//! Abstract definition of a matrix data storage.

use std::mem;
use std::any::Any;

use core::Scalar;
use dimension::Dim;
use allocator::{Allocator, SameShapeR, SameShapeC};

/*
 * Aliases for sum storage.
 */
/// The data storage for the sum of two matrices with dimensions `(R1, C1)` and `(R2, C2)`.
pub type SumStorage<N, R1, C1, R2, C2, SA> =
    <<SA as Storage<N, R1, C1>>::Alloc as Allocator<N, SameShapeR<R1, R2>, SameShapeC<C1, C2>>>::Buffer;

/*
 * Aliases for multiplication storage.
 */
/// The data storage for the multiplication of two matrices with dimensions `(R1, C1)` on the left
/// hand side, and with `C2` columns on the right hand side.
pub type MulStorage<N, R1, C1, C2, SA> =
    <<SA as Storage<N, R1, C1>>::Alloc as Allocator<N, R1, C2>>::Buffer;

/// The data storage for the multiplication of two matrices with dimensions `(R1, C1)` on the left
/// hand side, and with `C2` columns on the right hand side. The first matrix is implicitly
/// transposed.
pub type TrMulStorage<N, R1, C1, C2, SA> =
    <<SA as Storage<N, R1, C1>>::Alloc as Allocator<N, C1, C2>>::Buffer;

/*
 * Alias for allocation result.
 */
/// The owned data storage that can be allocated from `S`.
pub type Owned<N, R, C, A> =
    <A as Allocator<N, R, C>>::Buffer;


/// The trait shared by all matrix data storage.
///
/// FIXME: doc
///
/// Note that `Self` must always have a number of elements compatible with the matrix length (given
/// by `R` and `C` if they are known at compile-time). For example, implementors of this trait
/// should **not** allow the user to modify the size of the underlying buffer with safe methods
/// (for example the `MatrixVec::data_mut` method is unsafe because the user could change the
/// vector's size so that it no longer contains enough elements: this will lead to UB.
pub unsafe trait Storage<N: Scalar, R: Dim, C: Dim>: Sized {
    /// The static stride of this storage's rows.
    type RStride: Dim;

    /// The static stride of this storage's columns.
    type CStride: Dim;

    /// The allocator for this family of storage.
    type Alloc: Allocator<N, R, C>;

    /// Builds a matrix data storage that does not contain any reference.
    fn into_owned(self) -> Owned<N, R, C, Self::Alloc>;

    /// Clones this data storage into one that does not contain any reference.
    fn clone_owned(&self) -> Owned<N, R, C, Self::Alloc>;

    /// The matrix data pointer.
    fn ptr(&self) -> *const N;

    /// The dimension of the matrix at run-time. Arr length of zero indicates the additive identity
    /// element of any dimension. Must be equal to `Self::dimension()` if it is not `None`.
    fn shape(&self) -> (R, C);

    /// The spacing between concecutive row elements and consecutive column elements.
    ///
    /// For example this returns `(1, 5)` for a row-major matrix with 5 columns.
    fn strides(&self) -> (Self::RStride, Self::CStride);

    /// Compute the index corresponding to the irow-th row and icol-th column of this matrix. The
    /// index must be such that the following holds:
    ///
    /// ```.ignore
    /// let lindex = self.linear_index(irow, icol);
    /// assert!(*self.get_unchecked(irow, icol) == *self.get_unchecked_linear(lindex)
    /// ```
    #[inline]
    fn linear_index(&self, irow: usize, icol: usize) -> usize {
        let (rstride, cstride) = self.strides();

        irow * rstride.value() + icol * cstride.value()
    }

    /// Gets the address of the i-th matrix component without performing bound-checking.
    #[inline]
    unsafe fn get_address_unchecked_linear(&self, i: usize) -> *const N {
        self.ptr().offset(i as isize)
    }

    /// Gets the address of the i-th matrix component without performing bound-checking.
    #[inline]
    unsafe fn get_address_unchecked(&self, irow: usize, icol: usize) -> *const N {
        self.get_address_unchecked_linear(self.linear_index(irow, icol))
    }

    /// Retrieves a reference to the i-th element without bound-checking.
    #[inline]
    unsafe fn get_unchecked_linear(&self, i: usize) -> &N {
        &*self.get_address_unchecked_linear(i)
    }

    /// Retrieves a reference to the i-th element without bound-checking.
    #[inline]
    unsafe fn get_unchecked(&self, irow: usize, icol: usize) -> &N {
        self.get_unchecked_linear(self.linear_index(irow, icol))
    }
}


/// Trait implemented by matrix data storage that can provide a mutable access to its elements.
///
/// Note that a mutable access does not mean that the matrix owns its data. For example, a mutable
/// matrix slice can provide mutable access to its elements even if it does not own its data (it
/// contains only an internal reference to them).
pub unsafe trait StorageMut<N: Scalar, R: Dim, C: Dim>: Storage<N, R, C> {
    /// The matrix mutable data pointer.
    fn ptr_mut(&mut self) -> *mut N;

    /// Gets the mutable address of the i-th matrix component without performing bound-checking.
    #[inline]
    unsafe fn get_address_unchecked_linear_mut(&mut self, i: usize) -> *mut N {
        self.ptr_mut().offset(i as isize)
    }

    /// Gets the mutable address of the i-th matrix component without performing bound-checking.
    #[inline]
    unsafe fn get_address_unchecked_mut(&mut self, irow: usize, icol: usize) -> *mut N {
        let lid = self.linear_index(irow, icol);
        self.get_address_unchecked_linear_mut(lid)
    }

    /// Retrieves a mutable reference to the i-th element without bound-checking.
    unsafe fn get_unchecked_linear_mut(&mut self, i: usize) -> &mut N {
        &mut *self.get_address_unchecked_linear_mut(i)
    }

    /// Retrieves a mutable reference to the element at `(irow, icol)` without bound-checking.
    #[inline]
    unsafe fn get_unchecked_mut(&mut self, irow: usize, icol: usize) -> &mut N {
        &mut *self.get_address_unchecked_mut(irow, icol)
    }

    /// Swaps two elements using their linear index without bound-checking.
    #[inline]
    unsafe fn swap_unchecked_linear(&mut self, i1: usize, i2: usize) {
        let a = self.get_address_unchecked_linear_mut(i1);
        let b = self.get_address_unchecked_linear_mut(i2);

        mem::swap(&mut *a, &mut *b);
    }

    /// Swaps two elements without bound-checking.
    #[inline]
    unsafe fn swap_unchecked(&mut self, row_col1: (usize, usize), row_col2: (usize, usize)) {
        let lid1 = self.linear_index(row_col1.0, row_col1.1);
        let lid2 = self.linear_index(row_col2.0, row_col2.1);

        self.swap_unchecked_linear(lid1, lid2)
    }
}

/// A matrix storage that does not contain any reference and that is stored contiguously in memory.
///
/// The storage requirement means that for any value of `i` in `[0, nrows * ncols[`, the value
/// `.get_unchecked_linear` succeeds. This trait is unsafe because failing to comply to this may
/// cause Undefined Behaviors.
pub unsafe trait OwnedStorage<N: Scalar, R: Dim, C: Dim>: StorageMut<N, R, C> + Clone + Any
    where Self::Alloc: Allocator<N, R, C, Buffer = Self> {
    // NOTE: We could auto-impl those two methods but we don't to make sure the user is aware that
    // data must be contiguous.
    /// Converts this data storage to a slice.
    #[inline]
    fn as_slice(&self) -> &[N];

    /// Converts this data storage to a mutable slice.
    #[inline]
    fn as_mut_slice(&mut self) -> &mut [N];
}