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// Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this software is governed by the Business Source License
// included in the LICENSE file.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0.

//! A multi-dimensional array data type.

use std::error::Error;
use std::fmt;
use std::mem;

use serde::{Deserialize, Serialize};

use crate::row::DatumList;
use std::cmp::Ordering;

use lowertest::MzReflect;

/// The maximum number of dimensions permitted in an array.
pub const MAX_ARRAY_DIMENSIONS: u8 = 6;

/// A variable-length multi-dimensional array.
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
pub struct Array<'a> {
    /// The elements in the array.
    pub(crate) elements: DatumList<'a>,
    /// The dimensions of the array.
    pub(crate) dims: ArrayDimensions<'a>,
}

impl<'a> Array<'a> {
    /// Returns the dimensions of the array.
    pub fn dims(&self) -> ArrayDimensions<'a> {
        self.dims
    }

    /// Returns the elements of the array.
    pub fn elements(&self) -> DatumList<'a> {
        self.elements
    }
}

/// The dimensions of an [`Array`].
#[derive(Clone, Copy, Eq, PartialEq, Hash)]
pub struct ArrayDimensions<'a> {
    pub(crate) data: &'a [u8],
}

impl ArrayDimensions<'_> {
    /// Returns the number of dimensions in the array as a [`u8`].
    pub fn ndims(&self) -> u8 {
        let ndims = self.data.len() / (mem::size_of::<usize>() * 2);
        ndims.try_into().expect("ndims is known to fit in a u8")
    }

    /// Returns the number of the dimensions in the array as a [`usize`].
    pub fn len(&self) -> usize {
        self.ndims().into()
    }

    /// Reports whether the number of dimensions in the array is zero.
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }
}

impl Ord for ArrayDimensions<'_> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.ndims().cmp(&other.ndims())
    }
}

impl PartialOrd for ArrayDimensions<'_> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl fmt::Debug for ArrayDimensions<'_> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_list().entries(self.into_iter()).finish()
    }
}

impl<'a> IntoIterator for ArrayDimensions<'a> {
    type Item = ArrayDimension;
    type IntoIter = ArrayDimensionsIter<'a>;

    fn into_iter(self) -> ArrayDimensionsIter<'a> {
        ArrayDimensionsIter { data: self.data }
    }
}

/// An iterator over the dimensions in an [`ArrayDimensions`].
#[derive(Debug)]
pub struct ArrayDimensionsIter<'a> {
    data: &'a [u8],
}

impl Iterator for ArrayDimensionsIter<'_> {
    type Item = ArrayDimension;

    fn next(&mut self) -> Option<ArrayDimension> {
        if self.data.is_empty() {
            None
        } else {
            let sz = mem::size_of::<usize>();
            let lower_bound = usize::from_ne_bytes(self.data[..sz].try_into().unwrap());
            self.data = &self.data[sz..];
            let length = usize::from_ne_bytes(self.data[..sz].try_into().unwrap());
            self.data = &self.data[sz..];
            Some(ArrayDimension {
                lower_bound,
                length,
            })
        }
    }
}

/// The specification of one dimension of an [`Array`].
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
pub struct ArrayDimension {
    /// The index at which this dimension begins.
    pub lower_bound: usize,
    /// The number of elements in this array.
    pub length: usize,
}

/// An error that can occur when constructing an array.
#[derive(
    Clone, Copy, Debug, Eq, PartialEq, Hash, Ord, PartialOrd, Serialize, Deserialize, MzReflect,
)]
pub enum InvalidArrayError {
    /// The number of dimensions in the array exceedes [`MAX_ARRAY_DIMENSIONS]`.
    TooManyDimensions(usize),
    /// The number of array elements does not match the cardinality derived from
    /// its dimensions.
    WrongCardinality { actual: usize, expected: usize },
}

impl fmt::Display for InvalidArrayError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            InvalidArrayError::TooManyDimensions(n) => write!(
                f,
                "number of array dimensions ({}) exceeds the maximum allowed ({})",
                n, MAX_ARRAY_DIMENSIONS
            ),
            InvalidArrayError::WrongCardinality { actual, expected } => write!(
                f,
                "number of array elements ({}) does not match declared cardinality ({})",
                actual, expected
            ),
        }
    }
}

impl Error for InvalidArrayError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        None
    }
}