Dart API for adding punctuations to text (#1182)

flutter/sherpa_onnx/lib/src/punctuation.dart

@@ -0,0 +1,91 @@
+// Copyright (c)  2024  Xiaomi Corporation
+import 'dart:ffi';
+import 'package:ffi/ffi.dart';
+
+import './sherpa_onnx_bindings.dart';
+
+class OfflinePunctuationModelConfig {
+  OfflinePunctuationModelConfig(
+      {required this.ctTransformer,
+      this.numThreads = 1,
+      this.provider = 'cpu',
+      this.debug = true});
+
+  @override
+  String toString() {
+    return 'OfflinePunctuationModelConfig(ctTransformer: $ctTransformer, numThreads: $numThreads, provider: $provider, debug: $debug)';
+  }
+
+  final String ctTransformer;
+  final int numThreads;
+  final String provider;
+  final bool debug;
+}
+
+class OfflinePunctuationConfig {
+  OfflinePunctuationConfig({
+    required this.model,
+  });
+
+  @override
+  String toString() {
+    return 'OfflinePunctuationConfig(model: $model)';
+  }
+
+  final OfflinePunctuationModelConfig model;
+}
+
+class OfflinePunctuation {
+  OfflinePunctuation._({required this.ptr, required this.config});
+
+  // The user has to invoke OfflinePunctuation.free() to avoid memory leak.
+  factory OfflinePunctuation({required OfflinePunctuationConfig config}) {
+    final c = calloc<SherpaOnnxOfflinePunctuationConfig>();
+
+    final ctTransformerPtr = config.model.ctTransformer.toNativeUtf8();
+    c.ref.model.ctTransformer = ctTransformerPtr;
+    c.ref.model.numThreads = config.model.numThreads;
+    c.ref.model.debug = config.model.debug ? 1 : 0;
+
+    final providerPtr = config.model.provider.toNativeUtf8();
+    c.ref.model.provider = providerPtr;
+
+    final ptr =
+        SherpaOnnxBindings.sherpaOnnxCreateOfflinePunctuation?.call(c) ??
+            nullptr;
+
+    calloc.free(providerPtr);
+    calloc.free(ctTransformerPtr);
+    calloc.free(c);
+
+    return OfflinePunctuation._(ptr: ptr, config: config);
+  }
+
+  void free() {
+    SherpaOnnxBindings.sherpaOnnxDestroyOfflinePunctuation?.call(ptr);
+    ptr = nullptr;
+  }
+
+  String addPunct(String text) {
+    final textPtr = text.toNativeUtf8();
+
+    final p = SherpaOnnxBindings.sherpaOfflinePunctuationAddPunct
+            ?.call(ptr, textPtr) ??
+        nullptr;
+
+    calloc.free(textPtr);
+
+    if (p == nullptr) {
+      return '';
+    }
+
+    final ans = p.toDartString();
+
+    SherpaOnnxBindings.sherpaOfflinePunctuationFreeText?.call(p);
+
+    return ans;
+  }
+
+  Pointer<SherpaOnnxOfflinePunctuation> ptr;
+  final OfflinePunctuationConfig config;
+}