Research-Stack/5-Applications/parquet_compressor/src/shifters/rle.rs

use crate::shifters::{ManifoldState, Shifter};
use serde_json::json;

pub struct RunLengthShifter;

impl Shifter for RunLengthShifter {
    fn name(&self) -> &'static str {
        "run_length"
    }

    fn encode(&self, state: &mut ManifoldState) -> anyhow::Result<()> {
        let data = if !state.encoded.is_empty() {
            &state.encoded
        } else {
            &state.raw_bytes
        };
        let mut result = Vec::new();
        let mut i = 0;
        while i < data.len() {
            let b = data[i];
            let mut count = 1;
            while i + count < data.len() && data[i + count] == b && count < 255 {
                count += 1;
            }
            result.push(count as u8);
            result.push(b);
            i += count;
        }

        let ratio = data.len() as f64 / result.len().max(1) as f64;
        state.update(
            result,
            self.name(),
            json!({"original": data.len(), "ratio": ratio}),
        );
        Ok(())
    }

    fn decode(&self, state: &mut ManifoldState) -> anyhow::Result<()> {
        let data = &state.encoded;
        let mut result = Vec::new();
        for i in (0..data.len()).step_by(2) {
            if i + 1 >= data.len() {
                break;
            }
            let count = data[i] as usize;
            let b = data[i + 1];
            for _ in 0..count {
                result.push(b);
            }
        }
        state.encoded = result;
        Ok(())
    }
}