Refactor offline recognizer. (#94)

* Refactor offline recognizer.

The purpose is to make it easier to support different types of models.

sherpa-onnx/csrc/offline-recognizer-impl.cc

@@ -0,0 +1,43 @@
+// sherpa-onnx/csrc/offline-recognizer-impl.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#include "sherpa-onnx/csrc/offline-recognizer-impl.h"
+
+#include <string>
+
+#include "onnxruntime_cxx_api.h"  // NOLINT
+#include "sherpa-onnx/csrc/macros.h"
+#include "sherpa-onnx/csrc/offline-recognizer-transducer-impl.h"
+#include "sherpa-onnx/csrc/onnx-utils.h"
+#include "sherpa-onnx/csrc/text-utils.h"
+
+namespace sherpa_onnx {
+
+std::unique_ptr<OfflineRecognizerImpl> OfflineRecognizerImpl::Create(
+    const OfflineRecognizerConfig &config) {
+  Ort::Env env;
+
+  Ort::SessionOptions sess_opts;
+  auto buf = ReadFile(config.model_config.encoder_filename);
+
+  auto encoder_sess =
+      std::make_unique<Ort::Session>(env, buf.data(), buf.size(), sess_opts);
+
+  Ort::ModelMetadata meta_data = encoder_sess->GetModelMetadata();
+
+  Ort::AllocatorWithDefaultOptions allocator;  // used in the macro below
+
+  std::string model_type;
+  SHERPA_ONNX_READ_META_DATA_STR(model_type, "model_type");
+
+  if (model_type == "conformer") {
+    return std::make_unique<OfflineRecognizerTransducerImpl>(config);
+  }
+
+  SHERPA_ONNX_LOGE("Unsupported model_type: %s\n", model_type.c_str());
+
+  exit(-1);
+}
+
+}  // namespace sherpa_onnx