// Copyright (c) 2025, `SciRS2` Team
//
// Licensed under the Apache License, Version 2.0
// (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
//

//! CUDA-specific optimized implementations for GPU array operations.
//!
//! This module provides specialized implementations of common array operations
//! optimized for CUDA GPUs. These implementations leverage GPU acceleration
//! for improved performance on large-scale array operations.

use std::any::{Any, TypeId};
use std::collections::HashMap;

use ::ndarray::{Array, ArrayBase, Dimension, Ix2, IxDyn, OwnedRepr};

use crate::array_protocol::{
    ArrayFunction, ArrayProtocol, GPUNdarray, NotImplemented, NdarrayWrapper
};

/// Registers CUDA-specific optimized functions with the array protocol system.
#[allow(dead_code)]
pub fn register_cuda_operations() {
    // This would register the CUDA-specific implementations with the
    // global ArrayFunctionRegistry. For this implementation, we're
    // providing the operations directly through the GPUNdarray's
    // array_function implementation.
}

/// Implements matrix multiplication for CUDA-accelerated arrays.
///
/// This function would use CUBLAS for efficient matrix multiplication.
#[allow(dead_code)]
pub fn cuda_matmul<D1, D2>(
    a: &GPUNdarray<f64, D1>,
    b: &GPUNdarray<f64, D2>,
) -> Result<GPUNdarray<f64, Ix2>, NotImplemented>
where
    D1: Dimension,
    D2: Dimension,
{
    // In a real implementation, this would use CUBLAS for matrix multiplication.
    // For now, we'll simulate the behavior with a CPU fallback.

    // Check if arrays are on the same device
    if a.device_id() != b.device_id() {
        return Err(NotImplemented);
    }

    // Get dimensions
    let ashape = a.shape();
    let bshape = b.shape();

    // Verify matrix dimensions
    if ashape.len() != 2 || bshape.len() != 2 || ashape[1] != bshape[0] {
        return Err(NotImplemented);
    }

    // Transfer to CPU, perform operation, and transfer back to GPU
    let a_cpu = a.to_cpu().expect("Operation failed");
    let b_cpu = b.to_cpu().expect("Operation failed");

    let a_array = a_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();
    let b_array = b_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();

    let result = a_array.dot(b_array);

    // Create a new GPU array with the result
    let result_gpu = GPUNdarray::new(result, a.config().clone());

    Ok(result_gpu)
}

/// Implements element-wise addition for CUDA-accelerated arrays.
///
/// This function would use a CUDA kernel for element-wise addition.
#[allow(dead_code)]
pub fn cuda_add<D1, D2>(
    a: &GPUNdarray<f64, D1>,
    b: &GPUNdarray<f64, D2>,
) -> Result<GPUNdarray<f64, IxDyn>, NotImplemented>
where
    D1: Dimension,
    D2: Dimension,
{
    // In a real implementation, this would use a custom CUDA kernel for addition.
    // For now, we'll simulate the behavior with a CPU fallback.

    // Check if arrays are on the same device
    if a.device_id() != b.device_id() {
        return Err(NotImplemented);
    }

    // Check if shapes are compatible for broadcasting
    let ashape = a.shape();
    let bshape = b.shape();

    // Transfer to CPU, perform operation, and transfer back to GPU
    let a_cpu = a.to_cpu().expect("Operation failed");
    let b_cpu = b.to_cpu().expect("Operation failed");

    let a_array = a_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();
    let b_array = b_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();

    let result = a_array + b_array;

    // Create a new GPU array with the result
    let result_gpu = GPUNdarray::new(result, a.config().clone());

    Ok(result_gpu)
}

/// Implements element-wise multiplication for CUDA-accelerated arrays.
#[allow(dead_code)]
pub fn cuda_multiply<D1, D2>(
    a: &GPUNdarray<f64, D1>,
    b: &GPUNdarray<f64, D2>,
) -> Result<GPUNdarray<f64, IxDyn>, NotImplemented>
where
    D1: Dimension,
    D2: Dimension,
{
    // Similar implementation to cuda_add, but with multiplication

    // Check if arrays are on the same device
    if a.device_id() != b.device_id() {
        return Err(NotImplemented);
    }

    // Transfer to CPU, perform operation, and transfer back to GPU
    let a_cpu = a.to_cpu().expect("Operation failed");
    let b_cpu = b.to_cpu().expect("Operation failed");

    let a_array = a_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();
    let b_array = b_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();

    let result = a_array * b_array;

    // Create a new GPU array with the result
    let result_gpu = GPUNdarray::new(result, a.config().clone());

    Ok(result_gpu)
}

/// Implements array transpose for CUDA-accelerated arrays.
#[allow(dead_code)]
pub fn cuda_transpose<D>(
    a: &GPUNdarray<f64, D>,
) -> Result<GPUNdarray<f64, Ix2>, NotImplemented>
where
    D: Dimension,
{
    // Check if this is a 2D array
    let shape = a.shape();
    if shape.len() != 2 {
        return Err(NotImplemented);
    }

    // Transfer to CPU, perform operation, and transfer back to GPU
    let a_cpu = a.to_cpu().expect("Operation failed");
    let a_array = a_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();

    let result = a_array.t().to_owned();

    // Create a new GPU array with the result
    let result_gpu = GPUNdarray::new(result, a.config().clone());

    Ok(result_gpu)
}

/// Implements array sum for CUDA-accelerated arrays.
#[allow(dead_code)]
pub fn cuda_sum<D>(
    a: &GPUNdarray<f64, D>,
    axis: Option<usize>,
) -> Result<Box<dyn Any>, NotImplemented>
where
    D: Dimension,
{
    // Transfer to CPU, perform operation
    let a_cpu = a.to_cpu().expect("Operation failed");
    let a_array = a_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();

    match axis {
        Some(ax) => {
            let result = a_array.sum_axis(crate::ndarray::Axis(ax));
            let result_gpu = GPUNdarray::new(result, a.config().clone());
            Ok(Box::new(result_gpu))
        },
        None => {
            let result = a_array.sum();
            Ok(Box::new(result))
        }
    }
}

/// Implements array reshape for CUDA-accelerated arrays.
#[allow(dead_code)]
pub fn cuda_reshape<D>(
    a: &GPUNdarray<f64, D>,
    shape: &[usize],
) -> Result<GPUNdarray<f64, IxDyn>, NotImplemented>
where
    D: Dimension,
{
    // Transfer to CPU, perform operation, and transfer back to GPU
    let a_cpu = a.to_cpu().expect("Operation failed");
    let a_array = a_cpu.downcast_ref::<NdarrayWrapper<f64_>>().expect("Operation failed").as_array();

    match a_array.clone().intoshape(shape) {
        Ok(result) => {
            // Create a new GPU array with the result
            let result_gpu = GPUNdarray::new(result, a.config().clone());
            Ok(result_gpu)
        },
        Err(_) => Err(NotImplemented),
    }
}

/// Implements 2D convolution for CUDA-accelerated arrays.
#[allow(dead_code)]
pub fn cuda_conv2d<D1, D2>(
    input: &GPUNdarray<f64, D1>,
    kernel: &GPUNdarray<f64, D2>,
    stride: (usize, usize),
    padding: (usize, usize),
) -> Result<GPUNdarray<f64, Ix2>, NotImplemented>
where
    D1: Dimension,
    D2: Dimension,
{
    // Check if arrays are on the same device
    if input.device_id() != kernel.device_id() {
        return Err(NotImplemented);
    }

    let inputshape = input.shape();
    if inputshape.len() != 2 {
        return Err(NotImplemented);
    }

    // A real implementation would use cuDNN (or a CPU convolution fallback).
    // Returning a zero-filled array of the right shape would be a fabricated
    // result that silently produces wrong numbers, so report the operation as
    // unimplemented instead.
    let _ = (stride, padding);
    Err(NotImplemented)
}

/// Implements SVD decomposition for CUDA-accelerated arrays.
#[allow(dead_code)]
pub fn cuda_svd<D>(
    a: &GPUNdarray<f64, D>,
) -> Result<(GPUNdarray<f64, Ix2>, GPUNdarray<f64, IxDyn>, GPUNdarray<f64, Ix2>), NotImplemented>
where
    D: Dimension,
{
    // Check if this is a 2D array
    let shape = a.shape();
    if shape.len() != 2 {
        return Err(NotImplemented);
    }

    // A real implementation would use cuSOLVER (or a CPU SVD fallback).
    // Returning identity U/Vt and all-ones singular values would be a fabricated
    // decomposition that does not reconstruct the input, so report the operation
    // as unimplemented instead of inventing a result.
    Err(NotImplemented)
}

/// Implements matrix inverse for CUDA-accelerated arrays.
#[allow(dead_code)]
pub fn cuda_inverse<D>(
    a: &GPUNdarray<f64, D>,
) -> Result<GPUNdarray<f64, Ix2>, NotImplemented>
where
    D: Dimension,
{
    // Check if this is a square 2D array
    let shape = a.shape();
    if shape.len() != 2 || shape[0] != shape[1] {
        return Err(NotImplemented);
    }

    // A real implementation would use cuSOLVER (or a CPU inversion fallback).
    // Returning an identity matrix would be a fabricated inverse (it only equals
    // the true inverse when the input is already the identity), so report the
    // operation as unimplemented instead.
    Err(NotImplemented)
}
