using System;
using System.Runtime.InteropServices;
using System.Security.Principal;

namespace Core.Security {
    /// <summary>
    /// Impersonates a windows user within the context of a disposable pattern:
    ///<example>
    /// using(ImpersonationContext context = ImpersonationContext.ImpersonateUser("Joe","MyDomain","MyPasswrd")) { 
    ///     //Do stuff under impersonated user credentials
    /// }
    /// </example>
    /// </summary>
    public class ImpersonationContext:IDisposable {

        public static ImpersonationContext ImpersonateUser(String userName,String domain,String password) {
            var context = new ImpersonationContext();
            if(context.ImpersonateValidUser(userName,domain,password)) {
                return context;
            }
            return null;
        }

        WindowsImpersonationContext _impersonationContext;
        bool _impersonating;

        ImpersonationContext() {
           
        }

        const int LOGON32_LOGON_INTERACTIVE = 2;
        const int LOGON32_PROVIDER_DEFAULT = 0;

        [DllImport("advapi32.dll")]
        static extern int LogonUserA(String lpszUserName,
            String lpszDomain,
            String lpszPassword,
            int dwLogonType,
            int dwLogonProvider,
            ref IntPtr phToken);

        [DllImport("advapi32.dll",CharSet = CharSet.Auto,SetLastError = true)]
        static extern int DuplicateToken(IntPtr hToken,
            int impersonationLevel,
            ref IntPtr hNewToken);

        [DllImport("advapi32.dll",CharSet = CharSet.Auto,SetLastError = true)]
        static extern bool RevertToSelf();

        [DllImport("kernel32.dll",CharSet = CharSet.Auto)]
        static extern bool CloseHandle(IntPtr handle);

        bool ImpersonateValidUser(String userName,String domain,String password) {
            
            _impersonating = false;

            WindowsIdentity tempWindowsIdentity;
            IntPtr token = IntPtr.Zero;
            IntPtr tokenDuplicate = IntPtr.Zero;

            if(RevertToSelf()) {
                if(LogonUserA(userName,domain,password,LOGON32_LOGON_INTERACTIVE,
                    LOGON32_PROVIDER_DEFAULT,ref token) != 0) {
                    if(DuplicateToken(token,2,ref tokenDuplicate) != 0) {
                        tempWindowsIdentity = new WindowsIdentity(tokenDuplicate);
                        _impersonationContext = tempWindowsIdentity.Impersonate();
                        if(_impersonationContext != null) {
                            CloseHandle(token);
                            CloseHandle(tokenDuplicate);
                            _impersonating = true;
                            return true;
                        }
                    }
                }
            }
            if(token != IntPtr.Zero)
                CloseHandle(token);
            if(tokenDuplicate != IntPtr.Zero)
                CloseHandle(tokenDuplicate);
            return false;
        }

        void UndoImpersonation() {
            if(_impersonationContext == null)
                return;
            _impersonationContext.Undo();
        }

        #region IDisposable Pattern

        protected bool IsDisposed { get; private set; }

        protected void EnsureNotDisposed() {
            if(IsDisposed)
                throw new ObjectDisposedException(GetType().Name);
        }

        public virtual void Dispose() {
            if(IsDisposed)
                throw new ObjectDisposedException(this.GetType().Name);
            try {
                this.Dispose(true);
            }
            finally {
                GC.SuppressFinalize(this);
            }
        }
        protected virtual void Dispose(bool disposing) {

            if(disposing) {
                try {
                    if(!IsDisposed) {
                        if(_impersonating)
                            UndoImpersonation();
                    }
                }
                finally {
                    IsDisposed = true;
                }
            }

        }
        //Only add Finalizer in you need to dispose of resources with out call Dispose() directly
        ~ImpersonationContext() {
            Dispose(!IsDisposed);
        }
        #endregion
    }
}