zipora 3.1.2

//! Real-time compression with adaptive algorithms
//!
//! This module provides adaptive compression algorithms that automatically
//! choose the best compression method based on data characteristics and
//! performance requirements.

pub mod adaptive;
pub mod dict_zip;
#[cfg(feature = "async")]
pub mod realtime;
pub mod simd_lz77;
pub mod simd_pattern_match;
pub mod stream_vbyte;
pub mod suffix_array;

pub use adaptive::{AdaptiveCompressor, AdaptiveConfig, CompressionProfile};
pub use dict_zip::{
    DictionaryBuilder as PaZipDictionaryBuilder, DictionaryBuilderConfig, SuffixArrayDictionary, SuffixArrayDictionaryConfig,
    PatternMatcher, DfaCache, Match,
};
pub use simd_lz77::{
    SimdLz77Compressor, SimdLz77Config, SimdLz77Match, SimdLz77Stats,
    CompressionTier, CompressionParallelMode, DictionaryConfig,
    SimdLz77CompressorX1, SimdLz77CompressorX2, SimdLz77CompressorX4, SimdLz77CompressorX8,
    get_global_simd_lz77_compressor, compress_with_simd_lz77, decompress_with_simd_lz77,
};
pub use simd_pattern_match::{
    SimdPatternMatcher, SimdPatternConfig, SimdMatchResult, SimdPatternTier, ParallelMode,
    get_global_simd_pattern_matcher,
};
#[cfg(feature = "async")]
pub use realtime::{CompressionMode, RealtimeCompressor, RealtimeConfig};
pub use suffix_array::{
    EnhancedSuffixArray, SuffixArrayCompressor, SuffixArrayConfig, SuffixArrayStats,
};

use crate::entropy::dictionary::{DictionaryBuilder, DictionaryCompressor};
use crate::entropy::huffman::{HuffmanDecoder, HuffmanEncoder, HuffmanTree};
use crate::entropy::rans::{Rans64Decoder, Rans64Encoder, ParallelX1};
use crate::error::{Result, ZiporaError};
use std::time::Duration;

/// Compression algorithm types
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Algorithm {
    /// No compression
    None,
    /// Fast LZ4 compression
    Lz4,
    /// ZSTD compression with configurable level
    Zstd(i32),
    /// Huffman coding (for entropy-heavy data)
    Huffman,
    /// rANS encoding (for statistical compression)
    Rans,
    /// Dictionary-based compression
    Dictionary,
    /// SIMD-accelerated LZ77 compression
    SimdLz77,
    /// Hybrid approach using multiple algorithms
    Hybrid,
}

impl Algorithm {
    /// Get the expected compression speed (operations per second)
    pub fn compression_speed(&self) -> f64 {
        match self {
            Algorithm::None => f64::INFINITY,
            Algorithm::Lz4 => 500_000_000.0, // Very fast
            Algorithm::Zstd(level) => match level {
                1..=3 => 200_000_000.0, // Fast levels
                4..=9 => 50_000_000.0,  // Medium levels
                _ => 10_000_000.0,      // Slow levels
            },
            Algorithm::Huffman => 100_000_000.0, // Fast entropy coding
            Algorithm::Rans => 80_000_000.0,     // Good entropy coding
            Algorithm::Dictionary => 150_000_000.0, // Fast pattern matching
            Algorithm::SimdLz77 => 300_000_000.0, // SIMD-accelerated LZ77
            Algorithm::Hybrid => 50_000_000.0,   // Depends on mix
        }
    }

    /// Get the expected compression ratio (0.0 to 1.0, lower = better)
    pub fn compression_ratio(&self) -> f64 {
        match self {
            Algorithm::None => 1.0,
            Algorithm::Lz4 => 0.6,
            Algorithm::Zstd(level) => match level {
                1..=3 => 0.5,
                4..=9 => 0.4,
                _ => 0.3,
            },
            Algorithm::Huffman => 0.65,
            Algorithm::Rans => 0.55,
            Algorithm::Dictionary => 0.45,
            Algorithm::SimdLz77 => 0.35, // Better compression with SIMD acceleration
            Algorithm::Hybrid => 0.35,
        }
    }

    /// Get the memory usage in bytes per input byte
    pub fn memory_usage(&self) -> f64 {
        match self {
            Algorithm::None => 0.0,
            Algorithm::Lz4 => 0.1,
            Algorithm::Zstd(level) => match level {
                1..=3 => 0.5,
                4..=9 => 2.0,
                _ => 8.0,
            },
            Algorithm::Huffman => 1.0,
            Algorithm::Rans => 1.5,
            Algorithm::Dictionary => 3.0,
            Algorithm::SimdLz77 => 2.5, // Efficient memory usage with SIMD
            Algorithm::Hybrid => 4.0,
        }
    }
}

/// Performance requirements for compression
#[derive(Debug, Clone)]
pub struct PerformanceRequirements {
    /// Maximum acceptable latency
    pub max_latency: Duration,
    /// Minimum required throughput (bytes per second)
    pub min_throughput: u64,
    /// Maximum memory usage (bytes)
    pub max_memory: usize,
    /// Target compression ratio (0.0 to 1.0)
    pub target_ratio: f64,
    /// Priority: speed vs compression quality (0.0 = speed, 1.0 = quality)
    pub speed_vs_quality: f64,
}

impl Default for PerformanceRequirements {
    fn default() -> Self {
        Self {
            max_latency: Duration::from_millis(100),
            min_throughput: 100_000_000,  // 100 MB/s
            max_memory: 64 * 1024 * 1024, // 64 MB
            target_ratio: 0.5,
            speed_vs_quality: 0.5,
        }
    }
}

/// Statistics for compression operations
#[derive(Debug, Clone, Default)]
pub struct CompressionStats {
    /// Total operations performed
    pub operations: u64,
    /// Total bytes processed
    pub bytes_processed: u64,
    /// Total bytes after compression
    pub bytes_compressed: u64,
    /// Total compression time
    pub total_time: Duration,
    /// Algorithm usage statistics
    pub algorithm_usage: std::collections::HashMap<Algorithm, u64>,
    /// Average compression ratio
    pub avg_ratio: f64,
    /// Average throughput (bytes/sec)
    pub avg_throughput: f64,
}

impl CompressionStats {
    /// Calculate overall compression ratio
    pub fn compression_ratio(&self) -> f64 {
        if self.bytes_processed == 0 {
            0.0
        } else {
            self.bytes_compressed as f64 / self.bytes_processed as f64
        }
    }

    /// Calculate average throughput
    pub fn throughput(&self) -> f64 {
        if self.total_time.as_secs_f64() == 0.0 {
            0.0
        } else {
            self.bytes_processed as f64 / self.total_time.as_secs_f64()
        }
    }

    /// Update statistics with a new operation
    pub fn update(
        &mut self,
        input_size: usize,
        output_size: usize,
        duration: Duration,
        algorithm: Algorithm,
    ) {
        self.operations += 1;
        self.bytes_processed += input_size as u64;
        self.bytes_compressed += output_size as u64;
        self.total_time += duration;

        *self.algorithm_usage.entry(algorithm).or_insert(0) += 1;

        // Update rolling averages
        let ratio = output_size as f64 / input_size as f64;
        self.avg_ratio =
            (self.avg_ratio * (self.operations - 1) as f64 + ratio) / self.operations as f64;

        let throughput = input_size as f64 / duration.as_secs_f64();
        self.avg_throughput = (self.avg_throughput * (self.operations - 1) as f64 + throughput)
            / self.operations as f64;
    }
}

/// Base trait for compression algorithms
pub trait Compressor: Send + Sync {
    /// Compress data
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>>;

    /// Decompress data
    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>>;

    /// Get the algorithm type
    fn algorithm(&self) -> Algorithm;

    /// Estimate compression ratio for given data
    fn estimate_ratio(&self, data: &[u8]) -> f64 {
        // Default implementation: try compression on a sample
        if data.len() > 1024 {
            let sample = &data[..1024];
            if let Ok(compressed) = self.compress(sample) {
                return compressed.len() as f64 / sample.len() as f64;
            }
        }
        self.algorithm().compression_ratio()
    }

    /// Check if this compressor is suitable for the given requirements
    fn is_suitable(&self, requirements: &PerformanceRequirements, data_size: usize) -> bool {
        let algo = self.algorithm();
        let expected_time = data_size as f64 / algo.compression_speed();
        let expected_memory = (data_size as f64 * algo.memory_usage()) as usize;

        Duration::from_secs_f64(expected_time) <= requirements.max_latency
            && expected_memory <= requirements.max_memory
            && algo.compression_ratio() <= requirements.target_ratio
    }
}

/// No-op compressor (pass-through)
pub struct NoCompressor;

impl Compressor for NoCompressor {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        Ok(data.to_vec())
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        Ok(data.to_vec())
    }

    fn algorithm(&self) -> Algorithm {
        Algorithm::None
    }
}

/// LZ4 compressor wrapper
pub struct Lz4Compressor;

impl Compressor for Lz4Compressor {
    fn compress(
        &self,
        #[cfg_attr(not(feature = "lz4"), allow(unused_variables))] data: &[u8],
    ) -> Result<Vec<u8>> {
        #[cfg(feature = "lz4")]
        {
            Ok(lz4_flex::compress_prepend_size(data))
        }
        #[cfg(not(feature = "lz4"))]
        {
            Err(ZiporaError::not_supported("LZ4 compression not enabled"))
        }
    }

    fn decompress(
        &self,
        #[cfg_attr(not(feature = "lz4"), allow(unused_variables))] data: &[u8],
    ) -> Result<Vec<u8>> {
        #[cfg(feature = "lz4")]
        {
            lz4_flex::decompress_size_prepended(data)
                .map_err(|e| ZiporaError::compression(&format!("LZ4 decompression failed: {}", e)))
        }
        #[cfg(not(feature = "lz4"))]
        {
            Err(ZiporaError::not_supported("LZ4 decompression not enabled"))
        }
    }

    fn algorithm(&self) -> Algorithm {
        Algorithm::Lz4
    }
}

#[cfg(feature = "zstd")]
/// ZSTD compressor wrapper
pub struct ZstdCompressor {
    level: i32,
}

#[cfg(feature = "zstd")]
impl ZstdCompressor {
    /// Create a new ZSTD compressor with the specified compression level
    ///
    /// # Arguments
    /// * `level` - Compression level (1-22, higher is better compression but slower)
    pub fn new(level: i32) -> Self {
        Self { level }
    }
}

#[cfg(feature = "zstd")]
impl Compressor for ZstdCompressor {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        zstd::bulk::compress(data, self.level)
            .map_err(|e| ZiporaError::compression(&format!("ZSTD compression failed: {}", e)))
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        zstd::bulk::decompress(data, 100 * 1024 * 1024) // 100MB limit
            .map_err(|e| ZiporaError::compression(&format!("ZSTD decompression failed: {}", e)))
    }

    fn algorithm(&self) -> Algorithm {
        Algorithm::Zstd(self.level)
    }
}

/// Huffman compressor wrapper
pub struct HuffmanCompressor {
    encoder: HuffmanEncoder,
    tree_data: Vec<u8>,
}

impl HuffmanCompressor {
    /// Create a new Huffman compressor trained on the provided data
    ///
    /// # Arguments
    /// * `training_data` - Sample data to build frequency tables (must not be empty)
    pub fn new(training_data: &[u8]) -> Result<Self> {
        let encoder = HuffmanEncoder::new(training_data)?;
        let tree_data = encoder.tree().serialize();
        Ok(Self { encoder, tree_data })
    }

    /// Get the serialized tree data for storage with compressed data
    ///
    /// This tree data must be stored alongside compressed data for decompression
    pub fn tree_data(&self) -> &[u8] {
        &self.tree_data
    }
}

impl Compressor for HuffmanCompressor {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        // Encode the data
        let compressed_data = self.encoder.encode(data)?;

        // Create output with header: tree_size(4) + tree_data + original_size(4) + compressed_data
        let mut result = Vec::new();

        // Write tree size and tree data
        let tree_size = self.tree_data.len() as u32;
        result.extend_from_slice(&tree_size.to_le_bytes());
        result.extend_from_slice(&self.tree_data);

        // Write original data size
        let original_size = data.len() as u32;
        result.extend_from_slice(&original_size.to_le_bytes());

        // Write compressed data
        result.extend_from_slice(&compressed_data);

        Ok(result)
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        if data.len() < 8 {
            return Err(ZiporaError::invalid_data(
                "Huffman compressed data too short",
            ));
        }

        // Read tree size
        let tree_size = u32::from_le_bytes([data[0], data[1], data[2], data[3]]) as usize;

        if data.len() < 8 + tree_size {
            return Err(ZiporaError::invalid_data(
                "Huffman compressed data truncated",
            ));
        }

        // Read tree data and reconstruct tree
        let tree_data = &data[4..4 + tree_size];
        let tree = HuffmanTree::deserialize(tree_data)?;
        let decoder = HuffmanDecoder::new(tree);

        // Read original data size
        let size_offset = 4 + tree_size;
        let original_size = u32::from_le_bytes([
            data[size_offset],
            data[size_offset + 1],
            data[size_offset + 2],
            data[size_offset + 3],
        ]) as usize;

        // Read and decode compressed data
        let compressed_data = &data[size_offset + 4..];
        decoder.decode(compressed_data, original_size)
    }

    fn algorithm(&self) -> Algorithm {
        Algorithm::Huffman
    }
}

/// rANS-based compressor
pub struct RansCompressor {
    encoder: Rans64Encoder<ParallelX1>,
}

impl RansCompressor {
    /// Create a new rANS compressor trained on the provided data
    ///
    /// # Arguments
    /// * `training_data` - Sample data to build frequency tables (must not be empty)
    pub fn new(training_data: &[u8]) -> Result<Self> {
        if training_data.is_empty() {
            return Err(ZiporaError::invalid_data(
                "rANS compressor requires training data",
            ));
        }

        // Count symbol frequencies
        let mut frequencies = [0u32; 256];
        for &byte in training_data {
            frequencies[byte as usize] += 1;
        }

        // Ensure no zero frequencies for symbols that appear in training data
        let mut symbol_exists = [false; 256];
        for &byte in training_data {
            symbol_exists[byte as usize] = true;
        }

        for (i, freq) in frequencies.iter_mut().enumerate() {
            if *freq == 0 && symbol_exists[i] {
                *freq = 1; // Minimum frequency for existing symbols
            }
        }

        let encoder = Rans64Encoder::<ParallelX1>::new(&frequencies)?;
        Ok(Self { encoder })
    }
}

impl Compressor for RansCompressor {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        let mut result = Vec::new();

        // Store frequencies table (4 bytes per frequency)
        for i in 0..=255u8 {
            let freq = self.encoder.get_symbol(i).freq;
            result.extend_from_slice(&freq.to_le_bytes());
        }

        // Store original data size
        let original_size = data.len() as u32;
        result.extend_from_slice(&original_size.to_le_bytes());

        // Encode data
        let compressed_data = self.encoder.encode(data)?;
        result.extend_from_slice(&compressed_data);

        Ok(result)
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        if data.len() < 256 * 4 + 4 {
            return Err(ZiporaError::invalid_data(
                "Invalid rANS compressed data format",
            ));
        }

        // Read frequencies table
        let mut frequencies = [0u32; 256];
        for i in 0..256 {
            let start = i * 4;
            frequencies[i] = u32::from_le_bytes([
                data[start],
                data[start + 1],
                data[start + 2],
                data[start + 3],
            ]);
        }

        // Read original size
        let size_offset = 256 * 4;
        let original_size = u32::from_le_bytes([
            data[size_offset],
            data[size_offset + 1],
            data[size_offset + 2],
            data[size_offset + 3],
        ]) as usize;

        // Decode data
        let compressed_data = &data[size_offset + 4..];
        let temp_encoder = Rans64Encoder::<ParallelX1>::new(&frequencies)?;
        let decoder = Rans64Decoder::<ParallelX1>::new(&temp_encoder);
        decoder.decode(compressed_data, original_size)
    }

    fn estimate_ratio(&self, _data: &[u8]) -> f64 {
        0.6 // rANS typically achieves good compression
    }

    fn algorithm(&self) -> Algorithm {
        Algorithm::Rans
    }
}

/// Dictionary-based compressor
pub struct DictCompressor {
    dictionary: DictionaryCompressor,
}

impl DictCompressor {
    /// Create a new dictionary compressor trained on the provided data
    ///
    /// # Arguments
    /// * `training_data` - Sample data to build dictionary patterns (must not be empty)
    pub fn new(training_data: &[u8]) -> Result<Self> {
        if training_data.is_empty() {
            return Err(ZiporaError::invalid_data(
                "Dictionary compressor requires training data",
            ));
        }

        let builder = DictionaryBuilder::new();
        let dict = builder.build(training_data);
        let dictionary = DictionaryCompressor::new(dict);

        Ok(Self { dictionary })
    }
}

impl Compressor for DictCompressor {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        self.dictionary.compress(data)
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        self.dictionary.decompress(data)
    }

    fn estimate_ratio(&self, _data: &[u8]) -> f64 {
        0.7 // Dictionary compression ratio estimate
    }

    fn algorithm(&self) -> Algorithm {
        Algorithm::Dictionary
    }
}

/// Hybrid compressor that combines multiple algorithms
pub struct HybridCompressor {
    compressors: Vec<Box<dyn Compressor>>,
}

impl HybridCompressor {
    /// Create a new hybrid compressor that automatically selects the best algorithm
    ///
    /// The compressor will test multiple algorithms and choose the one with best compression
    ///
    /// # Arguments
    /// * `training_data` - Sample data for training all component compressors
    pub fn new(training_data: &[u8]) -> Result<Self> {
        let mut compressors: Vec<Box<dyn Compressor>> = Vec::new();

        // Add available compressors
        compressors.push(Box::new(HuffmanCompressor::new(training_data)?));
        compressors.push(Box::new(RansCompressor::new(training_data)?));
        compressors.push(Box::new(DictCompressor::new(training_data)?));

        Ok(Self { compressors })
    }
}

impl Compressor for HybridCompressor {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        let mut best_result = data.to_vec();
        let mut best_algorithm = 0u8;

        // Try each compressor and pick the best result
        for (i, compressor) in self.compressors.iter().enumerate() {
            if let Ok(compressed) = compressor.compress(data) {
                if compressed.len() < best_result.len() {
                    best_result = compressed;
                    best_algorithm = i as u8;
                }
            }
        }

        // Prepend algorithm identifier
        let mut result = vec![best_algorithm];
        result.extend_from_slice(&best_result);
        Ok(result)
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        if data.is_empty() {
            return Ok(Vec::new());
        }

        let algorithm_id = data[0] as usize;
        let compressed_data = &data[1..];

        if algorithm_id >= self.compressors.len() {
            return Err(ZiporaError::invalid_data(
                "Invalid algorithm identifier in hybrid data",
            ));
        }

        self.compressors[algorithm_id].decompress(compressed_data)
    }

    fn estimate_ratio(&self, data: &[u8]) -> f64 {
        // Return the best estimate from all compressors
        self.compressors
            .iter()
            .map(|c| c.estimate_ratio(data))
            .fold(1.0, f64::min)
    }

    fn algorithm(&self) -> Algorithm {
        Algorithm::Hybrid
    }
}

/// Factory for creating compressors
pub struct CompressorFactory;

impl CompressorFactory {
    /// Create a compressor for the given algorithm
    pub fn create(
        algorithm: Algorithm,
        training_data: Option<&[u8]>,
    ) -> Result<Box<dyn Compressor>> {
        match algorithm {
            Algorithm::None => Ok(Box::new(NoCompressor)),
            Algorithm::Lz4 => Ok(Box::new(Lz4Compressor)),
            #[cfg(feature = "zstd")]
            Algorithm::Zstd(level) => Ok(Box::new(ZstdCompressor::new(level))),
            #[cfg(not(feature = "zstd"))]
            Algorithm::Zstd(_) => Err(ZiporaError::configuration(
                "ZSTD compression not available - enable 'zstd' feature",
            )),
            Algorithm::Huffman => {
                if let Some(data) = training_data {
                    Ok(Box::new(HuffmanCompressor::new(data)?))
                } else {
                    Err(ZiporaError::invalid_data(
                        "Huffman compressor requires training data",
                    ))
                }
            }
            Algorithm::Rans => {
                if let Some(data) = training_data {
                    Ok(Box::new(RansCompressor::new(data)?))
                } else {
                    Err(ZiporaError::invalid_data(
                        "rANS compressor requires training data",
                    ))
                }
            }
            Algorithm::Dictionary => {
                if let Some(data) = training_data {
                    Ok(Box::new(DictCompressor::new(data)?))
                } else {
                    Err(ZiporaError::invalid_data(
                        "Dictionary compressor requires training data",
                    ))
                }
            }
            Algorithm::SimdLz77 => {
                Ok(Box::new(
                    crate::compression::simd_lz77::SimdLz77Compressor::default()
                ))
            }
            Algorithm::Hybrid => {
                if let Some(data) = training_data {
                    Ok(Box::new(HybridCompressor::new(data)?))
                } else {
                    Err(ZiporaError::invalid_data(
                        "Hybrid compressor requires training data",
                    ))
                }
            }
        }
    }

    /// Get all available algorithms
    pub fn available_algorithms() -> Vec<Algorithm> {
        #[cfg(feature = "zstd")]
        {
            vec![
                Algorithm::None,
                Algorithm::Lz4,
                Algorithm::Zstd(1),
                Algorithm::Zstd(3),
                Algorithm::Zstd(6),
                Algorithm::Zstd(9),
                Algorithm::Huffman,
                Algorithm::Rans,
                Algorithm::Dictionary,
                Algorithm::Hybrid,
            ]
        }
        #[cfg(not(feature = "zstd"))]
        {
            vec![
                Algorithm::None,
                Algorithm::Lz4,
                Algorithm::Huffman,
                Algorithm::Rans,
                Algorithm::Dictionary,
                Algorithm::Hybrid,
            ]
        }
    }

    /// Select the best algorithm for given requirements and data
    pub fn select_best(requirements: &PerformanceRequirements, data: &[u8]) -> Algorithm {
        let available = Self::available_algorithms();
        let mut best_algorithm = Algorithm::None;
        let mut best_score = f64::NEG_INFINITY;

        for algorithm in available {
            // Skip algorithms that require training data if not available
            if matches!(
                algorithm,
                Algorithm::Huffman | Algorithm::Rans | Algorithm::Dictionary
            ) {
                continue;
            }

            let speed = algorithm.compression_speed();
            let ratio = algorithm.compression_ratio();
            let memory = algorithm.memory_usage() * data.len() as f64;

            // Check hard constraints
            if memory > requirements.max_memory as f64 {
                continue;
            }

            let expected_time = data.len() as f64 / speed;
            if Duration::from_secs_f64(expected_time) > requirements.max_latency {
                continue;
            }

            // Calculate score based on requirements
            let speed_score = speed / 1_000_000_000.0; // Normalize to GB/s
            let ratio_score = 1.0 - ratio; // Better ratio = higher score
            let memory_score = 1.0 - (memory / requirements.max_memory as f64);

            let weighted_score = requirements.speed_vs_quality * ratio_score
                + (1.0 - requirements.speed_vs_quality) * speed_score
                + 0.1 * memory_score;

            if weighted_score > best_score {
                best_score = weighted_score;
                best_algorithm = algorithm;
            }
        }

        best_algorithm
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_algorithm_properties() {
        assert_eq!(Algorithm::None.compression_ratio(), 1.0);
        assert!(Algorithm::Lz4.compression_speed() > Algorithm::Zstd(9).compression_speed());
        assert!(Algorithm::Zstd(9).compression_ratio() < Algorithm::Lz4.compression_ratio());
    }

    #[test]
    fn test_performance_requirements() {
        let req = PerformanceRequirements::default();
        assert_eq!(req.speed_vs_quality, 0.5);
        assert!(req.max_latency > Duration::ZERO);
    }

    #[test]
    fn test_compression_stats() {
        let mut stats = CompressionStats::default();

        stats.update(1000, 500, Duration::from_millis(10), Algorithm::Lz4);
        assert_eq!(stats.operations, 1);
        assert_eq!(stats.compression_ratio(), 0.5);

        stats.update(2000, 800, Duration::from_millis(20), Algorithm::Zstd(3));
        assert_eq!(stats.operations, 2);
        assert!(stats.compression_ratio() < 0.7);
    }

    #[test]
    fn test_no_compressor() {
        let compressor = NoCompressor;
        let data = b"test data";

        let compressed = compressor.compress(data).unwrap();
        assert_eq!(compressed, data);

        let decompressed = compressor.decompress(&compressed).unwrap();
        assert_eq!(decompressed, data);

        assert_eq!(compressor.algorithm(), Algorithm::None);
    }

    #[cfg(feature = "lz4")]
    #[test]
    fn test_lz4_compressor() {
        let compressor = Lz4Compressor;
        let data = b"test data that should compress well with repeated patterns";

        let compressed = compressor.compress(data).unwrap();
        let decompressed = compressor.decompress(&compressed).unwrap();

        assert_eq!(decompressed, data);
        assert_eq!(compressor.algorithm(), Algorithm::Lz4);
    }

    #[test]
    #[cfg(feature = "zstd")]
    fn test_zstd_compressor() {
        let compressor = ZstdCompressor::new(3);
        let data = b"test data that should compress well with repeated patterns and more text";

        let compressed = compressor.compress(data).unwrap();
        let decompressed = compressor.decompress(&compressed).unwrap();

        assert_eq!(decompressed, data);
        assert_eq!(compressor.algorithm(), Algorithm::Zstd(3));
        assert!(compressed.len() < data.len());
    }

    #[test]
    fn test_compressor_factory() {
        let algorithms = CompressorFactory::available_algorithms();
        assert!(!algorithms.is_empty());
        assert!(algorithms.contains(&Algorithm::None));
        assert!(algorithms.contains(&Algorithm::Lz4));
    }

    #[test]
    fn test_algorithm_selection() {
        let req = PerformanceRequirements {
            max_latency: Duration::from_millis(1),
            speed_vs_quality: 0.9, // Prioritize speed
            ..Default::default()
        };

        let data = vec![0u8; 1000];
        let algorithm = CompressorFactory::select_best(&req, &data);

        // Should select a fast algorithm
        assert!(matches!(algorithm, Algorithm::None | Algorithm::Lz4));
    }

    #[test]
    fn test_huffman_compressor() {
        let training_data = b"hello world! this is sample training data for huffman compression.";
        let compressor = HuffmanCompressor::new(training_data).unwrap();

        // Test basic compression/decompression
        let test_data = b"hello world! this uses the same patterns as training.";
        let compressed = compressor.compress(test_data).unwrap();
        let decompressed = compressor.decompress(&compressed).unwrap();

        assert_eq!(decompressed, test_data);
        assert_eq!(compressor.algorithm(), Algorithm::Huffman);

        // Compressed data should include header with tree and original size
        assert!(compressed.len() >= 8); // At least tree_size(4) + original_size(4)
    }

    #[test]
    fn test_huffman_compressor_empty_data() {
        let training_data = b"sample data";
        let compressor = HuffmanCompressor::new(training_data).unwrap();

        let empty_data = b"";
        let compressed = compressor.compress(empty_data).unwrap();
        let decompressed = compressor.decompress(&compressed).unwrap();

        assert_eq!(decompressed, empty_data);
        assert!(compressed.is_empty());
    }

    #[test]
    fn test_huffman_compressor_single_symbol() {
        let training_data = b"aaaaaaaaaa"; // Single symbol
        let compressor = HuffmanCompressor::new(training_data).unwrap();

        let test_data = b"aaaa";
        let compressed = compressor.compress(test_data).unwrap();
        let decompressed = compressor.decompress(&compressed).unwrap();

        assert_eq!(decompressed, test_data);
    }

    #[test]
    fn test_huffman_compressor_high_entropy() {
        // Use high-entropy data for training
        let training_data: Vec<u8> = (0..=255).cycle().take(1000).collect();
        let compressor = HuffmanCompressor::new(&training_data).unwrap();

        let test_data: Vec<u8> = (0..100).map(|i| (i * 7) as u8).collect();
        let compressed = compressor.compress(&test_data).unwrap();
        let decompressed = compressor.decompress(&compressed).unwrap();

        assert_eq!(decompressed, test_data);
    }

    #[test]
    fn test_huffman_compressor_repeated_patterns() {
        let training_data = b"abcdefghijklmnopqrstuvwxyz";
        let compressor = HuffmanCompressor::new(training_data).unwrap();

        // Test data with repeated patterns (should compress well)
        let test_data = b"aaaaaabbbbbbccccccdddddd";
        let compressed = compressor.compress(test_data).unwrap();
        let decompressed = compressor.decompress(&compressed).unwrap();

        assert_eq!(decompressed, test_data);

        // Should achieve some compression due to repeated patterns
        // Note: actual compression depends on how well test data matches training data distribution
    }

    #[test]
    fn test_huffman_compressor_invalid_compressed_data() {
        let training_data = b"sample data";
        let compressor = HuffmanCompressor::new(training_data).unwrap();

        // Test with truncated data
        let invalid_data = b"abc"; // Too short for valid compressed data
        let result = compressor.decompress(invalid_data);
        assert!(result.is_err());

        // Test with malformed header
        let malformed_data = vec![1, 0, 0, 0, 255]; // tree_size=1, but insufficient data
        let result = compressor.decompress(&malformed_data);
        assert!(result.is_err());
    }

    #[test]
    fn test_huffman_compressor_tree_data() {
        let training_data = b"hello world";
        let compressor = HuffmanCompressor::new(training_data).unwrap();

        let tree_data = compressor.tree_data();
        assert!(!tree_data.is_empty());

        // Tree data should be serialized Huffman tree
        assert!(tree_data.len() >= 2); // At least symbol count
    }

    #[test]
    #[cfg(feature = "lz4")]
    fn test_compressor_suitability() {
        let compressor = Lz4Compressor;
        // Use requirements suitable for LZ4's characteristics (compression ratio: 0.6)
        let req = PerformanceRequirements {
            target_ratio: 0.7, // LZ4 has ratio 0.6, so 0.7 should pass
            ..Default::default()
        };

        assert!(compressor.is_suitable(&req, 1024));

        let strict_req = PerformanceRequirements {
            max_latency: Duration::from_nanos(1),
            ..Default::default()
        };

        assert!(!compressor.is_suitable(&strict_req, 1024 * 1024));
    }
}