onnx: flatten operatos bridge hierarchy (#1846)

Signed-off-by: Artur Wojcik <artur.wojcik@intel.com>

src/ngraph/frontend/onnx_import/onnx.cpp

@@ -62,7 +62,7 @@ namespace ngraph
             std::vector<std::shared_ptr<Function>> output_functions;
             Model model{model_proto};
             Graph graph{model_proto.graph(),
-                        ops_bridge::get_operator_set(model.get_opset_version())};
+                        OperatorsBridge::get_operator_set(model.get_opset_version())};
             for (const auto& output : graph.get_outputs())
             {
                 output_functions.emplace_back(std::make_shared<Function>(

src/ngraph/frontend/onnx_import/ops_bridge.hpp

@@ -17,6 +17,11 @@
 #pragma once
 
 #include <cstdint>
+#include <map>
+#include <string>
+#include <unordered_map>
+
+#include "ngraph/except.hpp"
 
 #include "core/operator_set.hpp"
 
@@ -24,11 +29,61 @@ namespace ngraph
 {
     namespace onnx_import
     {
-        namespace ops_bridge
+        namespace error
+        {
+            struct UnknownOperator : ngraph_error
+            {
+                explicit UnknownOperator(const std::string& op_type)
+                    : ngraph_error{"unknown operator: \"" + op_type + "\""}
+                {
+                }
+            };
+
+            struct UnsupportedVersion : ngraph_error
+            {
+                explicit UnsupportedVersion(std::int64_t version)
+                    : ngraph_error{"unsupported operator set version: " + std::to_string(version)}
+                {
+                }
+            };
+
+        } // namespace error
+
+        class OperatorsBridge
         {
-            const OperatorSet& get_operator_set(std::int64_t version);
+        public:
+            OperatorsBridge(const OperatorsBridge&) = delete;
+            OperatorsBridge& operator=(const OperatorsBridge&) = delete;
+            OperatorsBridge(OperatorsBridge&&) = delete;
+            OperatorsBridge& operator=(OperatorsBridge&&) = delete;
+
+            static const OperatorSet& get_operator_set(std::int64_t version)
+            {
+                return instance().get_operator_set_version(version);
+            }
+
+        private:
+            std::unordered_map<std::string, std::map<std::int64_t, Operator>> m_map;
+
+            OperatorsBridge();
+
+            static const OperatorsBridge& instance()
+            {
+                static OperatorsBridge instance;
+                return instance;
+            }
 
-        } // namespace ops_bridge
+            const OperatorSet& get_operator_set_version_1() const;
+            const OperatorSet& get_operator_set_version_2() const;
+            const OperatorSet& get_operator_set_version_3() const;
+            const OperatorSet& get_operator_set_version_4() const;
+            const OperatorSet& get_operator_set_version_5() const;
+            const OperatorSet& get_operator_set_version_6() const;
+            const OperatorSet& get_operator_set_version_7() const;
+            const OperatorSet& get_operator_set_version_8() const;
+            const OperatorSet& get_operator_set_version_9() const;
+            const OperatorSet& get_operator_set_version(std::int64_t version) const;
+        };
 
     } // namespace onnx_import