//! Tensor Core optimizations for high-performance GPU acceleration
//!
//! This module leverages NVIDIA Tensor Cores for accelerated matrix operations
//! in optimization algorithms, providing significant speedup for suitable workloads.

use crate::error::{ScirsError, ScirsResult};
use scirs2_core::gpu::{GpuContext, GpuKernelHandle};
use scirs2_core::ndarray::{Array1, Array2};
use std::sync::Arc;

/// Tensor Core acceleration configuration
#[derive(Debug, Clone)]
pub struct TensorCoreOptimizationConfig {
    /// Use mixed precision (FP16 for computation, FP32 for accumulation)
    pub mixed_precision: bool,
    /// Tile size for matrix operations
    pub tile_size: usize,
    /// Whether to use automatic mixed precision (AMP)
    pub use_amp: bool,
    /// Loss scaling for numerical stability in mixed precision
    pub loss_scale: f32,
    /// Gradient clipping threshold
    pub gradient_clip_threshold: Option<f32>,
}

impl Default for TensorCoreOptimizationConfig {
    fn default() -> Self {
        Self {
            mixed_precision: true,
            tile_size: 16, // Optimal for most Tensor Core operations
            use_amp: true,
            loss_scale: 65536.0,
            gradient_clip_threshold: Some(1.0),
        }
    }
}

/// Tensor Core-accelerated matrix operations for optimization
pub struct TensorCoreOptimizer {
    context: Arc<GpuContext>,
    config: TensorCoreOptimizationConfig,
    gemm_kernel: GpuKernelHandle,
    batch_gemm_kernel: GpuKernelHandle,
    gradient_kernel: GpuKernelHandle,
}

impl TensorCoreOptimizer {
    /// Create a new Tensor Core optimizer
    pub fn new(
        context: Arc<GpuContext>,
        config: TensorCoreOptimizationConfig,
    ) -> ScirsResult<Self> {
        // Check Tensor Core capability
        // TODO: Add proper tensor core capability check when available in scirs2_core
        let _supports_tensor_cores = true; // Assume tensor cores are available for now
        if !_supports_tensor_cores {
            return Err(ScirsError::NotImplementedError(
                scirs2_core::error::ErrorContext::new(
                    "Tensor Cores not available on this device".to_string(),
                ),
            ));
        }

        let gemm_kernel = Self::create_gemm_kernel(&context, &config)?;
        let batch_gemm_kernel = Self::create_batch_gemm_kernel(&context, &config)?;
        let gradient_kernel = Self::create_gradient_kernel(&context, &config)?;

        Ok(Self {
            context,
            config,
            gemm_kernel,
            batch_gemm_kernel,
            gradient_kernel,
        })
    }

    /// Create optimized GEMM kernel using Tensor Cores
    fn create_gemm_kernel(
        context: &Arc<GpuContext>,
        config: &TensorCoreOptimizationConfig,
    ) -> ScirsResult<GpuKernelHandle> {
        let kernel_source = if config.mixed_precision {
            r#"
                #include <cuda_fp16.h>
                #include <mma.h>
                
                using namespace nvcuda;
                
                extern "C" __global__ void tensor_core_gemm_mixed(
                    const half* A,
                    const half* B,
                    float* C,
                    int M, int N, int K,
                    float alpha, float beta
                ) {
                    const int WMMA_M = 16;
                    const int WMMA_N = 16;
                    const int WMMA_K = 16;
                    
                    int warpM = (blockIdx.x * blockDim.x + threadIdx.x) / warpSize;
                    int warpN = (blockIdx.y * blockDim.y + threadIdx.y);
                    
                    wmma::fragment<wmma::matrix_a, WMMA_M, WMMA_N, WMMA_K, half, wmma::row_major> a_frag;
                    wmma::fragment<wmma::matrix_b, WMMA_M, WMMA_N, WMMA_K, half, wmma::col_major> b_frag;
                    wmma::fragment<wmma::accumulator, WMMA_M, WMMA_N, WMMA_K, float> acc_frag;
                    wmma::fragment<wmma::accumulator, WMMA_M, WMMA_N, WMMA_K, float> c_frag;
                    
                    wmma::fill_fragment(acc_frag, 0.0f);
                    
                    for (int i = 0; i < K; i += WMMA_K) {
                        int aRow = warpM * WMMA_M;
                        int aCol = i;
                        int bRow = i;
                        int bCol = warpN * WMMA_N;
                        
                        if (aRow < M && aCol < K && bRow < K && bCol < N) {
                            wmma::load_matrix_sync(a_frag, A + aRow * K + aCol, K);
                            wmma::load_matrix_sync(b_frag, B + bRow * N + bCol, N);
                            wmma::mma_sync(acc_frag, a_frag, b_frag, acc_frag);
                        }
                    }
                    
                    int cRow = warpM * WMMA_M;
                    int cCol = warpN * WMMA_N;
                    
                    if (cRow < M && cCol < N) {
                        wmma::load_matrix_sync(c_frag, C + cRow * N + cCol, N, wmma::mem_row_major);
                        for (int i = 0; i < c_frag.num_elements; i++) {
                            c_frag.x[i] = alpha * acc_frag.x[i] + beta * c_frag.x[i];
                        }
                        wmma::store_matrix_sync(C + cRow * N + cCol, c_frag, N, wmma::mem_row_major);
                    }
                }
            "#.to_string()
        } else {
            r#"
                #include <mma.h>
                
                using namespace nvcuda;
                
                extern "C" __global__ void tensor_core_gemm_fp32(
                    const float* A,
                    const float* B,
                    float* C,
                    int M, int N, int K,
                    float alpha, float beta
                ) {
                    // Standard FP32 Tensor Core implementation
                    const int WMMA_M = 16;
                    const int WMMA_N = 16;
                    const int WMMA_K = 8;
                    
                    int warpM = (blockIdx.x * blockDim.x + threadIdx.x) / warpSize;
                    int warpN = (blockIdx.y * blockDim.y + threadIdx.y);
                    
                    wmma::fragment<wmma::matrix_a, WMMA_M, WMMA_N, WMMA_K, wmma::precision::tf32, wmma::row_major> a_frag;
                    wmma::fragment<wmma::matrix_b, WMMA_M, WMMA_N, WMMA_K, wmma::precision::tf32, wmma::col_major> b_frag;
                    wmma::fragment<wmma::accumulator, WMMA_M, WMMA_N, WMMA_K, float> acc_frag;
                    wmma::fragment<wmma::accumulator, WMMA_M, WMMA_N, WMMA_K, float> c_frag;
                    
                    wmma::fill_fragment(acc_frag, 0.0f);
                    
                    for (int i = 0; i < K; i += WMMA_K) {
                        int aRow = warpM * WMMA_M;
                        int aCol = i;
                        int bRow = i;
                        int bCol = warpN * WMMA_N;
                        
                        if (aRow < M && aCol < K && bRow < K && bCol < N) {
                            wmma::load_matrix_sync(a_frag, A + aRow * K + aCol, K);
                            wmma::load_matrix_sync(b_frag, B + bRow * N + bCol, N);
                            wmma::mma_sync(acc_frag, a_frag, b_frag, acc_frag);
                        }
                    }
                    
                    int cRow = warpM * WMMA_M;
                    int cCol = warpN * WMMA_N;
                    
                    if (cRow < M && cCol < N) {
                        wmma::load_matrix_sync(c_frag, C + cRow * N + cCol, N, wmma::mem_row_major);
                        for (int i = 0; i < c_frag.num_elements; i++) {
                            c_frag.x[i] = alpha * acc_frag.x[i] + beta * c_frag.x[i];
                        }
                        wmma::store_matrix_sync(C + cRow * N + cCol, c_frag, N, wmma::mem_row_major);
                    }
                }
            "#.to_string()
        };

        let kernel_name = if config.mixed_precision {
            "tensor_core_gemm_mixed"
        } else {
            "tensor_core_gemm_fp32"
        };

        context
            .execute(|compiler| compiler.compile(&kernel_source))
            .map_err(|e| {
                ScirsError::ComputationError(scirs2_core::error::ErrorContext::new(format!(
                    "Failed to compile kernel: {}",
                    e
                )))
            })
    }

    /// Create batch GEMM kernel for multiple matrix multiplications
    fn create_batch_gemm_kernel(
        context: &Arc<GpuContext>,
        config: &TensorCoreOptimizationConfig,
    ) -> ScirsResult<GpuKernelHandle> {
        let kernel_source = r#"
            #include <cuda_fp16.h>
            #include <mma.h>
            
            using namespace nvcuda;
            
            extern "C" __global__ void tensor_core_batch_gemm(
                const half** A_array,
                const half** B_array,
                float** C_array,
                int* M_array,
                int* N_array,
                int* K_array,
                float* alpha_array,
                float* beta_array,
                int batch_count
            ) {
                int batch_id = blockIdx.z;
                if (batch_id >= batch_count) return;
                
                const half* A = A_array[batch_id];
                const half* B = B_array[batch_id];
                float* C = C_array[batch_id];
                int M = M_array[batch_id];
                int N = N_array[batch_id];
                int K = K_array[batch_id];
                float alpha = alpha_array[batch_id];
                float beta = beta_array[batch_id];
                
                const int WMMA_M = 16;
                const int WMMA_N = 16;
                const int WMMA_K = 16;
                
                int warpM = (blockIdx.x * blockDim.x + threadIdx.x) / warpSize;
                int warpN = (blockIdx.y * blockDim.y + threadIdx.y);
                
                wmma::fragment<wmma::matrix_a, WMMA_M, WMMA_N, WMMA_K, half, wmma::row_major> a_frag;
                wmma::fragment<wmma::matrix_b, WMMA_M, WMMA_N, WMMA_K, half, wmma::col_major> b_frag;
                wmma::fragment<wmma::accumulator, WMMA_M, WMMA_N, WMMA_K, float> acc_frag;
                wmma::fragment<wmma::accumulator, WMMA_M, WMMA_N, WMMA_K, float> c_frag;
                
                wmma::fill_fragment(acc_frag, 0.0f);
                
                for (int i = 0; i < K; i += WMMA_K) {
                    int aRow = warpM * WMMA_M;
                    int aCol = i;
                    int bRow = i;
                    int bCol = warpN * WMMA_N;
                    
                    if (aRow < M && aCol < K && bRow < K && bCol < N) {
                        wmma::load_matrix_sync(a_frag, A + aRow * K + aCol, K);
                        wmma::load_matrix_sync(b_frag, B + bRow * N + bCol, N);
                        wmma::mma_sync(acc_frag, a_frag, b_frag, acc_frag);
                    }
                }
                
                int cRow = warpM * WMMA_M;
                int cCol = warpN * WMMA_N;
                
                if (cRow < M && cCol < N) {
                    wmma::load_matrix_sync(c_frag, C + cRow * N + cCol, N, wmma::mem_row_major);
                    for (int i = 0; i < c_frag.num_elements; i++) {
                        c_frag.x[i] = alpha * acc_frag.x[i] + beta * c_frag.x[i];
                    }
                    wmma::store_matrix_sync(C + cRow * N + cCol, c_frag, N, wmma::mem_row_major);
                }
            }
        "#;

        context
            .execute(|compiler| compiler.compile(kernel_source))
            .map_err(|e| {
                ScirsError::ComputationError(scirs2_core::error::ErrorContext::new(format!(
                    "Failed to compile batch kernel: {}",
                    e
                )))
            })
    }

    /// Create gradient computation kernel with Tensor Core acceleration
    fn create_gradient_kernel(
        context: &Arc<GpuContext>,
        config: &TensorCoreOptimizationConfig,
    ) -> ScirsResult<GpuKernelHandle> {
        let kernel_source = r#"
            #include <cuda_fp16.h>
            #include <mma.h>
            
            using namespace nvcuda;
            
            extern "C" __global__ void tensor_core_gradient_computation(
                const half* jacobian,
                const half* residuals,
                float* gradients,
                int n_points,
                int n_dims,
                float loss_scale
            ) {
                // Use Tensor Cores to compute J^T * r efficiently
                const int WMMA_M = 16;
                const int WMMA_N = 16;
                const int WMMA_K = 16;
                
                int warpM = (blockIdx.x * blockDim.x + threadIdx.x) / warpSize;
                int warpN = (blockIdx.y * blockDim.y + threadIdx.y);
                
                wmma::fragment<wmma::matrix_a, WMMA_M, WMMA_N, WMMA_K, half, wmma::row_major> jt_frag;
                wmma::fragment<wmma::matrix_b, WMMA_M, WMMA_N, WMMA_K, half, wmma::col_major> r_frag;
                wmma::fragment<wmma::accumulator, WMMA_M, WMMA_N, WMMA_K, float> acc_frag;
                
                wmma::fill_fragment(acc_frag, 0.0f);
                
                // Compute J^T * r using Tensor Cores
                for (int k = 0; k < n_points; k += WMMA_K) {
                    if (warpM * WMMA_M < n_dims && k < n_points) {
                        // Load transposed Jacobian and residuals
                        wmma::load_matrix_sync(jt_frag, jacobian + k * n_dims + warpM * WMMA_M, n_dims);
                        wmma::load_matrix_sync(r_frag, residuals + k, 1);
                        wmma::mma_sync(acc_frag, jt_frag, r_frag, acc_frag);
                    }
                }
                
                // Store result with loss scaling
                if (warpM * WMMA_M < n_dims) {
                    for (int i = 0; i < WMMA_M && warpM * WMMA_M + i < n_dims; i++) {
                        gradients[warpM * WMMA_M + i] = acc_frag.x[i] / loss_scale;
                    }
                }
            }
        "#;

        context
            .execute(|compiler| compiler.compile(kernel_source))
            .map_err(|e| {
                ScirsError::ComputationError(scirs2_core::error::ErrorContext::new(format!(
                    "Failed to compile gradient kernel: {}",
                    e
                )))
            })
    }

    /// Perform optimized matrix multiplication using Tensor Cores
    #[allow(dead_code)]
    pub fn gemm(
        &self,
        _a: &Array2<f64>,
        _b: &Array2<f64>,
        _c: &mut Array2<f64>,
        _alpha: f64,
        _beta: f64,
    ) -> ScirsResult<()> {
        // TODO: Implement when GPU buffer creation from arrays is supported
        Err(ScirsError::NotImplementedError(
            scirs2_core::error::ErrorContext::new("GEMM not yet implemented".to_string()),
        ))
    }

    /// Perform batch matrix multiplication using Tensor Cores
    #[allow(dead_code)]
    pub fn batch_gemm(
        &self,
        _a_batch: &[&Array2<f64>],
        _b_batch: &[&Array2<f64>],
        _c_batch: &mut [&mut Array2<f64>],
        _alpha_batch: &[f64],
        _beta_batch: &[f64],
    ) -> ScirsResult<()> {
        // TODO: Implement when GPU API supports batch operations
        Err(ScirsError::NotImplementedError(
            scirs2_core::error::ErrorContext::new("Batch GEMM not yet implemented".to_string()),
        ))
    }

    /// Compute gradients using Tensor Core acceleration
    #[allow(dead_code)]
    pub fn compute_gradients(
        &self,
        _jacobian: &Array2<f64>,
        _residuals: &Array1<f64>,
    ) -> ScirsResult<Array1<f64>> {
        // TODO: Implement when GPU API supports gradient computation
        Err(ScirsError::NotImplementedError(
            scirs2_core::error::ErrorContext::new(
                "Gradient computation not yet implemented".to_string(),
            ),
        ))
    }

    /// Check if gradient clipping is needed and apply it
    #[allow(dead_code)]
    pub fn clip_gradients(&self, _gradients: &mut Array1<f64>) -> ScirsResult<()> {
        // TODO: Implement when GPU API supports array operations
        Ok(())
    }

    /// Get the current configuration
    pub fn config(&self) -> &TensorCoreOptimizationConfig {
        &self.config
    }

    /// Update loss scale for automatic mixed precision
    pub fn update_loss_scale(&mut self, loss_scale: f32) {
        self.config.loss_scale = loss_scale;
    }

    /// Check if computation overflowed (for AMP)
    #[allow(dead_code)]
    pub fn check_overflow(&self, _tensor: &Array2<f64>) -> ScirsResult<bool> {
        // TODO: Implement when GPU API supports NaN/Inf checking
        Ok(false)
    }
}

/// Automatic Mixed Precision (AMP) manager for optimization
pub struct AMPManager {
    loss_scale: f32,
    growth_factor: f32,
    backoff_factor: f32,
    growth_interval: u32,
    consecutive_unskipped: u32,
}

impl AMPManager {
    /// Create a new AMP manager
    pub fn new() -> Self {
        Self {
            loss_scale: 65536.0,
            growth_factor: 2.0,
            backoff_factor: 0.5,
            growth_interval: 2000,
            consecutive_unskipped: 0,
        }
    }

    /// Update loss scale based on overflow detection
    pub fn update(&mut self, found_overflow: bool) -> f32 {
        if found_overflow {
            self.loss_scale *= self.backoff_factor;
            self.consecutive_unskipped = 0;
        } else {
            self.consecutive_unskipped += 1;
            if self.consecutive_unskipped >= self.growth_interval {
                self.loss_scale *= self.growth_factor;
                self.consecutive_unskipped = 0;
            }
        }

        // Clamp loss scale to reasonable bounds
        self.loss_scale = self.loss_scale.max(1.0).min(2_f32.powi(20));
        self.loss_scale
    }

    /// Get current loss scale
    pub fn loss_scale(&self) -> f32 {
        self.loss_scale
    }
}

impl Default for AMPManager {
    fn default() -> Self {
        Self::new()
    }
}

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

    #[test]
    fn test_tensor_core_config() {
        let config = TensorCoreOptimizationConfig::default();
        assert!(config.mixed_precision);
        assert_eq!(config.tile_size, 16);
        assert!(config.use_amp);
        assert_eq!(config.loss_scale, 65536.0);
    }

    #[test]
    fn test_amp_manager() {
        let mut manager = AMPManager::new();
        assert_eq!(manager.loss_scale(), 65536.0);

        // Test overflow handling
        let new_scale = manager.update(true);
        assert_eq!(new_scale, 32768.0);

        // Test growth
        for _ in 0..2000 {
            manager.update(false);
        }
        let grown_scale = manager.loss_scale();
        assert!(grown_scale > 32768.0);
    }

    #[test]
    #[ignore = "Requires Tensor Core capable GPU"]
    fn test_tensor_core_optimizer() {
        // This would test the actual Tensor Core optimizer
        // Implementation depends on the actual scirs2-core GPU infrastructure
    }
}
