using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;
using Microsoft.Win32.SafeHandles;

// Some upstream DXF readers still use narrow std::ifstream for resource files.
// Give the native runtime an ASCII executable path while retaining the real
// portable folder for settings, projects and QI_ROOT. No CAD files are copied.
static class RuntimePath
{
    [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    static extern uint GetShortPathNameW(string longPath, StringBuilder shortPath, uint capacity);

    [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    static extern SafeFileHandle CreateFileW(string name, uint access, uint share, IntPtr security,
        uint creation, uint flags, IntPtr template);

    [DllImport("kernel32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool DeviceIoControl(SafeFileHandle file, uint control, byte[] input, uint inputSize,
        IntPtr output, uint outputSize, out uint returned, IntPtr overlapped);

    static bool IsAscii(string value) => value.All(c => c < 128);

    static string? ShortAsciiPath(string path)
    {
        if (IsAscii(path)) return path;
        var buffer = new StringBuilder(32768);
        var length = GetShortPathNameW(path, buffer, (uint)buffer.Capacity);
        return length > 0 && length < buffer.Capacity && IsAscii(buffer.ToString())
            ? buffer.ToString() : null;
    }

    public static string ForEngine(string root, string engine, bool allowShortPath = true)
    {
        if (allowShortPath && ShortAsciiPath(engine) is { } shortEngine) return shortEngine;
        var relativeEngine = Path.GetRelativePath(root, engine);
        if (relativeEngine.StartsWith(".." + Path.DirectorySeparatorChar) || Path.IsPathRooted(relativeEngine))
            throw new IOException("Путь CAD-движка находится за пределами переносимой папки.");
        var key = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(root.ToUpperInvariant())))[..32];
        var candidates = new[]
        {
            Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData),
            Path.GetTempPath(),
            Environment.GetFolderPath(Environment.SpecialFolder.CommonDocuments),
            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
        };
        Exception? lastError = null;
        foreach (var parent in candidates.Where(p => !string.IsNullOrWhiteSpace(p)).Distinct())
        {
            var asciiParent = ShortAsciiPath(Path.TrimEndingDirectorySeparator(parent));
            if (asciiParent is null) continue;
            var cache = Path.Combine(asciiParent, "QInventor", "RuntimeLinks");
            var link = Path.Combine(cache, key);
            try
            {
                Directory.CreateDirectory(cache);
                var info = new DirectoryInfo(link);
                if (info.Exists)
                {
                    var target = info.ResolveLinkTarget(false)?.FullName;
                    if (target is null || !string.Equals(Path.TrimEndingDirectorySeparator(Path.GetFullPath(target)),
                            root, StringComparison.OrdinalIgnoreCase))
                        throw new IOException("Существующая ссылка CAD-движка указывает на другую папку.");
                }
                else
                {
                    // Never remove an existing or dangling junction. Only create
                    // a fresh directory whose exact target is the validated root.
                    if (info.LinkTarget is not null)
                        throw new IOException("Служебная ссылка CAD-движка недоступна.");
                    Directory.CreateDirectory(link);
                    CreateJunction(link, root);
                }
                var aliasedEngine = Path.Combine(link, relativeEngine);
                if (!File.Exists(aliasedEngine))
                    throw new IOException("Служебная ссылка CAD-движка не содержит исполняемый файл.");
                return aliasedEngine;
            }
            catch (Exception ex) when (ex is IOException or UnauthorizedAccessException or Win32Exception)
            {
                lastError = ex;
            }
        }
        throw new IOException("Не удалось подготовить служебный путь CAD-движка. Перенесите папку QInventor в путь из латинских символов.", lastError);
    }

    static void CreateJunction(string link, string target)
    {
        if (target.StartsWith(@"\\"))
            throw new IOException("Сетевая папка без короткого пути не поддерживается CAD-движком.");
        var substitute = Encoding.Unicode.GetBytes(@"\??\" + target);
        var print = Encoding.Unicode.GetBytes(target);
        var buffer = new byte[16 + substitute.Length + 2 + print.Length + 2];
        void Write16(int offset, int value) => BitConverter.GetBytes(checked((ushort)value)).CopyTo(buffer, offset);
        BitConverter.GetBytes(0xA0000003u).CopyTo(buffer, 0); // IO_REPARSE_TAG_MOUNT_POINT
        Write16(4, buffer.Length - 8);
        Write16(8, 0);
        Write16(10, substitute.Length);
        Write16(12, substitute.Length + 2);
        Write16(14, print.Length);
        substitute.CopyTo(buffer, 16);
        print.CopyTo(buffer, 18 + substitute.Length);
        using var handle = CreateFileW(link, 0x40000000, 0, IntPtr.Zero, 3,
            0x00200000 | 0x02000000, IntPtr.Zero);
        if (handle.IsInvalid) throw new Win32Exception(Marshal.GetLastWin32Error());
        if (!DeviceIoControl(handle, 0x000900A4, buffer, (uint)buffer.Length,
                IntPtr.Zero, 0, out _, IntPtr.Zero))
            throw new Win32Exception(Marshal.GetLastWin32Error());
    }
}