//! Unified memory pool system across all backends

use crate::{BackendType, Device, MemoryPool, MemoryPoolConfig, MemoryStats, PoolStats};
use parking_lot::{Mutex, RwLock};
use std::collections::HashMap;
use std::sync::Arc;
use torsh_core::{
    device::DeviceType,
    error::{Result, TorshError},
};

// Helper conversion from DeviceType to BackendType
impl From<DeviceType> for BackendType {
    fn from(device_type: DeviceType) -> Self {
        match device_type {
            DeviceType::Cpu => BackendType::Cpu,
            DeviceType::Cuda(_) => BackendType::Cuda,
            DeviceType::Metal(_) => BackendType::Metal,
            DeviceType::Wgpu(_) => BackendType::WebGpu,
        }
    }
}

#[cfg(not(feature = "std"))]
use alloc::{boxed::Box, format, vec::Vec};

/// Unified memory pool that works across all backend types
pub struct UnifiedMemoryPool {
    /// Backend-specific memory pools
    backend_pools: RwLock<HashMap<BackendType, Arc<Mutex<Box<dyn MemoryPool>>>>>,

    /// Configuration for each backend type
    backend_configs: RwLock<HashMap<BackendType, MemoryPoolConfig>>,

    /// Global statistics aggregated across all backends
    global_stats: RwLock<MemoryStats>,

    /// Pool statistics per backend
    pool_stats: RwLock<HashMap<BackendType, PoolStats>>,

    /// Default configuration for new backends
    default_config: MemoryPoolConfig,

    /// Enable cross-backend memory sharing
    enable_cross_backend_sharing: bool,

    /// Memory pressure threshold (0.0 to 1.0)
    pressure_threshold: f32,

    /// Enable automatic garbage collection
    enable_auto_gc: bool,
}

impl UnifiedMemoryPool {
    /// Create a new unified memory pool
    pub fn new(default_config: MemoryPoolConfig) -> Self {
        Self {
            backend_pools: RwLock::new(HashMap::new()),
            backend_configs: RwLock::new(HashMap::new()),
            global_stats: RwLock::new(MemoryStats::default()),
            pool_stats: RwLock::new(HashMap::new()),
            default_config,
            enable_cross_backend_sharing: false,
            pressure_threshold: 0.85,
            enable_auto_gc: true,
        }
    }

    /// Create a unified memory pool with default configuration
    pub fn with_default_config() -> Self {
        Self::new(MemoryPoolConfig::default())
    }

    /// Register a backend-specific memory pool
    pub fn register_backend_pool(
        &self,
        backend_type: BackendType,
        pool: Box<dyn MemoryPool>,
        config: Option<MemoryPoolConfig>,
    ) -> Result<()> {
        let config = config.unwrap_or_else(|| self.default_config.clone());

        {
            let mut pools = self.backend_pools.write();
            pools.insert(backend_type, Arc::new(Mutex::new(pool)));
        }

        {
            let mut configs = self.backend_configs.write();
            configs.insert(backend_type, config);
        }

        self.update_global_stats()?;
        Ok(())
    }

    /// Unregister a backend pool
    pub fn unregister_backend_pool(&self, backend_type: BackendType) -> Result<()> {
        {
            let mut pools = self.backend_pools.write();
            pools.remove(&backend_type);
        }

        {
            let mut configs = self.backend_configs.write();
            configs.remove(&backend_type);
        }

        {
            let mut stats = self.pool_stats.write();
            stats.remove(&backend_type);
        }

        self.update_global_stats()?;
        Ok(())
    }

    /// Get or create a backend-specific pool
    pub fn get_or_create_pool(
        &self,
        backend_type: BackendType,
        device: &Device,
    ) -> Result<Arc<Mutex<Box<dyn MemoryPool>>>> {
        {
            let pools = self.backend_pools.read();
            if let Some(pool) = pools.get(&backend_type) {
                return Ok(Arc::clone(pool));
            }
        }

        // Create a new pool for this backend
        let config = self
            .backend_configs
            .read()
            .get(&backend_type)
            .cloned()
            .unwrap_or_else(|| self.default_config.clone());

        let pool = self.create_backend_pool(backend_type, device, config)?;
        self.register_backend_pool(backend_type, pool, None)?;

        let pools = self.backend_pools.read();
        pools
            .get(&backend_type)
            .cloned()
            .ok_or_else(|| TorshError::BackendError("Failed to create backend pool".to_string()))
    }

    /// Create a backend-specific memory pool
    fn create_backend_pool(
        &self,
        backend_type: BackendType,
        device: &Device,
        config: MemoryPoolConfig,
    ) -> Result<Box<dyn MemoryPool>> {
        match backend_type {
            BackendType::Cpu => Ok(Box::new(CpuMemoryPool::new(device.clone(), config))),
            BackendType::Cuda => Ok(Box::new(CudaMemoryPool::new(device.clone(), config))),
            BackendType::Metal => Ok(Box::new(MetalMemoryPool::new(device.clone(), config))),
            BackendType::WebGpu => Ok(Box::new(WebGpuMemoryPool::new(device.clone(), config))),
            BackendType::Rocm => Ok(Box::new(RocmMemoryPool::new(device.clone(), config))),
            BackendType::Auto => Err(TorshError::BackendError(
                "Cannot create pool for Auto backend type".to_string(),
            )),
        }
    }

    /// Allocate memory from the appropriate backend pool
    pub fn allocate(&self, device: &Device, size: usize, alignment: usize) -> Result<*mut u8> {
        let backend_type = device.device_type().into();
        let pool = self.get_or_create_pool(backend_type, device)?;

        // Check memory pressure before allocation
        if self.enable_auto_gc && self.is_under_pressure(backend_type)? {
            self.garbage_collect_backend(backend_type)?;
        }

        let result = {
            let mut pool = pool.lock();
            pool.allocate(size, alignment)
        };

        // Update statistics
        if result.is_ok() {
            self.update_global_stats()?;
        }

        result
    }

    /// Deallocate memory to the appropriate backend pool
    pub fn deallocate(&self, device: &Device, ptr: *mut u8, size: usize) -> Result<()> {
        let backend_type = device.device_type().into();
        let pool = self.get_or_create_pool(backend_type, device)?;

        let result = {
            let mut pool = pool.lock();
            pool.deallocate(ptr, size)
        };

        // Update statistics
        if result.is_ok() {
            self.update_global_stats()?;
        }

        result
    }

    /// Check if a backend is under memory pressure
    pub fn is_under_pressure(&self, backend_type: BackendType) -> Result<bool> {
        let pools = self.backend_pools.read();
        if let Some(pool) = pools.get(&backend_type) {
            let pool = pool.lock();
            let stats = pool.stats();
            let utilization = stats.allocated as f32 / stats.capacity as f32;
            Ok(utilization > self.pressure_threshold)
        } else {
            Ok(false)
        }
    }

    /// Garbage collect a specific backend
    pub fn garbage_collect_backend(&self, backend_type: BackendType) -> Result<usize> {
        let pools = self.backend_pools.read();
        let available = if let Some(pool) = pools.get(&backend_type) {
            let mut pool = pool.lock();
            pool.reset()?;
            let available = pool.available();
            // Drop the pool lock before updating global stats to avoid deadlock
            drop(pool);
            available
        } else {
            0
        };

        // Drop the pools read lock as well
        drop(pools);

        // Now update global stats without holding any locks
        self.update_global_stats()?;
        Ok(available)
    }

    /// Garbage collect all backends
    pub fn garbage_collect_all(&self) -> Result<usize> {
        let mut total_freed = 0;
        let backend_types: Vec<BackendType> =
            { self.backend_pools.read().keys().cloned().collect() };

        for backend_type in backend_types {
            total_freed += self.garbage_collect_backend(backend_type)?;
        }

        Ok(total_freed)
    }

    /// Defragment memory for a specific backend
    pub fn defragment_backend(
        &self,
        backend_type: BackendType,
    ) -> Result<crate::memory::DefragmentationResult> {
        use std::time::Instant;

        let pools = self.backend_pools.read();
        if let Some(pool) = pools.get(&backend_type) {
            let mut pool = pool.lock();
            let _start_time = Instant::now();

            // Get fragmentation info before defragmentation
            let _frag_before = pool.fragmentation_info();

            // Perform defragmentation
            let result = pool.defragment()?;

            // Update statistics
            self.update_global_stats()?;

            Ok(result)
        } else {
            Err(TorshError::BackendError(format!(
                "Backend {:?} not found for defragmentation",
                backend_type
            )))
        }
    }

    /// Defragment all backends that need it
    pub fn defragment_all(
        &self,
    ) -> Result<Vec<(BackendType, crate::memory::DefragmentationResult)>> {
        let mut results = Vec::new();
        let backend_types: Vec<BackendType> =
            { self.backend_pools.read().keys().cloned().collect() };

        for backend_type in backend_types {
            if self.backend_needs_defragmentation(backend_type)? {
                let result = self.defragment_backend(backend_type)?;
                results.push((backend_type, result));
            }
        }

        Ok(results)
    }

    /// Check if a backend needs defragmentation
    pub fn backend_needs_defragmentation(&self, backend_type: BackendType) -> Result<bool> {
        let pools = self.backend_pools.read();
        if let Some(pool) = pools.get(&backend_type) {
            let pool = pool.lock();
            Ok(pool.needs_defragmentation())
        } else {
            Ok(false)
        }
    }

    /// Get fragmentation information for a backend
    pub fn get_backend_fragmentation_info(
        &self,
        backend_type: BackendType,
    ) -> Result<crate::memory::FragmentationInfo> {
        let pools = self.backend_pools.read();
        if let Some(pool) = pools.get(&backend_type) {
            let pool = pool.lock();
            Ok(pool.fragmentation_info())
        } else {
            Err(TorshError::BackendError(format!(
                "Backend {:?} not found",
                backend_type
            )))
        }
    }

    /// Compact memory for a specific backend
    pub fn compact_backend(
        &self,
        backend_type: BackendType,
    ) -> Result<crate::memory::CompactionResult> {
        let pools = self.backend_pools.read();
        if let Some(pool) = pools.get(&backend_type) {
            let mut pool = pool.lock();
            let result = pool.compact()?;

            // Update statistics
            self.update_global_stats()?;

            Ok(result)
        } else {
            Err(TorshError::BackendError(format!(
                "Backend {:?} not found for compaction",
                backend_type
            )))
        }
    }

    /// Get overall fragmentation across all backends
    pub fn get_overall_fragmentation(&self) -> Result<crate::memory::FragmentationInfo> {
        let pools = self.backend_pools.read();
        let mut total_free_blocks = 0;
        let mut total_allocated_blocks = 0;
        let mut total_free_memory = 0;
        let mut total_allocated_memory = 0;
        let mut total_fragmentation = 0.0;
        let mut backend_count = 0;
        let mut largest_free_block = 0;
        let mut smallest_free_block = usize::MAX;

        for pool in pools.values() {
            let pool = pool.lock();
            let frag_info = pool.fragmentation_info();

            total_free_blocks += frag_info.free_blocks;
            total_allocated_blocks += frag_info.allocated_blocks;
            total_free_memory += frag_info.total_free_memory;
            total_allocated_memory += frag_info.total_allocated_memory;
            total_fragmentation += frag_info.overall_fragmentation;
            backend_count += 1;

            largest_free_block = largest_free_block.max(frag_info.largest_free_block);
            if frag_info.smallest_free_block > 0 {
                smallest_free_block = smallest_free_block.min(frag_info.smallest_free_block);
            }
        }

        if smallest_free_block == usize::MAX {
            smallest_free_block = 0;
        }

        let average_free_block = if total_free_blocks > 0 {
            total_free_memory / total_free_blocks
        } else {
            0
        };

        let overall_fragmentation = if backend_count > 0 {
            total_fragmentation / backend_count as f32
        } else {
            0.0
        };

        let utilization_efficiency = if total_free_memory + total_allocated_memory > 0 {
            total_allocated_memory as f32 / (total_free_memory + total_allocated_memory) as f32
        } else {
            0.0
        };

        Ok(crate::memory::FragmentationInfo {
            overall_fragmentation,
            external_fragmentation: overall_fragmentation * 0.8, // Estimate
            internal_fragmentation: overall_fragmentation * 0.2, // Estimate
            free_blocks: total_free_blocks,
            allocated_blocks: total_allocated_blocks,
            largest_free_block,
            smallest_free_block,
            average_free_block,
            total_free_memory,
            total_allocated_memory,
            utilization_efficiency,
            allocation_efficiency: utilization_efficiency, // Simplified
        })
    }

    /// Enable or disable automatic defragmentation
    pub fn set_auto_defragmentation(&mut self, enabled: bool) {
        self.enable_auto_gc = enabled;
    }

    /// Set memory pressure threshold for automatic defragmentation
    pub fn set_pressure_threshold(&mut self, threshold: f32) {
        self.pressure_threshold = threshold.clamp(0.0, 1.0);
    }

    /// Perform automatic maintenance (garbage collection and defragmentation)
    pub fn perform_automatic_maintenance(&self) -> Result<()> {
        if !self.enable_auto_gc {
            return Ok(());
        }

        let backend_types: Vec<BackendType> =
            { self.backend_pools.read().keys().cloned().collect() };

        for backend_type in backend_types {
            // Check if backend is under pressure
            if self.is_under_pressure(backend_type)? {
                // Try garbage collection first
                self.garbage_collect_backend(backend_type)?;

                // If still under pressure, try defragmentation
                if self.is_under_pressure(backend_type)? {
                    self.defragment_backend(backend_type)?;
                }
            } else if self.backend_needs_defragmentation(backend_type)? {
                // Even if not under pressure, defragment if highly fragmented
                let frag_info = self.get_backend_fragmentation_info(backend_type)?;
                if frag_info.is_severely_fragmented() {
                    self.defragment_backend(backend_type)?;
                }
            }
        }

        Ok(())
    }

    /// Update global statistics from all backend pools
    fn update_global_stats(&self) -> Result<()> {
        let mut total_capacity = 0;
        let mut total_allocated = 0;
        let mut total_available = 0;
        let mut backend_stats = HashMap::new();

        {
            let pools = self.backend_pools.read();
            for (backend_type, pool) in pools.iter() {
                let pool = pool.lock();
                let stats = pool.stats();

                total_capacity += stats.capacity;
                total_allocated += stats.allocated;
                total_available += stats.available;

                backend_stats.insert(*backend_type, stats);
            }
        }

        // Update pool stats
        {
            let mut pool_stats = self.pool_stats.write();
            *pool_stats = backend_stats;
        }

        // Update global stats
        {
            let mut global_stats = self.global_stats.write();
            global_stats.total_memory = total_capacity;
            global_stats.allocated_memory = total_allocated;
            global_stats.available_memory = total_available;
            global_stats.efficiency = if total_capacity > 0 {
                total_allocated as f32 / total_capacity as f32
            } else {
                0.0
            };
        }

        Ok(())
    }

    /// Get global memory statistics
    pub fn global_stats(&self) -> MemoryStats {
        self.global_stats.read().clone()
    }

    /// Get statistics for a specific backend
    pub fn backend_stats(&self, backend_type: BackendType) -> Option<PoolStats> {
        self.pool_stats.read().get(&backend_type).cloned()
    }

    /// Get all backend statistics
    pub fn all_backend_stats(&self) -> HashMap<BackendType, PoolStats> {
        self.pool_stats.read().clone()
    }

    /// Enable or disable automatic garbage collection
    pub fn set_auto_gc(&mut self, enable: bool) {
        self.enable_auto_gc = enable;
    }

    /// Enable or disable cross-backend memory sharing
    pub fn set_cross_backend_sharing(&mut self, enable: bool) {
        self.enable_cross_backend_sharing = enable;
    }

    /// Get list of registered backends
    pub fn registered_backends(&self) -> Vec<BackendType> {
        self.backend_pools.read().keys().cloned().collect()
    }

    /// Reset all backend pools
    pub fn reset_all(&self) -> Result<()> {
        let backend_types: Vec<BackendType> =
            { self.backend_pools.read().keys().cloned().collect() };

        for backend_type in backend_types {
            let pools = self.backend_pools.read();
            if let Some(pool) = pools.get(&backend_type) {
                let mut pool = pool.lock();
                pool.reset()?;
            }
        }

        self.update_global_stats()?;
        Ok(())
    }

    /// Get memory configuration for a backend
    pub fn backend_config(&self, backend_type: BackendType) -> Option<MemoryPoolConfig> {
        self.backend_configs.read().get(&backend_type).cloned()
    }

    /// Update memory configuration for a backend
    pub fn set_backend_config(
        &self,
        backend_type: BackendType,
        config: MemoryPoolConfig,
    ) -> Result<()> {
        {
            let mut configs = self.backend_configs.write();
            configs.insert(backend_type, config);
        }
        Ok(())
    }
}

/// Backend-specific memory pool implementations
mod backend_pools {
    use super::*;

    /// CPU memory pool implementation
    #[derive(Debug)]
    pub struct CpuMemoryPool {
        #[allow(dead_code)]
        device: Device,
        config: MemoryPoolConfig,
        allocated_blocks: RwLock<Vec<(usize, usize)>>, // (address as usize, size)
        stats: RwLock<PoolStats>,
    }

    impl CpuMemoryPool {
        pub fn new(device: Device, config: MemoryPoolConfig) -> Self {
            let stats = PoolStats {
                capacity: config.initial_size,
                available: config.initial_size,
                ..Default::default()
            };

            Self {
                device,
                config,
                allocated_blocks: RwLock::new(Vec::new()),
                stats: RwLock::new(stats),
            }
        }
    }

    impl MemoryPool for CpuMemoryPool {
        fn allocate(&mut self, size: usize, alignment: usize) -> Result<*mut u8> {
            use std::alloc::{alloc, Layout};

            let layout = Layout::from_size_align(size, alignment)
                .map_err(|e| TorshError::AllocationError(format!("Invalid layout: {}", e)))?;

            let ptr = unsafe { alloc(layout) };
            if ptr.is_null() {
                return Err(TorshError::AllocationError(
                    "Failed to allocate CPU memory".to_string(),
                ));
            }

            // Track allocation
            {
                let mut blocks = self.allocated_blocks.write();
                blocks.push((ptr as usize, size));
            }

            // Update stats
            {
                let mut stats = self.stats.write();
                stats.allocated += size;
                stats.available = stats.capacity.saturating_sub(stats.allocated);
                stats.allocated_blocks += 1;
            }

            Ok(ptr)
        }

        fn deallocate(&mut self, ptr: *mut u8, size: usize) -> Result<()> {
            use std::alloc::{dealloc, Layout};

            // Find and remove allocation
            {
                let mut blocks = self.allocated_blocks.write();
                if let Some(pos) = blocks
                    .iter()
                    .position(|(addr, s)| *addr == ptr as usize && *s == size)
                {
                    blocks.remove(pos);
                } else {
                    return Err(TorshError::InvalidArgument(
                        "Block not found for deallocation".to_string(),
                    ));
                }
            }

            // Deallocate memory
            let layout = Layout::from_size_align(size, self.config.alignment)
                .map_err(|e| TorshError::AllocationError(format!("Invalid layout: {}", e)))?;

            unsafe {
                dealloc(ptr, layout);
            }

            // Update stats
            {
                let mut stats = self.stats.write();
                stats.allocated = stats.allocated.saturating_sub(size);
                stats.available = stats.capacity.saturating_sub(stats.allocated);
                stats.allocated_blocks = stats.allocated_blocks.saturating_sub(1);
            }

            Ok(())
        }

        fn stats(&self) -> PoolStats {
            self.stats.read().clone()
        }

        fn reset(&mut self) -> Result<()> {
            use std::alloc::{dealloc, Layout};

            // Deallocate all blocks
            {
                let blocks = self.allocated_blocks.read().clone();
                for (addr, size) in blocks {
                    let layout =
                        Layout::from_size_align(size, self.config.alignment).map_err(|e| {
                            TorshError::AllocationError(format!("Invalid layout: {}", e))
                        })?;
                    unsafe {
                        dealloc(addr as *mut u8, layout);
                    }
                }
            }

            // Clear tracking
            {
                let mut blocks = self.allocated_blocks.write();
                blocks.clear();
            }

            // Reset stats
            {
                let mut stats = self.stats.write();
                stats.allocated = 0;
                stats.available = stats.capacity;
                stats.allocated_blocks = 0;
            }

            Ok(())
        }

        fn capacity(&self) -> usize {
            self.config.initial_size
        }

        fn available(&self) -> usize {
            self.stats.read().available
        }

        fn defragment(&mut self) -> Result<crate::memory::DefragmentationResult> {
            // Simple stub implementation - in a real implementation this would
            // move allocated blocks to reduce fragmentation
            Ok(crate::memory::DefragmentationResult {
                blocks_moved: 0,
                memory_compacted: 0,
                duration_ms: 0.0,
                fragmentation_before: 0.0,
                fragmentation_after: 0.0,
                efficiency_improvement: 0.0,
                success: true,
            })
        }

        fn needs_defragmentation(&self) -> bool {
            // Simple heuristic: check if we have many small allocations
            let stats = self.stats.read();
            stats.allocated_blocks > 10 && stats.allocated < stats.capacity / 2
        }

        fn fragmentation_info(&self) -> crate::memory::FragmentationInfo {
            let stats = self.stats.read();
            let fragmentation = if stats.capacity > 0 {
                1.0 - (stats.available as f32 / stats.capacity as f32)
            } else {
                0.0
            };

            crate::memory::FragmentationInfo {
                overall_fragmentation: fragmentation,
                external_fragmentation: fragmentation * 0.8,
                internal_fragmentation: fragmentation * 0.2,
                free_blocks: if stats.available > 0 { 1 } else { 0 },
                allocated_blocks: stats.allocated_blocks,
                largest_free_block: stats.available,
                smallest_free_block: if stats.available > 0 {
                    stats.available
                } else {
                    0
                },
                average_free_block: stats.available,
                total_free_memory: stats.available,
                total_allocated_memory: stats.allocated,
                utilization_efficiency: if stats.capacity > 0 {
                    stats.allocated as f32 / stats.capacity as f32
                } else {
                    0.0
                },
                allocation_efficiency: if stats.capacity > 0 {
                    stats.allocated as f32 / stats.capacity as f32
                } else {
                    0.0
                },
            }
        }

        fn compact(&mut self) -> Result<crate::memory::CompactionResult> {
            // Simple stub implementation - in a real implementation this would
            // move allocations to create larger contiguous free blocks
            Ok(crate::memory::CompactionResult {
                allocations_moved: 0,
                bytes_moved: 0,
                duration_ms: 0.0,
                largest_free_before: self.available(),
                largest_free_after: self.available(),
                free_blocks_before: 1,
                free_blocks_after: 1,
                success: true,
            })
        }
    }

    // Placeholder implementations for other backends
    // In a real implementation, these would use backend-specific allocation

    #[derive(Debug)]
    pub struct CudaMemoryPool {
        #[allow(dead_code)]
        device: Device,
        config: MemoryPoolConfig,
        stats: RwLock<PoolStats>,
    }

    impl CudaMemoryPool {
        pub fn new(device: Device, config: MemoryPoolConfig) -> Self {
            let stats = PoolStats {
                capacity: config.initial_size,
                available: config.initial_size,
                ..Default::default()
            };

            Self {
                device,
                config,
                stats: RwLock::new(stats),
            }
        }
    }

    impl MemoryPool for CudaMemoryPool {
        fn allocate(&mut self, _size: usize, _alignment: usize) -> Result<*mut u8> {
            // Placeholder - would use CUDA allocation
            Ok(std::ptr::null_mut())
        }

        fn deallocate(&mut self, _ptr: *mut u8, _size: usize) -> Result<()> {
            // Placeholder - would use CUDA deallocation
            Ok(())
        }

        fn stats(&self) -> PoolStats {
            self.stats.read().clone()
        }

        fn reset(&mut self) -> Result<()> {
            Ok(())
        }

        fn capacity(&self) -> usize {
            self.config.initial_size
        }

        fn available(&self) -> usize {
            self.stats.read().available
        }

        fn defragment(&mut self) -> Result<crate::memory::DefragmentationResult> {
            Ok(crate::memory::DefragmentationResult {
                blocks_moved: 0,
                memory_compacted: 0,
                duration_ms: 0.0,
                fragmentation_before: 0.0,
                fragmentation_after: 0.0,
                efficiency_improvement: 0.0,
                success: true,
            })
        }

        fn needs_defragmentation(&self) -> bool {
            false
        }

        fn fragmentation_info(&self) -> crate::memory::FragmentationInfo {
            let stats = self.stats.read();
            crate::memory::FragmentationInfo {
                overall_fragmentation: 0.0,
                external_fragmentation: 0.0,
                internal_fragmentation: 0.0,
                free_blocks: 1,
                allocated_blocks: stats.allocated_blocks,
                largest_free_block: stats.available,
                smallest_free_block: stats.available,
                average_free_block: stats.available,
                total_free_memory: stats.available,
                total_allocated_memory: stats.allocated,
                utilization_efficiency: 0.0,
                allocation_efficiency: 0.0,
            }
        }

        fn compact(&mut self) -> Result<crate::memory::CompactionResult> {
            Ok(crate::memory::CompactionResult {
                allocations_moved: 0,
                bytes_moved: 0,
                duration_ms: 0.0,
                largest_free_before: self.available(),
                largest_free_after: self.available(),
                free_blocks_before: 1,
                free_blocks_after: 1,
                success: true,
            })
        }
    }

    // Similar placeholder implementations for Metal, WebGPU, and ROCm

    #[derive(Debug)]
    pub struct MetalMemoryPool {
        #[allow(dead_code)]
        device: Device,
        config: MemoryPoolConfig,
        stats: RwLock<PoolStats>,
    }

    impl MetalMemoryPool {
        pub fn new(device: Device, config: MemoryPoolConfig) -> Self {
            let stats = PoolStats {
                capacity: config.initial_size,
                available: config.initial_size,
                ..Default::default()
            };

            Self {
                device,
                config,
                stats: RwLock::new(stats),
            }
        }
    }

    impl MemoryPool for MetalMemoryPool {
        fn allocate(&mut self, _size: usize, _alignment: usize) -> Result<*mut u8> {
            Ok(std::ptr::null_mut())
        }

        fn deallocate(&mut self, _ptr: *mut u8, _size: usize) -> Result<()> {
            Ok(())
        }

        fn stats(&self) -> PoolStats {
            self.stats.read().clone()
        }

        fn reset(&mut self) -> Result<()> {
            Ok(())
        }

        fn capacity(&self) -> usize {
            self.config.initial_size
        }

        fn available(&self) -> usize {
            self.stats.read().available
        }

        fn defragment(&mut self) -> Result<crate::memory::DefragmentationResult> {
            Ok(crate::memory::DefragmentationResult {
                blocks_moved: 0,
                memory_compacted: 0,
                duration_ms: 0.0,
                fragmentation_before: 0.0,
                fragmentation_after: 0.0,
                efficiency_improvement: 0.0,
                success: true,
            })
        }

        fn needs_defragmentation(&self) -> bool {
            false
        }

        fn fragmentation_info(&self) -> crate::memory::FragmentationInfo {
            let stats = self.stats.read();
            crate::memory::FragmentationInfo {
                overall_fragmentation: 0.0,
                external_fragmentation: 0.0,
                internal_fragmentation: 0.0,
                free_blocks: 1,
                allocated_blocks: stats.allocated_blocks,
                largest_free_block: stats.available,
                smallest_free_block: stats.available,
                average_free_block: stats.available,
                total_free_memory: stats.available,
                total_allocated_memory: stats.allocated,
                utilization_efficiency: 0.0,
                allocation_efficiency: 0.0,
            }
        }

        fn compact(&mut self) -> Result<crate::memory::CompactionResult> {
            Ok(crate::memory::CompactionResult {
                allocations_moved: 0,
                bytes_moved: 0,
                duration_ms: 0.0,
                largest_free_before: self.available(),
                largest_free_after: self.available(),
                free_blocks_before: 1,
                free_blocks_after: 1,
                success: true,
            })
        }
    }

    #[derive(Debug)]
    pub struct WebGpuMemoryPool {
        #[allow(dead_code)]
        device: Device,
        config: MemoryPoolConfig,
        stats: RwLock<PoolStats>,
    }

    impl WebGpuMemoryPool {
        pub fn new(device: Device, config: MemoryPoolConfig) -> Self {
            let stats = PoolStats {
                capacity: config.initial_size,
                available: config.initial_size,
                ..Default::default()
            };

            Self {
                device,
                config,
                stats: RwLock::new(stats),
            }
        }
    }

    impl MemoryPool for WebGpuMemoryPool {
        fn allocate(&mut self, _size: usize, _alignment: usize) -> Result<*mut u8> {
            Ok(std::ptr::null_mut())
        }

        fn deallocate(&mut self, _ptr: *mut u8, _size: usize) -> Result<()> {
            Ok(())
        }

        fn stats(&self) -> PoolStats {
            self.stats.read().clone()
        }

        fn reset(&mut self) -> Result<()> {
            Ok(())
        }

        fn capacity(&self) -> usize {
            self.config.initial_size
        }

        fn available(&self) -> usize {
            self.stats.read().available
        }

        fn defragment(&mut self) -> Result<crate::memory::DefragmentationResult> {
            Ok(crate::memory::DefragmentationResult {
                blocks_moved: 0,
                memory_compacted: 0,
                duration_ms: 0.0,
                fragmentation_before: 0.0,
                fragmentation_after: 0.0,
                efficiency_improvement: 0.0,
                success: true,
            })
        }

        fn needs_defragmentation(&self) -> bool {
            false
        }

        fn fragmentation_info(&self) -> crate::memory::FragmentationInfo {
            let stats = self.stats.read();
            crate::memory::FragmentationInfo {
                overall_fragmentation: 0.0,
                external_fragmentation: 0.0,
                internal_fragmentation: 0.0,
                free_blocks: 1,
                allocated_blocks: stats.allocated_blocks,
                largest_free_block: stats.available,
                smallest_free_block: stats.available,
                average_free_block: stats.available,
                total_free_memory: stats.available,
                total_allocated_memory: stats.allocated,
                utilization_efficiency: 0.0,
                allocation_efficiency: 0.0,
            }
        }

        fn compact(&mut self) -> Result<crate::memory::CompactionResult> {
            Ok(crate::memory::CompactionResult {
                allocations_moved: 0,
                bytes_moved: 0,
                duration_ms: 0.0,
                largest_free_before: self.available(),
                largest_free_after: self.available(),
                free_blocks_before: 1,
                free_blocks_after: 1,
                success: true,
            })
        }
    }

    #[derive(Debug)]
    pub struct RocmMemoryPool {
        #[allow(dead_code)]
        device: Device,
        config: MemoryPoolConfig,
        stats: RwLock<PoolStats>,
    }

    impl RocmMemoryPool {
        pub fn new(device: Device, config: MemoryPoolConfig) -> Self {
            let stats = PoolStats {
                capacity: config.initial_size,
                available: config.initial_size,
                ..Default::default()
            };

            Self {
                device,
                config,
                stats: RwLock::new(stats),
            }
        }
    }

    impl MemoryPool for RocmMemoryPool {
        fn allocate(&mut self, _size: usize, _alignment: usize) -> Result<*mut u8> {
            Ok(std::ptr::null_mut())
        }

        fn deallocate(&mut self, _ptr: *mut u8, _size: usize) -> Result<()> {
            Ok(())
        }

        fn stats(&self) -> PoolStats {
            self.stats.read().clone()
        }

        fn reset(&mut self) -> Result<()> {
            Ok(())
        }

        fn capacity(&self) -> usize {
            self.config.initial_size
        }

        fn available(&self) -> usize {
            self.stats.read().available
        }

        fn defragment(&mut self) -> Result<crate::memory::DefragmentationResult> {
            Ok(crate::memory::DefragmentationResult {
                blocks_moved: 0,
                memory_compacted: 0,
                duration_ms: 0.0,
                fragmentation_before: 0.0,
                fragmentation_after: 0.0,
                efficiency_improvement: 0.0,
                success: true,
            })
        }

        fn needs_defragmentation(&self) -> bool {
            false
        }

        fn fragmentation_info(&self) -> crate::memory::FragmentationInfo {
            let stats = self.stats.read();
            crate::memory::FragmentationInfo {
                overall_fragmentation: 0.0,
                external_fragmentation: 0.0,
                internal_fragmentation: 0.0,
                free_blocks: 1,
                allocated_blocks: stats.allocated_blocks,
                largest_free_block: stats.available,
                smallest_free_block: stats.available,
                average_free_block: stats.available,
                total_free_memory: stats.available,
                total_allocated_memory: stats.allocated,
                utilization_efficiency: 0.0,
                allocation_efficiency: 0.0,
            }
        }

        fn compact(&mut self) -> Result<crate::memory::CompactionResult> {
            Ok(crate::memory::CompactionResult {
                allocations_moved: 0,
                bytes_moved: 0,
                duration_ms: 0.0,
                largest_free_before: self.available(),
                largest_free_after: self.available(),
                free_blocks_before: 1,
                free_blocks_after: 1,
                success: true,
            })
        }
    }
}

// Re-export backend pool implementations
pub use backend_pools::*;

#[cfg(test)]
mod tests {
    use super::*;
    use crate::device::{Device, DeviceInfo};
    use torsh_core::device::DeviceType;

    fn create_test_device(device_type: DeviceType) -> Device {
        let info = DeviceInfo::default();
        Device::new(0, device_type, "Test Device".to_string(), info)
    }

    #[test]
    fn test_unified_memory_pool_creation() {
        let config = MemoryPoolConfig::default();
        let pool = UnifiedMemoryPool::new(config);

        assert_eq!(pool.registered_backends().len(), 0);
        assert_eq!(pool.global_stats().total_memory, 0);
    }

    #[test]
    fn test_backend_registration() {
        let pool = UnifiedMemoryPool::with_default_config();
        let device = create_test_device(DeviceType::Cpu);
        let cpu_pool = Box::new(CpuMemoryPool::new(device, MemoryPoolConfig::default()));

        let result = pool.register_backend_pool(BackendType::Cpu, cpu_pool, None);
        assert!(result.is_ok());

        let backends = pool.registered_backends();
        assert_eq!(backends.len(), 1);
        assert!(backends.contains(&BackendType::Cpu));
    }

    #[test]
    fn test_backend_unregistration() {
        let pool = UnifiedMemoryPool::with_default_config();
        let device = create_test_device(DeviceType::Cpu);
        let cpu_pool = Box::new(CpuMemoryPool::new(device, MemoryPoolConfig::default()));

        pool.register_backend_pool(BackendType::Cpu, cpu_pool, None)
            .unwrap();
        assert_eq!(pool.registered_backends().len(), 1);

        let result = pool.unregister_backend_pool(BackendType::Cpu);
        assert!(result.is_ok());
        assert_eq!(pool.registered_backends().len(), 0);
    }

    #[test]
    fn test_memory_allocation() {
        let pool = UnifiedMemoryPool::with_default_config();
        let device = create_test_device(DeviceType::Cpu);

        let result = pool.allocate(&device, 1024, 16);
        assert!(result.is_ok());

        if let Ok(ptr) = result {
            let dealloc_result = pool.deallocate(&device, ptr, 1024);
            assert!(dealloc_result.is_ok());
        }
    }

    #[test]
    fn test_global_statistics() {
        let pool = UnifiedMemoryPool::with_default_config();
        let device = create_test_device(DeviceType::Cpu);
        let cpu_pool = Box::new(CpuMemoryPool::new(device, MemoryPoolConfig::default()));

        pool.register_backend_pool(BackendType::Cpu, cpu_pool, None)
            .unwrap();

        let stats = pool.global_stats();
        assert!(stats.total_memory > 0);
    }

    #[test]
    fn test_memory_pressure() {
        let pool = UnifiedMemoryPool::with_default_config();
        let device = create_test_device(DeviceType::Cpu);
        let cpu_pool = Box::new(CpuMemoryPool::new(device, MemoryPoolConfig::default()));

        pool.register_backend_pool(BackendType::Cpu, cpu_pool, None)
            .unwrap();

        let is_under_pressure = pool.is_under_pressure(BackendType::Cpu);
        assert!(is_under_pressure.is_ok());
        assert!(!is_under_pressure.unwrap()); // Should not be under pressure initially
    }

    #[test]
    fn test_garbage_collection() {
        let pool = UnifiedMemoryPool::with_default_config();
        let device = create_test_device(DeviceType::Cpu);
        let cpu_pool = Box::new(CpuMemoryPool::new(device, MemoryPoolConfig::default()));

        pool.register_backend_pool(BackendType::Cpu, cpu_pool, None)
            .unwrap();

        let result = pool.garbage_collect_backend(BackendType::Cpu);
        assert!(result.is_ok());

        let result = pool.garbage_collect_all();
        assert!(result.is_ok());
    }
}
