// 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.

//! Defines kernels suitable to perform operations to primitive arrays.

use crate::array::{Array, ArrayData, PrimitiveArray};
use crate::buffer::Buffer;
use crate::datatypes::ArrowPrimitiveType;

#[inline]
fn into_primitive_array_data<I: ArrowPrimitiveType, O: ArrowPrimitiveType>(
    array: &PrimitiveArray<I>,
    buffer: Buffer,
) -> ArrayData {
    unsafe {
        ArrayData::new_unchecked(
            O::DATA_TYPE,
            array.len(),
            None,
            array
                .data_ref()
                .null_buffer()
                .map(|b| b.bit_slice(array.offset(), array.len())),
            0,
            vec![buffer],
            vec![],
        )
    }
}

/// Applies an unary and infallible function to a primitive array.
/// This is the fastest way to perform an operation on a primitive array when
/// the benefits of a vectorized operation outweights the cost of branching nulls and non-nulls.
/// # Implementation
/// This will apply the function for all values, including those on null slots.
/// This implies that the operation must be infallible for any value of the corresponding type
/// or this function may panic.
/// # Example
/// ```rust
/// # use arrow::array::Int32Array;
/// # use arrow::datatypes::Int32Type;
/// # use arrow::compute::kernels::arity::unary;
/// # fn main() {
/// let array = Int32Array::from(vec![Some(5), Some(7), None]);
/// let c = unary::<_, _, Int32Type>(&array, |x| x * 2 + 1);
/// assert_eq!(c, Int32Array::from(vec![Some(11), Some(15), None]));
/// # }
/// ```
pub fn unary<I, F, O>(array: &PrimitiveArray<I>, op: F) -> PrimitiveArray<O>
where
    I: ArrowPrimitiveType,
    O: ArrowPrimitiveType,
    F: Fn(I::Native) -> O::Native,
{
    let values = array.values().iter().map(|v| op(*v));
    // JUSTIFICATION
    //  Benefit
    //      ~60% speedup
    //  Soundness
    //      `values` is an iterator with a known size because arrays are sized.
    let buffer = unsafe { Buffer::from_trusted_len_iter(values) };

    let data = into_primitive_array_data::<_, O>(array, buffer);
    PrimitiveArray::<O>::from(data)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::array::{as_primitive_array, Float64Array};

    #[test]
    fn test_unary_f64_slice() {
        let input =
            Float64Array::from(vec![Some(5.1f64), None, Some(6.8), None, Some(7.2)]);
        let input_slice = input.slice(1, 4);
        let input_slice: &Float64Array = as_primitive_array(&input_slice);
        let result = unary(input_slice, |n| n.round());
        assert_eq!(
            result,
            Float64Array::from(vec![None, Some(7.0), None, Some(7.0)])
        )
    }
}
