using System;
using System.Runtime.InteropServices;

namespace CeresSharp.Native;

/// <summary>
/// Helper class for unsafe code patterns and pointer operations.
/// Provides utilities for array pinning and pointer conversions.
/// </summary>
internal static class UnsafeHelpers
{
    /// <summary>
    /// Executes an operation with a pinned array.
    /// </summary>
    /// <typeparam name="T">The unmanaged type of the array elements.</typeparam>
    /// <param name="array">The array to pin.</param>
    /// <param name="operation">The operation to execute with the pinned pointer.</param>
    /// <exception cref="ArgumentNullException">Thrown when array is null.</exception>
    internal static void WithPinnedArray<T>(T[] array, Action<IntPtr> operation) where T : unmanaged
    {
        if (array == null)
            throw new ArgumentNullException(nameof(array));

        unsafe
        {
            fixed (T* ptr = array)
            {
                operation((IntPtr)ptr);
            }
        }
    }

    /// <summary>
    /// Executes an operation with a pinned array and returns a result.
    /// </summary>
    /// <typeparam name="T">The unmanaged type of the array elements.</typeparam>
    /// <typeparam name="TResult">The return type.</typeparam>
    /// <param name="array">The array to pin.</param>
    /// <param name="operation">The operation to execute with the pinned pointer.</param>
    /// <returns>The result of the operation.</returns>
    /// <exception cref="ArgumentNullException">Thrown when array is null.</exception>
    internal static TResult WithPinnedArray<T, TResult>(T[] array, Func<IntPtr, TResult> operation) where T : unmanaged
    {
        if (array == null)
            throw new ArgumentNullException(nameof(array));

        unsafe
        {
            fixed (T* ptr = array)
            {
                return operation((IntPtr)ptr);
            }
        }
    }

    /// <summary>
    /// Executes an operation with multiple pinned arrays.
    /// </summary>
    /// <typeparam name="T">The unmanaged type of the array elements.</typeparam>
    /// <param name="arrays">The arrays to pin.</param>
    /// <param name="operation">The operation to execute with the pinned pointers.</param>
    /// <exception cref="ArgumentNullException">Thrown when arrays is null or contains null elements.</exception>
    internal static void WithPinnedArrays<T>(T[][] arrays, Action<IntPtr[]> operation) where T : unmanaged
    {
        if (arrays == null)
            throw new ArgumentNullException(nameof(arrays));

        unsafe
        {
            var pointers = new IntPtr[arrays.Length];
            var pins = new GCHandle[arrays.Length];

            try
            {
                for (int i = 0; i < arrays.Length; i++)
                {
                    if (arrays[i] == null)
                        throw new ArgumentException($"Array at index {i} is null", nameof(arrays));

                    pins[i] = GCHandle.Alloc(arrays[i], GCHandleType.Pinned);
                    pointers[i] = pins[i].AddrOfPinnedObject();
                }

                operation(pointers);
            }
            finally
            {
                foreach (var pin in pins)
                {
                    if (pin.IsAllocated)
                        pin.Free();
                }
            }
        }
    }

    /// <summary>
    /// Pins an array and returns a GCHandle that must be freed by the caller.
    /// </summary>
    /// <typeparam name="T">The unmanaged type of the array elements.</typeparam>
    /// <param name="array">The array to pin.</param>
    /// <returns>A GCHandle that pins the array.</returns>
    /// <exception cref="ArgumentNullException">Thrown when array is null.</exception>
    internal static GCHandle PinArray<T>(T[] array) where T : unmanaged
    {
        if (array == null)
            throw new ArgumentNullException(nameof(array));

        return GCHandle.Alloc(array, GCHandleType.Pinned);
    }

    /// <summary>
    /// Copies data from an IntPtr array to a managed array of arrays.
    /// </summary>
    /// <param name="parameterPtrs">Pointer to array of IntPtr pointers.</param>
    /// <param name="parameterBlockSizes">Array of sizes for each parameter block.</param>
    /// <returns>Array of parameter blocks.</returns>
    internal static double[][] CopyParameterBlocks(IntPtr parameterPtrs, int[] parameterBlockSizes)
    {
        if (parameterPtrs == IntPtr.Zero)
            throw new ArgumentException("Parameter pointers cannot be zero", nameof(parameterPtrs));
        if (parameterBlockSizes == null || parameterBlockSizes.Length == 0)
            throw new ArgumentException("Parameter block sizes cannot be null or empty", nameof(parameterBlockSizes));

        var parameterBlocks = new double[parameterBlockSizes.Length][];

        unsafe
        {
            var paramPtrs = (IntPtr*)parameterPtrs;
            for (int i = 0; i < parameterBlockSizes.Length; i++)
            {
                var size = parameterBlockSizes[i];
                if (size <= 0)
                    throw new ArgumentException($"Parameter block size at index {i} must be positive", nameof(parameterBlockSizes));

                parameterBlocks[i] = new double[size];
                Marshal.Copy(paramPtrs[i], parameterBlocks[i], 0, size);
            }
        }

        return parameterBlocks;
    }
}