use crate::{Error, Result, Shape};

#[derive(Debug, PartialEq, Eq, Clone)]
pub struct Layout {
    shape: Shape,
    // The strides are given in number of elements and not in bytes.
    stride: Vec<usize>,
    start_offset: usize,
}

impl Layout {
    pub fn contiguous_with_offset<S: Into<Shape>>(shape: S, start_offset: usize) -> Self {
        let shape = shape.into();
        let stride = shape.stride_contiguous();
        Self {
            shape,
            stride,
            start_offset,
        }
    }

    pub fn contiguous<S: Into<Shape>>(shape: S) -> Self {
        Self::contiguous_with_offset(shape, 0)
    }

    pub fn dims(&self) -> &[usize] {
        self.shape.dims()
    }

    pub fn shape(&self) -> &Shape {
        &self.shape
    }

    pub fn stride(&self) -> &[usize] {
        &self.stride
    }

    pub fn start_offset(&self) -> usize {
        self.start_offset
    }

    /// Returns the appropriate start and stop offset if the data is stored in a C
    /// contiguous (aka row major) way.
    pub fn contiguous_offsets(&self) -> Option<(usize, usize)> {
        if self.is_contiguous() {
            let start_o = self.start_offset;
            Some((start_o, start_o + self.shape.elem_count()))
        } else {
            None
        }
    }

    /// Returns true if the data is stored in a C contiguous (aka row major) way.
    pub fn is_contiguous(&self) -> bool {
        self.shape.is_contiguous(&self.stride)
    }

    /// Returns true if the data is stored in a Fortran contiguous (aka column major) way.
    pub fn is_fortran_contiguous(&self) -> bool {
        self.shape.is_fortran_contiguous(&self.stride)
    }

    pub(crate) fn narrow(&self, dim: usize, start: usize, len: usize) -> Result<Self> {
        let dims = self.shape().dims();
        if dim >= dims.len() {
            Err(Error::DimOutOfRange {
                shape: self.shape().clone(),
                dim: dim as i32,
                op: "narrow",
            })?
        }
        if start + len > dims[dim] {
            Err(Error::NarrowInvalidArgs {
                shape: self.shape.clone(),
                dim,
                start,
                len,
                msg: "start + len > dim_len",
            })?
        }
        let mut dims = dims.to_vec();
        dims[dim] = len;
        Ok(Self {
            shape: Shape::from(dims),
            stride: self.stride.clone(),
            start_offset: self.start_offset + self.stride[dim] * start,
        })
    }

    pub(crate) fn transpose(&self, dim1: usize, dim2: usize) -> Result<Self> {
        let rank = self.shape.rank();
        if rank <= dim1 || rank <= dim2 {
            return Err(Error::UnexpectedNumberOfDims {
                expected: usize::max(dim1, dim2),
                got: rank,
                shape: self.shape().clone(),
            });
        }
        let mut stride = self.stride().to_vec();
        let mut dims = self.shape().dims().to_vec();
        dims.swap(dim1, dim2);
        stride.swap(dim1, dim2);
        Ok(Self {
            shape: Shape::from(dims),
            stride,
            start_offset: self.start_offset,
        })
    }

    pub fn broadcast_as<S: Into<Shape>>(&self, shape: S) -> Result<Self> {
        let shape = shape.into();
        if shape.rank() < self.shape().rank() {
            Err(Error::BroadcastIncompatibleShapes {
                src_shape: self.shape().clone(),
                dst_shape: shape.clone(),
            })?
        }
        let added_dims = shape.rank() - self.shape().rank();
        let mut stride = vec![0; added_dims];
        for (&dst_dim, (&src_dim, &src_stride)) in shape.dims()[added_dims..]
            .iter()
            .zip(self.dims().iter().zip(self.stride()))
        {
            let s = if dst_dim == src_dim {
                src_stride
            } else if src_dim != 1 {
                return Err(Error::BroadcastIncompatibleShapes {
                    src_shape: self.shape().clone(),
                    dst_shape: shape,
                });
            } else {
                0
            };
            stride.push(s)
        }
        Ok(Self {
            shape,
            stride,
            start_offset: self.start_offset,
        })
    }

    pub(crate) fn strided_index(&self) -> crate::StridedIndex {
        crate::StridedIndex::new(self)
    }
}