Add support for defaulting to latest version and improve code structure

pkg/registry/factory.go

@@ -0,0 +1,37 @@
+package registry
+
+import (
+	"fmt"
+	"time"
+)
+
+// RegistryType represents different package registries
+type RegistryType string
+
+const (
+	RegistryNPM  RegistryType = "npm"
+	RegistryPyPI RegistryType = "pypi"
+	RegistryGo   RegistryType = "go"
+)
+
+// FetcherFactory creates appropriate fetchers based on registry type
+type FetcherFactory struct {
+	timeout time.Duration
+}
+
+// NewFetcherFactory creates a new factory for registry fetchers
+func NewFetcherFactory(timeout time.Duration) *FetcherFactory {
+	return &FetcherFactory{
+		timeout: timeout,
+	}
+}
+
+// CreateFetcher returns a fetcher for the specified registry type
+func (ff *FetcherFactory) CreateFetcher(registryType RegistryType) (Fetcher, error) {
+	switch registryType {
+	case RegistryNPM:
+		return NewNpmFetcher(ff.timeout), nil
+	default:
+		return nil, fmt.Errorf("unsupported registry type: %s", registryType)
+	}
+}