//! Modern WebGPU Backend Implementation for ToRSh

#[cfg(feature = "webgpu")]
use crate::webgpu::wgpu;
//!
//! This is a complete rewrite using wgpu 26.0.1 latest API patterns and best practices.
//! Features comprehensive async/await support, modern shader management (WGSL only),
//! proper memory management, and full compute pipeline implementation.

use crate::{
    Backend, BackendCapabilities, BackendCore, BackendDeviceManager, BackendExecutor,
    BackendLifecycle, BackendOperations, BackendOps, BackendResourceManager, BackendResult,
    BackendType, Buffer, BufferDescriptor, BufferHandle, CapabilityValue, Device, Kernel,
    KernelDescriptor, KernelHandle, MemoryManager, MemoryPool, MemoryStats, OperationsBundle,
    PerformanceHints, Profiler,
};
use crate::webgpu::{WebGpuError, WebGpuResult};
use async_trait::async_trait;
use futures::future::join_all;
use parking_lot::{RwLock, Mutex};
use std::{
    collections::HashMap,
    sync::Arc,
    time::{Duration, Instant},
};
use torsh_core::{device::DeviceType, dtype::DType, error::TorshError};
use wgpu::util::DeviceExt;

/// Modern WebGPU Backend Configuration
#[derive(Debug, Clone)]
pub struct ModernWebGpuConfig {
    pub device_descriptor: wgpu::DeviceDescriptor<'static>,
    pub instance_descriptor: wgpu::InstanceDescriptor,
    pub adapter_options: wgpu::RequestAdapterOptions<'static>,
    pub max_buffer_size: u64,
    pub enable_validation: bool,
    pub enable_spirv: bool,
    pub preferred_backend: Option<wgpu::Backends>,
}

impl Default for ModernWebGpuConfig {
    fn default() -> Self {
        Self {
            device_descriptor: wgpu::DeviceDescriptor {
                label: Some("ToRSh WebGPU Device"),
                required_features: wgpu::Features::empty(),
                required_limits: wgpu::Limits::downlevel_defaults(),
                memory_hints: wgpu::MemoryHints::default(),
            },
            instance_descriptor: wgpu::InstanceDescriptor {
                backends: wgpu::Backends::all(),
                flags: wgpu::InstanceFlags::default(),
                dx12_shader_compiler: wgpu::Dx12Compiler::Fxc,
                gles_minor_version: wgpu::Gles3MinorVersion::Automatic,
            },
            adapter_options: wgpu::RequestAdapterOptions {
                power_preference: wgpu::PowerPreference::HighPerformance,
                compatible_surface: None,
                force_fallback_adapter: false,
            },
            max_buffer_size: 256 * 1024 * 1024, // 256MB default
            enable_validation: true,
            enable_spirv: false, // Modern wgpu prefers WGSL
            preferred_backend: None,
        }
    }
}

/// Modern WebGPU Device Context
#[derive(Debug)]
pub struct ModernWebGpuDevice {
    pub instance: wgpu::Instance,
    pub adapter: wgpu::Adapter,
    pub device: wgpu::Device,
    pub queue: wgpu::Queue,
    pub info: wgpu::AdapterInfo,
    pub limits: wgpu::Limits,
    pub features: wgpu::Features,
    config: ModernWebGpuConfig,
    shader_cache: RwLock<HashMap<String, Arc<wgpu::ShaderModule>>>,
    pipeline_cache: RwLock<HashMap<String, Arc<wgpu::ComputePipeline>>>,
    bind_group_layout_cache: RwLock<HashMap<String, Arc<wgpu::BindGroupLayout>>>,
}

impl ModernWebGpuDevice {
    /// Create a new modern WebGPU device
    pub async fn new(config: ModernWebGpuConfig) -> WebGpuResult<Arc<Self>> {
        // Create instance
        let instance = wgpu::Instance::new(config.instance_descriptor.clone());

        // Request adapter
        let adapter = instance
            .request_adapter(&config.adapter_options)
            .await
            .ok_or_else(|| {
                WebGpuError::InitializationError("Failed to request WebGPU adapter".to_string())
            })?;

        let info = adapter.get_info();
        log::info!("WebGPU Adapter: {} ({:?})", info.name, info.backend);

        let mut required_features = config.device_descriptor.required_features;
        let mut required_limits = config.device_descriptor.required_limits.clone();

        // Adjust limits based on adapter capabilities
        let adapter_limits = adapter.limits();
        required_limits.max_buffer_size = required_limits
            .max_buffer_size
            .min(adapter_limits.max_buffer_size)
            .min(config.max_buffer_size);

        // Enable additional features if supported
        let supported_features = adapter.features();
        if supported_features.contains(wgpu::Features::TIMESTAMP_QUERY) {
            required_features |= wgpu::Features::TIMESTAMP_QUERY;
        }
        if supported_features.contains(wgpu::Features::BUFFER_BINDING_ARRAY) {
            required_features |= wgpu::Features::BUFFER_BINDING_ARRAY;
        }
        if supported_features.contains(wgpu::Features::STORAGE_RESOURCE_BINDING_ARRAY) {
            required_features |= wgpu::Features::STORAGE_RESOURCE_BINDING_ARRAY;
        }

        let device_descriptor = wgpu::DeviceDescriptor {
            label: config.device_descriptor.label,
            required_features,
            required_limits: required_limits.clone(),
            memory_hints: config.device_descriptor.memory_hints.clone(),
        };

        // Request device and queue
        let (device, queue) = adapter
            .request_device(&device_descriptor, None)
            .await
            .map_err(|e| {
                WebGpuError::InitializationError(format!("Failed to request WebGPU device: {}", e))
            })?;

        Ok(Arc::new(Self {
            instance,
            adapter,
            device,
            queue,
            info,
            limits: required_limits,
            features: required_features,
            config,
            shader_cache: RwLock::new(HashMap::new()),
            pipeline_cache: RwLock::new(HashMap::new()),
            bind_group_layout_cache: RwLock::new(HashMap::new()),
        }))
    }

    /// Create or get cached shader module from WGSL source
    pub fn create_shader_module(&self, label: &str, source: &str) -> Arc<wgpu::ShaderModule> {
        let key = format!("{}_{}", label, md5::compute(source.as_bytes()));

        {
            let cache = self.shader_cache.read();
            if let Some(shader) = cache.get(&key) {
                return shader.clone();
            }
        }

        let shader = Arc::new(self.device.create_shader_module(wgpu::ShaderModuleDescriptor {
            label: Some(label),
            source: wgpu::ShaderSource::Wgsl(source.into()),
        }));

        self.shader_cache.write().insert(key, shader.clone());
        shader
    }

    /// Create or get cached compute pipeline
    pub fn create_compute_pipeline(
        &self,
        label: &str,
        shader: &wgpu::ShaderModule,
        entry_point: &str,
        bind_group_layouts: &[&wgpu::BindGroupLayout],
    ) -> WebGpuResult<Arc<wgpu::ComputePipeline>> {
        let key = format!("{}_{}", label, entry_point);

        {
            let cache = self.pipeline_cache.read();
            if let Some(pipeline) = cache.get(&key) {
                return Ok(pipeline.clone());
            }
        }

        let pipeline_layout = self.device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
            label: Some(&format!("{}_layout", label)),
            bind_group_layouts,
            push_constant_ranges: &[],
        });

        let pipeline = Arc::new(
            self.device
                .create_compute_pipeline(&wgpu::ComputePipelineDescriptor {
                    label: Some(label),
                    layout: Some(&pipeline_layout),
                    module: shader,
                    entry_point: Some(entry_point),
                    compilation_options: wgpu::PipelineCompilationOptions::default(),
                    cache: None,
                }),
        );

        self.pipeline_cache.write().insert(key, pipeline.clone());
        Ok(pipeline)
    }

    /// Create buffer with proper error handling
    pub fn create_buffer_with_data<T: bytemuck::Pod>(&self, label: &str, data: &[T], usage: wgpu::BufferUsages) -> wgpu::Buffer {
        self.device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some(label),
            contents: bytemuck::cast_slice(data),
            usage,
        })
    }

    /// Submit work and wait for completion
    pub async fn submit_and_wait(&self, commands: impl IntoIterator<Item = wgpu::CommandBuffer>) -> WebGpuResult<()> {
        let submission_index = self.queue.submit(commands);

        // Map buffer to ensure completion
        let staging_buffer = self.device.create_buffer(&wgpu::BufferDescriptor {
            label: Some("staging_wait_buffer"),
            size: 4,
            usage: wgpu::BufferUsages::MAP_READ | wgpu::BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });

        staging_buffer.slice(..).map_async(wgpu::MapMode::Read, |result| {
            if let Err(e) = result {
                log::error!("Buffer mapping failed during wait: {:?}", e);
            }
        });

        let _ = self.device.poll(wgpu::Maintain::WaitForSubmissionIndex(submission_index));
        Ok(())
    }
}

/// Modern WebGPU Memory Manager
#[derive(Debug)]
pub struct ModernWebGpuMemoryManager {
    device: Arc<ModernWebGpuDevice>,
    buffer_pools: RwLock<HashMap<(u64, wgpu::BufferUsages), Vec<wgpu::Buffer>>>,
    allocation_stats: RwLock<MemoryStats>,
    next_buffer_id: Mutex<u64>,
}

impl ModernWebGpuMemoryManager {
    pub fn new(device: Arc<ModernWebGpuDevice>) -> Arc<Self> {
        Arc::new(Self {
            device,
            buffer_pools: RwLock::new(HashMap::new()),
            allocation_stats: RwLock::new(MemoryStats {
                total_allocated: 0,
                total_deallocated: 0,
                current_allocated: 0,
                peak_allocated: 0,
                allocation_count: 0,
                deallocation_count: 0,
            }),
            next_buffer_id: Mutex::new(0),
        })
    }

    pub fn allocate_buffer(&self, descriptor: &BufferDescriptor) -> WebGpuResult<ModernWebGpuBuffer> {
        let usage = self.convert_buffer_usage(&descriptor.usage)?;
        let size = descriptor.size as u64;

        // Try to get from pool first
        let mut pools = self.buffer_pools.write();
        let pool_key = (size, usage);

        let buffer = if let Some(pool) = pools.get_mut(&pool_key) {
            pool.pop().unwrap_or_else(|| {
                self.device.device.create_buffer(&wgpu::BufferDescriptor {
                    label: Some(&format!("ToRSh Buffer {}", descriptor.name.as_deref().unwrap_or("unnamed"))),
                    size,
                    usage,
                    mapped_at_creation: false,
                })
            })
        } else {
            self.device.device.create_buffer(&wgpu::BufferDescriptor {
                label: Some(&format!("ToRSh Buffer {}", descriptor.name.as_deref().unwrap_or("unnamed"))),
                size,
                usage,
                mapped_at_creation: false,
            })
        };

        let buffer_id = {
            let mut id = self.next_buffer_id.lock();
            let current_id = *id;
            *id += 1;
            current_id
        };

        // Update stats
        {
            let mut stats = self.allocation_stats.write();
            stats.total_allocated += size as usize;
            stats.current_allocated += size as usize;
            stats.peak_allocated = stats.peak_allocated.max(stats.current_allocated);
            stats.allocation_count += 1;
        }

        Ok(ModernWebGpuBuffer {
            buffer,
            device: self.device.clone(),
            handle: BufferHandle::WebGpu {
                buffer_ptr: buffer_id,
                size: descriptor.size,
            },
            size: descriptor.size,
            usage,
            label: descriptor.name.clone(),
        })
    }

    fn convert_buffer_usage(&self, usage: &crate::buffer::BufferUsage) -> WebGpuResult<wgpu::BufferUsages> {
        use crate::buffer::BufferUsage;

        let mut wgpu_usage = wgpu::BufferUsages::empty();

        match usage {
            BufferUsage::Uniform => wgpu_usage |= wgpu::BufferUsages::UNIFORM,
            BufferUsage::Storage => wgpu_usage |= wgpu::BufferUsages::STORAGE,
            BufferUsage::Vertex => wgpu_usage |= wgpu::BufferUsages::VERTEX,
            BufferUsage::Index => wgpu_usage |= wgpu::BufferUsages::INDEX,
        }

        // Always add copy operations for data transfer
        wgpu_usage |= wgpu::BufferUsages::COPY_SRC | wgpu::BufferUsages::COPY_DST;

        Ok(wgpu_usage)
    }

    pub fn return_buffer_to_pool(&self, buffer: ModernWebGpuBuffer) {
        let pool_key = (buffer.size as u64, buffer.usage);
        let mut pools = self.buffer_pools.write();
        pools.entry(pool_key).or_insert_with(Vec::new).push(buffer.buffer);

        // Update stats
        let mut stats = self.allocation_stats.write();
        stats.total_deallocated += buffer.size;
        stats.current_allocated = stats.current_allocated.saturating_sub(buffer.size);
        stats.deallocation_count += 1;
    }
}

/// Modern WebGPU Buffer
#[derive(Debug)]
pub struct ModernWebGpuBuffer {
    pub buffer: wgpu::Buffer,
    pub device: Arc<ModernWebGpuDevice>,
    pub handle: BufferHandle,
    pub size: usize,
    pub usage: wgpu::BufferUsages,
    pub label: Option<String>,
}

impl ModernWebGpuBuffer {
    /// Write data to buffer asynchronously
    pub async fn write_data<T: bytemuck::Pod>(&self, data: &[T]) -> WebGpuResult<()> {
        let bytes = bytemuck::cast_slice(data);
        if bytes.len() > self.size {
            return Err(WebGpuError::InvalidArgument(format!(
                "Data size {} exceeds buffer size {}",
                bytes.len(),
                self.size
            )));
        }

        self.device.queue.write_buffer(&self.buffer, 0, bytes);
        Ok(())
    }

    /// Read data from buffer asynchronously
    pub async fn read_data<T: bytemuck::Pod + Clone>(&self) -> WebGpuResult<Vec<T>> {
        // Create staging buffer
        let staging_buffer = self.device.device.create_buffer(&wgpu::BufferDescriptor {
            label: Some("staging_read_buffer"),
            size: self.size as u64,
            usage: wgpu::BufferUsages::MAP_READ | wgpu::BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });

        // Copy data to staging buffer
        let mut encoder = self.device.device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
            label: Some("buffer_read_copy"),
        });

        encoder.copy_buffer_to_buffer(
            &self.buffer,
            0,
            &staging_buffer,
            0,
            self.size as u64,
        );

        self.device.queue.submit([encoder.finish()]);

        // Map and read data
        let buffer_slice = staging_buffer.slice(..);
        let (tx, rx) = futures::channel::oneshot::channel();

        buffer_slice.map_async(wgpu::MapMode::Read, move |result| {
            let _ = tx.send(result);
        });

        let _ = self.device.device.poll(wgpu::Maintain::Wait);
        rx.await.expect("buffer mapping channel should not be dropped").map_err(|e| WebGpuError::RuntimeError(format!("Buffer mapping failed: {:?}", e)))?;

        let data = buffer_slice.get_mapped_range();
        let result: Vec<T> = bytemuck::cast_slice(&data).to_vec();

        drop(data);
        staging_buffer.unmap();

        Ok(result)
    }
}

/// Modern WebGPU Compute Operation
#[derive(Debug)]
pub struct ModernWebGpuCompute {
    device: Arc<ModernWebGpuDevice>,
    memory_manager: Arc<ModernWebGpuMemoryManager>,
}

impl ModernWebGpuCompute {
    pub fn new(device: Arc<ModernWebGpuDevice>) -> Self {
        let memory_manager = ModernWebGpuMemoryManager::new(device.clone());
        Self {
            device,
            memory_manager,
        }
    }

    /// Execute a compute shader with buffers
    pub async fn execute_compute(
        &self,
        shader_source: &str,
        entry_point: &str,
        buffers: &[&ModernWebGpuBuffer],
        workgroup_size: (u32, u32, u32),
    ) -> WebGpuResult<()> {
        // Create shader
        let shader = self.device.create_shader_module("compute_shader", shader_source);

        // Create bind group layout
        let mut bind_group_layout_entries = Vec::new();
        for (i, _buffer) in buffers.iter().enumerate() {
            bind_group_layout_entries.push(wgpu::BindGroupLayoutEntry {
                binding: i as u32,
                visibility: wgpu::ShaderStages::COMPUTE,
                ty: wgpu::BindingType::Buffer {
                    ty: wgpu::BufferBindingType::Storage { read_only: false },
                    has_dynamic_offset: false,
                    min_binding_size: None,
                },
                count: None,
            });
        }

        let bind_group_layout = self.device.device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
            label: Some("compute_bind_group_layout"),
            entries: &bind_group_layout_entries,
        });

        // Create compute pipeline
        let pipeline = self.device.create_compute_pipeline(
            "compute_pipeline",
            &shader,
            entry_point,
            &[&bind_group_layout],
        )?;

        // Create bind group
        let mut bind_group_entries = Vec::new();
        for (i, buffer) in buffers.iter().enumerate() {
            bind_group_entries.push(wgpu::BindGroupEntry {
                binding: i as u32,
                resource: buffer.buffer.as_entire_binding(),
            });
        }

        let bind_group = self.device.device.create_bind_group(&wgpu::BindGroupDescriptor {
            label: Some("compute_bind_group"),
            layout: &bind_group_layout,
            entries: &bind_group_entries,
        });

        // Create command encoder and dispatch
        let mut encoder = self.device.device.create_command_encoder(&wgpu::CommandEncoderDescriptor {
            label: Some("compute_encoder"),
        });

        {
            let mut compute_pass = encoder.begin_compute_pass(&wgpu::ComputePassDescriptor {
                label: Some("compute_pass"),
                timestamp_writes: None,
            });

            compute_pass.set_pipeline(&pipeline);
            compute_pass.set_bind_group(0, &bind_group, &[]);
            compute_pass.dispatch_workgroups(workgroup_size.0, workgroup_size.1, workgroup_size.2);
        }

        // Submit and wait
        self.device.submit_and_wait([encoder.finish()]).await?;
        Ok(())
    }
}

/// Modern WebGPU Backend - Main Implementation
#[derive(Debug)]
pub struct ModernWebGpuBackend {
    device: Arc<ModernWebGpuDevice>,
    memory_manager: Arc<ModernWebGpuMemoryManager>,
    compute: ModernWebGpuCompute,
    config: ModernWebGpuConfig,
}

impl ModernWebGpuBackend {
    pub async fn new(config: ModernWebGpuConfig) -> WebGpuResult<Self> {
        let device = ModernWebGpuDevice::new(config.clone()).await?;
        let memory_manager = ModernWebGpuMemoryManager::new(device.clone());
        let compute = ModernWebGpuCompute::new(device.clone());

        Ok(Self {
            device,
            memory_manager,
            compute,
            config,
        })
    }

    pub fn with_default() -> impl std::future::Future<Output = WebGpuResult<Self>> {
        Self::new(ModernWebGpuConfig::default())
    }
}

// Note: Full trait implementations will be added in subsequent files
// This provides the foundation for a modern, comprehensive WebGPU backend