using System;
using System.CodeDom;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace GeoSigmaDrawLib
{
    /// <summary>
    /// 表示一个按指定编码转换后的非托管内存文本缓冲区。
    /// 支持自动释放，避免内存泄漏。
    /// </summary>
    public class NativeTextBuffer : IDisposable
    {
        private const string GB2312 = "GB2312";

        /// <summary>
        /// 编码类型枚举，便于调用方选择
        /// </summary>
        public enum EncodingType
        {
            GBK,
            UTF8,
            UTF16,
        }

        /// <summary>
        /// 非托管内存指针
        /// </summary>
        public IntPtr Pointer { get; private set; }

        /// <summary>
        /// 缓冲区字节长度
        /// </summary>
        public int Length { get; private set; }

        /// <summary>
        /// 构造函数：根据指定编码将字符串转换为非托管内存缓冲区
        /// </summary>
        /// <param name="text">源文本</param>
        /// <param name="encoding">目标编码</param>
        public NativeTextBuffer(string text, EncodingType encoding = EncodingType.GBK)
        {
            if (text == null)
            {
                throw new ArgumentNullException(nameof(text));
            }

            Encoding enc = Encoding.GetEncoding(GB2312);

            switch (encoding)
            {
                case EncodingType.GBK:
                    enc = Encoding.GetEncoding(GB2312);
                    break;
                case EncodingType.UTF8:
                    enc = Encoding.UTF8;
                        break;
                case EncodingType.UTF16:
                    enc = Encoding.Unicode;
                    break;
            }

            byte[] bytes = enc.GetBytes(text);

            Pointer = Marshal.AllocHGlobal(bytes.Length);
            Marshal.Copy(bytes, 0, Pointer, bytes.Length);
            Length = bytes.Length;
        }

        /// <summary>
        /// 释放非托管内存
        /// </summary>
        public void Dispose()
        {
            if (Pointer != IntPtr.Zero)
            {
                Marshal.FreeHGlobal(Pointer);
                Pointer = IntPtr.Zero;
            }
        }
    }
}