using System.ComponentModel;
using System.Runtime.InteropServices;

namespace MusicBridge.Agent.Network;

// Windows DPAPI, scoped to the signed-in user. No UI or machine-wide key.
internal static class UserProtection
{
    public static byte[] Protect(byte[] bytes) => Transform(bytes, true);
    public static byte[] Unprotect(byte[] bytes) => Transform(bytes, false);

    private static byte[] Transform(byte[] bytes, bool protect)
    {
        var input = new Blob { Size = bytes.Length, Data = Marshal.AllocHGlobal(bytes.Length) };
        var output = new Blob();
        try
        {
            Marshal.Copy(bytes, 0, input.Data, bytes.Length);
            var ok = protect
                ? CryptProtectData(ref input, null, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, 1, out output)
                : CryptUnprotectData(ref input, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, 1, out output);
            if (!ok) throw new Win32Exception(Marshal.GetLastWin32Error(), "Не удалось открыть защищённое хранилище Windows.");
            var result = new byte[output.Size];
            Marshal.Copy(output.Data, result, 0, output.Size);
            return result;
        }
        finally
        {
            Marshal.Copy(new byte[input.Size], 0, input.Data, input.Size);
            Marshal.FreeHGlobal(input.Data);
            if (output.Data != IntPtr.Zero)
            {
                Marshal.Copy(new byte[output.Size], 0, output.Data, output.Size);
                LocalFree(output.Data);
            }
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct Blob { public int Size; public IntPtr Data; }
    [DllImport("crypt32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool CryptProtectData(ref Blob input, string? description, IntPtr entropy, IntPtr reserved,
        IntPtr prompt, uint flags, out Blob output);
    [DllImport("crypt32.dll", SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool CryptUnprotectData(ref Blob input, IntPtr description, IntPtr entropy, IntPtr reserved,
        IntPtr prompt, uint flags, out Blob output);
    [DllImport("kernel32.dll")]
    private static extern IntPtr LocalFree(IntPtr memory);
}