Replace CELExpressionExtractor with a more robust parser implementa…

…tion (#34)

This patch improves our CEL expression parsing system, replacing
the regex based CELExpressionsExtractor with a more robust
parser. The previous implementation relied heavily on regulars
expressions, which proved to be ineffective for handling complex nested
structures and led to limitations in accurat parsing and extracting
CEL expressions from kubernetes resource definitions (`resources[*].definition`)

The new parser uses a token aware string traversal approach. It scans
input character by character recognizing `"${"` and `"}"` tokens. It tracks
brace nesting to handle complex structures, including nestde dictionaries
and conditionals.

In a nutshell, this patch makes the following changes:

- Remove the celextractor package and its regex based functionality
- Introduce a new parser package with the token aware parsing algorithm
  - Support both schemaless and structured parsing.
- Update the `resourcegroup`/`controller` packages to integrate the new parser
- Add unit tests and reach 87.5% coverage.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

cmd/controller/main.go

@@ -35,7 +35,6 @@ import (
 	"github.com/aws-controllers-k8s/symphony/internal/dynamiccontroller"
 	"github.com/aws-controllers-k8s/symphony/internal/kubernetes"
 	"github.com/aws-controllers-k8s/symphony/internal/resourcegroup"
-	"github.com/aws-controllers-k8s/symphony/internal/typesystem/celextractor"
 	//+kubebuilder:scaffold:imports
 )
 
@@ -133,7 +132,6 @@ func main() {
 
 	resourceGroupGraphBuilder, err := resourcegroup.NewResourceGroupBuilder(
 		kConfig,
-		celextractor.NewCELExpressionParser(),
 	)
 	if err != nil {
 		setupLog.Error(err, "unable to create resource group graph builder")

internal/resourcegroup/builder.go

@@ -29,15 +29,14 @@ import (
 	"github.com/aws-controllers-k8s/symphony/internal/celutil"
 	"github.com/aws-controllers-k8s/symphony/internal/dag"
 	"github.com/aws-controllers-k8s/symphony/internal/k8smetadata"
-	"github.com/aws-controllers-k8s/symphony/internal/typesystem/celextractor"
 	"github.com/aws-controllers-k8s/symphony/internal/typesystem/celinspector"
 	"github.com/aws-controllers-k8s/symphony/internal/typesystem/emulator"
+	"github.com/aws-controllers-k8s/symphony/internal/typesystem/parser"
 	"github.com/aws-controllers-k8s/symphony/internal/typesystem/simpleschema"
 )
 
 func NewResourceGroupBuilder(
 	clientConfig *rest.Config,
-	celExpressionsExtractor *celextractor.CELExpressionsExtractor,
 ) (*GraphBuilder, error) {
 	schemaResolver, err := newCombinedResolver(clientConfig)
 	if err != nil {
@@ -49,15 +48,13 @@ func NewResourceGroupBuilder(
 	rgBuilder := &GraphBuilder{
 		resourceEmulator: resourceEmulator,
 		schemaResolver:   schemaResolver,
-		celParser:        celExpressionsExtractor,
 	}
 	return rgBuilder, nil
 }
 
 type GraphBuilder struct {
 	schemaResolver   resolver.SchemaResolver
 	resourceEmulator *emulator.Emulator
-	celParser        *celextractor.CELExpressionsExtractor
 }
 
 func (b *GraphBuilder) NewResourceGroup(rg *v1alpha1.ResourceGroup) (*ResourceGroup, error) {
@@ -125,7 +122,7 @@ func (b *GraphBuilder) NewResourceGroup(rg *v1alpha1.ResourceGroup) (*ResourceGr
 		}
 
 		// 5. Extract CEL celExpressions from the schema.
-		celExpressions, err := b.celParser.ExtractExpressions(unstructuredResource, resourceSchema)
+		celExpressions, err := parser.ParseResource(unstructuredResource, resourceSchema)
 		if err != nil {
 			return nil, fmt.Errorf("failed to extract CEL expressions from schema for resource %s: %w", rgResource.Name, err)
 		}
@@ -501,7 +498,7 @@ func (b *GraphBuilder) buildInstanceSpecSchema(definition *v1alpha1.Definition)
 	return instanceSchema, nil
 }
 
-func (b *GraphBuilder) buildStatusSchema(definition *v1alpha1.Definition, resources map[string]*Resource) (*extv1.JSONSchemaProps, []celextractor.ExpressionField, error) {
+func (b *GraphBuilder) buildStatusSchema(definition *v1alpha1.Definition, resources map[string]*Resource) (*extv1.JSONSchemaProps, []parser.ExpressionField, error) {
 	// The instance resource has a schema defined using the "SimpleSchema" format.
 	unstructuredStatus := map[string]interface{}{}
 	err := yaml.UnmarshalStrict(definition.Status.Raw, &unstructuredStatus)
@@ -511,7 +508,7 @@ func (b *GraphBuilder) buildStatusSchema(definition *v1alpha1.Definition, resour
 
 	// different from the instance spec, the status schema is inferred from the
 	// CEL expressions in the status field.
-	extracted, err := celextractor.NewCELExpressionParser().ExtractExpressionsUnstructured(unstructuredStatus)
+	extracted, err := parser.ParseSchemalessResource(unstructuredStatus)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to extract CEL expressions from status: %w", err)
 	}

internal/resourcegroup/resource.go

@@ -14,12 +14,11 @@
 package resourcegroup
 
 import (
+	"github.com/aws-controllers-k8s/symphony/internal/typesystem/parser"
 	extv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/kube-openapi/pkg/validation/spec"
-
-	"github.com/aws-controllers-k8s/symphony/internal/typesystem/celextractor"
 )
 
 // Resource represents a resource in a resource group, it hholds
@@ -48,7 +47,7 @@ const (
 )
 
 type ResourceVariable struct {
-	celextractor.ExpressionField
+	parser.ExpressionField
 	Kind ResourceVariableKind
 }
 

internal/resourcegroup/runtime.go

@@ -20,7 +20,7 @@ import (
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 
 	"github.com/aws-controllers-k8s/symphony/internal/celutil"
-	"github.com/aws-controllers-k8s/symphony/internal/typesystem/celextractor"
+	"github.com/aws-controllers-k8s/symphony/internal/typesystem/parser"
 	"github.com/aws-controllers-k8s/symphony/internal/typesystem/resolver"
 )
 
@@ -236,7 +236,7 @@ func (rt *RuntimeResourceGroup) ResolveResource(resource string) error {
 	}
 
 	rs := resolver.NewResolver(rt.Resources[resource].Object, exprValues)
-	exprFields := make([]celextractor.ExpressionField, len(rt.ResourceGroup.Resources[resource].Variables))
+	exprFields := make([]parser.ExpressionField, len(rt.ResourceGroup.Resources[resource].Variables))
 	for i, v := range rt.ResourceGroup.Resources[resource].Variables {
 		exprFields[i] = v.ExpressionField
 	}