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

namespace GeoSigmaDrawLib
{
    /// <summary>
    /// 负责为本应用程序注册本地原生库（DLL）的搜索路径。
    /// 此类不加载任何 DLL，仅通过 Windows API 设置系统搜索目录，
    /// 确保后续通过 P/Invoke 或 DllImport 加载的库能被正确找到。
    /// 
    /// 注意：必须在首次调用任何 GeoSigmaLib 的 P/Invoke 方法前调用此方法。
    /// </summary>
    public static class NativeLibraryPathRegistrar
    {
        private const string VtkDirectory = "vtk";

        private const string ThirdPartyDirectory = "thirdparty";
        private const string EnvPath = "PATH";

        /// <summary>
        /// 注册三方库目录
        /// </summary>
        public static void Register()
        {
            var baseDirectory = GetExecutableDirectory();

            AddToEnvironmentPath(Path.Combine(baseDirectory, VtkDirectory));
            AddToEnvironmentPath(Path.Combine(baseDirectory, ThirdPartyDirectory));
        }

        /// <summary>
        /// 添加目录到 Path 环境变量中
        /// </summary>
        /// <param name="directory">要添加的目录名，建议使用绝对路径</param>
        public static void AddToEnvironmentPath(string directory)
        {
            if (string.IsNullOrWhiteSpace(directory))
            {
                return;
            }

            string? current = Environment.GetEnvironmentVariable(EnvPath);
            string newPath = AppendToPath(current, directory);
            Environment.SetEnvironmentVariable(EnvPath, newPath);
        }

        public static string GetExecutableDirectory()
        {
            var executablePath = Process.GetCurrentProcess().MainModule?.FileName;
            if (string.IsNullOrEmpty(executablePath))
            {
                throw new InvalidOperationException("无法获取当前进程的可执行文件路径。");
            }

            if(string.IsNullOrWhiteSpace(executablePath))
            {
                executablePath = AppDomain.CurrentDomain.BaseDirectory;
                return executablePath;
            }

            return Path.GetDirectoryName(executablePath) ?? throw new InvalidOperationException("可执行文件路径无效。");
        }

        private static string AppendToPath(string? current, string directory)
        {
            if (string.IsNullOrWhiteSpace(directory))
            {
                return current ?? string.Empty;
            }

            if (string.IsNullOrWhiteSpace(current))
            {
                return directory;
            }

            char pathSeparator = Path.PathSeparator;
            var pathEntries = current.Split(pathSeparator)
                   .Where(p => !string.IsNullOrWhiteSpace(p)) // 过滤空项
                   .ToList();

            if (pathEntries.Contains(directory, StringComparer.OrdinalIgnoreCase))
            {
                return current;
            }

            pathEntries.Add(directory);
            return string.Join(pathSeparator, pathEntries);
        }
    }
}