flatten.rs

use arrow::bitmap::MutableBitmap;
use polars_utils::sync::SyncPtr;

use super::*;

pub fn flatten_df_iter(df: &DataFrame) -> impl Iterator<Item = DataFrame> + '_ {
    df.iter_chunks_physical().flat_map(|chunk| {
        let columns = df
            .iter()
            .zip(chunk.into_arrays())
            .map(|(s, arr)| {
                // SAFETY:
                // datatypes are correct
                let mut out = unsafe {
                    Series::from_chunks_and_dtype_unchecked(s.name().clone(), vec![arr], s.dtype())
                };
                out.set_sorted_flag(s.is_sorted_flag());
                Column::from(out)
            })
            .collect::<Vec<_>>();

        let height = DataFrame::infer_height(&columns);
        let df = unsafe { DataFrame::new_no_checks(height, columns) };
        if df.is_empty() { None } else { Some(df) }
    })
}

pub fn flatten_series(s: &Series) -> Vec<Series> {
    let name = s.name();
    let dtype = s.dtype();
    unsafe {
        s.chunks()
            .iter()
            .map(|arr| {
                Series::from_chunks_and_dtype_unchecked(name.clone(), vec![arr.clone()], dtype)
            })
            .collect()
    }
}

pub fn cap_and_offsets<I>(v: &[Vec<I>]) -> (usize, Vec<usize>) {
    let cap = v.iter().map(|v| v.len()).sum::<usize>();
    let offsets = v
        .iter()
        .scan(0_usize, |acc, v| {
            let out = *acc;
            *acc += v.len();
            Some(out)
        })
        .collect::<Vec<_>>();
    (cap, offsets)
}

pub fn flatten_par<T: Send + Sync + Copy, S: AsRef<[T]>>(bufs: &[S]) -> Vec<T> {
    let mut len = 0;
    let mut offsets = Vec::with_capacity(bufs.len());
    let bufs = bufs
        .iter()
        .map(|s| {
            offsets.push(len);
            let slice = s.as_ref();
            len += slice.len();
            slice
        })
        .collect::<Vec<_>>();
    flatten_par_impl(&bufs, len, offsets)
}

fn flatten_par_impl<T: Send + Sync + Copy>(
    bufs: &[&[T]],
    len: usize,
    offsets: Vec<usize>,
) -> Vec<T> {
    let mut out = Vec::with_capacity(len);
    let out_ptr = unsafe { SyncPtr::new(out.as_mut_ptr()) };

    POOL.install(|| {
        offsets.into_par_iter().enumerate().for_each(|(i, offset)| {
            let buf = bufs[i];
            let ptr: *mut T = out_ptr.get();
            unsafe {
                let dst = ptr.add(offset);
                let src = buf.as_ptr();
                std::ptr::copy_nonoverlapping(src, dst, buf.len())
            }
        })
    });
    unsafe {
        out.set_len(len);
    }
    out
}

pub fn flatten_nullable<S: AsRef<[NullableIdxSize]> + Send + Sync>(
    bufs: &[S],
) -> PrimitiveArray<IdxSize> {
    let a = || flatten_par(bufs);
    let b = || {
        let cap = bufs.iter().map(|s| s.as_ref().len()).sum::<usize>();
        let mut validity = MutableBitmap::with_capacity(cap);
        validity.extend_constant(cap, true);

        let mut count = 0usize;
        for s in bufs {
            let s = s.as_ref();

            for id in s {
                if id.is_null_idx() {
                    unsafe { validity.set_unchecked(count, false) };
                }

                count += 1;
            }
        }
        validity.freeze()
    };

    let (a, b) = POOL.join(a, b);
    PrimitiveArray::from_vec(bytemuck::cast_vec::<_, IdxSize>(a)).with_validity(Some(b))
}