na_nbt 0.2.1

High-performance NBT (Named Binary Tag) library with zero-copy parsing and serde support
Documentation 
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use std::{marker::PhantomData, ptr};

use zerocopy::byteorder;

use crate::{
    ByteOrder, ConfigRef, EMPTY_LIST, ListBase, ListRef, NBT, TagID, cold_path,
    mutable::{
        config::MutableConfig, size::mutable_tag_size, typed_list_ref::RefTypedList,
        value_ref::RefValue,
    },
};

#[derive(Clone)]
#[repr(transparent)]
pub struct RefList<'s, O: ByteOrder> {
    pub(crate) data: *const u8,
    pub(crate) _marker: PhantomData<(&'s (), O)>,
}

impl<'s, O: ByteOrder> Default for RefList<'s, O> {
    #[inline]
    fn default() -> Self {
        Self {
            data: EMPTY_LIST.as_ptr(),
            _marker: PhantomData,
        }
    }
}

unsafe impl<'s, O: ByteOrder> Send for RefList<'s, O> {}
unsafe impl<'s, O: ByteOrder> Sync for RefList<'s, O> {}

impl<'s, O: ByteOrder> IntoIterator for RefList<'s, O> {
    type Item = RefValue<'s, O>;
    type IntoIter = RefListIter<'s, O>;

    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        RefListIter {
            tag_id: self.element_tag_id(),
            remaining: self.len() as u32,
            data: unsafe { self.data.add(1 + 4) },
            _marker: PhantomData,
        }
    }
}

impl<'s, O: ByteOrder> ListBase for RefList<'s, O> {
    #[inline]
    fn element_tag_id(&self) -> TagID {
        unsafe { *self.data.cast() }
    }

    #[inline]
    fn len(&self) -> usize {
        unsafe { byteorder::U32::<O>::from_bytes(*self.data.add(1).cast()).get() as usize }
    }
}

impl<'s, O: ByteOrder> ListRef<'s> for RefList<'s, O> {
    type Config = MutableConfig<O>;

    #[inline]
    fn _to_read_params<'a>(&'a self) -> <Self::Config as ConfigRef>::ReadParams<'a>
    where
        's: 'a,
    {
        unsafe { self.data.add(1 + 4) }
    }

    #[inline]
    fn typed_<T: NBT>(self) -> Option<<Self::Config as ConfigRef>::TypedList<'s, T>> {
        self.element_is_::<T>().then_some(RefTypedList {
            data: self.data,
            _marker: PhantomData,
        })
    }

    #[inline]
    fn iter(&self) -> <Self::Config as ConfigRef>::ListIter<'s> {
        RefListIter {
            tag_id: self.element_tag_id(),
            remaining: self.len() as u32,
            data: unsafe { self.data.add(1 + 4) },
            _marker: PhantomData,
        }
    }
}

#[derive(Clone)]
pub struct RefListIter<'s, O: ByteOrder> {
    pub(crate) tag_id: TagID,
    pub(crate) remaining: u32,
    pub(crate) data: *const u8,
    pub(crate) _marker: PhantomData<(&'s (), O)>,
}

impl<'s, O: ByteOrder> Default for RefListIter<'s, O> {
    #[inline]
    fn default() -> Self {
        Self {
            tag_id: TagID::End,
            remaining: 0,
            data: ptr::null(),
            _marker: PhantomData,
        }
    }
}

unsafe impl<'s, O: ByteOrder> Send for RefListIter<'s, O> {}
unsafe impl<'s, O: ByteOrder> Sync for RefListIter<'s, O> {}

impl<'s, O: ByteOrder> Iterator for RefListIter<'s, O> {
    type Item = RefValue<'s, O>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.remaining == 0 {
            cold_path();
            return None;
        }

        self.remaining -= 1;

        let value = unsafe { <MutableConfig<O> as ConfigRef>::read_value(self.tag_id, self.data) };

        self.data = unsafe { self.data.add(mutable_tag_size(self.tag_id)) };

        Some(value)
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        let remaining = self.remaining as usize;
        (remaining, Some(remaining))
    }
}

impl<'s, O: ByteOrder> ExactSizeIterator for RefListIter<'s, O> {}