feat: add AddReference method to References

Signed-off-by: Yordis Prieto <[email protected]>

pkg/config/resource.go

@@ -165,10 +165,26 @@ type ExternalName struct {
 	IdentifierFields []string
 }
 
+var ErrReferenceAlreadyExists = errors.New("reference for field already exists")
+
 // References represents reference resolver configurations for the fields of a
 // given resource. Key should be the field path of the field to be referenced.
 type References map[string]Reference
 
+// AddReference adds a reference configuration for the given field path.
+// The fieldPath is the Terraform field path of the field to be referenced.
+//
+// Example: "vpc_id" or "forwarding_rule.certificate_name" in case of nested
+// in another object.
+func (r References) AddReference(fieldPath string, ref Reference) error {
+	if _, ok := r[fieldPath]; ok {
+		return ErrReferenceAlreadyExists
+	}
+
+	r[fieldPath] = ref
+	return nil
+}
+
 // Reference represents the Crossplane options used to generate
 // reference resolvers for fields
 type Reference struct {

pkg/config/resource_test.go

@@ -6,10 +6,10 @@ package config
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"testing"
 
-	"github.com/crossplane/crossplane-runtime/pkg/errors"
 	"github.com/crossplane/crossplane-runtime/pkg/fieldpath"
 	xpresource "github.com/crossplane/crossplane-runtime/pkg/resource"
 	"github.com/crossplane/crossplane-runtime/pkg/resource/fake"
@@ -112,3 +112,34 @@ func TestSetExternalTagsWithPaved(t *testing.T) {
 		})
 	}
 }
+
+func TestReferences_AddReference(t *testing.T) {
+	t.Run("Adding a reference", func(t *testing.T) {
+		r := &Resource{References: References{}}
+		err := r.References.AddReference("forwarding_rule.certificate_name", Reference{
+			TerraformName: "digitalocean_certificate",
+		})
+		if err != nil {
+			t.Fatalf("AddReference() got error: %v", err)
+		}
+		if len(r.References) != 1 {
+			t.Fatalf("AddReference() got error: %v", err)
+		}
+	})
+	t.Run("Adding twice a reference for a given field", func(t *testing.T) {
+		r := &Resource{References: References{}}
+		err := r.References.AddReference("forwarding_rule.certificate_name", Reference{
+			TerraformName: "digitalocean_certificate",
+		})
+		if err != nil {
+			t.Fatalf("AddReference() got error: %v", err)
+		}
+
+		err = r.References.AddReference("forwarding_rule.certificate_name", Reference{
+			TerraformName: "digitalocean_certificate",
+		})
+		if !errors.Is(err, ErrReferenceAlreadyExists) {
+			t.Fatalf("AddReference() should have returned an error")
+		}
+	})
+}