/*

 * Copyright 2021 Google Inc. All rights reserved.

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

use crate::follow::Follow;

use crate::vector::VectorIter;

use crate::EndianScalar;

use core::fmt::{Debug, Formatter, Result};

use core::marker::PhantomData;

use core::mem::size_of;

#[derive(Copy, Clone)]

pub struct Array<'a, T: 'a, const N: usize>(&'a [u8], PhantomData<T>);

impl<'a, T: 'a, const N: usize> Debug for Array<'a, T, N>

where

    T: 'a + Follow<'a>,

    <T as Follow<'a>>::Inner: Debug,

{

    fn fmt(&self, f: &mut Formatter) -> Result {

        f.debug_list().entries(self.iter()).finish()

    }

}

#[allow(clippy::len_without_is_empty)]

#[allow(clippy::from_over_into)] // TODO(caspern): Go from From to Into.

impl<'a, T: 'a, const N: usize> Array<'a, T, N> {

    /// # Safety

    ///

    /// buf must be a contiguous array of `T`

    ///

    /// # Panics

    ///

    /// Panics if `buf.len()` is not `size_of::<T>() * N`

    #[inline(always)]

    pub unsafe fn new(buf: &'a [u8]) -> Self {

        assert_eq!(size_of::<T>() * N, buf.len());

        Array(buf, PhantomData)

    }

    #[inline(always)]

    pub const fn len(&self) -> usize {

        N

    }

    pub fn as_ptr(&self) -> *const u8 {

        self.0.as_ptr()

    }

}

impl<'a, T: Follow<'a> + 'a, const N: usize> Array<'a, T, N> {

    #[inline(always)]

    pub fn get(&self, idx: usize) -> T::Inner {

        assert!(idx < N);

        let sz = size_of::<T>();

        // Safety:

        // self.0 was valid for length `N` on construction and have verified `idx < N`

        unsafe { T::follow(self.0, sz * idx) }

    }

    #[inline(always)]

    pub fn iter(&self) -> VectorIter<'a, T> {

        // Safety:

        // self.0 was valid for length N on construction

        unsafe { VectorIter::from_slice(self.0, self.len()) }

    }

}

impl<'a, T: Follow<'a> + Debug, const N: usize> From<Array<'a, T, N>> for [T::Inner; N] {

    fn from(array: Array<'a, T, N>) -> Self {

        array_init(|i| array.get(i))

    }

}

/// Implement Follow for all possible Arrays that have Follow-able elements.

impl<'a, T: Follow<'a> + 'a, const N: usize> Follow<'a> for Array<'a, T, N> {

    type Inner = Array<'a, T, N>;

    #[inline(always)]

    unsafe fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {

        Array::new(&buf[loc..loc + N * size_of::<T>()])

    }

}

/// Place an array of EndianScalar into the provided mutable byte slice. Performs

/// endian conversion, if necessary.

/// # Safety

/// Caller must ensure `s.len() >= size_of::<[T; N]>()`

pub unsafe fn emplace_scalar_array<T: EndianScalar, const N: usize>(

    buf: &mut [u8],

    loc: usize,

    src: &[T; N],

) {

    let mut buf_ptr = buf[loc..].as_mut_ptr();

    for item in src.iter() {

        let item_le = item.to_little_endian();

        core::ptr::copy_nonoverlapping(

            &item_le as *const T::Scalar as *const u8,

            buf_ptr,

            size_of::<T::Scalar>(),

        );

        buf_ptr = buf_ptr.add(size_of::<T::Scalar>());

    }

}

impl<'a, T: Follow<'a> + 'a, const N: usize> IntoIterator for Array<'a, T, N> {

    type Item = T::Inner;

    type IntoIter = VectorIter<'a, T>;

    #[inline]

    fn into_iter(self) -> Self::IntoIter {

        self.iter()

    }

}

#[inline]

pub fn array_init<F, T, const N: usize>(mut initializer: F) -> [T; N]

where

    F: FnMut(usize) -> T,

{

    let mut array: core::mem::MaybeUninit<[T; N]> = core::mem::MaybeUninit::uninit();

    let mut ptr_i = array.as_mut_ptr() as *mut T;

    // Safety:

    // array is aligned by T, and has length N

    unsafe {

        for i in 0..N {

            let value_i = initializer(i);

            ptr_i.write(value_i);

            ptr_i = ptr_i.add(1);

        }

        array.assume_init()

    }

}

#[cfg(feature = "serialize")]

impl<'a, T: 'a, const N: usize> serde::ser::Serialize for Array<'a, T, N>

where

    T: 'a + Follow<'a>,

    <T as Follow<'a>>::Inner: serde::ser::Serialize,

{

    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>

    where

        S: serde::ser::Serializer,

    {

        use serde::ser::SerializeSeq;

        let mut seq = serializer.serialize_seq(Some(self.len()))?;

        for element in self.iter() {

            seq.serialize_element(&element)?;

        }

        seq.end()

    }

}