using System;
using System.Runtime.InteropServices;
using System.Text;

namespace GeoSigmaDrawLib
{
    /// <summary>
    /// 内存管理辅助类
    /// </summary>
    public static class MarshalHelper
    {
        /// <summary>
        /// 将 string 转成 C++ 内存数据后调用 func
        /// </summary>
        /// <typeparam name="T">返回值类型</typeparam>
        /// <param name="data">要数据的字符串</param>
        /// <param name="func">被调用的业务函数</param>
        /// <returns>返回 func 的返回值</returns>
        public static T Call<T>(string data, Func<IntPtr, int, T> func)
        {
            IntPtr pBuff = IntPtr.Zero;

            try
            {
                pBuff = Marshal.StringToHGlobalAnsi(data);
                int nLen = Encoding.Default.GetByteCount(data);
                return func(pBuff, nLen);
            }
            finally
            {
                if (pBuff != IntPtr.Zero)
                {
                    Marshal.FreeHGlobal(pBuff);
                }
            }
        }

        /// <summary>
        /// 将 string 转成 C++ 内存数据后调用 action
        /// </summary>
        /// <param name="data">要数据的字符串</param>
        /// <param name="action">被调用的业务函数</param>
        public static void Execute(string data, Action<IntPtr, int> action)
        {
            IntPtr pBuff = IntPtr.Zero;

            try
            {
                pBuff = Marshal.StringToHGlobalAnsi(data);
                int nLen = Encoding.Default.GetByteCount(data);
                action(pBuff, nLen);
            }
            finally
            {
                if (pBuff != IntPtr.Zero)
                {
                    Marshal.FreeHGlobal(pBuff);
                }
            }
        }

        /// <summary>
        /// 将 C++ 内存转换为 string
        /// </summary>
        /// <param name="pBuff">C++ 内存对应的 IntPtr</param>
        /// <returns>当前 pBuff 为 IntPtr.Zero 时，返回空字符串，否则返回对应的字符串</returns>
        public static string ToString(IntPtr pBuff)
        {
            if (pBuff == IntPtr.Zero)
            {
                return string.Empty;
            }

            string strData = Marshal.PtrToStringBSTR(pBuff);
            Marshal.FreeBSTR(pBuff);
            return strData;
        }

        /// <summary>
        /// 将 C++ 的 double 数组(double *，并且必须是 new[]) 转换为 C# 的 double 数组
        /// </summary>
        /// <param name="pData">double *</param>
        /// <param name="length">元素个数</param>
        /// <returns>double[]</returns>
        public static double[] ToDoubleArray(IntPtr pData, int length)
        {
            if (pData == IntPtr.Zero)
            {
                throw new ArgumentException($"{nameof(pData)} cannot be equal to IntPtr.Zero");
            }

            if (length <= 0)
            {
                throw new ArgumentOutOfRangeException(nameof(length), "Length must be greater than zero.");
            }

            double[] result = new double[length];
            Marshal.Copy(pData, result, 0, length);
            GeoSigmaLib.PointerArrayDelete(pData);

            return result;
        }
    }
}