//! The arr crate is a simple fixed size array designed to allow huge array allocation without stack
//! overflows.
//!
//! Even in rustc 1.44 allocating arrays too large to fit on the stack (say 8MB in size) will
//! stack overflow even if the array is Boxed.
//!
//! Basic usage:
//! ```
//! use arr::Array;
//! // zero - fast allocation
//! let big_array: Array<u8> = Array::zero(1 << 25);
//! // default - slow allocation
//! let big_array2: Array<u8> = Array::new(1 << 25);
//! // template
//! let template = 10u8;
//! let big_array3: Array<u8> = Array::new_from_template(1 << 25, &template);
//!
//! // Also works for 2d arrays (note even the sub-array would ordinarily blow stack)
//! let big_2d_array: Array<[u8; 1 << 25]> = Array::zero(4);
//! ```
//!
//! Try to do this with a traditional array:
//! ```no_run
//! let big_array: Box<[u8; 1 << 25]> = Box::new([0u8; 1 << 25]);
//! ```
//!
//! Currently the array supports three modes of allocation, via `new` (requires types to have Default +
//! Copy) and `new_from_template`, only requiring Clone. The `zero` constructor uses an internal
//! Zeroable trait only set for primitive types and their arrays. In the future this concept may be
//! unsafely extended outside of this crate but for now it's private. As long as this type fits on the stack and
//! the array fits in memory this should be allocatable.
//!
#![feature(const_generics)]
mod zeroable;

use std::alloc::{alloc, alloc_zeroed, dealloc, Layout};
use std::ops::{Index, IndexMut, Range};

use crate::zeroable::Zeroable;

pub struct Array<T> {
    size: usize,
    ptr: *mut T,
}

unsafe impl<T> Sync for Array<T>{}
unsafe impl<T> Send for Array<T>{}

impl<T> Array<T> {
    /// Create an immutable iterator over elements in Array.
    pub fn iter<'a>(&'a self) -> ArrayIter<'a, T> {
        ArrayIter{
            arr: &self,
            iter: 0usize
        }
    }

    /// Convert to slice
    pub fn to_slice<'a>(&'a self) -> &'a [T] {
        unsafe { std::slice::from_raw_parts(self.ptr as *const T, self.size) }
    }

    /// Convert to mutable slice
    pub fn to_slice_mut<'a>(&'a mut self) -> &'a mut [T] {
        unsafe { std::slice::from_raw_parts_mut(self.ptr, self.size) }
    }

    //pub fn to_slice_mut<'a>(&'a mut self) -> &'a mut [T] {
    //    slice::

    /// The length of the array (number of elements T)
    pub fn len(&self) -> usize {
        self.size
    }
}

impl<T> Array<T>
  where T: Zeroable {
    /// Extremely fast initialization if all you want is 0's. Note that your type must be Zeroable.
    /// The auto-Zeroable types are u8, i8, u16, i16, u32, i32, u64, i64, usize, isize, f32, f64.
    /// `std::Array`s also implement Zeroable allowing for types like `[u8; 1 << 25]`.
    pub fn zero(size: usize) -> Self {
        let objsize = std::mem::size_of::<T>();
        let layout = Layout::from_size_align(size * objsize, 8).unwrap();
        let ptr = unsafe {
            alloc_zeroed(layout) as *mut T
        };
        Self{size, ptr}
    }
}

impl<T> Array<T>
  where T: Default + Copy {
    /// Easy initialization if all you want is your T's default instantiation
    pub fn new(size: usize) -> Self {
        let objsize = std::mem::size_of::<T>();
        let layout = Layout::from_size_align(size * objsize, 8).unwrap();
        let ptr = unsafe {
            alloc(layout) as *mut T
        };
        let default: T = Default::default();
        for i in 0..size {
            unsafe {
                (*(ptr.wrapping_offset(i as isize))) = default;
            }
        }
        Self{size, ptr}
    }
}

impl<T> Array<T>
  where T: Clone {
    /// More generic initialization instantiating all elements as copies of some template
    pub fn new_from_template(size: usize, template: &T) -> Self {
        let objsize = std::mem::size_of::<T>();
        let layout = Layout::from_size_align(size * objsize, 8).unwrap();
        let ptr = unsafe {
            alloc(layout) as *mut T
        };
        for i in 0..size {
            unsafe {
                (*(ptr.wrapping_offset(i as isize))) = template.clone();
            }
        }
        Self{size, ptr}
    }
}

impl<T> Index<usize> for Array<T> {
    type Output = T;

    fn index<'a>(&'a self, idx: usize) -> &'a Self::Output {

        unsafe {
            self.ptr.wrapping_offset(idx as isize).as_ref()
        }.unwrap()
    }
}

impl<T> IndexMut<usize> for Array<T> {

    fn index_mut<'a>(&'a mut self, idx: usize) -> &'a mut Self::Output {

        unsafe {
            self.ptr.wrapping_offset(idx as isize).as_mut()
        }.unwrap()
    }
}

impl<T> Index<Range<usize>> for Array<T> {
    type Output = [T];

    fn index<'a>(&'a self, idx: Range<usize>) -> &'a Self::Output {
        &self.to_slice()[idx]
    }
}

impl<T> IndexMut<Range<usize>> for Array<T> {

    fn index_mut<'a>(&'a mut self, idx: Range<usize>) -> &'a mut Self::Output {
        &mut self.to_slice_mut()[idx]
    }
}

impl<T> Drop for Array<T> {

    fn drop(&mut self) {
        let objsize = std::mem::size_of::<T>();
        let layout = Layout::from_size_align(self.size * objsize, 8).unwrap();
        unsafe {
            dealloc(self.ptr as *mut u8, layout);
        }
    }
}

impl<'a, T> IntoIterator for &'a Array<T> {
    type Item = &'a T;
    type IntoIter = ArrayIter<'a, T>;
    /// For now, you can only for loop iterate directly over the
    /// reference:
    /// ```
    /// use arr::Array;
    /// let arr: Array<usize> = Array::new(6);
    /// for i in &arr {
    ///     println!("{}", i);
    /// }
    /// ```
    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}

pub struct ArrayIter<'a, T> {
    arr: &'a Array<T>,
    iter: usize
}

impl<'a, T> Iterator for ArrayIter<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        match self.iter < self.arr.len() {
            true => {
                self.iter += 1;
                Some(&self.arr[self.iter - 1])
            },
            false => None
        }
    }
}

impl<'a, T> ExactSizeIterator for ArrayIter<'a, T> {

    fn len(&self) -> usize {
        self.arr.size - self.iter
    }
}

#[cfg(test)]
mod test {
    use std::thread;
    use std::sync::{Arc, Mutex};
    use super::*;

    #[test]
    fn test_default() {
        let arr: Array<f32> = Array::new(4 << 20); // Uses 16 MB - much to large for a stack
        assert_eq!(arr[4 << 20 - 1], 0.0);
    }

    #[test]
    fn test_template() {
        // template: 256 * 8 = 2^11
        let template: [u64; 256] = [65u64; 256];
        // num: 4096 => total size: 2^23, too large for the stack
        let arr: Array<[u64; 256]> = Array::new_from_template(4096, &template);
        assert_eq!(arr[4095][255], 65);
    }

    #[derive(Clone)]
    struct Unaligned {
        a: u64,
        b: u16
    }

    #[test]
    fn test_unaligned() {
        let unaligned_template = Unaligned{a: 15, b:32};
        let arr: Array<Unaligned> = Array::new_from_template(5, &unaligned_template);
        assert_eq!(arr[3].a, 15);
        assert_eq!(arr[3].b, 32);
        assert_eq!(arr[4].a, 15);
        assert_eq!(arr[4].b, 32);
    }

    #[test]
    fn test_zeroed() {
        // 8 * 4096 * 4096 = 8X16MB = 128MB
        let arr: Array<[usize; 4096]> = Array::zero(4096);
        assert_eq!(arr[4095][4095], 0);
    }

    #[test]
    fn test_async() {
        let arr: Array<usize> = Array::zero(5);

        let tid = thread::spawn(move || {
            assert_eq!(arr[3], 0);
        });

        let _ = tid.join();
    }

    #[test]
    fn test_mut_async() {
        let arr: Arc<Mutex<Array<usize>>> = Arc::new(Mutex::new(Array::zero(5)));
        {
            let mut arr = (&*arr).lock().unwrap();
            arr[4] = 1;
        }
        let carr = arr.clone();
        let tid = thread::spawn(move || {
            let mut arr = (&*carr).lock().unwrap();
            assert_eq!(arr[4], 1);
            arr[4] = 0;
        });
        tid.join().unwrap();
        assert_eq!((&*arr).lock().unwrap()[4], 0);
    }

    #[test]
    fn test_loop() {
        let arr: Array<usize> = Array::new_from_template(5, &5);
        let mut cnt = 0;
        for _ in arr.iter() {
            cnt += 1;
        }
        assert_eq!(cnt, 5);
    }

    #[test]
    fn test_copy_from() {
        let mut arr: Array<usize> = Array::new_from_template(5, &5);
        let from: [usize; 5] = [1usize; 5];
        arr.to_slice_mut().copy_from_slice(&from);
        assert_eq!(arr[4], 1);
    }

    #[test]
    fn test_range() {
        let arr: Array<usize> = Array::zero(10);
        let mut cnt = 0;
        for _i in &arr[0..5] {
            cnt += 1;
        }
        assert_eq!(cnt, 5);
    }

    #[test]
    fn test_range_mut() {
        let mut arr: Array<usize> = Array::zero(10);
        let slice = &mut arr[0..5];
        for i in slice {
            *i = 5;
        }
        assert_eq!(arr[4], 5);
    }
}