feat: add a global handler for getting items

provider.go

@@ -0,0 +1,56 @@
+package yourconfig
+
+import (
+	"context"
+	"os"
+	"sync/atomic"
+)
+
+var defaultLogger atomic.Pointer[Provider]
+
+func init() {
+	defaultLogger.Store(newProvider())
+}
+
+func SetDefault(provider *Provider) {
+	defaultLogger.Store(provider)
+}
+
+func Default() *Provider {
+	return defaultLogger.Load()
+}
+
+type Handler interface {
+	Get(ctx context.Context, key string) (string, error)
+}
+
+type Provider struct {
+	handler Handler
+}
+
+func (p *Provider) Get(ctx context.Context, key string) (string, error) {
+	return p.handler.Get(ctx, key)
+}
+
+func newProvider() *Provider {
+	return &Provider{
+		handler: defaultHandler(),
+	}
+}
+
+func New(handler Handler) *Provider {
+	return &Provider{
+		handler: handler,
+	}
+}
+
+type envHandler struct{}
+
+func (e *envHandler) Get(ctx context.Context, key string) (string, error) {
+	val := os.Getenv(key)
+	return val, nil
+}
+
+func defaultHandler() Handler {
+	return &envHandler{}
+}