Split online.cs and offline.csFile (#941)

Co-authored-by: 东风破 <birdfishs@163.com>

scripts/dotnet/OfflineTts.cs

@@ -0,0 +1,91 @@
+/// Copyright (c)  2024.5 by 东风破
+
+using System.Linq;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using System.Text;
+using System;
+
+namespace SherpaOnnx
+{
+    // IntPtr is actuallly a `const float*` from C++
+    public delegate void OfflineTtsCallback(IntPtr samples, int n);
+
+    public class OfflineTts : IDisposable
+    {
+        public OfflineTts(OfflineTtsConfig config)
+        {
+            IntPtr h = SherpaOnnxCreateOfflineTts(ref config);
+            _handle = new HandleRef(this, h);
+        }
+
+        public OfflineTtsGeneratedAudio Generate(String text, float speed, int speakerId)
+        {
+            IntPtr p = SherpaOnnxOfflineTtsGenerate(_handle.Handle, text, speakerId, speed);
+            return new OfflineTtsGeneratedAudio(p);
+        }
+
+        public OfflineTtsGeneratedAudio GenerateWithCallback(String text, float speed, int speakerId, OfflineTtsCallback callback)
+        {
+            IntPtr p = SherpaOnnxOfflineTtsGenerateWithCallback(_handle.Handle, text, speakerId, speed, callback);
+            return new OfflineTtsGeneratedAudio(p);
+        }
+
+        public void Dispose()
+        {
+            Cleanup();
+            // Prevent the object from being placed on the
+            // finalization queue
+            System.GC.SuppressFinalize(this);
+        }
+
+        ~OfflineTts()
+        {
+            Cleanup();
+        }
+
+        private void Cleanup()
+        {
+            SherpaOnnxDestroyOfflineTts(_handle.Handle);
+
+            // Don't permit the handle to be used again.
+            _handle = new HandleRef(this, IntPtr.Zero);
+        }
+
+        private HandleRef _handle;
+
+        public int SampleRate
+        {
+            get
+            {
+                return SherpaOnnxOfflineTtsSampleRate(_handle.Handle);
+            }
+        }
+
+        public int NumSpeakers
+        {
+            get
+            {
+                return SherpaOnnxOfflineTtsNumSpeakers(_handle.Handle);
+            }
+        }
+
+        [DllImport(Dll.Filename)]
+        private static extern IntPtr SherpaOnnxCreateOfflineTts(ref OfflineTtsConfig config);
+
+        [DllImport(Dll.Filename)]
+        private static extern void SherpaOnnxDestroyOfflineTts(IntPtr handle);
+
+        [DllImport(Dll.Filename)]
+        private static extern int SherpaOnnxOfflineTtsSampleRate(IntPtr handle);
+
+        [DllImport(Dll.Filename)]
+        private static extern int SherpaOnnxOfflineTtsNumSpeakers(IntPtr handle);
+
+        [DllImport(Dll.Filename)]
+        private static extern IntPtr SherpaOnnxOfflineTtsGenerate(IntPtr handle, [MarshalAs(UnmanagedType.LPStr)] string text, int sid, float speed);
+
+        [DllImport(Dll.Filename, CallingConvention = CallingConvention.Cdecl)]
+        private static extern IntPtr SherpaOnnxOfflineTtsGenerateWithCallback(IntPtr handle, [MarshalAs(UnmanagedType.LPStr)] string text, int sid, float speed, OfflineTtsCallback callback);
+    }
+}