added Go template support to annotations

Author: evghen1

README.md

@@ -104,3 +104,26 @@ spec:
     apiVersion: example.crossplane.io/v1
     kind: XR
 ```
+## Templates
+You could use simple Go template in function annotation for enable or disable composition resources conditionally using `.observed` and `.desired`, or even print name of resource:
+```yaml
+apiVersion: example.crossplane.io/v1
+kind: XR
+metadata:
+  name: example-xr
+  annotations:
+    switcher.fn.kndp.io/enabled: 'resourceThree,resourceOne'
+    switcher.fn.kndp.io/disabled: '{{ if ne .observed.composite.resource.status.ready true }}resourceThree{{ end }}'
+spec:
+  resourceOne:
+    field1: "one"
+    field2: "two"
+  resourceTwo:
+    field1: "three"
+    field2: "four"
+  resourceThree:
+    field1: "five"
+    field2: "six"
+status:
+  ready: false
+```

example/composition.yaml

@@ -16,7 +16,7 @@ spec:
       - name: resourceOne
         base:
           apiVersion: example.crossplane.io/v1
-          kind: Resource
+          kind: ResourceOne
           spec:
             field1: ""
             field2: ""
@@ -31,7 +31,7 @@ spec:
       - name: resourceTwo
         base:
           apiVersion: example.crossplane.io/v1
-          kind: Resource
+          kind: ResourceTwo
           spec:
             field1: ""
             field2: ""
@@ -46,7 +46,7 @@ spec:
       - name: resourceThree
         base:
           apiVersion: example.crossplane.io/v1
-          kind: Resource
+          kind: ResourceThree
           spec:
             field1: ""
             field2: ""

example/xr.yaml

@@ -3,7 +3,8 @@ kind: XR
 metadata:
   name: example-xr
   annotations:
-    switcher.fn.kndp.io/disabled: "resourceTwo"
+    switcher.fn.kndp.io/enabled: 'resourceThree,resourceOne'
+    switcher.fn.kndp.io/disabled: '{{ if ne .observed.composite.resource.status.ready true }}resourceThree{{ end }}'
 spec:
   resourceOne:
     field1: "one"
@@ -14,3 +15,5 @@ spec:
   resourceThree:
     field1: "five"
     field2: "six"
+status:
+  ready: false

fn.go

@@ -1,8 +1,10 @@
 package main
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
+	"html/template"
 	"slices"
 	"strings"
 
@@ -12,9 +14,15 @@ import (
 	"github.com/crossplane/function-sdk-go/resource"
 	"github.com/crossplane/function-sdk-go/response"
 	"github.com/pkg/errors"
+	"google.golang.org/protobuf/encoding/protojson"
 	v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 )
 
+const (
+	enableAnnotation = "switcher.fn.kndp.io/enabled"
+	disableAnnotaion = "switcher.fn.kndp.io/disabled"
+)
+
 // Function returns whatever response you ask it to.
 type Function struct {
 	fnv1beta1.UnimplementedFunctionRunnerServiceServer
@@ -34,7 +42,7 @@ func (f *Function) RunFunction(_ context.Context, req *fnv1beta1.RunFunctionRequ
 		return rsp, nil
 	}
 
-	switchOn, switchOff, err := collectSwitches(req, rsp)
+	switchOn, switchOff, err := f.collectSwitches(req, rsp)
 	if err != nil {
 		return rsp, err
 	}
@@ -51,7 +59,8 @@ func (f *Function) RunFunction(_ context.Context, req *fnv1beta1.RunFunctionRequ
 	return rsp, nil
 }
 
-func collectSwitches(req *fnv1beta1.RunFunctionRequest, rsp *fnv1beta1.RunFunctionResponse) ([]string, []string, error) {
+// Collect enabled and disable resources names from annotations
+func (f *Function) collectSwitches(req *fnv1beta1.RunFunctionRequest, rsp *fnv1beta1.RunFunctionResponse) ([]string, []string, error) {
 	oxr, err := request.GetObservedCompositeResource(req)
 	if err != nil {
 		response.Fatal(rsp, errors.Wrapf(err, "cannot get observed composite resource from %T", req))
@@ -67,17 +76,25 @@ func collectSwitches(req *fnv1beta1.RunFunctionRequest, rsp *fnv1beta1.RunFuncti
 	}
 
 	for k, v := range meta.Annotations {
-		if strings.Contains(k, "switcher.fn.kndp.io/enabled") {
+		if strings.Contains(k, enableAnnotation) {
 			if switchOn == nil {
 				switchOn = []string{}
 			}
+			v, err = f.renderTemplate(v, enableAnnotation, req)
+			if err != nil {
+				return []string{}, []string{}, err
+			}
 			switchOn = append(switchOn, strings.Split(v, ",")...)
 		}
 
-		if strings.Contains(k, "switcher.fn.kndp.io/disabled") {
+		if strings.Contains(k, disableAnnotaion) {
 			if switchOff == nil {
 				switchOff = []string{}
 			}
+			v, err = f.renderTemplate(v, disableAnnotaion, req)
+			if err != nil {
+				return []string{}, []string{}, err
+			}
 			switchOff = append(switchOff, strings.Split(v, ",")...)
 		}
 	}
@@ -113,3 +130,41 @@ func toMeta(m interface{}) (v1.ObjectMeta, error) {
 
 	return meta, nil
 }
+
+// Render Go template against request data
+func (f *Function) renderTemplate(tplString string, tplName string, req *fnv1beta1.RunFunctionRequest) (string, error) {
+	reqMap, err := convertToMap(req)
+	if err != nil {
+		return tplString, err
+	}
+
+	tmpl, err := template.New(tplName).Parse(tplString)
+	if err != nil {
+		return tplString, err
+	}
+	f.log.Debug("constructed request map", "request", reqMap)
+
+	buf := &bytes.Buffer{}
+
+	if err := tmpl.Execute(buf, reqMap); err != nil {
+		return tplString, err
+	}
+
+	f.log.Debug("rendered manifests", "manifests", buf.String())
+	return buf.String(), nil
+}
+
+// Convert function request to map
+func convertToMap(req *fnv1beta1.RunFunctionRequest) (map[string]any, error) {
+	jReq, err := protojson.Marshal(req)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot marshal request from proto to json")
+	}
+
+	var mReq map[string]any
+	if err := json.Unmarshal(jReq, &mReq); err != nil {
+		return nil, errors.Wrap(err, "cannot unmarshal json to map[string]any")
+	}
+
+	return mReq, nil
+}