oxirs_vec/

storage_optimizations.rs

//! Storage optimizations for vector indices
//!
//! This module provides optimized storage formats for efficient vector serialization:
//! - Binary formats for fast I/O
//! - Compression with multiple algorithms
//! - Streaming I/O for large datasets
//! - Memory-mapped file support

use crate::Vector;
use anyhow::{anyhow, Result};
use oxicode::{Decode, Encode};
use serde::{Deserialize, Serialize};
use std::fs::File;
use std::io::{BufReader, BufWriter, Read, Seek, SeekFrom, Write};
use std::path::Path;

/// Returns an oxicode configuration with fixed-int encoding.
/// This ensures header sizes are consistent regardless of the values stored.
fn bincode_config() -> oxicode::config::Configuration<
    oxicode::config::LittleEndian,
    oxicode::config::Fixint,
    oxicode::config::NoLimit,
> {
    oxicode::config::standard().with_fixed_int_encoding()
}

/// Compression methods for vector storage
#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize, Encode, Decode)]
pub enum CompressionType {
    /// No compression
    None,
    /// LZ4 fast compression
    Lz4,
    /// Zstandard balanced compression
    Zstd,
    /// Brotli high compression
    Brotli,
    /// Gzip standard compression
    Gzip,
    /// Custom vector quantization compression
    VectorQuantization,
}

/// Compress raw bytes with the given algorithm via OxiARC's Pure Rust
/// compression crates (COOLJAPAN compression policy: oxiarc-* only, never
/// flate2/zstd/zip/lz4/brotli/snap/tar from crates.io).
///
/// `level` is a generic 0-9 dial; it is remapped per algorithm (Zstd 1-22,
/// Brotli quality 0-11, Gzip 0-9, LZ4 uses its default fast mode).
///
/// [`CompressionType::VectorQuantization`] is not a general-purpose byte
/// compressor (it would require training a codebook over the *vectors*, not
/// raw bytes) and is intentionally left unimplemented here: it fails loudly
/// instead of silently returning uncompressed data.
pub fn compress_bytes(data: &[u8], compression: CompressionType, level: u8) -> Result<Vec<u8>> {
    match compression {
        CompressionType::None => Ok(data.to_vec()),
        CompressionType::Lz4 => {
            oxiarc_lz4::compress_bytes(data).map_err(|e| anyhow!("LZ4 compression failed: {e}"))
        }
        CompressionType::Zstd => {
            let zstd_level = (level as i32 * 2).clamp(1, 22);
            oxiarc_zstd::compress_with_level(data, zstd_level)
                .map_err(|e| anyhow!("Zstd compression failed: {e}"))
        }
        CompressionType::Brotli => {
            let quality = (level as u32).min(11);
            oxiarc_brotli::compress(data, quality)
                .map_err(|e| anyhow!("Brotli compression failed: {e}"))
        }
        CompressionType::Gzip => oxiarc_deflate::gzip_compress(data, level.min(9))
            .map_err(|e| anyhow!("Gzip compression failed: {e}")),
        CompressionType::VectorQuantization => Err(anyhow!(
            "CompressionType::VectorQuantization is not implemented as a raw-byte \
             compressor; use CompressionType::None or a real byte codec \
             (Lz4/Zstd/Brotli/Gzip) instead of silently storing uncompressed data"
        )),
    }
}

/// Decompress bytes previously produced by [`compress_bytes`] with the same
/// `compression` algorithm.
///
/// `original_size` (the uncompressed length) is required for LZ4: its raw
/// block format carries no length trailer of its own. Other algorithms are
/// self-describing and ignore this parameter.
pub fn decompress_bytes(
    data: &[u8],
    compression: CompressionType,
    original_size: usize,
) -> Result<Vec<u8>> {
    match compression {
        CompressionType::None => Ok(data.to_vec()),
        CompressionType::Lz4 => oxiarc_lz4::decompress_bytes(data, original_size)
            .map_err(|e| anyhow!("LZ4 decompression failed: {e}")),
        CompressionType::Zstd => {
            oxiarc_zstd::decompress(data).map_err(|e| anyhow!("Zstd decompression failed: {e}"))
        }
        CompressionType::Brotli => {
            oxiarc_brotli::decompress(data).map_err(|e| anyhow!("Brotli decompression failed: {e}"))
        }
        CompressionType::Gzip => oxiarc_deflate::gzip_decompress(data)
            .map_err(|e| anyhow!("Gzip decompression failed: {e}")),
        CompressionType::VectorQuantization => Err(anyhow!(
            "CompressionType::VectorQuantization is not implemented as a raw-byte \
             compressor"
        )),
    }
}

/// Binary storage format configuration
#[derive(Debug, Clone, Serialize, Deserialize, Encode, Decode)]
pub struct StorageConfig {
    /// Compression type to use
    pub compression: CompressionType,
    /// Compression level (0-9, algorithm dependent)
    pub compression_level: u8,
    /// Buffer size for streaming operations
    pub buffer_size: usize,
    /// Enable memory mapping for large files
    pub enable_mmap: bool,
    /// Block size for chunked reading/writing
    pub block_size: usize,
    /// Enable checksums for data integrity
    pub enable_checksums: bool,
    /// Metadata format version
    pub format_version: u32,
}

impl Default for StorageConfig {
    fn default() -> Self {
        Self {
            compression: CompressionType::Zstd,
            compression_level: 3,
            buffer_size: 1024 * 1024, // 1MB
            enable_mmap: true,
            block_size: 64 * 1024, // 64KB
            enable_checksums: true,
            format_version: 1,
        }
    }
}

/// Binary file header for vector storage
#[derive(Debug, Clone, Serialize, Deserialize, Encode, Decode)]
pub struct VectorFileHeader {
    /// Magic number for file format identification
    pub magic: [u8; 8],
    /// Format version
    pub version: u32,
    /// Number of vectors in file
    pub vector_count: u64,
    /// Vector dimensions
    pub dimensions: usize,
    /// Compression type used
    pub compression: CompressionType,
    /// Compression level
    pub compression_level: u8,
    /// Block size for chunked data
    pub block_size: usize,
    /// Checksum of header
    pub header_checksum: u32,
    /// Offset to vector data
    pub data_offset: u64,
    /// Total data size (compressed)
    pub data_size: u64,
    /// Original data size (uncompressed)
    pub original_size: u64,
    /// Reserved bytes for future use
    pub reserved: [u8; 32],
}

impl Default for VectorFileHeader {
    fn default() -> Self {
        Self {
            magic: *b"OXIRSVEC",
            version: 1,
            vector_count: 0,
            dimensions: 0,
            compression: CompressionType::None,
            compression_level: 0,
            block_size: 64 * 1024,
            header_checksum: 0,
            data_offset: 0,
            data_size: 0,
            original_size: 0,
            reserved: [0; 32],
        }
    }
}

impl VectorFileHeader {
    /// Calculate and set header checksum
    pub fn calculate_checksum(&mut self) {
        // Simple CRC32-like checksum
        let mut checksum = 0u32;
        checksum ^=
            u32::from_le_bytes([self.magic[0], self.magic[1], self.magic[2], self.magic[3]]);
        checksum ^=
            u32::from_le_bytes([self.magic[4], self.magic[5], self.magic[6], self.magic[7]]);
        checksum ^= self.version;
        checksum ^= self.vector_count as u32;
        checksum ^= self.dimensions as u32;
        checksum ^= self.compression as u8 as u32;
        checksum ^= self.compression_level as u32;
        self.header_checksum = checksum;
    }

    /// Verify header checksum
    pub fn verify_checksum(&self) -> bool {
        let mut temp_header = self.clone();
        temp_header.header_checksum = 0;
        temp_header.calculate_checksum();
        temp_header.header_checksum == self.header_checksum
    }
}

/// Vector block for chunked storage
#[derive(Debug, Clone)]
pub struct VectorBlock {
    /// Block index
    pub block_id: u32,
    /// Number of vectors in this block
    pub vector_count: u32,
    /// Compressed data
    pub data: Vec<u8>,
    /// Original size before compression
    pub original_size: u32,
    /// Block checksum
    pub checksum: u32,
}

/// Streaming vector writer for large datasets
pub struct VectorWriter {
    writer: BufWriter<File>,
    config: StorageConfig,
    header: VectorFileHeader,
    current_block: Vec<Vector>,
    blocks_written: u32,
    total_vectors: u64,
}

impl VectorWriter {
    /// Create a new vector writer
    pub fn new<P: AsRef<Path>>(path: P, config: StorageConfig) -> Result<Self> {
        let file = File::create(path)?;
        let mut writer = BufWriter::new(file);

        let header = VectorFileHeader {
            compression: config.compression,
            compression_level: config.compression_level,
            block_size: config.block_size,
            ..Default::default()
        };

        // Write a placeholder header first to reserve space
        let placeholder_header_bytes = oxicode::serde::encode_to_vec(&header, bincode_config())
            .map_err(|e| anyhow!("Failed to serialize placeholder header: {}", e))?;
        let _header_size = (4 + placeholder_header_bytes.len()) as u64;

        // Write placeholder header size and header
        writer.write_all(&(placeholder_header_bytes.len() as u32).to_le_bytes())?;
        writer.write_all(&placeholder_header_bytes)?;
        writer.flush()?;

        Ok(Self {
            writer,
            config,
            header,
            current_block: Vec::new(),
            blocks_written: 0,
            total_vectors: 0,
        })
    }

    /// Write a vector to the file
    pub fn write_vector(&mut self, vector: Vector) -> Result<()> {
        // Set dimensions from first vector
        if self.header.dimensions == 0 {
            self.header.dimensions = vector.dimensions;
        } else if self.header.dimensions != vector.dimensions {
            return Err(anyhow!(
                "Vector dimension mismatch: expected {}, got {}",
                self.header.dimensions,
                vector.dimensions
            ));
        }

        self.current_block.push(vector);
        self.total_vectors += 1;

        // Check if we need to flush the current block
        let block_size_estimate = self.current_block.len() * self.header.dimensions * 4; // 4 bytes per f32
        if block_size_estimate >= self.config.block_size {
            self.flush_block()?;
        }

        Ok(())
    }

    /// Write multiple vectors
    pub fn write_vectors(&mut self, vectors: &[Vector]) -> Result<()> {
        for vector in vectors {
            self.write_vector(vector.clone())?;
        }
        Ok(())
    }

    /// Flush current block to disk
    fn flush_block(&mut self) -> Result<()> {
        if self.current_block.is_empty() {
            return Ok(());
        }

        // For uncompressed mode, write raw vector data
        if self.config.compression == CompressionType::None {
            for vector in &self.current_block {
                let vector_bytes = vector.as_f32();
                for value in vector_bytes {
                    self.writer.write_all(&value.to_le_bytes())?;
                }
            }
            self.current_block.clear();
            return Ok(());
        }

        // Serialize vectors to binary
        let mut block_data = Vec::new();
        for vector in &self.current_block {
            let vector_bytes = vector.as_f32();
            for value in vector_bytes {
                block_data.extend_from_slice(&value.to_le_bytes());
            }
        }

        // Compress block data
        let compressed_data = self.compress_data(&block_data)?;

        // Create block header
        let block = VectorBlock {
            block_id: self.blocks_written,
            vector_count: self.current_block.len() as u32,
            original_size: block_data.len() as u32,
            checksum: self.calculate_data_checksum(&compressed_data),
            data: compressed_data,
        };

        // Write block to file
        self.write_block(&block)?;

        self.current_block.clear();
        self.blocks_written += 1;

        Ok(())
    }

    /// Compress data using the configured algorithm.
    fn compress_data(&self, data: &[u8]) -> Result<Vec<u8>> {
        compress_bytes(data, self.config.compression, self.config.compression_level)
    }

    /// Calculate checksum for data
    fn calculate_data_checksum(&self, data: &[u8]) -> u32 {
        // Simple checksum - in production use CRC32 or similar
        data.iter().fold(0u32, |acc, &b| acc.wrapping_add(b as u32))
    }

    /// Write block to file
    fn write_block(&mut self, block: &VectorBlock) -> Result<()> {
        // Write block header
        self.writer.write_all(&block.block_id.to_le_bytes())?;
        self.writer.write_all(&block.vector_count.to_le_bytes())?;
        self.writer.write_all(&block.original_size.to_le_bytes())?;
        self.writer.write_all(&block.checksum.to_le_bytes())?;
        self.writer
            .write_all(&(block.data.len() as u32).to_le_bytes())?;

        // Write block data
        self.writer.write_all(&block.data)?;

        Ok(())
    }

    /// Finalize and close the file
    pub fn finalize(mut self) -> Result<()> {
        // Flush any remaining vectors
        self.flush_block()?;

        // Update header with final counts
        self.header.vector_count = self.total_vectors;

        // The data offset is fixed at the position after the placeholder header
        // We need to calculate this the same way it was calculated in new()
        // First, serialize the header with correct vector_count to get actual size
        let mut temp_header = self.header.clone();
        temp_header.calculate_checksum();

        let temp_header_bytes = oxicode::serde::encode_to_vec(&temp_header, bincode_config())
            .map_err(|e| anyhow!("Failed to serialize header for size calculation: {}", e))?;

        // Calculate actual data_offset based on real header size
        self.header.data_offset = 4 + temp_header_bytes.len() as u64;
        self.header.calculate_checksum();

        // Flush before seeking to ensure all data is written
        self.writer.flush()?;

        // Seek to beginning and write header
        self.writer.get_mut().seek(SeekFrom::Start(0))?;

        let header_bytes = oxicode::serde::encode_to_vec(&self.header, bincode_config())
            .map_err(|e| anyhow!("Failed to serialize header: {}", e))?;

        // Write header size first, then header data
        let header_size = header_bytes.len() as u32;
        self.writer.write_all(&header_size.to_le_bytes())?;
        self.writer.write_all(&header_bytes)?;

        // Flush to ensure data is written to file
        self.writer.flush()?;

        // Explicitly drop the writer to close the file
        drop(self.writer);

        Ok(())
    }
}

/// Streaming vector reader for large datasets
pub struct VectorReader {
    reader: BufReader<File>,
    header: VectorFileHeader,
    current_position: u64,
    vectors_read: u64,
}

impl VectorReader {
    /// Open a vector file for reading
    pub fn open<P: AsRef<Path>>(path: P) -> Result<Self> {
        let file = File::open(path)?;
        let mut reader = BufReader::new(file);

        // Read and verify header
        let header = Self::read_header(&mut reader)?;
        let data_offset = header.data_offset;

        // Seek to data offset to position for reading vectors
        reader.get_mut().seek(SeekFrom::Start(data_offset))?;

        Ok(Self {
            reader,
            header,
            current_position: data_offset,
            vectors_read: 0,
        })
    }

    /// Read file header
    fn read_header(reader: &mut BufReader<File>) -> Result<VectorFileHeader> {
        // Read header size first
        let mut size_bytes = [0u8; 4];
        reader.read_exact(&mut size_bytes)?;
        let header_size = u32::from_le_bytes(size_bytes) as usize;

        // Read header data of exact size
        let mut header_data = vec![0u8; header_size];
        reader.read_exact(&mut header_data)?;

        let (header, _): (VectorFileHeader, _) =
            oxicode::serde::decode_from_slice(&header_data, bincode_config())
                .map_err(|e| anyhow!("Failed to deserialize header: {}", e))?;

        // Verify magic number
        if &header.magic != b"OXIRSVEC" {
            return Err(anyhow!("Invalid file format: magic number mismatch"));
        }

        // Verify checksum
        if !header.verify_checksum() {
            return Err(anyhow!("Header checksum verification failed"));
        }

        Ok(header)
    }

    /// Get file metadata
    pub fn metadata(&self) -> &VectorFileHeader {
        &self.header
    }

    /// Read next vector from file
    pub fn read_vector(&mut self) -> Result<Option<Vector>> {
        if self.vectors_read >= self.header.vector_count {
            return Ok(None);
        }

        // For simplicity, reading one vector at a time
        // In production, implement block-wise reading for efficiency
        let mut vector_data = vec![0f32; self.header.dimensions];

        for vector_item in vector_data.iter_mut().take(self.header.dimensions) {
            let mut bytes = [0u8; 4];
            self.reader.read_exact(&mut bytes)?;
            *vector_item = f32::from_le_bytes(bytes);
        }

        self.vectors_read += 1;
        self.current_position += (self.header.dimensions * 4) as u64;
        Ok(Some(Vector::new(vector_data)))
    }

    /// Read multiple vectors
    pub fn read_vectors(&mut self, count: usize) -> Result<Vec<Vector>> {
        let mut vectors = Vec::with_capacity(count);

        for _ in 0..count {
            if let Some(vector) = self.read_vector()? {
                vectors.push(vector);
            } else {
                break;
            }
        }

        Ok(vectors)
    }

    /// Read all remaining vectors
    pub fn read_all(&mut self) -> Result<Vec<Vector>> {
        let remaining = (self.header.vector_count - self.vectors_read) as usize;
        self.read_vectors(remaining)
    }

    /// Skip to specific vector index
    pub fn seek_to_vector(&mut self, index: u64) -> Result<()> {
        if index >= self.header.vector_count {
            return Err(anyhow!("Vector index {} out of bounds", index));
        }

        let byte_offset = self.header.data_offset + (index * self.header.dimensions as u64 * 4);
        self.reader.get_mut().seek(SeekFrom::Start(byte_offset))?;
        self.vectors_read = index;

        Ok(())
    }
}

/// Memory-mapped vector file for efficient random access
pub struct MmapVectorFile {
    _file: File,
    mmap: memmap2::Mmap,
    header: VectorFileHeader,
}

impl MmapVectorFile {
    /// Open file with memory mapping
    pub fn open<P: AsRef<Path>>(path: P) -> Result<Self> {
        let file = File::open(path)?;
        let mmap = unsafe { memmap2::Mmap::map(&file)? };

        // Read header size (first 4 bytes) and then header from memory map
        if mmap.len() < 4 {
            return Err(anyhow!("File too small to contain header"));
        }
        let header_size = u32::from_le_bytes([mmap[0], mmap[1], mmap[2], mmap[3]]) as usize;
        if mmap.len() < 4 + header_size {
            return Err(anyhow!("File too small to contain full header"));
        }
        let header_bytes = &mmap[4..4 + header_size];
        let (header, _): (VectorFileHeader, _) =
            oxicode::serde::decode_from_slice(header_bytes, bincode_config())
                .map_err(|e| anyhow!("Failed to deserialize header: {}", e))?;

        // Verify header
        if &header.magic != b"OXIRSVEC" {
            return Err(anyhow!("Invalid file format"));
        }

        if !header.verify_checksum() {
            return Err(anyhow!("Header checksum verification failed"));
        }

        Ok(Self {
            _file: file,
            mmap,
            header,
        })
    }

    /// Get vector by index (zero-copy)
    pub fn get_vector(&self, index: u64) -> Result<Vector> {
        if index >= self.header.vector_count {
            return Err(anyhow!("Vector index out of bounds"));
        }

        let offset =
            self.header.data_offset as usize + (index as usize * self.header.dimensions * 4);
        let end_offset = offset + (self.header.dimensions * 4);

        if end_offset > self.mmap.len() {
            return Err(anyhow!("Vector data extends beyond file"));
        }

        let vector_bytes = &self.mmap[offset..end_offset];
        let mut vector_data = vec![0f32; self.header.dimensions];

        for (i, chunk) in vector_bytes.chunks_exact(4).enumerate() {
            vector_data[i] = f32::from_le_bytes([chunk[0], chunk[1], chunk[2], chunk[3]]);
        }

        Ok(Vector::new(vector_data))
    }

    /// Get slice of vectors
    pub fn get_vectors(&self, start: u64, count: usize) -> Result<Vec<Vector>> {
        let mut vectors = Vec::with_capacity(count);

        for i in 0..count {
            let index = start + i as u64;
            if index >= self.header.vector_count {
                break;
            }
            vectors.push(self.get_vector(index)?);
        }

        Ok(vectors)
    }

    /// Get total vector count
    pub fn vector_count(&self) -> u64 {
        self.header.vector_count
    }

    /// Get vector dimensions
    pub fn dimensions(&self) -> usize {
        self.header.dimensions
    }
}

/// Utility functions for storage operations
pub struct StorageUtils;

impl StorageUtils {
    /// Convert vectors to binary format
    pub fn vectors_to_binary(vectors: &[Vector]) -> Result<Vec<u8>> {
        let mut data = Vec::new();

        for vector in vectors {
            let vector_f32 = vector.as_f32();
            for value in vector_f32 {
                data.extend_from_slice(&value.to_le_bytes());
            }
        }

        Ok(data)
    }

    /// Convert binary data to vectors
    pub fn binary_to_vectors(data: &[u8], dimensions: usize) -> Result<Vec<Vector>> {
        if data.len() % (dimensions * 4) != 0 {
            return Err(anyhow!("Invalid binary data length for given dimensions"));
        }

        let vector_count = data.len() / (dimensions * 4);
        let mut vectors = Vec::with_capacity(vector_count);

        for i in 0..vector_count {
            let start = i * dimensions * 4;
            let end = start + dimensions * 4;
            let vector_bytes = &data[start..end];

            let mut vector_data = vec![0f32; dimensions];
            for (j, chunk) in vector_bytes.chunks_exact(4).enumerate() {
                vector_data[j] = f32::from_le_bytes([chunk[0], chunk[1], chunk[2], chunk[3]]);
            }

            vectors.push(Vector::new(vector_data));
        }

        Ok(vectors)
    }

    /// Rough *heuristic* storage-size estimate for capacity planning when no
    /// actual vector data is available yet (only counts/dimensions are known).
    ///
    /// These ratios are empirical averages for typical dense f32 embedding
    /// data; they are NOT measured against `vectors` (there are none to
    /// measure here). For a real, measured ratio on actual data use
    /// [`StorageUtils::benchmark_compression`], which drives the same
    /// [`compress_bytes`] codepath used by [`VectorWriter`].
    pub fn estimate_storage_size(
        vector_count: usize,
        dimensions: usize,
        compression: CompressionType,
    ) -> usize {
        let raw_size = vector_count * dimensions * 4; // 4 bytes per f32
        let header_size = std::mem::size_of::<VectorFileHeader>();

        let compressed_size = match compression {
            CompressionType::None => raw_size,
            CompressionType::Lz4 => (raw_size as f64 * 0.6) as usize, // ~40% compression (heuristic)
            CompressionType::Zstd => (raw_size as f64 * 0.5) as usize, // ~50% compression (heuristic)
            CompressionType::Brotli => (raw_size as f64 * 0.4) as usize, // ~60% compression (heuristic)
            CompressionType::Gzip => (raw_size as f64 * 0.5) as usize, // ~50% compression (heuristic)
            // VectorQuantization has no raw-byte compressor implementation
            // (see `compress_bytes`); report as uncompressed rather than
            // fabricating a ratio that `compress_bytes` cannot deliver.
            CompressionType::VectorQuantization => raw_size,
        };

        header_size + compressed_size
    }

    /// Benchmark compression algorithms by actually compressing `vectors`
    /// through the same [`compress_bytes`] codepath used by [`VectorWriter`],
    /// so the reported sizes and timings reflect real OxiARC output.
    pub fn benchmark_compression(vectors: &[Vector]) -> Result<Vec<(CompressionType, f64, usize)>> {
        let binary_data = Self::vectors_to_binary(vectors)?;

        let algorithms = [
            CompressionType::None,
            CompressionType::Lz4,
            CompressionType::Zstd,
            CompressionType::Brotli,
            CompressionType::Gzip,
        ];

        let mut results = Vec::new();

        for &algorithm in &algorithms {
            let start_time = std::time::Instant::now();
            let compressed = compress_bytes(&binary_data, algorithm, 3)?;
            let duration = start_time.elapsed().as_secs_f64();
            results.push((algorithm, duration, compressed.len()));
        }

        Ok(results)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use anyhow::Result;
    use tempfile::NamedTempFile;

    #[test]
    fn test_vector_file_header() {
        let mut header = VectorFileHeader {
            vector_count: 1000,
            dimensions: 128,
            ..Default::default()
        };
        header.calculate_checksum();

        assert!(header.verify_checksum());

        // Modify header and verify checksum fails
        header.vector_count = 2000;
        assert!(!header.verify_checksum());
    }

    #[test]
    fn test_storage_utils() -> Result<()> {
        let vectors = vec![
            Vector::new(vec![1.0, 2.0, 3.0]),
            Vector::new(vec![4.0, 5.0, 6.0]),
        ];

        let binary_data = StorageUtils::vectors_to_binary(&vectors)?;
        let restored_vectors = StorageUtils::binary_to_vectors(&binary_data, 3)?;

        assert_eq!(vectors.len(), restored_vectors.len());
        for (original, restored) in vectors.iter().zip(restored_vectors.iter()) {
            assert_eq!(original.as_f32(), restored.as_f32());
        }
        Ok(())
    }

    #[test]
    fn test_vector_writer_reader() -> Result<()> {
        let temp_file = NamedTempFile::new()?;
        let file_path = temp_file.path();

        // Write vectors
        {
            let config = StorageConfig {
                compression: CompressionType::None,
                ..Default::default()
            };
            let mut writer = VectorWriter::new(file_path, config)?;

            let vectors = vec![
                Vector::new(vec![1.0, 2.0, 3.0, 4.0]),
                Vector::new(vec![5.0, 6.0, 7.0, 8.0]),
                Vector::new(vec![9.0, 10.0, 11.0, 12.0]),
            ];

            writer.write_vectors(&vectors)?;
            writer.finalize()?;
        }

        // Read vectors back
        {
            let mut reader = VectorReader::open(file_path)?;
            let metadata = reader.metadata();

            assert_eq!(metadata.vector_count, 3);
            assert_eq!(metadata.dimensions, 4);

            let vectors = reader.read_all()?;
            assert_eq!(vectors.len(), 3);

            assert_eq!(vectors[0].as_f32(), &[1.0, 2.0, 3.0, 4.0]);
            assert_eq!(vectors[1].as_f32(), &[5.0, 6.0, 7.0, 8.0]);
            assert_eq!(vectors[2].as_f32(), &[9.0, 10.0, 11.0, 12.0]);
        }

        Ok(())
    }

    #[test]
    fn test_compression_benchmark() -> Result<()> {
        let vectors = vec![
            Vector::new(vec![1.0; 128]),
            Vector::new(vec![2.0; 128]),
            Vector::new(vec![3.0; 128]),
        ];

        let results = StorageUtils::benchmark_compression(&vectors)?;
        assert_eq!(results.len(), 5); // 5 compression algorithms

        // Verify that some compression types reduce size
        let none_size = results
            .iter()
            .find(|(t, _, _)| *t == CompressionType::None)
            .expect("None compression type should be present")
            .2;
        let zstd_size = results
            .iter()
            .find(|(t, _, _)| *t == CompressionType::Zstd)
            .expect("Zstd compression type should be present")
            .2;

        assert!(zstd_size < none_size);
        Ok(())
    }

    /// Regression test for the P0 finding: `compress_data`/`compress_bytes`
    /// used to be a no-op returning the input unchanged for every
    /// `CompressionType` variant. Verify real compress/decompress round-trips
    /// for every implemented algorithm, and that highly-repetitive data
    /// actually shrinks (proving compression really ran, not just a copy).
    #[test]
    fn test_compress_bytes_round_trip_all_algorithms() -> Result<()> {
        // Repetitive data compresses well and makes a no-op regression obvious.
        let data: Vec<u8> = (0..8192u32).map(|i| (i % 7) as u8).collect();

        for &algorithm in &[
            CompressionType::None,
            CompressionType::Lz4,
            CompressionType::Zstd,
            CompressionType::Brotli,
            CompressionType::Gzip,
        ] {
            let compressed = compress_bytes(&data, algorithm, 5)?;
            let restored = decompress_bytes(&compressed, algorithm, data.len())?;
            assert_eq!(
                restored, data,
                "{:?} round-trip should reproduce the original bytes exactly",
                algorithm
            );

            if algorithm != CompressionType::None {
                assert!(
                    compressed.len() < data.len(),
                    "{:?} should actually shrink highly-repetitive data (no-op regression check)",
                    algorithm
                );
            }
        }

        Ok(())
    }

    /// `VectorQuantization` is not a real byte-oriented compressor (see
    /// `compress_bytes` docs); it must fail loudly instead of silently
    /// returning the input unchanged.
    #[test]
    fn test_compress_bytes_vector_quantization_errors_loudly() {
        let data = vec![1u8, 2, 3, 4, 5];
        let result = compress_bytes(&data, CompressionType::VectorQuantization, 3);
        assert!(
            result.is_err(),
            "VectorQuantization must error instead of silently passing data through"
        );
    }
}