Add new interfaces

Flow.Launcher.Plugin/Interfaces/IAsyncEmptyQuery.cs

@@ -0,0 +1,23 @@
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Flow.Launcher.Plugin
+{
+    /// <summary>
+    /// Asynchronous Query Model for Flow Launcher When Query Text is Empty
+    /// </summary>
+    public interface IAsyncEmptyQuery
+    {
+        /// <summary>
+        /// Asynchronous Querying When Query Text is Empty
+        /// </summary>
+        /// <para>
+        /// If the Querying method requires high IO transmission
+        /// or performing CPU intense jobs (performing better with cancellation), please use this IAsyncEmptyQuery interface
+        /// </para>
+        /// <param name="token">Cancel when querying job is obsolete</param>
+        /// <returns></returns>
+        Task<List<Result>> EmptyQueryAsync(CancellationToken token);
+    }
+}

Flow.Launcher.Plugin/Interfaces/IEmptyQuery.cs

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+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Flow.Launcher.Plugin
+{
+    /// <summary>
+    /// Synchronous Query Model for Flow Launcher When Query Text is Empty
+    /// <para>
+    /// If the Querying method requires high IO transmission
+    /// or performaing CPU intense jobs (performing better with cancellation), please try the IAsyncEmptyQuery interface
+    /// </para>
+    /// </summary>
+    public interface IEmptyQuery : IAsyncEmptyQuery
+    {
+        /// <summary>
+        /// Querying When Query Text is Empty
+        /// <para>
+        /// This method will be called within a Task.Run,
+        /// so please avoid synchrously wait for long.
+        /// </para>
+        /// </summary>
+        /// <returns></returns>
+        List<Result> EmptyQuery();
+
+        Task<List<Result>> IAsyncEmptyQuery.EmptyQueryAsync(CancellationToken token) => Task.Run(EmptyQuery);
+    }
+}