Implement backend factory

include/backend.hpp

@@ -1,14 +1,55 @@
 #pragma once
 
 #include <cstddef>
+#include <stdexcept>
 
 #include "shape.hpp"
+#ifdef USE_CUDA
+#include "backend/cuda/cuda.cuh"
+#endif
 
 namespace CUDANet {
 
 // Forward declaration
 class Tensor;
 
+enum BackendType { CUDA_BACKEND, CPU_BACKEND };
+
+struct BackendConfig {
+    int device_id = 0;
+};
+
+class BackendFactory {
+  public:
+    static std::unique_ptr<Backend> create(BackendType backend_type, const BackendConfig& config) {
+        switch (backend_type)
+        {
+        case BackendType::CUDA_BACKEND:
+            #ifdef USE_CUDA
+
+            if (!CUDANet::Backends::CUDA::is_cuda_available()) {
+                throw std::runtime_error("No CUDA devices found")
+            }
+
+            auto cuda = std::make_unique<CUDANet::Backends::CUDA>(config);
+            cuda.initialize();
+
+            return cuda;
+
+            #else
+            throw std::runtime_error("Library was compiled without CUDA support.");
+            #endif
+
+            break;
+        
+        default:
+            break;
+        }
+
+        return nullptr;
+    }
+};
+
 class Backend {
   public:
     // Memory management