Refactor online recognizer (#250)

* Refactor online recognizer.

Make it easier to support other streaming models.

Note that it is a breaking change for the Python API.
`sherpa_onnx.OnlineRecognizer()` used before should be
replaced by `sherpa_onnx.OnlineRecognizer.from_transducer()`.

sherpa-onnx/csrc/online-model-config.cc

@@ -0,0 +1,61 @@
+// sherpa-onnx/csrc/online-model-config.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+#include "sherpa-onnx/csrc/online-model-config.h"
+
+#include <string>
+
+#include "sherpa-onnx/csrc/file-utils.h"
+#include "sherpa-onnx/csrc/macros.h"
+
+namespace sherpa_onnx {
+
+void OnlineModelConfig::Register(ParseOptions *po) {
+  transducer.Register(po);
+
+  po->Register("tokens", &tokens, "Path to tokens.txt");
+
+  po->Register("num-threads", &num_threads,
+               "Number of threads to run the neural network");
+
+  po->Register("debug", &debug,
+               "true to print model information while loading it.");
+
+  po->Register("provider", &provider,
+               "Specify a provider to use: cpu, cuda, coreml");
+
+  po->Register("model-type", &model_type,
+               "Specify it to reduce model initialization time. "
+               "Valid values are: conformer, lstm, zipformer, zipformer2."
+               "All other values lead to loading the model twice.");
+}
+
+bool OnlineModelConfig::Validate() const {
+  if (num_threads < 1) {
+    SHERPA_ONNX_LOGE("num_threads should be > 0. Given %d", num_threads);
+    return false;
+  }
+
+  if (!FileExists(tokens)) {
+    SHERPA_ONNX_LOGE("tokens: %s does not exist", tokens.c_str());
+    return false;
+  }
+
+  return transducer.Validate();
+}
+
+std::string OnlineModelConfig::ToString() const {
+  std::ostringstream os;
+
+  os << "OnlineModelConfig(";
+  os << "transducer=" << transducer.ToString() << ", ";
+  os << "tokens=\"" << tokens << "\", ";
+  os << "num_threads=" << num_threads << ", ";
+  os << "debug=" << (debug ? "True" : "False") << ", ";
+  os << "provider=\"" << provider << "\", ";
+  os << "model_type=\"" << model_type << "\")";
+
+  return os.str();
+}
+
+}  // namespace sherpa_onnx