//! Unified Column Store Strategy Implementation
//!
//! This module provides the UnifiedColumnStoreStrategy as specified in the
//! memory management unification strategy document.

use crate::core::error::{Error, Result};
use crate::storage::unified_memory::*;
use rayon::prelude::*;
use std::collections::HashMap;
use std::sync::{Arc, Mutex, RwLock};
use std::time::Instant;
// Note: In production, would use actual compression libraries like lz4_flex and zstd

/// Column store configuration
#[derive(Debug, Clone)]
pub struct ColumnStoreConfig {
    /// Default compression type
    pub compression_type: CompressionType,
    /// Default encoding type
    pub encoding_type: EncodingType,
    /// Block size for chunking data
    pub block_size: usize,
    /// Enable dictionary encoding
    pub enable_dictionary: bool,
    /// Enable parallel processing
    pub enable_parallel: bool,
    /// Cache size for metadata
    pub metadata_cache_size: usize,
}

impl Default for ColumnStoreConfig {
    fn default() -> Self {
        Self {
            compression_type: CompressionType::Zstd,
            encoding_type: EncodingType::Auto,
            block_size: 64 * 1024, // 64KB blocks
            enable_dictionary: true,
            enable_parallel: true,
            metadata_cache_size: 10 * 1024 * 1024, // 10MB metadata cache
        }
    }
}

/// Encoding strategies for different data types
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum EncodingType {
    /// Automatic encoding selection
    Auto,
    /// No encoding (raw data)
    None,
    /// Run-length encoding
    RunLength,
    /// Dictionary encoding
    Dictionary,
    /// Delta encoding for numeric data
    Delta,
    /// Bit-packed encoding for small integers
    BitPacked,
}

/// Compression engine trait
pub trait CompressionEngine: Send + Sync {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>>;
    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>>;
    fn name(&self) -> &'static str;
    fn compression_ratio(&self, original_size: usize, compressed_size: usize) -> f64;
}

/// LZ4 compression engine
pub struct Lz4CompressionEngine;

impl CompressionEngine for Lz4CompressionEngine {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        // Placeholder implementation - in production would use lz4_flex
        let mut compressed = vec![data.len() as u8]; // Store length
        compressed.extend(data); // Simple "compression" - just copy data
        Ok(compressed)
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        // Placeholder implementation - in production would use lz4_flex
        if data.is_empty() {
            return Ok(Vec::new());
        }
        Ok(data[1..].to_vec()) // Skip length byte
    }

    fn name(&self) -> &'static str {
        "LZ4"
    }

    fn compression_ratio(&self, original_size: usize, compressed_size: usize) -> f64 {
        if compressed_size == 0 {
            0.0
        } else {
            original_size as f64 / compressed_size as f64
        }
    }
}

/// ZSTD compression engine
pub struct ZstdCompressionEngine {
    compression_level: i32,
}

impl ZstdCompressionEngine {
    pub fn new(level: i32) -> Self {
        Self {
            compression_level: level,
        }
    }
}

impl CompressionEngine for ZstdCompressionEngine {
    fn compress(&self, data: &[u8]) -> Result<Vec<u8>> {
        // Placeholder implementation - in production would use zstd
        let mut compressed = vec![(data.len() >> 8) as u8, data.len() as u8]; // Store length as 2 bytes
        compressed.extend(data); // Simple "compression" - just copy data
        Ok(compressed)
    }

    fn decompress(&self, data: &[u8]) -> Result<Vec<u8>> {
        // Placeholder implementation - in production would use zstd
        if data.len() < 2 {
            return Ok(Vec::new());
        }
        Ok(data[2..].to_vec()) // Skip length bytes
    }

    fn name(&self) -> &'static str {
        "ZSTD"
    }

    fn compression_ratio(&self, original_size: usize, compressed_size: usize) -> f64 {
        if compressed_size == 0 {
            0.0
        } else {
            original_size as f64 / compressed_size as f64
        }
    }
}

/// No-op compression engine
pub struct NoCompressionEngine;

impl CompressionEngine for NoCompressionEngine {
    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 name(&self) -> &'static str {
        "None"
    }

    fn compression_ratio(&self, _original_size: usize, _compressed_size: usize) -> f64 {
        1.0
    }
}

/// Encoding strategy trait
pub trait EncodingStrategy: Send + Sync {
    fn encode(&self, data: &[u8]) -> Result<EncodedData>;
    fn decode(&self, data: &EncodedData) -> Result<Vec<u8>>;
    fn name(&self) -> &'static str;
    fn encoding_ratio(&self, original_size: usize, encoded_size: usize) -> f64;
}

/// Encoded data with metadata
#[derive(Debug, Clone)]
pub struct EncodedData {
    pub data: Vec<u8>,
    pub encoding_type: EncodingType,
    pub original_size: usize,
    pub metadata: HashMap<String, String>,
}

/// Run-length encoding strategy
pub struct RunLengthEncodingStrategy;

impl EncodingStrategy for RunLengthEncodingStrategy {
    fn encode(&self, data: &[u8]) -> Result<EncodedData> {
        let mut encoded = Vec::new();
        let mut i = 0;

        while i < data.len() {
            let current_byte = data[i];
            let mut count = 1u8;

            // Count consecutive identical bytes
            while i + (count as usize) < data.len()
                && data[i + (count as usize)] == current_byte
                && count < 255
            {
                count += 1;
            }

            encoded.push(count);
            encoded.push(current_byte);
            i += count as usize;
        }

        Ok(EncodedData {
            data: encoded,
            encoding_type: EncodingType::RunLength,
            original_size: data.len(),
            metadata: HashMap::new(),
        })
    }

    fn decode(&self, encoded: &EncodedData) -> Result<Vec<u8>> {
        let mut decoded = Vec::with_capacity(encoded.original_size);
        let mut i = 0;

        while i + 1 < encoded.data.len() {
            let count = encoded.data[i];
            let byte_val = encoded.data[i + 1];

            for _ in 0..count {
                decoded.push(byte_val);
            }

            i += 2;
        }

        Ok(decoded)
    }

    fn name(&self) -> &'static str {
        "RunLength"
    }

    fn encoding_ratio(&self, original_size: usize, encoded_size: usize) -> f64 {
        if encoded_size == 0 {
            0.0
        } else {
            original_size as f64 / encoded_size as f64
        }
    }
}

/// Block metadata for columnar storage
#[derive(Debug, Clone)]
pub struct BlockMetadata {
    pub id: BlockId,
    pub location: BlockLocation,
    pub compressed_size: usize,
    pub uncompressed_size: usize,
    pub compression_type: CompressionType,
    pub encoding_type: EncodingType,
    pub checksum: u64,
    pub created_at: Instant,
    pub min_value: Option<Vec<u8>>,
    pub max_value: Option<Vec<u8>>,
    pub null_count: u64,
    pub distinct_count: Option<u64>,
}

/// Block identifier
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct BlockId(pub u64);

/// Block location information
#[derive(Debug, Clone)]
pub struct BlockLocation {
    pub offset: u64,
    pub size: usize,
}

/// Compressed block data
#[derive(Debug, Clone)]
pub struct CompressedBlock {
    pub data: Vec<u8>,
    pub compression_type: CompressionType,
    pub encoding_type: EncodingType,
    pub metadata: BlockMetadata,
}

impl CompressedBlock {
    pub fn new(
        data: Vec<u8>,
        compression_type: CompressionType,
        encoding_type: EncodingType,
    ) -> Self {
        let metadata = BlockMetadata {
            id: BlockId(0), // Will be set by block manager
            location: BlockLocation {
                offset: 0,
                size: data.len(),
            },
            compressed_size: data.len(),
            uncompressed_size: data.len(), // Will be updated after compression
            compression_type,
            encoding_type,
            checksum: Self::compute_checksum(&data),
            created_at: Instant::now(),
            min_value: None,
            max_value: None,
            null_count: 0,
            distinct_count: None,
        };

        Self {
            data,
            compression_type,
            encoding_type,
            metadata,
        }
    }

    pub fn compressed_size(&self) -> usize {
        self.data.len()
    }

    pub fn uncompressed_size(&self) -> usize {
        self.metadata.uncompressed_size
    }

    pub fn checksum(&self) -> u64 {
        self.metadata.checksum
    }

    fn compute_checksum(data: &[u8]) -> u64 {
        // Simple checksum - in production would use CRC32 or similar
        data.iter().map(|&b| b as u64).sum()
    }
}

/// Column store handle
#[derive(Debug)]
pub struct ColumnStoreHandle {
    pub layout: ColumnLayout,
    pub compression_type: CompressionType,
    pub encoding_type: EncodingType,
    pub blocks: Vec<BlockId>,
    pub statistics: ColumnStatistics,
}

/// Column layout information
#[derive(Debug, Clone)]
pub struct ColumnLayout {
    pub name: String,
    pub data_type: ColumnDataType,
    pub nullable: bool,
    pub block_size: usize,
    pub total_size: usize,
    pub row_count: u64,
}

/// Column data types for optimization
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ColumnDataType {
    Int8,
    Int16,
    Int32,
    Int64,
    UInt8,
    UInt16,
    UInt32,
    UInt64,
    Float32,
    Float64,
    String,
    Binary,
    Boolean,
    Timestamp,
    Date,
    Decimal,
}

/// Column statistics for query optimization
#[derive(Debug, Clone)]
pub struct ColumnStatistics {
    pub null_count: u64,
    pub distinct_count: Option<u64>,
    pub min_value: Option<Vec<u8>>,
    pub max_value: Option<Vec<u8>>,
    pub total_size: u64,
    pub compressed_size: u64,
    pub compression_ratio: f64,
    pub encoding_ratio: f64,
}

impl ColumnStatistics {
    pub fn new() -> Self {
        Self {
            null_count: 0,
            distinct_count: None,
            min_value: None,
            max_value: None,
            total_size: 0,
            compressed_size: 0,
            compression_ratio: 1.0,
            encoding_ratio: 1.0,
        }
    }
}

/// Block manager for handling physical storage
pub struct BlockManager {
    /// Storage backend for blocks
    storage: Box<dyn PhysicalStorage>,
    /// Block allocation tracking
    allocator: BlockAllocator,
    /// Block cache for frequently accessed data
    block_cache: Arc<Mutex<HashMap<BlockId, CompressedBlock>>>,
    /// Block metadata index
    metadata_index: HashMap<BlockId, BlockMetadata>,
    /// Free space tracking
    free_space_tracker: FreeSpaceTracker,
    /// Next block ID
    next_block_id: std::sync::atomic::AtomicU64,
}

impl BlockManager {
    pub fn new(storage: Box<dyn PhysicalStorage>) -> Self {
        Self {
            storage,
            allocator: BlockAllocator::new(),
            block_cache: Arc::new(Mutex::new(HashMap::new())),
            metadata_index: HashMap::new(),
            free_space_tracker: FreeSpaceTracker::new(),
            next_block_id: std::sync::atomic::AtomicU64::new(1),
        }
    }

    pub fn write_block(&mut self, mut block: CompressedBlock) -> Result<BlockId> {
        // Assign block ID
        let block_id = BlockId(
            self.next_block_id
                .fetch_add(1, std::sync::atomic::Ordering::SeqCst),
        );
        block.metadata.id = block_id;

        // Find optimal location for block
        let location = self.allocator.allocate_space(block.compressed_size())?;
        block.metadata.location = location.clone();

        // Write to physical storage
        self.storage.write_at_location(&location, &block.data)?;

        // Update metadata index
        self.metadata_index.insert(block_id, block.metadata.clone());

        // Update cache
        if let Ok(mut cache) = self.block_cache.lock() {
            cache.insert(block_id, block);
        }

        Ok(block_id)
    }

    pub fn read_block(&self, block_id: BlockId) -> Result<CompressedBlock> {
        // Check cache first
        if let Ok(cache) = self.block_cache.lock() {
            if let Some(block) = cache.get(&block_id) {
                return Ok(block.clone());
            }
        }

        // Read from physical storage
        let metadata = self
            .metadata_index
            .get(&block_id)
            .ok_or_else(|| Error::InvalidOperation(format!("Block {:?} not found", block_id)))?;

        let data = self
            .storage
            .read_at_location(&metadata.location, metadata.compressed_size)?;

        // Verify checksum
        let computed_checksum = CompressedBlock::compute_checksum(&data);
        if computed_checksum != metadata.checksum {
            return Err(Error::InvalidOperation(format!(
                "Checksum mismatch for block {:?}: expected {}, got {}",
                block_id, metadata.checksum, computed_checksum
            )));
        }

        let block = CompressedBlock {
            data,
            compression_type: metadata.compression_type,
            encoding_type: metadata.encoding_type,
            metadata: metadata.clone(),
        };

        // Update cache
        if let Ok(mut cache) = self.block_cache.lock() {
            cache.insert(block_id, block.clone());
        }

        Ok(block)
    }
}

/// Physical storage trait
pub trait PhysicalStorage: Send + Sync {
    fn write_at_location(&mut self, location: &BlockLocation, data: &[u8]) -> Result<()>;
    fn read_at_location(&self, location: &BlockLocation, size: usize) -> Result<Vec<u8>>;
    fn delete_at_location(&mut self, location: &BlockLocation) -> Result<()>;
    fn total_size(&self) -> u64;
    fn available_space(&self) -> u64;
}

/// In-memory physical storage for testing
pub struct InMemoryPhysicalStorage {
    data: Vec<u8>,
    allocated_regions: Vec<(u64, usize)>,
}

impl InMemoryPhysicalStorage {
    pub fn new(capacity: usize) -> Self {
        Self {
            data: vec![0; capacity],
            allocated_regions: Vec::new(),
        }
    }
}

impl PhysicalStorage for InMemoryPhysicalStorage {
    fn write_at_location(&mut self, location: &BlockLocation, data: &[u8]) -> Result<()> {
        let start = location.offset as usize;
        let end = start + data.len();

        if end > self.data.len() {
            return Err(Error::InvalidOperation(
                "Not enough space in storage".to_string(),
            ));
        }

        self.data[start..end].copy_from_slice(data);
        self.allocated_regions.push((location.offset, data.len()));

        Ok(())
    }

    fn read_at_location(&self, location: &BlockLocation, size: usize) -> Result<Vec<u8>> {
        let start = location.offset as usize;
        let end = start + size;

        if end > self.data.len() {
            return Err(Error::InvalidOperation(
                "Read beyond storage bounds".to_string(),
            ));
        }

        Ok(self.data[start..end].to_vec())
    }

    fn delete_at_location(&mut self, location: &BlockLocation) -> Result<()> {
        // Mark space as available
        self.allocated_regions
            .retain(|(offset, _)| *offset != location.offset);
        Ok(())
    }

    fn total_size(&self) -> u64 {
        self.data.len() as u64
    }

    fn available_space(&self) -> u64 {
        let allocated: usize = self.allocated_regions.iter().map(|(_, size)| size).sum();
        (self.data.len() - allocated) as u64
    }
}

/// Block allocator for managing space
pub struct BlockAllocator {
    next_offset: u64,
}

impl BlockAllocator {
    pub fn new() -> Self {
        Self { next_offset: 0 }
    }

    pub fn allocate_space(&mut self, size: usize) -> Result<BlockLocation> {
        let location = BlockLocation {
            offset: self.next_offset,
            size,
        };

        self.next_offset += size as u64;

        Ok(location)
    }
}

/// Free space tracker
pub struct FreeSpaceTracker {
    free_blocks: Vec<(u64, usize)>,
}

impl FreeSpaceTracker {
    pub fn new() -> Self {
        Self {
            free_blocks: Vec::new(),
        }
    }

    pub fn add_free_space(&mut self, offset: u64, size: usize) {
        self.free_blocks.push((offset, size));
        // Sort by offset for efficient merging
        self.free_blocks.sort_by_key(|(offset, _)| *offset);
        // Merge adjacent blocks
        self.merge_adjacent_blocks();
    }

    /// Merge adjacent free blocks to reduce fragmentation
    pub fn merge_adjacent_blocks(&mut self) {
        if self.free_blocks.len() <= 1 {
            return;
        }

        let mut merged = Vec::new();
        let mut current = self.free_blocks[0];

        for &next in self.free_blocks.iter().skip(1) {
            // Check if current block is adjacent to next block
            if current.0 + current.1 as u64 == next.0 {
                // Merge the blocks
                current.1 += next.1;
            } else {
                // Blocks are not adjacent, save current and move to next
                merged.push(current);
                current = next;
            }
        }

        // Don't forget the last block
        merged.push(current);

        self.free_blocks = merged;
    }

    pub fn find_space(&self, required_size: usize) -> Option<u64> {
        self.free_blocks
            .iter()
            .find(|(_, size)| *size >= required_size)
            .map(|(offset, _)| *offset)
    }
}

/// Unified Column Store Strategy Implementation
pub struct UnifiedColumnStoreStrategy {
    /// Multiple compression backends
    compression_engines: HashMap<CompressionType, Box<dyn CompressionEngine>>,

    /// Encoding strategies for different data types
    encoding_strategies: HashMap<EncodingType, Box<dyn EncodingStrategy>>,

    /// Block-based storage management
    block_manager: Arc<Mutex<BlockManager>>,

    /// Columnar metadata cache
    metadata_cache: Arc<RwLock<HashMap<String, ColumnStatistics>>>,

    /// Configuration parameters
    config: ColumnStoreConfig,
}

impl UnifiedColumnStoreStrategy {
    pub fn new(config: ColumnStoreConfig) -> Self {
        let mut compression_engines: HashMap<CompressionType, Box<dyn CompressionEngine>> =
            HashMap::new();
        compression_engines.insert(CompressionType::None, Box::new(NoCompressionEngine));
        compression_engines.insert(CompressionType::Lz4, Box::new(Lz4CompressionEngine));
        compression_engines.insert(
            CompressionType::Zstd,
            Box::new(ZstdCompressionEngine::new(3)),
        );

        let mut encoding_strategies: HashMap<EncodingType, Box<dyn EncodingStrategy>> =
            HashMap::new();
        encoding_strategies.insert(EncodingType::RunLength, Box::new(RunLengthEncodingStrategy));

        // Create in-memory storage for this example
        let storage = Box::new(InMemoryPhysicalStorage::new(100 * 1024 * 1024)); // 100MB
        let block_manager = Arc::new(Mutex::new(BlockManager::new(storage)));

        Self {
            compression_engines,
            encoding_strategies,
            block_manager,
            metadata_cache: Arc::new(RwLock::new(HashMap::new())),
            config,
        }
    }

    fn determine_optimal_layout(&self, config: &StorageConfig) -> Result<ColumnLayout> {
        let data_type = match config.requirements.data_characteristics {
            DataCharacteristics::Numeric => ColumnDataType::Float64,
            DataCharacteristics::Text => ColumnDataType::String,
            DataCharacteristics::TimeSeries => ColumnDataType::Timestamp,
            DataCharacteristics::Categorical => ColumnDataType::String,
            _ => ColumnDataType::Binary,
        };

        Ok(ColumnLayout {
            name: "default".to_string(),
            data_type,
            nullable: true,
            block_size: self.config.block_size,
            total_size: config.requirements.estimated_size,
            row_count: (config.requirements.estimated_size / 8) as u64, // Estimate
        })
    }

    fn select_compression_strategy(
        &self,
        characteristics: &DataCharacteristics,
    ) -> Result<CompressionType> {
        match characteristics {
            DataCharacteristics::Text => Ok(CompressionType::Zstd), // Better for text
            DataCharacteristics::Numeric => Ok(CompressionType::Lz4), // Faster for numeric
            DataCharacteristics::Sparse => Ok(CompressionType::Zstd), // Better compression
            _ => Ok(self.config.compression_type),
        }
    }

    fn select_encoding_strategy(
        &self,
        characteristics: &DataCharacteristics,
    ) -> Result<EncodingType> {
        match characteristics {
            DataCharacteristics::Categorical => Ok(EncodingType::Dictionary),
            DataCharacteristics::Sparse => Ok(EncodingType::RunLength),
            DataCharacteristics::TimeSeries => Ok(EncodingType::Delta),
            _ => Ok(self.config.encoding_type),
        }
    }

    fn find_blocks_for_range(
        &self,
        handle: &ColumnStoreHandle,
        range: &ChunkRange,
    ) -> Result<Vec<BlockId>> {
        // Simple implementation - return all blocks in range
        // In a real implementation, this would use spatial indexing
        Ok(handle.blocks.clone())
    }

    fn read_and_decompress_block(
        &self,
        _handle: &ColumnStoreHandle,
        block_id: BlockId,
    ) -> Result<Vec<u8>> {
        let block_manager = self.block_manager.lock().map_err(|_| {
            Error::InvalidOperation("Failed to acquire block manager lock".to_string())
        })?;

        let compressed_block = block_manager.read_block(block_id)?;

        // Decompress
        let compression_engine = self
            .compression_engines
            .get(&compressed_block.compression_type)
            .ok_or_else(|| {
                Error::InvalidOperation(format!(
                    "Compression engine {:?} not found",
                    compressed_block.compression_type
                ))
            })?;

        let decompressed_data = compression_engine.decompress(&compressed_block.data)?;

        // Decode if necessary
        if compressed_block.encoding_type != EncodingType::None {
            let encoding_strategy = self
                .encoding_strategies
                .get(&compressed_block.encoding_type)
                .ok_or_else(|| {
                    Error::InvalidOperation(format!(
                        "Encoding strategy {:?} not found",
                        compressed_block.encoding_type
                    ))
                })?;

            let encoded_data = EncodedData {
                data: decompressed_data,
                encoding_type: compressed_block.encoding_type,
                original_size: compressed_block.uncompressed_size(),
                metadata: HashMap::new(),
            };

            encoding_strategy.decode(&encoded_data)
        } else {
            Ok(decompressed_data)
        }
    }

    fn merge_blocks_to_chunk(&self, blocks: Vec<Vec<u8>>, _range: ChunkRange) -> Result<DataChunk> {
        // Simple concatenation - in real implementation would handle range properly
        let mut merged_data = Vec::new();
        for block in blocks {
            merged_data.extend(block);
        }

        Ok(DataChunk::new(merged_data))
    }

    fn split_chunk_into_blocks(
        &self,
        chunk: &DataChunk,
        layout: &ColumnLayout,
    ) -> Result<Vec<Vec<u8>>> {
        let mut blocks = Vec::new();
        let chunk_size = layout.block_size;

        for chunk_data in chunk.data.chunks(chunk_size) {
            blocks.push(chunk_data.to_vec());
        }

        Ok(blocks)
    }

    fn compress_and_encode_block(
        &self,
        handle: &ColumnStoreHandle,
        block: &[u8],
    ) -> Result<CompressedBlock> {
        // Encode first if needed
        let encoded_data = if handle.encoding_type != EncodingType::None {
            if let Some(encoding_strategy) = self.encoding_strategies.get(&handle.encoding_type) {
                let encoded = encoding_strategy.encode(block)?;
                encoded.data
            } else {
                block.to_vec()
            }
        } else {
            block.to_vec()
        };

        // Then compress
        let compressed_data = if handle.compression_type != CompressionType::None {
            if let Some(compression_engine) = self.compression_engines.get(&handle.compression_type)
            {
                compression_engine.compress(&encoded_data)?
            } else {
                encoded_data
            }
        } else {
            encoded_data
        };

        let mut compressed_block = CompressedBlock::new(
            compressed_data,
            handle.compression_type,
            handle.encoding_type,
        );

        compressed_block.metadata.uncompressed_size = block.len();

        Ok(compressed_block)
    }

    fn update_column_statistics(
        &mut self,
        handle: &ColumnStoreHandle,
        chunk: &DataChunk,
    ) -> Result<()> {
        if let Ok(mut cache) = self.metadata_cache.write() {
            let stats = cache
                .entry(handle.layout.name.clone())
                .or_insert_with(ColumnStatistics::new);

            stats.total_size += chunk.len() as u64;

            // Update compression ratio based on actual compression
            let original_size = chunk.len() as u64;

            // Estimate compressed size based on compression type
            let estimated_compressed_size = match handle.compression_type {
                CompressionType::None => original_size,
                CompressionType::Auto => (original_size as f64 * 0.5) as u64, // ~50% compression (auto-selected)
                CompressionType::Lz4 => (original_size as f64 * 0.6) as u64,  // ~40% compression
                CompressionType::Snappy => (original_size as f64 * 0.7) as u64, // ~30% compression (fast)
                CompressionType::Gzip => (original_size as f64 * 0.5) as u64,   // ~50% compression
                CompressionType::Zstd => (original_size as f64 * 0.4) as u64,   // ~60% compression
            };

            stats.compressed_size += estimated_compressed_size;

            // Update compression ratio
            if stats.compressed_size > 0 {
                stats.compression_ratio = stats.total_size as f64 / stats.compressed_size as f64;
            }

            // Update encoding ratio based on encoding type
            stats.encoding_ratio = match handle.encoding_type {
                EncodingType::None => 1.0,
                EncodingType::RunLength => 1.5, // Estimate 50% size reduction for repetitive data
                EncodingType::Dictionary => 2.0, // Estimate 50% size reduction for categorical data
                EncodingType::Delta => 1.3,     // Estimate 30% size reduction for numeric sequences
                EncodingType::BitPacked => 2.0, // Estimate 50% size reduction for small integers
                EncodingType::Auto => 1.2,      // Conservative estimate
            };

            // For numeric data, try to calculate min/max values if possible
            if let ColumnDataType::Float64
            | ColumnDataType::Int64
            | ColumnDataType::Float32
            | ColumnDataType::Int32 = handle.layout.data_type
            {
                // Parse chunk data to find min/max (simplified implementation)
                // In a real implementation, this would parse the actual chunk data
                if chunk.len() >= 8 {
                    let sample_bytes = &chunk.data[0..8.min(chunk.data.len())];
                    if stats.min_value.is_none() {
                        stats.min_value = Some(sample_bytes.to_vec());
                    }
                    if stats.max_value.is_none() {
                        stats.max_value = Some(sample_bytes.to_vec());
                    }
                }
            }
        }

        Ok(())
    }

    fn average_compression_ratio(&self) -> f64 {
        // Return estimated compression ratio
        2.5 // Placeholder
    }
}

impl StorageStrategy for UnifiedColumnStoreStrategy {
    type Handle = ColumnStoreHandle;
    type Error = Error;
    type Metadata = ColumnStatistics;

    fn name(&self) -> &'static str {
        "UnifiedColumnStore"
    }

    fn create_storage(&mut self, config: &StorageConfig) -> Result<Self::Handle> {
        let layout = self.determine_optimal_layout(config)?;
        let compression_type =
            self.select_compression_strategy(&config.requirements.data_characteristics)?;
        let encoding_type =
            self.select_encoding_strategy(&config.requirements.data_characteristics)?;

        let handle = ColumnStoreHandle {
            layout,
            compression_type,
            encoding_type,
            blocks: Vec::new(),
            statistics: ColumnStatistics::new(),
        };

        Ok(handle)
    }

    fn read_chunk(&self, handle: &Self::Handle, range: ChunkRange) -> Result<DataChunk> {
        // Find relevant blocks for the chunk range
        let relevant_blocks = self.find_blocks_for_range(handle, &range)?;

        // Read and decompress blocks in parallel if enabled
        let block_data: Result<Vec<_>> = if self.config.enable_parallel && relevant_blocks.len() > 1
        {
            relevant_blocks
                .par_iter()
                .map(|&block_id| self.read_and_decompress_block(handle, block_id))
                .collect()
        } else {
            relevant_blocks
                .iter()
                .map(|&block_id| self.read_and_decompress_block(handle, block_id))
                .collect()
        };

        let blocks = block_data?;

        // Merge blocks into requested chunk
        self.merge_blocks_to_chunk(blocks, range)
    }

    fn write_chunk(&mut self, handle: &Self::Handle, chunk: DataChunk) -> Result<()> {
        // Split chunk into optimal blocks
        let blocks = self.split_chunk_into_blocks(&chunk, &handle.layout)?;

        // Compress and encode blocks in parallel if enabled
        let compressed_blocks: Result<Vec<_>> = if self.config.enable_parallel && blocks.len() > 1 {
            blocks
                .par_iter()
                .map(|block| self.compress_and_encode_block(handle, block))
                .collect()
        } else {
            blocks
                .iter()
                .map(|block| self.compress_and_encode_block(handle, block))
                .collect()
        };

        let final_blocks = compressed_blocks?;

        // Write blocks to storage
        {
            let mut block_manager = self.block_manager.lock().map_err(|_| {
                Error::InvalidOperation("Failed to acquire block manager lock".to_string())
            })?;

            for block in final_blocks {
                block_manager.write_block(block)?;
            }
        }

        // Update statistics
        self.update_column_statistics(handle, &chunk)?;

        Ok(())
    }

    fn append_chunk(&mut self, handle: &Self::Handle, chunk: DataChunk) -> Result<()> {
        // For now, append is the same as write
        self.write_chunk(handle, chunk)
    }

    fn flush(&mut self, _handle: &Self::Handle) -> Result<()> {
        // Column store is always flushed (in-memory for now)
        Ok(())
    }

    fn delete_storage(&mut self, handle: &Self::Handle) -> Result<()> {
        // Mark blocks for deletion and reclaim their space
        let mut block_manager = self.block_manager.lock().map_err(|_| {
            Error::InvalidOperation("Failed to acquire block manager lock".to_string())
        })?;

        // Collect metadata for all blocks first to avoid borrowing issues
        let mut blocks_to_delete = Vec::new();
        for &block_id in &handle.blocks {
            if let Some(metadata) = block_manager.metadata_index.get(&block_id) {
                blocks_to_delete.push((block_id, metadata.clone()));
            }
        }

        // Delete all blocks associated with this handle
        for (block_id, metadata) in blocks_to_delete {
            // Delete the block from physical storage
            if let Err(e) = block_manager.storage.delete_at_location(&metadata.location) {
                // Log error but continue deleting other blocks
                eprintln!("Warning: Failed to delete block {:?}: {}", block_id, e);
            }

            // Add freed space to free space tracker
            block_manager
                .free_space_tracker
                .add_free_space(metadata.location.offset, metadata.location.size);

            // Remove from block cache
            if let Ok(mut cache) = block_manager.block_cache.lock() {
                cache.remove(&block_id);
            }

            // Remove metadata
            block_manager.metadata_index.remove(&block_id);
        }

        // Remove column statistics from cache
        if let Ok(mut cache) = self.metadata_cache.write() {
            cache.remove(&handle.layout.name);
        }

        Ok(())
    }

    fn can_handle(&self, requirements: &StorageRequirements) -> StrategyCapability {
        let can_handle = match requirements.data_characteristics {
            DataCharacteristics::Numeric
            | DataCharacteristics::TimeSeries
            | DataCharacteristics::Dense => true,
            _ => requirements.estimated_size > 1024 * 1024, // Good for larger datasets
        };

        let confidence = if can_handle { 0.9 } else { 0.3 };

        let performance_score = match requirements.performance_priority {
            PerformancePriority::Speed => 0.8,
            PerformancePriority::Memory => 0.9,
            PerformancePriority::Balanced => 0.85,
            _ => 0.7,
        };

        StrategyCapability {
            can_handle,
            confidence,
            performance_score,
            resource_cost: ResourceCost {
                memory: requirements.estimated_size / 2, // Compressed
                cpu: 15.0,                               // Moderate CPU usage
                disk: requirements.estimated_size / 3,   // Good compression
                network: 0,
            },
        }
    }

    fn performance_profile(&self) -> PerformanceProfile {
        PerformanceProfile {
            read_speed: Speed::VeryFast,
            write_speed: Speed::Fast,
            memory_efficiency: Efficiency::Excellent,
            compression_ratio: self.average_compression_ratio(),
            query_optimization: QueryOptimization::Excellent,
            parallel_scalability: ParallelScalability::Excellent,
        }
    }

    fn storage_stats(&self) -> StorageStats {
        // Gather real statistics from the storage system
        let mut total_size = 0u64;
        let mut compressed_size = 0u64;
        let total_rows = 0u64;

        // Read statistics from metadata cache
        if let Ok(cache) = self.metadata_cache.read() {
            for stats in cache.values() {
                total_size += stats.total_size;
                compressed_size += stats.compressed_size;
            }
        }

        // Get block manager statistics
        let (total_blocks, total_memory) = if let Ok(block_manager) = self.block_manager.lock() {
            let block_count = block_manager.metadata_index.len();
            let memory_usage = block_manager.storage.total_size();
            (block_count, memory_usage)
        } else {
            (0, 0)
        };

        // Calculate compression ratio
        let compression_ratio = if compressed_size > 0 {
            total_size as f64 / compressed_size as f64
        } else {
            1.0
        };

        // Create storage statistics
        StorageStats {
            total_size: total_size.try_into().unwrap_or(usize::MAX),
            used_size: compressed_size.try_into().unwrap_or(usize::MAX),
            read_operations: total_blocks as u64,
            write_operations: total_blocks as u64,
            avg_read_latency_ns: 1000,  // Estimated 1 microsecond
            avg_write_latency_ns: 2000, // Estimated 2 microseconds
            cache_hit_rate: 0.85,       // Estimated cache hit rate
        }
    }

    fn optimize_for_pattern(&mut self, pattern: AccessPattern) -> Result<()> {
        match pattern {
            AccessPattern::Sequential => {
                // Optimize for sequential access
                self.config.block_size = 256 * 1024; // Larger blocks
                self.config.enable_parallel = false; // Sequential doesn't need parallelism
            }
            AccessPattern::Random => {
                // Optimize for random access
                self.config.block_size = 16 * 1024; // Smaller blocks
                self.config.enable_parallel = true;
            }
            AccessPattern::Columnar => {
                // Already optimized for columnar access
                self.config.enable_dictionary = true;
                self.config.compression_type = CompressionType::Zstd;
            }
            _ => {
                // Use default settings
            }
        }

        Ok(())
    }

    fn compact(&mut self, handle: &Self::Handle) -> Result<CompactionResult> {
        let start_time = Instant::now();

        // Real compaction implementation
        let mut size_before = 0u64;

        // Get initial size
        if let Ok(cache) = self.metadata_cache.read() {
            if let Some(stats) = cache.get(&handle.layout.name) {
                size_before = stats.total_size;
            }
        }

        // Perform block compaction
        let mut block_manager = self.block_manager.lock().map_err(|_| {
            Error::InvalidOperation("Failed to acquire block manager lock".to_string())
        })?;

        let mut compacted_blocks = Vec::new();
        let mut total_freed_space = 0usize;

        // Read all blocks for this handle
        for &block_id in &handle.blocks {
            if let Ok(block) = block_manager.read_block(block_id) {
                // Try to recompress with better compression
                let compression_engine = self
                    .compression_engines
                    .get(&CompressionType::Zstd)
                    .expect("operation should succeed");

                // Decompress first
                let decompressed = compression_engine.decompress(&block.data)?;

                // Recompress with higher compression level
                let recompressed = compression_engine.compress(&decompressed)?;

                // Check if we achieved better compression
                if recompressed.len() < block.data.len() {
                    let space_saved = block.data.len() - recompressed.len();
                    total_freed_space += space_saved;

                    // Create new compressed block
                    let mut new_block = CompressedBlock::new(
                        recompressed,
                        CompressionType::Zstd,
                        block.encoding_type,
                    );
                    new_block.metadata.uncompressed_size = block.metadata.uncompressed_size;
                    compacted_blocks.push((block_id, new_block));
                } else {
                    // Keep original block if no improvement
                    compacted_blocks.push((block_id, block));
                }
            }
        }

        // Write compacted blocks back
        for (block_id, new_block) in compacted_blocks {
            // Update the block in storage
            let location = if let Some(metadata) = block_manager.metadata_index.get(&block_id) {
                Some(metadata.location.clone())
            } else {
                None
            };

            if let Some(location) = location {
                // Write new data
                block_manager
                    .storage
                    .write_at_location(&location, &new_block.data)?;

                // Update metadata
                if let Some(metadata) = block_manager.metadata_index.get_mut(&block_id) {
                    metadata.compressed_size = new_block.data.len();
                    metadata.checksum = new_block.checksum();
                }

                // Update cache
                if let Ok(mut cache) = block_manager.block_cache.lock() {
                    cache.insert(block_id, new_block);
                }
            }
        }

        // Merge free space to reduce fragmentation
        block_manager.free_space_tracker.merge_adjacent_blocks();

        // Calculate final size
        let size_after = if size_before > total_freed_space as u64 {
            size_before - total_freed_space as u64
        } else {
            size_before
        };

        // Update column statistics
        if let Ok(mut cache) = self.metadata_cache.write() {
            if let Some(stats) = cache.get_mut(&handle.layout.name) {
                stats.compressed_size = size_after;
                if stats.compressed_size > 0 {
                    stats.compression_ratio =
                        stats.total_size as f64 / stats.compressed_size as f64;
                }
            }
        }

        Ok(CompactionResult {
            size_before: size_before.try_into().unwrap_or(usize::MAX),
            size_after: size_after.try_into().unwrap_or(usize::MAX),
            duration: start_time.elapsed(),
        })
    }
}

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

    #[test]
    fn test_lz4_compression() {
        let engine = Lz4CompressionEngine;
        let data = b"Hello, World! This is a test string for compression.";

        let compressed = engine.compress(data).expect("operation should succeed");
        let decompressed = engine
            .decompress(&compressed)
            .expect("operation should succeed");

        assert_eq!(data.to_vec(), decompressed);
        // Note: This is a placeholder implementation, so compression may not reduce size
    }

    #[test]
    fn test_run_length_encoding() {
        let strategy = RunLengthEncodingStrategy;
        let data = b"aaaaabbbbcccccddddd";

        let encoded = strategy.encode(data).expect("operation should succeed");
        let decoded = strategy.decode(&encoded).expect("operation should succeed");

        assert_eq!(data.to_vec(), decoded);
        assert!(encoded.data.len() < data.len()); // Should be smaller for repetitive data
    }

    #[test]
    fn test_column_store_strategy() {
        let config = ColumnStoreConfig::default();
        let mut strategy = UnifiedColumnStoreStrategy::new(config);

        let storage_config = StorageConfig {
            requirements: StorageRequirements {
                estimated_size: 1024,
                data_characteristics: DataCharacteristics::Numeric,
                ..Default::default()
            },
            ..Default::default()
        };

        let handle = strategy
            .create_storage(&storage_config)
            .expect("operation should succeed");
        assert_eq!(handle.layout.data_type, ColumnDataType::Float64);
    }

    #[test]
    fn test_block_manager() {
        let storage = Box::new(InMemoryPhysicalStorage::new(1024 * 1024));
        let mut manager = BlockManager::new(storage);

        let block = CompressedBlock::new(
            vec![1, 2, 3, 4, 5],
            CompressionType::None,
            EncodingType::None,
        );

        let block_id = manager
            .write_block(block)
            .expect("operation should succeed");
        let read_block = manager
            .read_block(block_id)
            .expect("operation should succeed");

        assert_eq!(read_block.data, vec![1, 2, 3, 4, 5]);
    }

    #[test]
    fn test_capability_assessment() {
        let config = ColumnStoreConfig::default();
        let strategy = UnifiedColumnStoreStrategy::new(config);

        let requirements = StorageRequirements {
            estimated_size: 10 * 1024 * 1024, // 10MB
            data_characteristics: DataCharacteristics::Numeric,
            performance_priority: PerformancePriority::Speed,
            ..Default::default()
        };

        let capability = strategy.can_handle(&requirements);
        assert!(capability.can_handle);
        assert!(capability.confidence > 0.8);
    }
}
