Some internal refactoring.

NTwain/ITwainSession.cs

@@ -0,0 +1,63 @@
+using NTwain.Data;
+using System;
+using System.ComponentModel;
+namespace NTwain
+{
+    /// <summary>
+    /// Interface for keeping track of current TWAIN state with current app and source ids.
+    /// </summary>
+    public interface ITwainSession : INotifyPropertyChanged
+    {
+        /// <summary>
+        /// Gets the app id used for the session.
+        /// </summary>
+        /// <value>The app id.</value>
+        TWIdentity AppId { get; }
+        
+        /// <summary>
+        /// Gets the source id used for the session.
+        /// </summary>
+        /// <value>The source id.</value>
+        TWIdentity SourceId { get; }
+
+        /// <summary>
+        /// Gets the current state number as defined by the TWAIN spec.
+        /// </summary>
+        /// <value>The state.</value>
+        int State { get; }
+    }
+
+    /// <summary>
+    /// Internal interface for state management.
+    /// </summary>
+    interface ITwainSessionInternal : ITwainSession
+    {
+        /// <summary>
+        /// Gets or sets a value indicating whether calls to triplets will verify the current twain session state.
+        /// </summary>
+        /// <value>
+        ///   <c>true</c> if state value is enforced; otherwise, <c>false</c>.
+        /// </value>
+        bool EnforceState { get; set; }
+
+        /// <summary>
+        /// Changes the state right away.
+        /// </summary>
+        /// <param name="newState">The new state.</param>
+        /// <param name="notifyChange">if set to <c>true</c> to notify change.</param>
+        void ChangeState(int newState, bool notifyChange);
+
+        /// <summary>
+        /// Gets the pending state changer and tentatively changes the session state to the specified value.
+        /// Value will only stick if committed.
+        /// </summary>
+        /// <param name="newState">The new state.</param>
+        /// <returns></returns>
+        ICommitable GetPendingStateChanger(int newState);
+    }
+
+    interface ICommitable : IDisposable
+    {
+        void Commit();
+    }
+}