using System;
using System.Runtime.InteropServices;
using System.Security.Principal;
#nullable disable

namespace Wabbajack.Common.IO
{
    /// <summary>
    /// Represents a special Windows directory and provides methods to retrieve information about it.
    /// </summary>
    public sealed class KnownFolder
    {
        // ---- CONSTRUCTORS & DESTRUCTOR ------------------------------------------------------------------------------

        /// <summary>
        /// Initializes a new instance of the <see cref="KnownFolder"/> class for the folder of the given type. It
        /// provides the values for the current user.
        /// </summary>
        /// <param name="type">The <see cref="KnownFolderType"/> of the known folder to represent.</param>
        public KnownFolder(KnownFolderType type) : this(type, WindowsIdentity.GetCurrent()) { }

        /// <summary>
        /// Initializes a new instance of the <see cref="KnownFolder"/> class for the folder of the given type. It
        /// provides the values for the given impersonated user.
        /// </summary>
        /// <param name="type">The <see cref="KnownFolderType"/> of the known folder to represent.</param>
        /// <param name="identity">The <see cref="WindowsIdentity"/> of the impersonated user which values will be
        /// provided.</param>
        public KnownFolder(KnownFolderType type, WindowsIdentity identity)
        {
            Type = type;
            Identity = identity;
        }

        // ---- PROPERTIES ---------------------------------------------------------------------------------------------

        /// <summary>
        /// Gets the type of the known folder which is represented.
        /// </summary>
        public KnownFolderType Type { get; }

        /// <summary>
        /// Gets the <see cref="WindowsIdentity"/> of the user whose folder values are provided.
        /// </summary>
        public WindowsIdentity Identity { get; }

        /// <summary>
        /// Gets the default path of the folder. This does not require the folder to be existent.
        /// </summary>
        /// <exception cref="ExternalException">The known folder could not be retrieved.</exception>
        public string DefaultPath
        {
            get => GetPath(KnownFolderFlags.DontVerify | KnownFolderFlags.DefaultPath);
        }

        /// <summary>
        /// Gets or sets the path as currently configured. This does not require the folder to be existent.
        /// </summary>
        /// <exception cref="ExternalException">The known folder could not be retrieved.</exception>
        public string Path
        {
            get => GetPath(KnownFolderFlags.DontVerify);
            set => SetPath(KnownFolderFlags.None, value);
        }

        /// <summary>
        /// Gets or sets the path as currently configured, with all environment variables expanded.
        /// This does not require the folder to be existent.
        /// </summary>
        /// <exception cref="ExternalException">The known folder could not be retrieved.</exception>
        public string ExpandedPath
        {
            get => GetPath(KnownFolderFlags.DontVerify | KnownFolderFlags.NoAlias);
            set => SetPath(KnownFolderFlags.DontUnexpand, value);
        }

        // ---- METHODS (PUBLIC) ---------------------------------------------------------------------------------------

        /// <summary>
        /// Creates the folder using its Desktop.ini settings.
        /// </summary>
        /// <exception cref="ExternalException">The known folder could not be retrieved.</exception>
        public void Create()
        {
            GetPath(KnownFolderFlags.Init | KnownFolderFlags.Create);
        }

        // ---- METHODS (PRIVATE) --------------------------------------------------------------------------------------

        private string GetPath(KnownFolderFlags flags)
        {
            int result = SHGetKnownFolderPath(Type.GetGuid(), (uint)flags, Identity.Token, out IntPtr outPath);
            if (result >= 0)
            {
                string path = Marshal.PtrToStringUni(outPath);
                Marshal.FreeCoTaskMem(outPath);
                return path;
            }
            else
            {
                throw new ExternalException("Cannot get the known folder path. It may not be available on this system.",
                    result);
            }
        }

        private void SetPath(KnownFolderFlags flags, string path)
        {
            int result = SHSetKnownFolderPath(Type.GetGuid(), (uint)flags, Identity.Token, path);
            if (result < 0)
            {
                throw new ExternalException("Cannot set the known folder path. It may not be available on this system.",
                    result);
            }
        }

        /// <summary>
        /// Retrieves the full path of a known folder identified by the folder's known folder ID.
        /// </summary>
        /// <param name="rfid">A known folder ID that identifies the folder.</param>
        /// <param name="dwFlags">Flags that specify special retrieval options. This value can be 0; otherwise, one or
        /// more of the <see cref="KnownFolderFlags"/> values.</param>
        /// <param name="hToken">An access token that represents a particular user. If this parameter is NULL, which is
        /// the most common usage, the function requests the known folder for the current user. Assigning a value of -1
        /// indicates the Default User. The default user profile is duplicated when any new user account is created.
        /// Note that access to the Default User folders requires administrator privileges.</param>
        /// <param name="ppszPath">When this method returns, contains the address of a string that specifies the path of
        /// the known folder. The returned path does not include a trailing backslash.</param>
        /// <returns>Returns S_OK if successful, or an error value otherwise.</returns>
        /// <msdn-id>bb762188</msdn-id>
        [DllImport("Shell32.dll")]
        private static extern int SHGetKnownFolderPath([MarshalAs(UnmanagedType.LPStruct)]Guid rfid, uint dwFlags,
            IntPtr hToken, out IntPtr ppszPath);

        /// <summary>
        /// Redirects a known folder to a new location.
        /// </summary>
        /// <param name="rfid">A <see cref="Guid"/> that identifies the known folder.</param>
        /// <param name="dwFlags">Either 0 or <see cref="KnownFolderFlags.DontUnexpand"/>.</param>
        /// <param name="hToken"></param>
        /// <param name="pszPath"></param>
        /// <returns></returns>
        /// <msdn-id>bb762249</msdn-id>
        [DllImport("Shell32.dll")]
        private static extern int SHSetKnownFolderPath([MarshalAs(UnmanagedType.LPStruct)]Guid rfid, uint dwFlags,
            IntPtr hToken, [MarshalAs(UnmanagedType.LPWStr)]string pszPath);

        // ---- ENUMERATIONS -------------------------------------------------------------------------------------------

        /// <summary>
        /// Represents the retrieval options for known folders.
        /// </summary>
        /// <msdn-id>dd378447</msdn-id>
        [Flags]
        private enum KnownFolderFlags : uint
        {
            None = 0x00000000,
            SimpleIDList = 0x00000100,
            NotParentRelative = 0x00000200,
            DefaultPath = 0x00000400,
            Init = 0x00000800,
            NoAlias = 0x00001000,
            DontUnexpand = 0x00002000,
            DontVerify = 0x00004000,
            Create = 0x00008000,
            NoAppcontainerRedirection = 0x00010000,
            AliasOnly = 0x80000000
        }
    }
}