use crate::vec::VecResolver;
use crate::{
    ser::{ScratchSpace, Serializer},
    vec::ArchivedVec,
    Archive, Archived, Serialize,
};

#[cfg(not(feature = "std"))]
use ::alloc::{alloc, boxed::Box, vec::Vec};
use core::borrow::{Borrow, BorrowMut};
use core::{
    fmt,
    ops::{Deref, DerefMut, Index, IndexMut},
    ptr::NonNull,
    slice,
};
#[cfg(feature = "std")]
use std::{alloc, io};

/// A vector of bytes that aligns its memory to 16 bytes.
///
/// The alignment also applies to `ArchivedAlignedVec`, which is useful for aligning opaque bytes inside of an archived data
/// type.
///
/// ```
/// # use rkyv::{archived_value, AlignedBytes, AlignedVec, Archive, Serialize};
/// # use rkyv::ser::Serializer;
/// # use rkyv::ser::serializers::CoreSerializer;
/// #
/// #[derive(Archive, Serialize)]
/// struct HasAlignedBytes {
///     pub bytes: AlignedVec,
/// }
///
/// let mut serializer = CoreSerializer::<256, 0>::default();
///
/// // Write a single byte to force re-alignment.
/// serializer.write(&[0]).unwrap();
/// assert_eq!(serializer.pos(), 1);
///
/// let mut bytes = AlignedVec::new();
/// bytes.extend_from_slice(&[1, 2, 3]);
/// let pos = serializer.serialize_value(&HasAlignedBytes { bytes }).unwrap();
///
/// // Make sure we can recover the archived type with the expected alignment.
/// let buf = serializer.into_serializer().into_inner();
/// let archived = unsafe { archived_value::<HasAlignedBytes>(buf.as_ref(), pos) };
/// assert_eq!(archived.bytes.as_slice(), &[1, 2, 3]);
/// assert_eq!(archived.bytes.as_ptr().align_offset(16), 0);
/// ```
pub struct AlignedVec {
    ptr: NonNull<u8>,
    cap: usize,
    len: usize,
}

impl Drop for AlignedVec {
    #[inline]
    fn drop(&mut self) {
        if self.cap != 0 {
            unsafe {
                alloc::dealloc(self.ptr.as_ptr(), self.layout());
            }
        }
    }
}

impl AlignedVec {
    /// The alignment of the vector
    pub const ALIGNMENT: usize = 16;

    /// Maximum capacity of the vector.
    /// Dictated by the requirements of
    /// [`alloc::Layout`](https://doc.rust-lang.org/alloc/alloc/struct.Layout.html).
    /// "`size`, when rounded up to the nearest multiple of `align`, must not overflow `isize`
    /// (i.e. the rounded value must be less than or equal to `isize::MAX`)".
    pub const MAX_CAPACITY: usize = isize::MAX as usize - (Self::ALIGNMENT - 1);

    /// Constructs a new, empty `AlignedVec`.
    ///
    /// The vector will not allocate until elements are pushed into it.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// ```
    #[inline]
    pub fn new() -> Self {
        AlignedVec {
            ptr: NonNull::dangling(),
            cap: 0,
            len: 0,
        }
    }

    /// Constructs a new, empty `AlignedVec` with the specified capacity.
    ///
    /// The vector will be able to hold exactly `capacity` bytes without reallocating. If
    /// `capacity` is 0, the vector will not allocate.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::with_capacity(10);
    ///
    /// // The vector contains no items, even though it has capacity for more
    /// assert_eq!(vec.len(), 0);
    /// assert_eq!(vec.capacity(), 10);
    ///
    /// // These are all done without reallocating...
    /// for i in 0..10 {
    ///     vec.push(i);
    /// }
    /// assert_eq!(vec.len(), 10);
    /// assert_eq!(vec.capacity(), 10);
    ///
    /// // ...but this may make the vector reallocate
    /// vec.push(11);
    /// assert_eq!(vec.len(), 11);
    /// assert!(vec.capacity() >= 11);
    /// ```
    #[inline]
    pub fn with_capacity(capacity: usize) -> Self {
        if capacity == 0 {
            Self::new()
        } else {
            assert!(
                capacity <= Self::MAX_CAPACITY,
                "`capacity` cannot exceed isize::MAX - 15"
            );
            let ptr = unsafe {
                let layout = alloc::Layout::from_size_align_unchecked(capacity, Self::ALIGNMENT);
                let ptr = alloc::alloc(layout);
                if ptr.is_null() {
                    alloc::handle_alloc_error(layout);
                }
                NonNull::new_unchecked(ptr)
            };
            Self {
                ptr,
                cap: capacity,
                len: 0,
            }
        }
    }

    #[inline]
    fn layout(&self) -> alloc::Layout {
        unsafe { alloc::Layout::from_size_align_unchecked(self.cap, Self::ALIGNMENT) }
    }

    /// Clears the vector, removing all values.
    ///
    /// Note that this method has no effect on the allocated capacity of the vector.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut v = AlignedVec::new();
    /// v.extend_from_slice(&[1, 2, 3, 4]);
    ///
    /// v.clear();
    ///
    /// assert!(v.is_empty());
    /// ```
    #[inline]
    pub fn clear(&mut self) {
        self.len = 0;
    }

    /// Change capacity of vector.
    ///
    /// Will set capacity to exactly `new_cap`.
    /// Can be used to either grow or shrink capacity.
    /// Backing memory will be reallocated.
    ///
    /// Usually the safe methods `reserve` or `reserve_exact` are a better choice.
    /// This method only exists as a micro-optimization for very performance-sensitive
    /// code where where the calculation of capacity required has already been
    /// performed, and you want to avoid doing it again, or if you want to implement
    /// a different growth strategy.
    ///
    /// # Safety
    ///
    /// - `new_cap` must be less than or equal to [`MAX_CAPACITY`](AlignedVec::MAX_CAPACITY)
    /// - `new_cap` must be greater than or equal to [`len()`](AlignedVec::len)
    #[inline]
    pub unsafe fn change_capacity(&mut self, new_cap: usize) {
        debug_assert!(new_cap <= Self::MAX_CAPACITY);
        debug_assert!(new_cap >= self.len);

        if new_cap > 0 {
            let new_ptr = if self.cap > 0 {
                let new_ptr = alloc::realloc(self.ptr.as_ptr(), self.layout(), new_cap);
                if new_ptr.is_null() {
                    alloc::handle_alloc_error(alloc::Layout::from_size_align_unchecked(
                        new_cap,
                        Self::ALIGNMENT,
                    ));
                }
                new_ptr
            } else {
                let layout = alloc::Layout::from_size_align_unchecked(new_cap, Self::ALIGNMENT);
                let new_ptr = alloc::alloc(layout);
                if new_ptr.is_null() {
                    alloc::handle_alloc_error(layout);
                }
                new_ptr
            };
            self.ptr = NonNull::new_unchecked(new_ptr);
            self.cap = new_cap;
        } else if self.cap > 0 {
            alloc::dealloc(self.ptr.as_ptr(), self.layout());
            self.ptr = NonNull::dangling();
            self.cap = 0;
        }
    }

    /// Shrinks the capacity of the vector as much as possible.
    ///
    /// It will drop down as close as possible to the length but the allocator may still inform the
    /// vector that there is space for a few more elements.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::with_capacity(10);
    /// vec.extend_from_slice(&[1, 2, 3]);
    /// assert_eq!(vec.capacity(), 10);
    /// vec.shrink_to_fit();
    /// assert!(vec.capacity() >= 3);
    ///
    /// vec.clear();
    /// vec.shrink_to_fit();
    /// assert!(vec.capacity() == 0);
    /// ```
    #[inline]
    pub fn shrink_to_fit(&mut self) {
        if self.cap != self.len {
            // New capacity cannot exceed max as it's shrinking
            unsafe { self.change_capacity(self.len) };
        }
    }

    /// Returns an unsafe mutable pointer to the vector's buffer.
    ///
    /// The caller must ensure that the vector outlives the pointer this function returns, or else
    /// it will end up pointing to garbage. Modifying the vector may cause its buffer to be
    /// reallocated, which would also make any pointers to it invalid.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// // Allocate vecotr big enough for 4 bytes.
    /// let size = 4;
    /// let mut x = AlignedVec::with_capacity(size);
    /// let x_ptr = x.as_mut_ptr();
    ///
    /// // Initialize elements via raw pointer writes, then set length.
    /// unsafe {
    ///     for i in 0..size {
    ///         *x_ptr.add(i) = i as u8;
    ///     }
    ///     x.set_len(size);
    /// }
    /// assert_eq!(&*x, &[0, 1, 2, 3]);
    /// ```
    #[inline]
    pub fn as_mut_ptr(&mut self) -> *mut u8 {
        self.ptr.as_ptr()
    }

    /// Extracts a mutable slice of the entire vector.
    ///
    /// Equivalent to `&mut s[..]`.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.extend_from_slice(&[1, 2, 3, 4, 5]);
    /// assert_eq!(vec.as_mut_slice().len(), 5);
    /// for i in 0..5 {
    ///     assert_eq!(vec.as_mut_slice()[i], i as u8 + 1);
    ///     vec.as_mut_slice()[i] = i as u8;
    ///     assert_eq!(vec.as_mut_slice()[i], i as u8);
    /// }
    /// ```
    #[inline]
    pub fn as_mut_slice(&mut self) -> &mut [u8] {
        unsafe { slice::from_raw_parts_mut(self.ptr.as_ptr(), self.len) }
    }

    /// Returns a raw pointer to the vector's buffer.
    ///
    /// The caller must ensure that the vector outlives the pointer this function returns, or else
    /// it will end up pointing to garbage. Modifying the vector may cause its buffer to be
    /// reallocated, which would also make any pointers to it invalid.
    ///
    /// The caller must also ensure that the memory the pointer (non-transitively) points to is
    /// never written to (except inside an `UnsafeCell`) using this pointer or any pointer derived
    /// from it. If you need to mutate the contents of the slice, use
    /// [`as_mut_ptr`](AlignedVec::as_mut_ptr).
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut x = AlignedVec::new();
    /// x.extend_from_slice(&[1, 2, 4]);
    /// let x_ptr = x.as_ptr();
    ///
    /// unsafe {
    ///     for i in 0..x.len() {
    ///         assert_eq!(*x_ptr.add(i), 1 << i);
    ///     }
    /// }
    /// ```
    #[inline]
    pub fn as_ptr(&self) -> *const u8 {
        self.ptr.as_ptr()
    }

    /// Extracts a slice containing the entire vector.
    ///
    /// Equivalent to `&s[..]`.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.extend_from_slice(&[1, 2, 3, 4, 5]);
    /// assert_eq!(vec.as_slice().len(), 5);
    /// for i in 0..5 {
    ///     assert_eq!(vec.as_slice()[i], i as u8 + 1);
    /// }
    /// ```
    #[inline]
    pub fn as_slice(&self) -> &[u8] {
        unsafe { slice::from_raw_parts(self.ptr.as_ptr(), self.len) }
    }

    /// Returns the number of elements the vector can hold without reallocating.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let vec = AlignedVec::with_capacity(10);
    /// assert_eq!(vec.capacity(), 10);
    /// ```
    #[inline]
    pub fn capacity(&self) -> usize {
        self.cap
    }

    /// Reserves capacity for at least `additional` more bytes to be inserted into the given
    /// `AlignedVec`. The collection may reserve more space to avoid frequent reallocations. After
    /// calling `reserve`, capacity will be greater than or equal to `self.len() + additional`. Does
    /// nothing if capacity is already sufficient.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX - 15` bytes.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.push(1);
    /// vec.reserve(10);
    /// assert!(vec.capacity() >= 11);
    /// ```
    #[inline]
    pub fn reserve(&mut self, additional: usize) {
        // Cannot wrap because capacity always exceeds len,
        // but avoids having to handle potential overflow here
        let remaining = self.cap.wrapping_sub(self.len);
        if additional > remaining {
            self.do_reserve(additional);
        }
    }

    /// Extend capacity after `reserve` has found it's necessary.
    ///
    /// Actually performing the extension is in this separate function marked
    /// `#[cold]` to hint to compiler that this branch is not often taken.
    /// This keeps the path for common case where capacity is already sufficient
    /// as fast as possible, and makes `reserve` more likely to be inlined.
    /// This is the same trick that Rust's `Vec::reserve` uses.
    #[cold]
    fn do_reserve(&mut self, additional: usize) {
        let new_cap = self
            .len
            .checked_add(additional)
            .expect("cannot reserve a larger AlignedVec");
        unsafe { self.grow_capacity_to(new_cap) };
    }

    /// Grows total capacity of vector to `new_cap` or more.
    ///
    /// Capacity after this call will be `new_cap` rounded up to next power of 2,
    /// unless that would exceed maximum capacity, in which case capacity
    /// is capped at the maximum.
    ///
    /// This is same growth strategy used by `reserve`, `push` and `extend_from_slice`.
    ///
    /// Usually the safe methods `reserve` or `reserve_exact` are a better choice.
    /// This method only exists as a micro-optimization for very performance-sensitive
    /// code where where the calculation of capacity required has already been
    /// performed, and you want to avoid doing it again.
    ///
    /// Maximum capacity is `isize::MAX - 15` bytes.
    ///
    /// # Panics
    ///
    /// Panics if `new_cap` exceeds `isize::MAX - 15` bytes.
    ///
    /// # Safety
    ///
    /// - `new_cap` must be greater than current [`capacity()`](AlignedVec::capacity)
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.push(1);
    /// unsafe { vec.grow_capacity_to(50) };
    /// assert_eq!(vec.len(), 1);
    /// assert_eq!(vec.capacity(), 64);
    /// ```
    #[inline]
    pub unsafe fn grow_capacity_to(&mut self, new_cap: usize) {
        debug_assert!(new_cap > self.cap);

        let new_cap = if new_cap > (isize::MAX as usize + 1) >> 1 {
            // Rounding up to next power of 2 would result in `isize::MAX + 1` or higher,
            // which exceeds max capacity. So cap at max instead.
            assert!(
                new_cap <= Self::MAX_CAPACITY,
                "cannot reserve a larger AlignedVec"
            );
            Self::MAX_CAPACITY
        } else {
            // Cannot overflow due to check above
            new_cap.next_power_of_two()
        };
        self.change_capacity(new_cap);
    }

    /// Resizes the Vec in-place so that len is equal to new_len.
    ///
    /// If new_len is greater than len, the Vec is extended by the difference, with each additional slot filled with value. If new_len is less than len, the Vec is simply truncated.
    ///
    /// # Panics
    ///
    /// Panics if the new length exceeds `isize::MAX - 15` bytes.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.push(3);
    /// vec.resize(3, 2);
    /// assert_eq!(vec.as_slice(), &[3, 2, 2]);
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.extend_from_slice(&[1, 2, 3, 4]);
    /// vec.resize(2, 0);
    /// assert_eq!(vec.as_slice(), &[1, 2]);
    /// ```
    #[inline]
    pub fn resize(&mut self, new_len: usize, value: u8) {
        if new_len > self.len {
            let additional = new_len - self.len;
            self.reserve(additional);
            unsafe {
                core::ptr::write_bytes(self.ptr.as_ptr().add(self.len), value, additional);
            }
        }
        unsafe {
            self.set_len(new_len);
        }
    }

    /// Returns `true` if the vector contains no elements.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut v = Vec::new();
    /// assert!(v.is_empty());
    ///
    /// v.push(1);
    /// assert!(!v.is_empty());
    /// ```
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len == 0
    }

    /// Returns the number of elements in the vector, also referred to as its 'length'.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut a = AlignedVec::new();
    /// a.extend_from_slice(&[1, 2, 3]);
    /// assert_eq!(a.len(), 3);
    /// ```
    #[inline]
    pub fn len(&self) -> usize {
        self.len
    }

    /// Copies and appends all bytes in a slice to the `AlignedVec`.
    ///
    /// The elements of the slice are appended in-order.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.push(1);
    /// vec.extend_from_slice(&[2, 3, 4]);
    /// assert_eq!(vec.as_slice(), &[1, 2, 3, 4]);
    /// ```
    #[inline]
    pub fn extend_from_slice(&mut self, other: &[u8]) {
        if !other.is_empty() {
            self.reserve(other.len());
            unsafe {
                core::ptr::copy_nonoverlapping(
                    other.as_ptr(),
                    self.as_mut_ptr().add(self.len()),
                    other.len(),
                );
            }
            self.len += other.len();
        }
    }

    /// Removes the last element from a vector and returns it, or `None` if it is empty.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.extend_from_slice(&[1, 2, 3]);
    /// assert_eq!(vec.pop(), Some(3));
    /// assert_eq!(vec.as_slice(), &[1, 2]);
    /// ```
    #[inline]
    pub fn pop(&mut self) -> Option<u8> {
        if self.len == 0 {
            None
        } else {
            let result = self[self.len - 1];
            self.len -= 1;
            Some(result)
        }
    }

    /// Appends an element to the back of a collection.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity exceeds `isize::MAX - 15` bytes.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.extend_from_slice(&[1, 2]);
    /// vec.push(3);
    /// assert_eq!(vec.as_slice(), &[1, 2, 3]);
    /// ```
    #[inline]
    pub fn push(&mut self, value: u8) {
        if self.len == self.cap {
            self.reserve_for_push();
        }

        unsafe {
            self.as_mut_ptr().add(self.len).write(value);
            self.len += 1;
        }
    }

    /// Extend capacity by at least 1 byte after `push` has found it's necessary.
    ///
    /// Actually performing the extension is in this separate function marked
    /// `#[cold]` to hint to compiler that this branch is not often taken.
    /// This keeps the path for common case where capacity is already sufficient
    /// as fast as possible, and makes `push` more likely to be inlined.
    /// This is the same trick that Rust's `Vec::push` uses.
    #[cold]
    fn reserve_for_push(&mut self) {
        // `len` is always less than `isize::MAX`, so no possibility of overflow here
        let new_cap = self.len + 1;
        unsafe { self.grow_capacity_to(new_cap) };
    }

    /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
    /// given `AlignedVec`. After calling `reserve_exact`, capacity will be greater than or equal
    /// to `self.len() + additional`. Does nothing if the capacity is already sufficient.
    ///
    /// Note that the allocator may give the collection more space than it requests. Therefore,
    /// capacity can not be relied upon to be precisely minimal. Prefer reserve if future insertions
    /// are expected.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `isize::MAX - 15`.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::new();
    /// vec.push(1);
    /// vec.reserve_exact(10);
    /// assert!(vec.capacity() >= 11);
    /// ```
    #[inline]
    pub fn reserve_exact(&mut self, additional: usize) {
        // This function does not use the hot/cold paths trick that `reserve`
        // and `push` do, on assumption that user probably knows this will require
        // an increase in capacity. Otherwise, they'd likely use `reserve`.
        let new_cap = self
            .len
            .checked_add(additional)
            .expect("cannot reserve a larger AlignedVec");
        if new_cap > self.cap {
            assert!(
                new_cap <= Self::MAX_CAPACITY,
                "cannot reserve a larger AlignedVec"
            );
            unsafe { self.change_capacity(new_cap) };
        }
    }

    /// Forces the length of the vector to `new_len`.
    ///
    /// This is a low-level operation that maintains none of the normal invariants of the type.
    ///
    /// # Safety
    ///
    /// - `new_len` must be less than or equal to [`capacity()`](AlignedVec::capacity)
    /// - The elements at `old_len..new_len` must be initialized
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::with_capacity(3);
    /// vec.extend_from_slice(&[1, 2, 3]);
    ///
    /// // SAFETY:
    /// // 1. `old_len..0` is empty to no elements need to be initialized.
    /// // 2. `0 <= capacity` always holds whatever capacity is.
    /// unsafe {
    ///     vec.set_len(0);
    /// }
    /// ```
    #[inline]
    pub unsafe fn set_len(&mut self, new_len: usize) {
        debug_assert!(new_len <= self.capacity());

        self.len = new_len;
    }

    /// Converts the vector into `Box<[u8]>`.
    ///
    /// This method reallocates and copies the underlying bytes. Any excess capacity is dropped.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut v = AlignedVec::new();
    /// v.extend_from_slice(&[1, 2, 3]);
    ///
    /// let slice = v.into_boxed_slice();
    /// ```
    ///
    /// Any excess capacity is removed:
    ///
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut vec = AlignedVec::with_capacity(10);
    /// vec.extend_from_slice(&[1, 2, 3]);
    ///
    /// assert_eq!(vec.capacity(), 10);
    /// let slice = vec.into_boxed_slice();
    /// assert_eq!(slice.len(), 3);
    /// ```
    #[inline]
    pub fn into_boxed_slice(self) -> Box<[u8]> {
        self.into_vec().into_boxed_slice()
    }

    /// Converts the vector into `Vec<u8>`.
    ///
    /// This method reallocates and copies the underlying bytes. Any excess capacity is dropped.
    ///
    /// # Examples
    /// ```
    /// use rkyv::AlignedVec;
    ///
    /// let mut v = AlignedVec::new();
    /// v.extend_from_slice(&[1, 2, 3]);
    ///
    /// let vec = v.into_vec();
    /// assert_eq!(vec.len(), 3);
    /// assert_eq!(vec.as_slice(), &[1, 2, 3]);
    /// ```
    #[inline]
    pub fn into_vec(self) -> Vec<u8> {
        Vec::from(self.as_ref())
    }
}

#[cfg(feature = "std")]
const _: () = {
    use std::io::{ErrorKind, Read};

    impl AlignedVec {
        /// Reads all bytes until EOF from `r` and appends them to this `AlignedVec`.
        ///
        /// If successful, this function will return the total number of bytes read.
        ///
        /// # Examples
        /// ```
        /// use rkyv::AlignedVec;
        ///
        /// let source = (0..4096).map(|x| (x % 256) as u8).collect::<Vec<_>>();
        /// let mut bytes = AlignedVec::new();
        /// bytes.extend_from_reader(&mut source.as_slice()).unwrap();
        ///
        /// assert_eq!(bytes.len(), 4096);
        /// assert_eq!(bytes[0], 0);
        /// assert_eq!(bytes[100], 100);
        /// assert_eq!(bytes[2945], 129);
        /// ```
        pub fn extend_from_reader<R: Read + ?Sized>(
            &mut self,
            r: &mut R,
        ) -> std::io::Result<usize> {
            let start_len = self.len();
            let start_cap = self.capacity();

            // Extra initialized bytes from previous loop iteration.
            let mut initialized = 0;
            loop {
                if self.len() == self.capacity() {
                    // No available capacity, reserve some space.
                    self.reserve(32);
                }

                let read_buf_start = unsafe { self.as_mut_ptr().add(self.len) };
                let read_buf_len = self.capacity() - self.len();

                // Initialize the uninitialized portion of the available space.
                unsafe {
                    // The first `initialized` bytes don't need to be zeroed.
                    // This leaves us `read_buf_len - initialized` bytes to zero
                    // starting at `initialized`.
                    core::ptr::write_bytes(
                        read_buf_start.add(initialized),
                        0,
                        read_buf_len - initialized,
                    );
                }

                // The entire read buffer is now initialized, so we can create a
                // mutable slice of it.
                let read_buf =
                    unsafe { core::slice::from_raw_parts_mut(read_buf_start, read_buf_len) };

                match r.read(read_buf) {
                    Ok(read) => {
                        // We filled `read` additional bytes.
                        unsafe {
                            self.set_len(self.len() + read);
                        }
                        initialized = read_buf_len - read;

                        if read == 0 {
                            return Ok(self.len() - start_len);
                        }
                    }
                    Err(e) if e.kind() == ErrorKind::Interrupted => continue,
                    Err(e) => return Err(e),
                }

                if self.len() == self.capacity() && self.capacity() == start_cap {
                    // The buffer might be an exact fit. Let's read into a probe buffer
                    // and see if it returns `Ok(0)`. If so, we've avoided an
                    // unnecessary doubling of the capacity. But if not, append the
                    // probe buffer to the primary buffer and let its capacity grow.
                    let mut probe = [0u8; 32];

                    loop {
                        match r.read(&mut probe) {
                            Ok(0) => return Ok(self.len() - start_len),
                            Ok(n) => {
                                self.extend_from_slice(&probe[..n]);
                                break;
                            }
                            Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
                            Err(e) => return Err(e),
                        }
                    }
                }
            }
        }
    }
};

impl From<AlignedVec> for Vec<u8> {
    #[inline]
    fn from(aligned: AlignedVec) -> Self {
        aligned.to_vec()
    }
}

impl Archive for AlignedVec {
    type Archived = ArchivedVec<u8>;
    type Resolver = VecResolver;

    #[inline]
    unsafe fn resolve(&self, pos: usize, resolver: Self::Resolver, out: *mut Self::Archived) {
        ArchivedVec::resolve_from_slice(self.as_slice(), pos, resolver, out);
    }
}

impl AsMut<[u8]> for AlignedVec {
    #[inline]
    fn as_mut(&mut self) -> &mut [u8] {
        self.as_mut_slice()
    }
}

impl AsRef<[u8]> for AlignedVec {
    #[inline]
    fn as_ref(&self) -> &[u8] {
        self.as_slice()
    }
}

impl Borrow<[u8]> for AlignedVec {
    #[inline]
    fn borrow(&self) -> &[u8] {
        self.as_slice()
    }
}

impl BorrowMut<[u8]> for AlignedVec {
    #[inline]
    fn borrow_mut(&mut self) -> &mut [u8] {
        self.as_mut_slice()
    }
}

impl Clone for AlignedVec {
    #[inline]
    fn clone(&self) -> Self {
        unsafe {
            let mut result = AlignedVec::with_capacity(self.len);
            result.len = self.len;
            core::ptr::copy_nonoverlapping(self.as_ptr(), result.as_mut_ptr(), self.len);
            result
        }
    }
}

impl fmt::Debug for AlignedVec {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.as_slice().fmt(f)
    }
}

impl Default for AlignedVec {
    #[inline]
    fn default() -> Self {
        Self::new()
    }
}

impl Deref for AlignedVec {
    type Target = [u8];

    #[inline]
    fn deref(&self) -> &Self::Target {
        self.as_slice()
    }
}

impl DerefMut for AlignedVec {
    #[inline]
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.as_mut_slice()
    }
}

impl<I: slice::SliceIndex<[u8]>> Index<I> for AlignedVec {
    type Output = <I as slice::SliceIndex<[u8]>>::Output;

    #[inline]
    fn index(&self, index: I) -> &Self::Output {
        &self.as_slice()[index]
    }
}

impl<I: slice::SliceIndex<[u8]>> IndexMut<I> for AlignedVec {
    #[inline]
    fn index_mut(&mut self, index: I) -> &mut Self::Output {
        &mut self.as_mut_slice()[index]
    }
}

#[cfg(feature = "std")]
impl io::Write for AlignedVec {
    #[inline]
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.extend_from_slice(buf);
        Ok(buf.len())
    }

    #[inline]
    fn write_vectored(&mut self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
        let len = bufs.iter().map(|b| b.len()).sum();
        self.reserve(len);
        for buf in bufs {
            self.extend_from_slice(buf);
        }
        Ok(len)
    }

    #[inline]
    fn write_all(&mut self, buf: &[u8]) -> io::Result<()> {
        self.extend_from_slice(buf);
        Ok(())
    }

    fn flush(&mut self) -> io::Result<()> {
        Ok(())
    }
}

// SAFETY: AlignedVec is safe to send to another thread
unsafe impl Send for AlignedVec {}

impl<S: ScratchSpace + Serializer + ?Sized> Serialize<S> for AlignedVec {
    #[inline]
    fn serialize(&self, serializer: &mut S) -> Result<Self::Resolver, S::Error> {
        serializer.align(Self::ALIGNMENT)?;
        ArchivedVec::<Archived<u8>>::serialize_from_slice(self.as_slice(), serializer)
    }
}

// SAFETY: AlignedVec is safe to share between threads
unsafe impl Sync for AlignedVec {}

impl Unpin for AlignedVec {}