast_to(&self) -> $t {
                    [self.0, self.1, self.2, self.3].cast_to()
                }
            }
        )+
    };
}
macro_rules! impl_from_traits_tuple8
{
    ($($t:ty),+) => {
        $(
            unsafe impl FromBytesCastLazy<$t> for (u8, u8, u8, u8, u8, u8, u8, u8) {
                #[inline]
                fn cast_to(&self) -> $t {
                    [self.0, self.1, self.2, self.3, self.4, self.5, self.6, self.7].cast_to()
                }
            }
        )+
    };
}
macro_rules! impl_from_traits_tuple16
{
    ($($t:ty),+) => {
        $(
            unsafe impl FromBytesCastLazy<$t> for (u8, u8, u8, u8, u8, u8, u8, u8, u8, u8, u8, u8, u8, u8, u8, u8) {
                #[inline]
                fn cast_to(&self) -> $t {
                    [self.0, self.1, self.2, self.3, self.4, self.5, self.6, self.7, self.8, self.9, self.10, self.11, self.12, self.13, self.14, self.15].cast_to()
                }
            }
        )+
    };
}
macro_rules! impl_from_traits_tuple2
{
    ($($t:ty),+) => {
        $(
            unsafe impl FromBytesCastLazy<$t> for (u8, u8) {
                #[inline]
                fn cast_to(&self) -> $t {
                    [self.0, self.1].cast_to()
                }
            }
        )+
    };
}

impl_from_traits_tuple2!(i16, u16);
impl_from_traits_tuple4!(i32, u32, f32);
impl_from_traits_tuple8!(i64, u64, f64);
impl_from_traits_tuple16!(i128, u128);

#[cfg(target_pointer_width = "64")]
impl_from_traits_tuple8!(isize, usize);

#[cfg(target_pointer_width = "32")]
impl_from_traits_tuple4!(isize, usize);