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use vortex_array::aliases::hash_set::HashSet;
use vortex_array::array::PrimitiveEncoding;
use vortex_array::encoding::{Encoding, EncodingRef};
use vortex_array::stats::ArrayStatistics;
use vortex_array::{ArrayData, IntoArrayData, IntoArrayVariant};
use vortex_error::VortexResult;
use vortex_runend::compress::runend_encode;
use vortex_runend::{RunEndArray, RunEndEncoding};

use crate::compressors::{CompressedArray, CompressionTree, EncodingCompressor};
use crate::downscale::downscale_integer_array;
use crate::{constants, SamplingCompressor};

pub const DEFAULT_RUN_END_COMPRESSOR: RunEndCompressor = RunEndCompressor { ree_threshold: 2.0 };

#[derive(Debug, Clone, Copy)]
pub struct RunEndCompressor {
    ree_threshold: f32,
}

impl EncodingCompressor for RunEndCompressor {
    fn id(&self) -> &str {
        RunEndEncoding::ID.as_ref()
    }

    fn cost(&self) -> u8 {
        constants::RUN_END_COST
    }

    fn can_compress(&self, array: &ArrayData) -> Option<&dyn EncodingCompressor> {
        if !array.is_encoding(PrimitiveEncoding::ID) {
            return None;
        }

        let avg_run_length = array.len() as f32
            / array
                .statistics()
                .compute_run_count()
                .unwrap_or(array.len()) as f32;
        if avg_run_length < self.ree_threshold {
            return None;
        }

        Some(self)
    }

    fn compress<'a>(
        &'a self,
        array: &ArrayData,
        like: Option<CompressionTree<'a>>,
        ctx: SamplingCompressor<'a>,
    ) -> VortexResult<CompressedArray<'a>> {
        let primitive_array = array.clone().into_primitive()?;
        let (ends, values) = runend_encode(&primitive_array)?;
        let ends = downscale_integer_array(ends.into_array())?.into_primitive()?;

        let compressed_ends = ctx
            .auxiliary("ends")
            .compress(&ends.into_array(), like.as_ref().and_then(|l| l.child(0)))?;
        let compressed_values = ctx
            .named("values")
            .excluding(self)
            .compress(&values, like.as_ref().and_then(|l| l.child(1)))?;

        Ok(CompressedArray::compressed(
            RunEndArray::try_new(compressed_ends.array, compressed_values.array)
                .map(|a| a.into_array())?,
            Some(CompressionTree::new(
                self,
                vec![compressed_ends.path, compressed_values.path],
            )),
            array,
        ))
    }

    fn used_encodings(&self) -> HashSet<EncodingRef> {
        HashSet::from([&RunEndEncoding as EncodingRef])
    }
}