arrow_array/array/

union_array.rs

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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.
#![allow(clippy::enum_clike_unportable_variant)]

use crate::{Array, ArrayRef, make_array};
use arrow_buffer::bit_chunk_iterator::{BitChunkIterator, BitChunks};
use arrow_buffer::buffer::NullBuffer;
use arrow_buffer::{BooleanBuffer, Buffer, MutableBuffer, ScalarBuffer};
use arrow_data::{ArrayData, ArrayDataBuilder};
use arrow_schema::{ArrowError, DataType, UnionFields, UnionMode};
/// Contains the `UnionArray` type.
///
use std::any::Any;
use std::collections::HashSet;
use std::sync::Arc;

/// An array of [values of varying types](https://arrow.apache.org/docs/format/Columnar.html#union-layout)
///
/// Each slot in a [UnionArray] can have a value chosen from a number
/// of types.  Each of the possible types are named like the fields of
/// a [`StructArray`](crate::StructArray).  A `UnionArray` can
/// have two possible memory layouts, "dense" or "sparse".  For more
/// information on please see the
/// [specification](https://arrow.apache.org/docs/format/Columnar.html#union-layout).
///
/// [UnionBuilder](crate::builder::UnionBuilder) can be used to
/// create [UnionArray]'s of primitive types. `UnionArray`'s of nested
/// types are also supported but not via `UnionBuilder`, see the tests
/// for examples.
///
/// # Examples
/// ## Create a dense UnionArray `[1, 3.2, 34]`
/// ```
/// use arrow_buffer::ScalarBuffer;
/// use arrow_schema::*;
/// use std::sync::Arc;
/// use arrow_array::{Array, Int32Array, Float64Array, UnionArray};
///
/// let int_array = Int32Array::from(vec![1, 34]);
/// let float_array = Float64Array::from(vec![3.2]);
/// let type_ids = [0, 1, 0].into_iter().collect::<ScalarBuffer<i8>>();
/// let offsets = [0, 0, 1].into_iter().collect::<ScalarBuffer<i32>>();
///
/// let union_fields = [
///     (0, Arc::new(Field::new("A", DataType::Int32, false))),
///     (1, Arc::new(Field::new("B", DataType::Float64, false))),
/// ].into_iter().collect::<UnionFields>();
///
/// let children = vec![
///     Arc::new(int_array) as Arc<dyn Array>,
///     Arc::new(float_array),
/// ];
///
/// let array = UnionArray::try_new(
///     union_fields,
///     type_ids,
///     Some(offsets),
///     children,
/// ).unwrap();
///
/// let value = array.value(0).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
/// assert_eq!(1, value);
///
/// let value = array.value(1).as_any().downcast_ref::<Float64Array>().unwrap().value(0);
/// assert!(3.2 - value < f64::EPSILON);
///
/// let value = array.value(2).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
/// assert_eq!(34, value);
/// ```
///
/// ## Create a sparse UnionArray `[1, 3.2, 34]`
/// ```
/// use arrow_buffer::ScalarBuffer;
/// use arrow_schema::*;
/// use std::sync::Arc;
/// use arrow_array::{Array, Int32Array, Float64Array, UnionArray};
///
/// let int_array = Int32Array::from(vec![Some(1), None, Some(34)]);
/// let float_array = Float64Array::from(vec![None, Some(3.2), None]);
/// let type_ids = [0_i8, 1, 0].into_iter().collect::<ScalarBuffer<i8>>();
///
/// let union_fields = [
///     (0, Arc::new(Field::new("A", DataType::Int32, false))),
///     (1, Arc::new(Field::new("B", DataType::Float64, false))),
/// ].into_iter().collect::<UnionFields>();
///
/// let children = vec![
///     Arc::new(int_array) as Arc<dyn Array>,
///     Arc::new(float_array),
/// ];
///
/// let array = UnionArray::try_new(
///     union_fields,
///     type_ids,
///     None,
///     children,
/// ).unwrap();
///
/// let value = array.value(0).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
/// assert_eq!(1, value);
///
/// let value = array.value(1).as_any().downcast_ref::<Float64Array>().unwrap().value(0);
/// assert!(3.2 - value < f64::EPSILON);
///
/// let value = array.value(2).as_any().downcast_ref::<Int32Array>().unwrap().value(0);
/// assert_eq!(34, value);
/// ```
#[derive(Clone)]
pub struct UnionArray {
    data_type: DataType,
    type_ids: ScalarBuffer<i8>,
    offsets: Option<ScalarBuffer<i32>>,
    fields: Vec<Option<ArrayRef>>,
}

impl UnionArray {
    /// Creates a new `UnionArray`.
    ///
    /// Accepts type ids, child arrays and optionally offsets (for dense unions) to create
    /// a new `UnionArray`.  This method makes no attempt to validate the data provided by the
    /// caller and assumes that each of the components are correct and consistent with each other.
    /// See `try_new` for an alternative that validates the data provided.
    ///
    /// # Safety
    ///
    /// The `type_ids` values should be non-negative and must match one of the type ids of the fields provided in `fields`.
    /// These values are used to index into the `children` arrays.
    ///
    /// The `offsets` is provided in the case of a dense union, sparse unions should use `None`.
    /// If provided the `offsets` values should be non-negative and must be less than the length of the
    /// corresponding array.
    ///
    /// In both cases above we use signed integer types to maintain compatibility with other
    /// Arrow implementations.
    pub unsafe fn new_unchecked(
        fields: UnionFields,
        type_ids: ScalarBuffer<i8>,
        offsets: Option<ScalarBuffer<i32>>,
        children: Vec<ArrayRef>,
    ) -> Self {
        let mode = if offsets.is_some() {
            UnionMode::Dense
        } else {
            UnionMode::Sparse
        };

        let len = type_ids.len();
        let builder = ArrayData::builder(DataType::Union(fields, mode))
            .add_buffer(type_ids.into_inner())
            .child_data(children.into_iter().map(Array::into_data).collect())
            .len(len);

        let data = match offsets {
            Some(offsets) => unsafe { builder.add_buffer(offsets.into_inner()).build_unchecked() },
            None => unsafe { builder.build_unchecked() },
        };
        Self::from(data)
    }

    /// Attempts to create a new `UnionArray`, validating the inputs provided.
    ///
    /// The order of child arrays child array order must match the fields order
    pub fn try_new(
        fields: UnionFields,
        type_ids: ScalarBuffer<i8>,
        offsets: Option<ScalarBuffer<i32>>,
        children: Vec<ArrayRef>,
    ) -> Result<Self, ArrowError> {
        // There must be a child array for every field.
        if fields.len() != children.len() {
            return Err(ArrowError::InvalidArgumentError(
                "Union fields length must match child arrays length".to_string(),
            ));
        }

        if let Some(offsets) = &offsets {
            // There must be an offset value for every type id value.
            if offsets.len() != type_ids.len() {
                return Err(ArrowError::InvalidArgumentError(
                    "Type Ids and Offsets lengths must match".to_string(),
                ));
            }
        } else {
            // Sparse union child arrays must be equal in length to the length of the union
            for child in &children {
                if child.len() != type_ids.len() {
                    return Err(ArrowError::InvalidArgumentError(
                        "Sparse union child arrays must be equal in length to the length of the union".to_string(),
                    ));
                }
            }
        }

        // Create mapping from type id to array lengths.
        let max_id = fields.iter().map(|(i, _)| i).max().unwrap_or_default() as usize;
        let mut array_lens = vec![None; max_id + 1];
        for (cd, (field_id, _)) in children.iter().zip(fields.iter()) {
            array_lens[field_id as usize] = Some(cd.len());
        }

        // Type id values must match one of the fields.
        for id in &type_ids {
            match array_lens.get(*id as usize) {
                Some(Some(_)) => {}
                _ => {
                    return Err(ArrowError::InvalidArgumentError(
                        "Type Ids values must match one of the field type ids".to_owned(),
                    ));
                }
            }
        }

        // Check the value offsets are in bounds.
        if let Some(offsets) = &offsets {
            let mut iter = type_ids.iter().zip(offsets.iter());
            if iter.any(|(type_id, &offset)| {
                offset < 0 || offset as usize >= array_lens[*type_id as usize].unwrap()
            }) {
                return Err(ArrowError::InvalidArgumentError(
                    "Offsets must be non-negative and within the length of the Array".to_owned(),
                ));
            }
        }

        // Safety:
        // - Arguments validated above.
        let union_array = unsafe { Self::new_unchecked(fields, type_ids, offsets, children) };
        Ok(union_array)
    }

    /// Accesses the child array for `type_id`.
    ///
    /// # Panics
    ///
    /// Panics if the `type_id` provided is not present in the array's DataType
    /// in the `Union`.
    pub fn child(&self, type_id: i8) -> &ArrayRef {
        assert!((type_id as usize) < self.fields.len());
        let boxed = &self.fields[type_id as usize];
        boxed.as_ref().expect("invalid type id")
    }

    /// Returns the `type_id` for the array slot at `index`.
    ///
    /// # Panics
    ///
    /// Panics if `index` is greater than or equal to the number of child arrays
    pub fn type_id(&self, index: usize) -> i8 {
        assert!(index < self.type_ids.len());
        self.type_ids[index]
    }

    /// Returns the `type_ids` buffer for this array
    pub fn type_ids(&self) -> &ScalarBuffer<i8> {
        &self.type_ids
    }

    /// Returns the `offsets` buffer if this is a dense array
    pub fn offsets(&self) -> Option<&ScalarBuffer<i32>> {
        self.offsets.as_ref()
    }

    /// Returns the offset into the underlying values array for the array slot at `index`.
    ///
    /// # Panics
    ///
    /// Panics if `index` is greater than or equal the length of the array.
    pub fn value_offset(&self, index: usize) -> usize {
        assert!(index < self.len());
        match &self.offsets {
            Some(offsets) => offsets[index] as usize,
            None => self.offset() + index,
        }
    }

    /// Returns the array's value at index `i`.
    ///
    /// Note: This method does not check for nulls and the value is arbitrary
    /// (but still well-defined) if [`is_null`](Self::is_null) returns true for the index.
    ///
    /// # Panics
    /// Panics if index `i` is out of bounds
    pub fn value(&self, i: usize) -> ArrayRef {
        let type_id = self.type_id(i);
        let value_offset = self.value_offset(i);
        let child = self.child(type_id);
        child.slice(value_offset, 1)
    }

    /// Returns the names of the types in the union.
    pub fn type_names(&self) -> Vec<&str> {
        match self.data_type() {
            DataType::Union(fields, _) => fields
                .iter()
                .map(|(_, f)| f.name().as_str())
                .collect::<Vec<&str>>(),
            _ => unreachable!("Union array's data type is not a union!"),
        }
    }

    /// Returns the [`UnionFields`] for the union.
    pub fn fields(&self) -> &UnionFields {
        match self.data_type() {
            DataType::Union(fields, _) => fields,
            _ => unreachable!("Union array's data type is not a union!"),
        }
    }

    /// Returns whether the `UnionArray` is dense (or sparse if `false`).
    pub fn is_dense(&self) -> bool {
        match self.data_type() {
            DataType::Union(_, mode) => mode == &UnionMode::Dense,
            _ => unreachable!("Union array's data type is not a union!"),
        }
    }

    /// Returns a zero-copy slice of this array with the indicated offset and length.
    ///
    /// # Panics
    /// Panics if `offset + length > self.len()`
    pub fn slice(&self, offset: usize, length: usize) -> Self {
        let (offsets, fields) = match self.offsets.as_ref() {
            // If dense union, slice offsets
            Some(offsets) => (Some(offsets.slice(offset, length)), self.fields.clone()),
            // Otherwise need to slice sparse children
            None => {
                let fields = self
                    .fields
                    .iter()
                    .map(|x| x.as_ref().map(|x| x.slice(offset, length)))
                    .collect();
                (None, fields)
            }
        };

        Self {
            data_type: self.data_type.clone(),
            type_ids: self.type_ids.slice(offset, length),
            offsets,
            fields,
        }
    }

    /// Deconstruct this array into its constituent parts
    ///
    /// # Example
    ///
    /// ```
    /// # use arrow_array::array::UnionArray;
    /// # use arrow_array::types::Int32Type;
    /// # use arrow_array::builder::UnionBuilder;
    /// # use arrow_buffer::ScalarBuffer;
    /// # fn main() -> Result<(), arrow_schema::ArrowError> {
    /// let mut builder = UnionBuilder::new_dense();
    /// builder.append::<Int32Type>("a", 1).unwrap();
    /// let union_array = builder.build()?;
    ///
    /// // Deconstruct into parts
    /// let (union_fields, type_ids, offsets, children) = union_array.into_parts();
    ///
    /// // Reconstruct from parts
    /// let union_array = UnionArray::try_new(
    ///     union_fields,
    ///     type_ids,
    ///     offsets,
    ///     children,
    /// );
    /// # Ok(())
    /// # }
    /// ```
    pub fn into_parts(
        self,
    ) -> (
        UnionFields,
        ScalarBuffer<i8>,
        Option<ScalarBuffer<i32>>,
        Vec<ArrayRef>,
    ) {
        let Self {
            data_type,
            type_ids,
            offsets,
            mut fields,
        } = self;
        match data_type {
            DataType::Union(union_fields, _) => {
                let children = union_fields
                    .iter()
                    .map(|(type_id, _)| fields[type_id as usize].take().unwrap())
                    .collect();
                (union_fields, type_ids, offsets, children)
            }
            _ => unreachable!(),
        }
    }

    /// Computes the logical nulls for a sparse union, optimized for when there's a lot of fields without nulls
    fn mask_sparse_skip_without_nulls(&self, nulls: Vec<(i8, NullBuffer)>) -> BooleanBuffer {
        // Example logic for a union with 5 fields, a, b & c with nulls, d & e without nulls:
        // let [a_nulls, b_nulls, c_nulls] = nulls;
        // let [is_a, is_b, is_c] = masks;
        // let is_d_or_e = !(is_a | is_b | is_c)
        // let union_chunk_nulls = is_d_or_e  | (is_a & a_nulls) | (is_b & b_nulls) | (is_c & c_nulls)
        let fold = |(with_nulls_selected, union_nulls), (is_field, field_nulls)| {
            (
                with_nulls_selected | is_field,
                union_nulls | (is_field & field_nulls),
            )
        };

        self.mask_sparse_helper(
            nulls,
            |type_ids_chunk_array, nulls_masks_iters| {
                let (with_nulls_selected, union_nulls) = nulls_masks_iters
                    .iter_mut()
                    .map(|(field_type_id, field_nulls)| {
                        let field_nulls = field_nulls.next().unwrap();
                        let is_field = selection_mask(type_ids_chunk_array, *field_type_id);

                        (is_field, field_nulls)
                    })
                    .fold((0, 0), fold);

                // In the example above, this is the is_d_or_e = !(is_a | is_b) part
                let without_nulls_selected = !with_nulls_selected;

                // if a field without nulls is selected, the value is always true(set bit)
                // otherwise, the true/set bits have been computed above
                without_nulls_selected | union_nulls
            },
            |type_ids_remainder, bit_chunks| {
                let (with_nulls_selected, union_nulls) = bit_chunks
                    .iter()
                    .map(|(field_type_id, field_bit_chunks)| {
                        let field_nulls = field_bit_chunks.remainder_bits();
                        let is_field = selection_mask(type_ids_remainder, *field_type_id);

                        (is_field, field_nulls)
                    })
                    .fold((0, 0), fold);

                let without_nulls_selected = !with_nulls_selected;

                without_nulls_selected | union_nulls
            },
        )
    }

    /// Computes the logical nulls for a sparse union, optimized for when there's a lot of fields fully null
    fn mask_sparse_skip_fully_null(&self, mut nulls: Vec<(i8, NullBuffer)>) -> BooleanBuffer {
        let DataType::Union(fields, _) = self.data_type() else {
            unreachable!("Union array's data type is not a union!")
        };

        let type_ids = fields.iter().map(|(id, _)| id).collect::<HashSet<_>>();
        let with_nulls = nulls.iter().map(|(id, _)| *id).collect::<HashSet<_>>();

        let without_nulls_ids = type_ids
            .difference(&with_nulls)
            .copied()
            .collect::<Vec<_>>();

        nulls.retain(|(_, nulls)| nulls.null_count() < nulls.len());

        // Example logic for a union with 6 fields, a, b & c with nulls, d & e without nulls, and f fully_null:
        // let [a_nulls, b_nulls, c_nulls] = nulls;
        // let [is_a, is_b, is_c, is_d, is_e] = masks;
        // let union_chunk_nulls = is_d | is_e | (is_a & a_nulls) | (is_b & b_nulls) | (is_c & c_nulls)
        self.mask_sparse_helper(
            nulls,
            |type_ids_chunk_array, nulls_masks_iters| {
                let union_nulls = nulls_masks_iters.iter_mut().fold(
                    0,
                    |union_nulls, (field_type_id, nulls_iter)| {
                        let field_nulls = nulls_iter.next().unwrap();

                        if field_nulls == 0 {
                            union_nulls
                        } else {
                            let is_field = selection_mask(type_ids_chunk_array, *field_type_id);

                            union_nulls | (is_field & field_nulls)
                        }
                    },
                );

                // Given the example above, this is the is_d_or_e = (is_d | is_e) part
                let without_nulls_selected =
                    without_nulls_selected(type_ids_chunk_array, &without_nulls_ids);

                // if a field without nulls is selected, the value is always true(set bit)
                // otherwise, the true/set bits have been computed above
                union_nulls | without_nulls_selected
            },
            |type_ids_remainder, bit_chunks| {
                let union_nulls =
                    bit_chunks
                        .iter()
                        .fold(0, |union_nulls, (field_type_id, field_bit_chunks)| {
                            let is_field = selection_mask(type_ids_remainder, *field_type_id);
                            let field_nulls = field_bit_chunks.remainder_bits();

                            union_nulls | is_field & field_nulls
                        });

                union_nulls | without_nulls_selected(type_ids_remainder, &without_nulls_ids)
            },
        )
    }

    /// Computes the logical nulls for a sparse union, optimized for when all fields contains nulls
    fn mask_sparse_all_with_nulls_skip_one(&self, nulls: Vec<(i8, NullBuffer)>) -> BooleanBuffer {
        // Example logic for a union with 3 fields, a, b & c, all containing nulls:
        // let [a_nulls, b_nulls, c_nulls] = nulls;
        // We can skip the first field: it's selection mask is the negation of all others selection mask
        // let [is_b, is_c] = selection_masks;
        // let is_a = !(is_b | is_c)
        // let union_chunk_nulls = (is_a & a_nulls) | (is_b & b_nulls) | (is_c & c_nulls)
        self.mask_sparse_helper(
            nulls,
            |type_ids_chunk_array, nulls_masks_iters| {
                let (is_not_first, union_nulls) = nulls_masks_iters[1..] // skip first
                    .iter_mut()
                    .fold(
                        (0, 0),
                        |(is_not_first, union_nulls), (field_type_id, nulls_iter)| {
                            let field_nulls = nulls_iter.next().unwrap();
                            let is_field = selection_mask(type_ids_chunk_array, *field_type_id);

                            (
                                is_not_first | is_field,
                                union_nulls | (is_field & field_nulls),
                            )
                        },
                    );

                let is_first = !is_not_first;
                let first_nulls = nulls_masks_iters[0].1.next().unwrap();

                (is_first & first_nulls) | union_nulls
            },
            |type_ids_remainder, bit_chunks| {
                bit_chunks
                    .iter()
                    .fold(0, |union_nulls, (field_type_id, field_bit_chunks)| {
                        let field_nulls = field_bit_chunks.remainder_bits();
                        // The same logic as above, except that since this runs at most once,
                        // it doesn't make difference to speed-up the first selection mask
                        let is_field = selection_mask(type_ids_remainder, *field_type_id);

                        union_nulls | (is_field & field_nulls)
                    })
            },
        )
    }

    /// Maps `nulls` to `BitChunk's` and then to `BitChunkIterator's`, then divides `self.type_ids` into exact chunks of 64 values,
    /// calling `mask_chunk` for every exact chunk, and `mask_remainder` for the remainder, if any, collecting the result in a `BooleanBuffer`
    fn mask_sparse_helper(
        &self,
        nulls: Vec<(i8, NullBuffer)>,
        mut mask_chunk: impl FnMut(&[i8; 64], &mut [(i8, BitChunkIterator)]) -> u64,
        mask_remainder: impl FnOnce(&[i8], &[(i8, BitChunks)]) -> u64,
    ) -> BooleanBuffer {
        let bit_chunks = nulls
            .iter()
            .map(|(type_id, nulls)| (*type_id, nulls.inner().bit_chunks()))
            .collect::<Vec<_>>();

        let mut nulls_masks_iter = bit_chunks
            .iter()
            .map(|(type_id, bit_chunks)| (*type_id, bit_chunks.iter()))
            .collect::<Vec<_>>();

        let (chunks_exact, remainder) = self.type_ids.as_chunks::<64>();

        let chunks = chunks_exact
            .iter()
            .map(|type_ids_chunk| mask_chunk(type_ids_chunk, &mut nulls_masks_iter));

        // SAFETY:
        // chunks is a ChunksExact iterator, which implements TrustedLen, and correctly reports its length
        let mut buffer = unsafe { MutableBuffer::from_trusted_len_iter(chunks) };

        if !remainder.is_empty() {
            buffer.push(mask_remainder(remainder, &bit_chunks));
        }

        BooleanBuffer::new(buffer.into(), 0, self.type_ids.len())
    }

    /// Computes the logical nulls for a sparse or dense union, by gathering individual bits from the null buffer of the selected field
    fn gather_nulls(&self, nulls: Vec<(i8, NullBuffer)>) -> BooleanBuffer {
        let one_null = NullBuffer::new_null(1);
        let one_valid = NullBuffer::new_valid(1);

        // Unsafe code below depend on it:
        // To remove one branch from the loop, if the a type_id is not utilized, or it's logical_nulls is None/all set,
        // we use a null buffer of len 1 and a index_mask of 0, or the true null buffer and usize::MAX otherwise.
        // We then unconditionally access the null buffer with index & index_mask,
        // which always return 0 for the 1-len buffer, or the true index unchanged otherwise
        // We also use a 256 array, so llvm knows that `type_id as u8 as usize` is always in bounds
        let mut logical_nulls_array = [(&one_valid, Mask::Zero); 256];

        for (type_id, nulls) in &nulls {
            if nulls.null_count() == nulls.len() {
                // Similarly, if all values are null, use a 1-null null-buffer to reduce cache pressure a bit
                logical_nulls_array[*type_id as u8 as usize] = (&one_null, Mask::Zero);
            } else {
                logical_nulls_array[*type_id as u8 as usize] = (nulls, Mask::Max);
            }
        }

        match &self.offsets {
            Some(offsets) => {
                assert_eq!(self.type_ids.len(), offsets.len());

                BooleanBuffer::collect_bool(self.type_ids.len(), |i| unsafe {
                    // SAFETY: BooleanBuffer::collect_bool calls us 0..self.type_ids.len()
                    let type_id = *self.type_ids.get_unchecked(i);
                    // SAFETY: We asserted that offsets len and self.type_ids len are equal
                    let offset = *offsets.get_unchecked(i);

                    let (nulls, offset_mask) = &logical_nulls_array[type_id as u8 as usize];

                    // SAFETY:
                    // If offset_mask is Max
                    // 1. Offset validity is checked at union creation
                    // 2. If the null buffer len equals it's array len is checked at array creation
                    // If offset_mask is Zero, the null buffer len is 1
                    nulls
                        .inner()
                        .value_unchecked(offset as usize & *offset_mask as usize)
                })
            }
            None => {
                BooleanBuffer::collect_bool(self.type_ids.len(), |index| unsafe {
                    // SAFETY: BooleanBuffer::collect_bool calls us 0..self.type_ids.len()
                    let type_id = *self.type_ids.get_unchecked(index);

                    let (nulls, index_mask) = &logical_nulls_array[type_id as u8 as usize];

                    // SAFETY:
                    // If index_mask is Max
                    // 1. On sparse union, every child len match it's parent, this is checked at union creation
                    // 2. If the null buffer len equals it's array len is checked at array creation
                    // If index_mask is Zero, the null buffer len is 1
                    nulls.inner().value_unchecked(index & *index_mask as usize)
                })
            }
        }
    }

    /// Returns a vector of tuples containing each field's type_id and its logical null buffer.
    /// Only fields with non-zero null counts are included.
    fn fields_logical_nulls(&self) -> Vec<(i8, NullBuffer)> {
        self.fields
            .iter()
            .enumerate()
            .filter_map(|(type_id, field)| Some((type_id as i8, field.as_ref()?.logical_nulls()?)))
            .filter(|(_, nulls)| nulls.null_count() > 0)
            .collect()
    }
}

impl From<ArrayData> for UnionArray {
    fn from(data: ArrayData) -> Self {
        let (data_type, len, _nulls, offset, buffers, child_data) = data.into_parts();

        let (fields, mode) = match &data_type {
            DataType::Union(fields, mode) => (fields, mode),
            d => panic!("UnionArray expected ArrayData with type Union got {d}"),
        };

        let (type_ids, offsets) = match mode {
            UnionMode::Sparse => {
                let [buffer]: [Buffer; 1] = buffers.try_into().expect("1 buffer for type_ids");
                (ScalarBuffer::new(buffer, offset, len), None)
            }
            UnionMode::Dense => {
                let [type_ids_buffer, offsets_buffer]: [Buffer; 2] = buffers
                    .try_into()
                    .expect("2 buffers for type_ids and offsets");
                (
                    ScalarBuffer::new(type_ids_buffer, offset, len),
                    Some(ScalarBuffer::new(offsets_buffer, offset, len)),
                )
            }
        };

        let max_id = fields.iter().map(|(i, _)| i).max().unwrap_or_default() as usize;
        let mut boxed_fields = vec![None; max_id + 1];
        for (cd, (field_id, _)) in child_data.into_iter().zip(fields.iter()) {
            boxed_fields[field_id as usize] = Some(make_array(cd));
        }
        Self {
            data_type,
            type_ids,
            offsets,
            fields: boxed_fields,
        }
    }
}

impl From<UnionArray> for ArrayData {
    fn from(array: UnionArray) -> Self {
        let len = array.len();
        let DataType::Union(f, _) = &array.data_type else {
            unreachable!()
        };
        let buffers = match array.offsets {
            Some(o) => vec![array.type_ids.into_inner(), o.into_inner()],
            None => vec![array.type_ids.into_inner()],
        };

        let child = f
            .iter()
            .map(|(i, _)| array.fields[i as usize].as_ref().unwrap().to_data())
            .collect();

        let builder = ArrayDataBuilder::new(array.data_type)
            .len(len)
            .buffers(buffers)
            .child_data(child);
        unsafe { builder.build_unchecked() }
    }
}

/// SAFETY: Correctly implements the contract of Arrow Arrays
unsafe impl Array for UnionArray {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn to_data(&self) -> ArrayData {
        self.clone().into()
    }

    fn into_data(self) -> ArrayData {
        self.into()
    }

    fn data_type(&self) -> &DataType {
        &self.data_type
    }

    fn slice(&self, offset: usize, length: usize) -> ArrayRef {
        Arc::new(self.slice(offset, length))
    }

    fn len(&self) -> usize {
        self.type_ids.len()
    }

    fn is_empty(&self) -> bool {
        self.type_ids.is_empty()
    }

    fn shrink_to_fit(&mut self) {
        self.type_ids.shrink_to_fit();
        if let Some(offsets) = &mut self.offsets {
            offsets.shrink_to_fit();
        }
        for array in self.fields.iter_mut().flatten() {
            array.shrink_to_fit();
        }
        self.fields.shrink_to_fit();
    }

    fn offset(&self) -> usize {
        0
    }

    fn nulls(&self) -> Option<&NullBuffer> {
        None
    }

    fn logical_nulls(&self) -> Option<NullBuffer> {
        let DataType::Union(fields, _) = self.data_type() else {
            unreachable!()
        };

        if fields.len() <= 1 {
            return self.fields.iter().find_map(|field_opt| {
                field_opt
                    .as_ref()
                    .and_then(|field| field.logical_nulls())
                    .map(|logical_nulls| {
                        if self.is_dense() {
                            self.gather_nulls(vec![(0, logical_nulls)]).into()
                        } else {
                            logical_nulls
                        }
                    })
            });
        }

        let logical_nulls = self.fields_logical_nulls();

        if logical_nulls.is_empty() {
            return None;
        }

        let fully_null_count = logical_nulls
            .iter()
            .filter(|(_, nulls)| nulls.null_count() == nulls.len())
            .count();

        if fully_null_count == fields.len() {
            if let Some((_, exactly_sized)) = logical_nulls
                .iter()
                .find(|(_, nulls)| nulls.len() == self.len())
            {
                return Some(exactly_sized.clone());
            }

            if let Some((_, bigger)) = logical_nulls
                .iter()
                .find(|(_, nulls)| nulls.len() > self.len())
            {
                return Some(bigger.slice(0, self.len()));
            }

            return Some(NullBuffer::new_null(self.len()));
        }

        let boolean_buffer = match &self.offsets {
            Some(_) => self.gather_nulls(logical_nulls),
            None => {
                // Choose the fastest way to compute the logical nulls
                // Gather computes one null per iteration, while the others work on 64 nulls chunks,
                // but must also compute selection masks, which is expensive,
                // so it's cost is the number of selection masks computed per chunk
                // Since computing the selection mask gets auto-vectorized, it's performance depends on which simd feature is enabled
                // For gather, the cost is the threshold where masking becomes slower than gather, which is determined with benchmarks
                // TODO: bench on avx512f(feature is still unstable)
                let gather_relative_cost = if cfg!(target_feature = "avx2") {
                    10
                } else if cfg!(target_feature = "sse4.1") {
                    3
                } else if cfg!(target_arch = "x86") || cfg!(target_arch = "x86_64") {
                    // x86 baseline includes sse2
                    2
                } else {
                    // TODO: bench on non x86
                    // Always use gather on non benchmarked archs because even though it may slower on some cases,
                    // it's performance depends only on the union length, without being affected by the number of fields
                    0
                };

                let strategies = [
                    (SparseStrategy::Gather, gather_relative_cost, true),
                    (
                        SparseStrategy::MaskAllFieldsWithNullsSkipOne,
                        fields.len() - 1,
                        fields.len() == logical_nulls.len(),
                    ),
                    (
                        SparseStrategy::MaskSkipWithoutNulls,
                        logical_nulls.len(),
                        true,
                    ),
                    (
                        SparseStrategy::MaskSkipFullyNull,
                        fields.len() - fully_null_count,
                        true,
                    ),
                ];

                let (strategy, _, _) = strategies
                    .iter()
                    .filter(|(_, _, applicable)| *applicable)
                    .min_by_key(|(_, cost, _)| cost)
                    .unwrap();

                match strategy {
                    SparseStrategy::Gather => self.gather_nulls(logical_nulls),
                    SparseStrategy::MaskAllFieldsWithNullsSkipOne => {
                        self.mask_sparse_all_with_nulls_skip_one(logical_nulls)
                    }
                    SparseStrategy::MaskSkipWithoutNulls => {
                        self.mask_sparse_skip_without_nulls(logical_nulls)
                    }
                    SparseStrategy::MaskSkipFullyNull => {
                        self.mask_sparse_skip_fully_null(logical_nulls)
                    }
                }
            }
        };

        let null_buffer = NullBuffer::from(boolean_buffer);

        if null_buffer.null_count() > 0 {
            Some(null_buffer)
        } else {
            None
        }
    }

    fn is_nullable(&self) -> bool {
        self.fields
            .iter()
            .flatten()
            .any(|field| field.is_nullable())
    }

    fn get_buffer_memory_size(&self) -> usize {
        let mut sum = self.type_ids.inner().capacity();
        if let Some(o) = self.offsets.as_ref() {
            sum += o.inner().capacity()
        }
        self.fields
            .iter()
            .filter_map(|x| x.as_ref().map(|x| x.get_buffer_memory_size()))
            .sum::<usize>()
            + sum
    }

    fn get_array_memory_size(&self) -> usize {
        let mut sum = self.type_ids.inner().capacity();
        if let Some(o) = self.offsets.as_ref() {
            sum += o.inner().capacity()
        }
        std::mem::size_of::<Self>()
            + self
                .fields
                .iter()
                .filter_map(|x| x.as_ref().map(|x| x.get_array_memory_size()))
                .sum::<usize>()
            + sum
    }

    #[cfg(feature = "pool")]
    fn claim(&self, pool: &dyn arrow_buffer::MemoryPool) {
        self.type_ids.claim(pool);
        if let Some(offsets) = &self.offsets {
            offsets.claim(pool);
        }
        for field in self.fields.iter().flatten() {
            field.claim(pool);
        }
    }
}

impl std::fmt::Debug for UnionArray {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        let header = if self.is_dense() {
            "UnionArray(Dense)\n["
        } else {
            "UnionArray(Sparse)\n["
        };
        writeln!(f, "{header}")?;

        writeln!(f, "-- type id buffer:")?;
        writeln!(f, "{:?}", self.type_ids)?;

        if let Some(offsets) = &self.offsets {
            writeln!(f, "-- offsets buffer:")?;
            writeln!(f, "{offsets:?}")?;
        }

        let DataType::Union(fields, _) = self.data_type() else {
            unreachable!()
        };

        for (type_id, field) in fields.iter() {
            let child = self.child(type_id);
            writeln!(
                f,
                "-- child {}: \"{}\" ({:?})",
                type_id,
                field.name(),
                field.data_type()
            )?;
            std::fmt::Debug::fmt(child, f)?;
            writeln!(f)?;
        }
        writeln!(f, "]")
    }
}

/// How to compute the logical nulls of a sparse union. All strategies return the same result.
/// Those starting with Mask perform bitwise masking for each chunk of 64 values, including
/// computing expensive selection masks of fields: which fields masks must be computed is the
/// difference between them
enum SparseStrategy {
    /// Gather individual bits from the null buffer of the selected field
    Gather,
    /// All fields contains nulls, so we can skip the selection mask computation of one field by negating the others
    MaskAllFieldsWithNullsSkipOne,
    /// Skip the selection mask computation of the fields without nulls
    MaskSkipWithoutNulls,
    /// Skip the selection mask computation of the fully nulls fields
    MaskSkipFullyNull,
}

#[derive(Copy, Clone)]
#[repr(usize)]
enum Mask {
    Zero = 0,
    Max = usize::MAX,
}

fn selection_mask(type_ids_chunk: &[i8], type_id: i8) -> u64 {
    type_ids_chunk
        .iter()
        .copied()
        .enumerate()
        .fold(0, |packed, (bit_idx, v)| {
            packed | (((v == type_id) as u64) << bit_idx)
        })
}

/// Returns a bitmask where bits indicate if any id from `without_nulls_ids` exist in `type_ids_chunk`.
fn without_nulls_selected(type_ids_chunk: &[i8], without_nulls_ids: &[i8]) -> u64 {
    without_nulls_ids
        .iter()
        .fold(0, |fully_valid_selected, field_type_id| {
            fully_valid_selected | selection_mask(type_ids_chunk, *field_type_id)
        })
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::HashSet;

    use crate::array::Int8Type;
    use crate::builder::UnionBuilder;
    use crate::cast::AsArray;
    use crate::types::{Float32Type, Float64Type, Int32Type, Int64Type};
    use crate::{Float64Array, Int32Array, Int64Array, NullArray, StringArray};
    use crate::{Int8Array, RecordBatch};
    use arrow_buffer::Buffer;
    use arrow_schema::{Field, Schema};

    #[test]
    fn test_dense_i32() {
        let mut builder = UnionBuilder::new_dense();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Int32Type>("b", 2).unwrap();
        builder.append::<Int32Type>("c", 3).unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        builder.append::<Int32Type>("c", 5).unwrap();
        builder.append::<Int32Type>("a", 6).unwrap();
        builder.append::<Int32Type>("b", 7).unwrap();
        let union = builder.build().unwrap();

        let expected_type_ids = vec![0_i8, 1, 2, 0, 2, 0, 1];
        let expected_offsets = vec![0_i32, 0, 0, 1, 1, 2, 1];
        let expected_array_values = [1_i32, 2, 3, 4, 5, 6, 7];

        // Check type ids
        assert_eq!(*union.type_ids(), expected_type_ids);
        for (i, id) in expected_type_ids.iter().enumerate() {
            assert_eq!(id, &union.type_id(i));
        }

        // Check offsets
        assert_eq!(*union.offsets().unwrap(), expected_offsets);
        for (i, id) in expected_offsets.iter().enumerate() {
            assert_eq!(union.value_offset(i), *id as usize);
        }

        // Check data
        assert_eq!(
            *union.child(0).as_primitive::<Int32Type>().values(),
            [1_i32, 4, 6]
        );
        assert_eq!(
            *union.child(1).as_primitive::<Int32Type>().values(),
            [2_i32, 7]
        );
        assert_eq!(
            *union.child(2).as_primitive::<Int32Type>().values(),
            [3_i32, 5]
        );

        assert_eq!(expected_array_values.len(), union.len());
        for (i, expected_value) in expected_array_values.iter().enumerate() {
            assert!(!union.is_null(i));
            let slot = union.value(i);
            let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
            assert_eq!(slot.len(), 1);
            let value = slot.value(0);
            assert_eq!(expected_value, &value);
        }
    }

    #[test]
    fn slice_union_array_single_field() {
        // Dense Union
        // [1, null, 3, null, 4]
        let union_array = {
            let mut builder = UnionBuilder::new_dense();
            builder.append::<Int32Type>("a", 1).unwrap();
            builder.append_null::<Int32Type>("a").unwrap();
            builder.append::<Int32Type>("a", 3).unwrap();
            builder.append_null::<Int32Type>("a").unwrap();
            builder.append::<Int32Type>("a", 4).unwrap();
            builder.build().unwrap()
        };

        // [null, 3, null]
        let union_slice = union_array.slice(1, 3);
        let logical_nulls = union_slice.logical_nulls().unwrap();

        assert_eq!(logical_nulls.len(), 3);
        assert!(logical_nulls.is_null(0));
        assert!(logical_nulls.is_valid(1));
        assert!(logical_nulls.is_null(2));
    }

    #[test]
    fn test_dense_i32_large() {
        let mut builder = UnionBuilder::new_dense();

        let expected_type_ids = vec![0_i8; 1024];
        let expected_offsets: Vec<_> = (0..1024).collect();
        let expected_array_values: Vec<_> = (1..=1024).collect();

        expected_array_values
            .iter()
            .for_each(|v| builder.append::<Int32Type>("a", *v).unwrap());

        let union = builder.build().unwrap();

        // Check type ids
        assert_eq!(*union.type_ids(), expected_type_ids);
        for (i, id) in expected_type_ids.iter().enumerate() {
            assert_eq!(id, &union.type_id(i));
        }

        // Check offsets
        assert_eq!(*union.offsets().unwrap(), expected_offsets);
        for (i, id) in expected_offsets.iter().enumerate() {
            assert_eq!(union.value_offset(i), *id as usize);
        }

        for (i, expected_value) in expected_array_values.iter().enumerate() {
            assert!(!union.is_null(i));
            let slot = union.value(i);
            let slot = slot.as_primitive::<Int32Type>();
            assert_eq!(slot.len(), 1);
            let value = slot.value(0);
            assert_eq!(expected_value, &value);
        }
    }

    #[test]
    fn test_dense_mixed() {
        let mut builder = UnionBuilder::new_dense();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Int64Type>("c", 3).unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        builder.append::<Int64Type>("c", 5).unwrap();
        builder.append::<Int32Type>("a", 6).unwrap();
        let union = builder.build().unwrap();

        assert_eq!(5, union.len());
        for i in 0..union.len() {
            let slot = union.value(i);
            assert!(!union.is_null(i));
            match i {
                0 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(1_i32, value);
                }
                1 => {
                    let slot = slot.as_any().downcast_ref::<Int64Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(3_i64, value);
                }
                2 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(4_i32, value);
                }
                3 => {
                    let slot = slot.as_any().downcast_ref::<Int64Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(5_i64, value);
                }
                4 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(6_i32, value);
                }
                _ => unreachable!(),
            }
        }
    }

    #[test]
    fn test_dense_mixed_with_nulls() {
        let mut builder = UnionBuilder::new_dense();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Int64Type>("c", 3).unwrap();
        builder.append::<Int32Type>("a", 10).unwrap();
        builder.append_null::<Int32Type>("a").unwrap();
        builder.append::<Int32Type>("a", 6).unwrap();
        let union = builder.build().unwrap();

        assert_eq!(5, union.len());
        for i in 0..union.len() {
            let slot = union.value(i);
            match i {
                0 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(1_i32, value);
                }
                1 => {
                    let slot = slot.as_any().downcast_ref::<Int64Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(3_i64, value);
                }
                2 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(10_i32, value);
                }
                3 => assert!(slot.is_null(0)),
                4 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(6_i32, value);
                }
                _ => unreachable!(),
            }
        }
    }

    #[test]
    fn test_dense_mixed_with_nulls_and_offset() {
        let mut builder = UnionBuilder::new_dense();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Int64Type>("c", 3).unwrap();
        builder.append::<Int32Type>("a", 10).unwrap();
        builder.append_null::<Int32Type>("a").unwrap();
        builder.append::<Int32Type>("a", 6).unwrap();
        let union = builder.build().unwrap();

        let slice = union.slice(2, 3);
        let new_union = slice.as_any().downcast_ref::<UnionArray>().unwrap();

        assert_eq!(3, new_union.len());
        for i in 0..new_union.len() {
            let slot = new_union.value(i);
            match i {
                0 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(10_i32, value);
                }
                1 => assert!(slot.is_null(0)),
                2 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(6_i32, value);
                }
                _ => unreachable!(),
            }
        }
    }

    #[test]
    fn test_dense_mixed_with_str() {
        let string_array = StringArray::from(vec!["foo", "bar", "baz"]);
        let int_array = Int32Array::from(vec![5, 6]);
        let float_array = Float64Array::from(vec![10.0]);

        let type_ids = [1, 0, 0, 2, 0, 1].into_iter().collect::<ScalarBuffer<i8>>();
        let offsets = [0, 0, 1, 0, 2, 1]
            .into_iter()
            .collect::<ScalarBuffer<i32>>();

        let fields = [
            (0, Arc::new(Field::new("A", DataType::Utf8, false))),
            (1, Arc::new(Field::new("B", DataType::Int32, false))),
            (2, Arc::new(Field::new("C", DataType::Float64, false))),
        ]
        .into_iter()
        .collect::<UnionFields>();
        let children = [
            Arc::new(string_array) as Arc<dyn Array>,
            Arc::new(int_array),
            Arc::new(float_array),
        ]
        .into_iter()
        .collect();
        let array =
            UnionArray::try_new(fields, type_ids.clone(), Some(offsets.clone()), children).unwrap();

        // Check type ids
        assert_eq!(*array.type_ids(), type_ids);
        for (i, id) in type_ids.iter().enumerate() {
            assert_eq!(id, &array.type_id(i));
        }

        // Check offsets
        assert_eq!(*array.offsets().unwrap(), offsets);
        for (i, id) in offsets.iter().enumerate() {
            assert_eq!(*id as usize, array.value_offset(i));
        }

        // Check values
        assert_eq!(6, array.len());

        let slot = array.value(0);
        let value = slot.as_any().downcast_ref::<Int32Array>().unwrap().value(0);
        assert_eq!(5, value);

        let slot = array.value(1);
        let value = slot
            .as_any()
            .downcast_ref::<StringArray>()
            .unwrap()
            .value(0);
        assert_eq!("foo", value);

        let slot = array.value(2);
        let value = slot
            .as_any()
            .downcast_ref::<StringArray>()
            .unwrap()
            .value(0);
        assert_eq!("bar", value);

        let slot = array.value(3);
        let value = slot
            .as_any()
            .downcast_ref::<Float64Array>()
            .unwrap()
            .value(0);
        assert_eq!(10.0, value);

        let slot = array.value(4);
        let value = slot
            .as_any()
            .downcast_ref::<StringArray>()
            .unwrap()
            .value(0);
        assert_eq!("baz", value);

        let slot = array.value(5);
        let value = slot.as_any().downcast_ref::<Int32Array>().unwrap().value(0);
        assert_eq!(6, value);
    }

    #[test]
    fn test_sparse_i32() {
        let mut builder = UnionBuilder::new_sparse();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Int32Type>("b", 2).unwrap();
        builder.append::<Int32Type>("c", 3).unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        builder.append::<Int32Type>("c", 5).unwrap();
        builder.append::<Int32Type>("a", 6).unwrap();
        builder.append::<Int32Type>("b", 7).unwrap();
        let union = builder.build().unwrap();

        let expected_type_ids = vec![0_i8, 1, 2, 0, 2, 0, 1];
        let expected_array_values = [1_i32, 2, 3, 4, 5, 6, 7];

        // Check type ids
        assert_eq!(*union.type_ids(), expected_type_ids);
        for (i, id) in expected_type_ids.iter().enumerate() {
            assert_eq!(id, &union.type_id(i));
        }

        // Check offsets, sparse union should only have a single buffer
        assert!(union.offsets().is_none());

        // Check data
        assert_eq!(
            *union.child(0).as_primitive::<Int32Type>().values(),
            [1_i32, 0, 0, 4, 0, 6, 0],
        );
        assert_eq!(
            *union.child(1).as_primitive::<Int32Type>().values(),
            [0_i32, 2_i32, 0, 0, 0, 0, 7]
        );
        assert_eq!(
            *union.child(2).as_primitive::<Int32Type>().values(),
            [0_i32, 0, 3_i32, 0, 5, 0, 0]
        );

        assert_eq!(expected_array_values.len(), union.len());
        for (i, expected_value) in expected_array_values.iter().enumerate() {
            assert!(!union.is_null(i));
            let slot = union.value(i);
            let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
            assert_eq!(slot.len(), 1);
            let value = slot.value(0);
            assert_eq!(expected_value, &value);
        }
    }

    #[test]
    fn test_sparse_mixed() {
        let mut builder = UnionBuilder::new_sparse();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Float64Type>("c", 3.0).unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        builder.append::<Float64Type>("c", 5.0).unwrap();
        builder.append::<Int32Type>("a", 6).unwrap();
        let union = builder.build().unwrap();

        let expected_type_ids = vec![0_i8, 1, 0, 1, 0];

        // Check type ids
        assert_eq!(*union.type_ids(), expected_type_ids);
        for (i, id) in expected_type_ids.iter().enumerate() {
            assert_eq!(id, &union.type_id(i));
        }

        // Check offsets, sparse union should only have a single buffer, i.e. no offsets
        assert!(union.offsets().is_none());

        for i in 0..union.len() {
            let slot = union.value(i);
            assert!(!union.is_null(i));
            match i {
                0 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(1_i32, value);
                }
                1 => {
                    let slot = slot.as_any().downcast_ref::<Float64Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(value, 3_f64);
                }
                2 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(4_i32, value);
                }
                3 => {
                    let slot = slot.as_any().downcast_ref::<Float64Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(5_f64, value);
                }
                4 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(6_i32, value);
                }
                _ => unreachable!(),
            }
        }
    }

    #[test]
    fn test_sparse_mixed_with_nulls() {
        let mut builder = UnionBuilder::new_sparse();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append_null::<Int32Type>("a").unwrap();
        builder.append::<Float64Type>("c", 3.0).unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        let union = builder.build().unwrap();

        let expected_type_ids = vec![0_i8, 0, 1, 0];

        // Check type ids
        assert_eq!(*union.type_ids(), expected_type_ids);
        for (i, id) in expected_type_ids.iter().enumerate() {
            assert_eq!(id, &union.type_id(i));
        }

        // Check offsets, sparse union should only have a single buffer, i.e. no offsets
        assert!(union.offsets().is_none());

        for i in 0..union.len() {
            let slot = union.value(i);
            match i {
                0 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(1_i32, value);
                }
                1 => assert!(slot.is_null(0)),
                2 => {
                    let slot = slot.as_any().downcast_ref::<Float64Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(value, 3_f64);
                }
                3 => {
                    let slot = slot.as_any().downcast_ref::<Int32Array>().unwrap();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(4_i32, value);
                }
                _ => unreachable!(),
            }
        }
    }

    #[test]
    fn test_sparse_mixed_with_nulls_and_offset() {
        let mut builder = UnionBuilder::new_sparse();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append_null::<Int32Type>("a").unwrap();
        builder.append::<Float64Type>("c", 3.0).unwrap();
        builder.append_null::<Float64Type>("c").unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        let union = builder.build().unwrap();

        let slice = union.slice(1, 4);
        let new_union = slice.as_any().downcast_ref::<UnionArray>().unwrap();

        assert_eq!(4, new_union.len());
        for i in 0..new_union.len() {
            let slot = new_union.value(i);
            match i {
                0 => assert!(slot.is_null(0)),
                1 => {
                    let slot = slot.as_primitive::<Float64Type>();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(value, 3_f64);
                }
                2 => assert!(slot.is_null(0)),
                3 => {
                    let slot = slot.as_primitive::<Int32Type>();
                    assert!(!slot.is_null(0));
                    assert_eq!(slot.len(), 1);
                    let value = slot.value(0);
                    assert_eq!(4_i32, value);
                }
                _ => unreachable!(),
            }
        }
    }

    fn test_union_validity(union_array: &UnionArray) {
        assert_eq!(union_array.null_count(), 0);

        for i in 0..union_array.len() {
            assert!(!union_array.is_null(i));
            assert!(union_array.is_valid(i));
        }
    }

    #[test]
    fn test_union_array_validity() {
        let mut builder = UnionBuilder::new_sparse();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append_null::<Int32Type>("a").unwrap();
        builder.append::<Float64Type>("c", 3.0).unwrap();
        builder.append_null::<Float64Type>("c").unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        let union = builder.build().unwrap();

        test_union_validity(&union);

        let mut builder = UnionBuilder::new_dense();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append_null::<Int32Type>("a").unwrap();
        builder.append::<Float64Type>("c", 3.0).unwrap();
        builder.append_null::<Float64Type>("c").unwrap();
        builder.append::<Int32Type>("a", 4).unwrap();
        let union = builder.build().unwrap();

        test_union_validity(&union);
    }

    #[test]
    fn test_type_check() {
        let mut builder = UnionBuilder::new_sparse();
        builder.append::<Float32Type>("a", 1.0).unwrap();
        let err = builder.append::<Int32Type>("a", 1).unwrap_err().to_string();
        assert!(
            err.contains(
                "Attempt to write col \"a\" with type Int32 doesn't match existing type Float32"
            ),
            "{}",
            err
        );
    }

    #[test]
    fn slice_union_array() {
        // [1, null, 3.0, null, 4]
        fn create_union(mut builder: UnionBuilder) -> UnionArray {
            builder.append::<Int32Type>("a", 1).unwrap();
            builder.append_null::<Int32Type>("a").unwrap();
            builder.append::<Float64Type>("c", 3.0).unwrap();
            builder.append_null::<Float64Type>("c").unwrap();
            builder.append::<Int32Type>("a", 4).unwrap();
            builder.build().unwrap()
        }

        fn create_batch(union: UnionArray) -> RecordBatch {
            let schema = Schema::new(vec![Field::new(
                "struct_array",
                union.data_type().clone(),
                true,
            )]);

            RecordBatch::try_new(Arc::new(schema), vec![Arc::new(union)]).unwrap()
        }

        fn test_slice_union(record_batch_slice: RecordBatch) {
            let union_slice = record_batch_slice
                .column(0)
                .as_any()
                .downcast_ref::<UnionArray>()
                .unwrap();

            assert_eq!(union_slice.type_id(0), 0);
            assert_eq!(union_slice.type_id(1), 1);
            assert_eq!(union_slice.type_id(2), 1);

            let slot = union_slice.value(0);
            let array = slot.as_primitive::<Int32Type>();
            assert_eq!(array.len(), 1);
            assert!(array.is_null(0));

            let slot = union_slice.value(1);
            let array = slot.as_primitive::<Float64Type>();
            assert_eq!(array.len(), 1);
            assert!(array.is_valid(0));
            assert_eq!(array.value(0), 3.0);

            let slot = union_slice.value(2);
            let array = slot.as_primitive::<Float64Type>();
            assert_eq!(array.len(), 1);
            assert!(array.is_null(0));
        }

        // Sparse Union
        let builder = UnionBuilder::new_sparse();
        let record_batch = create_batch(create_union(builder));
        // [null, 3.0, null]
        let record_batch_slice = record_batch.slice(1, 3);
        test_slice_union(record_batch_slice);

        // Dense Union
        let builder = UnionBuilder::new_dense();
        let record_batch = create_batch(create_union(builder));
        // [null, 3.0, null]
        let record_batch_slice = record_batch.slice(1, 3);
        test_slice_union(record_batch_slice);
    }

    #[test]
    fn test_custom_type_ids() {
        let data_type = DataType::Union(
            UnionFields::try_new(
                vec![8, 4, 9],
                vec![
                    Field::new("strings", DataType::Utf8, false),
                    Field::new("integers", DataType::Int32, false),
                    Field::new("floats", DataType::Float64, false),
                ],
            )
            .unwrap(),
            UnionMode::Dense,
        );

        let string_array = StringArray::from(vec!["foo", "bar", "baz"]);
        let int_array = Int32Array::from(vec![5, 6, 4]);
        let float_array = Float64Array::from(vec![10.0]);

        let type_ids = Buffer::from_vec(vec![4_i8, 8, 4, 8, 9, 4, 8]);
        let value_offsets = Buffer::from_vec(vec![0_i32, 0, 1, 1, 0, 2, 2]);

        let data = ArrayData::builder(data_type)
            .len(7)
            .buffers(vec![type_ids, value_offsets])
            .child_data(vec![
                string_array.into_data(),
                int_array.into_data(),
                float_array.into_data(),
            ])
            .build()
            .unwrap();

        let array = UnionArray::from(data);

        let v = array.value(0);
        assert_eq!(v.data_type(), &DataType::Int32);
        assert_eq!(v.len(), 1);
        assert_eq!(v.as_primitive::<Int32Type>().value(0), 5);

        let v = array.value(1);
        assert_eq!(v.data_type(), &DataType::Utf8);
        assert_eq!(v.len(), 1);
        assert_eq!(v.as_string::<i32>().value(0), "foo");

        let v = array.value(2);
        assert_eq!(v.data_type(), &DataType::Int32);
        assert_eq!(v.len(), 1);
        assert_eq!(v.as_primitive::<Int32Type>().value(0), 6);

        let v = array.value(3);
        assert_eq!(v.data_type(), &DataType::Utf8);
        assert_eq!(v.len(), 1);
        assert_eq!(v.as_string::<i32>().value(0), "bar");

        let v = array.value(4);
        assert_eq!(v.data_type(), &DataType::Float64);
        assert_eq!(v.len(), 1);
        assert_eq!(v.as_primitive::<Float64Type>().value(0), 10.0);

        let v = array.value(5);
        assert_eq!(v.data_type(), &DataType::Int32);
        assert_eq!(v.len(), 1);
        assert_eq!(v.as_primitive::<Int32Type>().value(0), 4);

        let v = array.value(6);
        assert_eq!(v.data_type(), &DataType::Utf8);
        assert_eq!(v.len(), 1);
        assert_eq!(v.as_string::<i32>().value(0), "baz");
    }

    #[test]
    fn into_parts() {
        let mut builder = UnionBuilder::new_dense();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Int8Type>("b", 2).unwrap();
        builder.append::<Int32Type>("a", 3).unwrap();
        let dense_union = builder.build().unwrap();

        let field = [
            &Arc::new(Field::new("a", DataType::Int32, false)),
            &Arc::new(Field::new("b", DataType::Int8, false)),
        ];
        let (union_fields, type_ids, offsets, children) = dense_union.into_parts();
        assert_eq!(
            union_fields
                .iter()
                .map(|(_, field)| field)
                .collect::<Vec<_>>(),
            field
        );
        assert_eq!(type_ids, [0, 1, 0]);
        assert!(offsets.is_some());
        assert_eq!(offsets.as_ref().unwrap(), &[0, 0, 1]);

        let result = UnionArray::try_new(union_fields, type_ids, offsets, children);
        assert!(result.is_ok());
        assert_eq!(result.unwrap().len(), 3);

        let mut builder = UnionBuilder::new_sparse();
        builder.append::<Int32Type>("a", 1).unwrap();
        builder.append::<Int8Type>("b", 2).unwrap();
        builder.append::<Int32Type>("a", 3).unwrap();
        let sparse_union = builder.build().unwrap();

        let (union_fields, type_ids, offsets, children) = sparse_union.into_parts();
        assert_eq!(type_ids, [0, 1, 0]);
        assert!(offsets.is_none());

        let result = UnionArray::try_new(union_fields, type_ids, offsets, children);
        assert!(result.is_ok());
        assert_eq!(result.unwrap().len(), 3);
    }

    #[test]
    fn into_parts_custom_type_ids() {
        let set_field_type_ids: [i8; 3] = [8, 4, 9];
        let data_type = DataType::Union(
            UnionFields::try_new(
                set_field_type_ids,
                [
                    Field::new("strings", DataType::Utf8, false),
                    Field::new("integers", DataType::Int32, false),
                    Field::new("floats", DataType::Float64, false),
                ],
            )
            .unwrap(),
            UnionMode::Dense,
        );
        let string_array = StringArray::from(vec!["foo", "bar", "baz"]);
        let int_array = Int32Array::from(vec![5, 6, 4]);
        let float_array = Float64Array::from(vec![10.0]);
        let type_ids = Buffer::from_vec(vec![4_i8, 8, 4, 8, 9, 4, 8]);
        let value_offsets = Buffer::from_vec(vec![0_i32, 0, 1, 1, 0, 2, 2]);
        let data = ArrayData::builder(data_type)
            .len(7)
            .buffers(vec![type_ids, value_offsets])
            .child_data(vec![
                string_array.into_data(),
                int_array.into_data(),
                float_array.into_data(),
            ])
            .build()
            .unwrap();
        let array = UnionArray::from(data);

        let (union_fields, type_ids, offsets, children) = array.into_parts();
        assert_eq!(
            type_ids.iter().collect::<HashSet<_>>(),
            set_field_type_ids.iter().collect::<HashSet<_>>()
        );
        let result = UnionArray::try_new(union_fields, type_ids, offsets, children);
        assert!(result.is_ok());
        let array = result.unwrap();
        assert_eq!(array.len(), 7);
    }

    #[test]
    fn test_dense_union_large_child() {
        let fields =
            UnionFields::try_new([3], [Field::new("nulls", DataType::Null, true)]).unwrap();

        // NullArray represents these lengths without allocating a values buffer.
        for child_len in [i32::MAX as usize + 1, i32::MAX as usize + 2] {
            let array = UnionArray::try_new(
                fields.clone(),
                vec![3, 3].into(),
                Some(vec![0, i32::MAX].into()),
                vec![Arc::new(NullArray::new(child_len))],
            )
            .unwrap();

            assert_eq!(array.child(3).len(), child_len);
            assert_eq!(array.value(1).len(), 1);
            array.to_data().validate_full().unwrap();
        }
    }

    #[test]
    fn test_invalid() {
        let fields = UnionFields::try_new(
            [3, 2],
            [
                Field::new("a", DataType::Utf8, false),
                Field::new("b", DataType::Utf8, false),
            ],
        )
        .unwrap();
        let children = vec![
            Arc::new(StringArray::from_iter_values(["a", "b"])) as _,
            Arc::new(StringArray::from_iter_values(["c", "d"])) as _,
        ];

        let type_ids = vec![3, 3, 2].into();
        let err =
            UnionArray::try_new(fields.clone(), type_ids, None, children.clone()).unwrap_err();
        assert_eq!(
            err.to_string(),
            "Invalid argument error: Sparse union child arrays must be equal in length to the length of the union"
        );

        let type_ids = vec![1, 2].into();
        let err =
            UnionArray::try_new(fields.clone(), type_ids, None, children.clone()).unwrap_err();
        assert_eq!(
            err.to_string(),
            "Invalid argument error: Type Ids values must match one of the field type ids"
        );

        let type_ids = vec![7, 2].into();
        let err = UnionArray::try_new(fields.clone(), type_ids, None, children).unwrap_err();
        assert_eq!(
            err.to_string(),
            "Invalid argument error: Type Ids values must match one of the field type ids"
        );

        let children = vec![
            Arc::new(StringArray::from_iter_values(["a", "b"])) as _,
            Arc::new(StringArray::from_iter_values(["c"])) as _,
        ];
        let type_ids = ScalarBuffer::from(vec![3_i8, 3, 2]);
        let offsets = Some(vec![0, 1, 0].into());
        UnionArray::try_new(fields.clone(), type_ids.clone(), offsets, children.clone()).unwrap();

        let offsets = Some(vec![0, 1, 1].into());
        let err = UnionArray::try_new(fields.clone(), type_ids.clone(), offsets, children.clone())
            .unwrap_err();

        assert_eq!(
            err.to_string(),
            "Invalid argument error: Offsets must be non-negative and within the length of the Array"
        );

        let offsets = Some(vec![0, -1, 0].into());
        let err = UnionArray::try_new(fields.clone(), type_ids.clone(), offsets, children.clone())
            .unwrap_err();

        assert_eq!(
            err.to_string(),
            "Invalid argument error: Offsets must be non-negative and within the length of the Array"
        );

        let offsets = Some(vec![0, 1].into());
        let err =
            UnionArray::try_new(fields.clone(), type_ids.clone(), offsets, children).unwrap_err();

        assert_eq!(
            err.to_string(),
            "Invalid argument error: Type Ids and Offsets lengths must match"
        );

        let err = UnionArray::try_new(fields.clone(), type_ids, None, vec![]).unwrap_err();

        assert_eq!(
            err.to_string(),
            "Invalid argument error: Union fields length must match child arrays length"
        );
    }

    #[test]
    fn test_logical_nulls_fast_paths() {
        // fields.len() <= 1
        let array = UnionArray::try_new(UnionFields::empty(), vec![].into(), None, vec![]).unwrap();

        assert_eq!(array.logical_nulls(), None);

        let fields = UnionFields::try_new(
            [1, 3],
            [
                Field::new("a", DataType::Int8, false), // non nullable
                Field::new("b", DataType::Int8, false), // non nullable
            ],
        )
        .unwrap();
        let array = UnionArray::try_new(
            fields,
            vec![1].into(),
            None,
            vec![
                Arc::new(Int8Array::from_value(5, 1)),
                Arc::new(Int8Array::from_value(5, 1)),
            ],
        )
        .unwrap();

        assert_eq!(array.logical_nulls(), None);

        let nullable_fields = UnionFields::try_new(
            [1, 3],
            [
                Field::new("a", DataType::Int8, true), // nullable but without nulls
                Field::new("b", DataType::Int8, true), // nullable but without nulls
            ],
        )
        .unwrap();
        let array = UnionArray::try_new(
            nullable_fields.clone(),
            vec![1, 1].into(),
            None,
            vec![
                Arc::new(Int8Array::from_value(-5, 2)), // nullable but without nulls
                Arc::new(Int8Array::from_value(-5, 2)), // nullable but without nulls
            ],
        )
        .unwrap();

        assert_eq!(array.logical_nulls(), None);

        let array = UnionArray::try_new(
            nullable_fields.clone(),
            vec![1, 1].into(),
            None,
            vec![
                // every child is completely null
                Arc::new(Int8Array::new_null(2)), // all null, same len as it's parent
                Arc::new(Int8Array::new_null(2)), // all null, same len as it's parent
            ],
        )
        .unwrap();

        assert_eq!(array.logical_nulls(), Some(NullBuffer::new_null(2)));

        let array = UnionArray::try_new(
            nullable_fields.clone(),
            vec![1, 1].into(),
            Some(vec![0, 1].into()),
            vec![
                // every child is completely null
                Arc::new(Int8Array::new_null(3)), // bigger that parent
                Arc::new(Int8Array::new_null(3)), // bigger that parent
            ],
        )
        .unwrap();

        assert_eq!(array.logical_nulls(), Some(NullBuffer::new_null(2)));
    }

    #[test]
    fn test_dense_union_logical_nulls_gather() {
        // union of [{A=1}, {A=2}, {B=3.2}, {B=}, {C=}, {C=}]
        let int_array = Int32Array::from(vec![1, 2]);
        let float_array = Float64Array::from(vec![Some(3.2), None]);
        let str_array = StringArray::new_null(1);
        let type_ids = [1, 1, 3, 3, 4, 4].into_iter().collect::<ScalarBuffer<i8>>();
        let offsets = [0, 1, 0, 1, 0, 0]
            .into_iter()
            .collect::<ScalarBuffer<i32>>();

        let children = vec![
            Arc::new(int_array) as Arc<dyn Array>,
            Arc::new(float_array),
            Arc::new(str_array),
        ];

        let array = UnionArray::try_new(union_fields(), type_ids, Some(offsets), children).unwrap();

        let expected = BooleanBuffer::from(vec![true, true, true, false, false, false]);

        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(expected, array.gather_nulls(array.fields_logical_nulls()));
    }

    #[test]
    fn test_sparse_union_logical_nulls_mask_all_nulls_skip_one() {
        let fields: UnionFields = [
            (1, Arc::new(Field::new("A", DataType::Int32, true))),
            (3, Arc::new(Field::new("B", DataType::Float64, true))),
        ]
        .into_iter()
        .collect();

        // union of [{A=}, {A=}, {B=3.2}, {B=}]
        let int_array = Int32Array::new_null(4);
        let float_array = Float64Array::from(vec![None, None, Some(3.2), None]);
        let type_ids = [1, 1, 3, 3].into_iter().collect::<ScalarBuffer<i8>>();

        let children = vec![Arc::new(int_array) as Arc<dyn Array>, Arc::new(float_array)];

        let array = UnionArray::try_new(fields.clone(), type_ids, None, children).unwrap();

        let expected = BooleanBuffer::from(vec![false, false, true, false]);

        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(
            expected,
            array.mask_sparse_all_with_nulls_skip_one(array.fields_logical_nulls())
        );

        //like above, but repeated to generate two exact bitmasks and a non empty remainder
        let len = 2 * 64 + 32;

        let int_array = Int32Array::new_null(len);
        let float_array = Float64Array::from_iter([Some(3.2), None].into_iter().cycle().take(len));
        let type_ids = ScalarBuffer::from_iter([1, 1, 3, 3].into_iter().cycle().take(len));

        let array = UnionArray::try_new(
            fields,
            type_ids,
            None,
            vec![Arc::new(int_array), Arc::new(float_array)],
        )
        .unwrap();

        let expected =
            BooleanBuffer::from_iter([false, false, true, false].into_iter().cycle().take(len));

        assert_eq!(array.len(), len);
        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(
            expected,
            array.mask_sparse_all_with_nulls_skip_one(array.fields_logical_nulls())
        );
    }

    #[test]
    fn test_sparse_union_logical_mask_mixed_nulls_skip_fully_valid() {
        // union of [{A=2}, {A=2}, {B=3.2}, {B=}, {C=}, {C=}]
        let int_array = Int32Array::from_value(2, 6);
        let float_array = Float64Array::from_value(4.2, 6);
        let str_array = StringArray::new_null(6);
        let type_ids = [1, 1, 3, 3, 4, 4].into_iter().collect::<ScalarBuffer<i8>>();

        let children = vec![
            Arc::new(int_array) as Arc<dyn Array>,
            Arc::new(float_array),
            Arc::new(str_array),
        ];

        let array = UnionArray::try_new(union_fields(), type_ids, None, children).unwrap();

        let expected = BooleanBuffer::from(vec![true, true, true, true, false, false]);

        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(
            expected,
            array.mask_sparse_skip_without_nulls(array.fields_logical_nulls())
        );

        //like above, but repeated to generate two exact bitmasks and a non empty remainder
        let len = 2 * 64 + 32;

        let int_array = Int32Array::from_value(2, len);
        let float_array = Float64Array::from_value(4.2, len);
        let str_array = StringArray::from_iter([None, Some("a")].into_iter().cycle().take(len));
        let type_ids = ScalarBuffer::from_iter([1, 1, 3, 3, 4, 4].into_iter().cycle().take(len));

        let children = vec![
            Arc::new(int_array) as Arc<dyn Array>,
            Arc::new(float_array),
            Arc::new(str_array),
        ];

        let array = UnionArray::try_new(union_fields(), type_ids, None, children).unwrap();

        let expected = BooleanBuffer::from_iter(
            [true, true, true, true, false, true]
                .into_iter()
                .cycle()
                .take(len),
        );

        assert_eq!(array.len(), len);
        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(
            expected,
            array.mask_sparse_skip_without_nulls(array.fields_logical_nulls())
        );
    }

    #[test]
    fn test_sparse_union_logical_mask_mixed_nulls_skip_fully_null() {
        // union of [{A=}, {A=}, {B=4.2}, {B=4.2}, {C=}, {C=}]
        let int_array = Int32Array::new_null(6);
        let float_array = Float64Array::from_value(4.2, 6);
        let str_array = StringArray::new_null(6);
        let type_ids = [1, 1, 3, 3, 4, 4].into_iter().collect::<ScalarBuffer<i8>>();

        let children = vec![
            Arc::new(int_array) as Arc<dyn Array>,
            Arc::new(float_array),
            Arc::new(str_array),
        ];

        let array = UnionArray::try_new(union_fields(), type_ids, None, children).unwrap();

        let expected = BooleanBuffer::from(vec![false, false, true, true, false, false]);

        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(
            expected,
            array.mask_sparse_skip_fully_null(array.fields_logical_nulls())
        );

        //like above, but repeated to generate two exact bitmasks and a non empty remainder
        let len = 2 * 64 + 32;

        let int_array = Int32Array::new_null(len);
        let float_array = Float64Array::from_value(4.2, len);
        let str_array = StringArray::new_null(len);
        let type_ids = ScalarBuffer::from_iter([1, 1, 3, 3, 4, 4].into_iter().cycle().take(len));

        let children = vec![
            Arc::new(int_array) as Arc<dyn Array>,
            Arc::new(float_array),
            Arc::new(str_array),
        ];

        let array = UnionArray::try_new(union_fields(), type_ids, None, children).unwrap();

        let expected = BooleanBuffer::from_iter(
            [false, false, true, true, false, false]
                .into_iter()
                .cycle()
                .take(len),
        );

        assert_eq!(array.len(), len);
        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(
            expected,
            array.mask_sparse_skip_fully_null(array.fields_logical_nulls())
        );
    }

    #[test]
    fn test_sparse_union_logical_nulls_gather() {
        let n_fields = 50;

        let non_null = Int32Array::from_value(2, 4);
        let mixed = Int32Array::from(vec![None, None, Some(1), None]);
        let fully_null = Int32Array::new_null(4);

        let array = UnionArray::try_new(
            (1..)
                .step_by(2)
                .map(|i| {
                    (
                        i,
                        Arc::new(Field::new(format!("f{i}"), DataType::Int32, true)),
                    )
                })
                .take(n_fields)
                .collect(),
            vec![1, 3, 3, 5].into(),
            None,
            [
                Arc::new(non_null) as ArrayRef,
                Arc::new(mixed),
                Arc::new(fully_null),
            ]
            .into_iter()
            .cycle()
            .take(n_fields)
            .collect(),
        )
        .unwrap();

        let expected = BooleanBuffer::from(vec![true, false, true, false]);

        assert_eq!(expected, array.logical_nulls().unwrap().into_inner());
        assert_eq!(expected, array.gather_nulls(array.fields_logical_nulls()));
    }

    fn union_fields() -> UnionFields {
        [
            (1, Arc::new(Field::new("A", DataType::Int32, true))),
            (3, Arc::new(Field::new("B", DataType::Float64, true))),
            (4, Arc::new(Field::new("C", DataType::Utf8, true))),
        ]
        .into_iter()
        .collect()
    }

    #[test]
    fn test_is_nullable() {
        assert!(!create_union_array(false, false).is_nullable());
        assert!(create_union_array(true, false).is_nullable());
        assert!(create_union_array(false, true).is_nullable());
        assert!(create_union_array(true, true).is_nullable());
    }

    /// Create a union array with a float and integer field
    ///
    /// If the `int_nullable` is true, the integer field will have nulls
    /// If the `float_nullable` is true, the float field will have nulls
    ///
    /// Note the `Field` definitions are always declared to be nullable
    fn create_union_array(int_nullable: bool, float_nullable: bool) -> UnionArray {
        let int_array = if int_nullable {
            Int32Array::from(vec![Some(1), None, Some(3)])
        } else {
            Int32Array::from(vec![1, 2, 3])
        };
        let float_array = if float_nullable {
            Float64Array::from(vec![Some(3.2), None, Some(4.2)])
        } else {
            Float64Array::from(vec![3.2, 4.2, 5.2])
        };
        let type_ids = [0, 1, 0].into_iter().collect::<ScalarBuffer<i8>>();
        let offsets = [0, 0, 0].into_iter().collect::<ScalarBuffer<i32>>();
        let union_fields = [
            (0, Arc::new(Field::new("A", DataType::Int32, true))),
            (1, Arc::new(Field::new("B", DataType::Float64, true))),
        ]
        .into_iter()
        .collect::<UnionFields>();

        let children = vec![Arc::new(int_array) as Arc<dyn Array>, Arc::new(float_array)];

        UnionArray::try_new(union_fields, type_ids, Some(offsets), children).unwrap()
    }
}