From e4dba3163dad08b30b4e933ed8164dffeb41ab0e Mon Sep 17 00:00:00 2001
From: Jeremy Gustie <jeremy@stormforge.io>
Date: Fri, 9 Feb 2024 12:17:54 -0500
Subject: [PATCH] Add a patch filter for applying patches

---
 go.mod               |  3 +-
 go.sum               |  2 +
 pkg/filters/patch.go | 89 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 93 insertions(+), 1 deletion(-)
 create mode 100644 pkg/filters/patch.go

diff --git a/go.mod b/go.mod
index 5ba58f2..8122512 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,7 @@ module github.com/thestormforge/konjure
 go 1.21
 
 require (
+	github.com/evanphx/json-patch/v5 v5.8.1
 	github.com/fatih/color v1.16.0
 	github.com/google/go-jsonnet v0.20.0
 	github.com/google/uuid v1.6.0
@@ -16,6 +17,7 @@ require (
 	golang.org/x/sync v0.6.0
 	k8s.io/kube-openapi v0.0.0-20230601164746-7562a1006961
 	sigs.k8s.io/kustomize/kyaml v0.16.0
+	sigs.k8s.io/yaml v1.4.0
 )
 
 require (
@@ -40,5 +42,4 @@ require (
 	golang.org/x/sys v0.16.0 // indirect
 	google.golang.org/protobuf v1.30.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
-	sigs.k8s.io/yaml v1.4.0 // indirect
 )
diff --git a/go.sum b/go.sum
index b040271..705c841 100644
--- a/go.sum
+++ b/go.sum
@@ -7,6 +7,8 @@ github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ3
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/evanphx/json-patch/v5 v5.8.1 h1:iPEdwg0XayoS+E7Mth9JxwUtOgyVxnDTXHtKhZPlZxA=
+github.com/evanphx/json-patch/v5 v5.8.1/go.mod h1:VNkHZ/282BpEyt/tObQO8s5CMPmYYq14uClGH4abBuQ=
 github.com/fatih/color v1.13.0/go.mod h1:kLAiJbzzSOZDVNGyDpeOxJ47H46qBXwg5ILebYFFOfk=
 github.com/fatih/color v1.16.0 h1:zmkK9Ngbjj+K0yRhTVONQh1p/HknKYSlNT+vZCzyokM=
 github.com/fatih/color v1.16.0/go.mod h1:fL2Sau1YI5c0pdGEVCbKQbLXB6edEj1ZgiY4NijnWvE=
diff --git a/pkg/filters/patch.go b/pkg/filters/patch.go
new file mode 100644
index 0000000..b0d6fa7
--- /dev/null
+++ b/pkg/filters/patch.go
@@ -0,0 +1,89 @@
+package filters
+
+import (
+	"bytes"
+	"fmt"
+
+	jsonpatch "github.com/evanphx/json-patch/v5"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+	"sigs.k8s.io/kustomize/kyaml/yaml/merge2"
+	yaml2 "sigs.k8s.io/yaml"
+)
+
+// UnsupportedPatchError is raised when a patch format is not recognized.
+type UnsupportedPatchError struct {
+	PatchType string
+}
+
+func (e *UnsupportedPatchError) Error() string {
+	return fmt.Sprintf("unsupported patch type: %q", e.PatchType)
+}
+
+// PatchFilter is used to apply an arbitrary patch.
+type PatchFilter struct {
+	// The media type of the patch being applied.
+	PatchType string
+	// The actual raw patch.
+	PatchData []byte
+}
+
+// Filter applies the configured patch.
+func (f *PatchFilter) Filter(node *yaml.RNode) (*yaml.RNode, error) {
+	switch f.PatchType {
+	case "application/strategic-merge-patch+json", "strategic", "application/merge-patch+json", "merge", "":
+		// The patch is likely JSON, parse it as YAML and just clear the style
+		patchNode := yaml.NewRNode(&yaml.Node{})
+		if err := yaml.NewDecoder(bytes.NewReader(f.PatchData)).Decode(patchNode.YNode()); err != nil {
+			return nil, err
+		}
+		f.resetNodeStyle(patchNode.YNode())
+
+		// Strategic Merge/Merge Patch is just the merge2 logic
+		opts := yaml.MergeOptions{
+			ListIncreaseDirection: yaml.MergeOptionsListPrepend,
+		}
+		return merge2.Merge(patchNode, node, opts)
+
+	case "application/json-patch+json", "json":
+		// The patch is likely JSON, but might be YAML that needs to be converted to JSON
+		patchData := f.PatchData
+		if !bytes.HasPrefix(patchData, []byte("[")) {
+			jsonData, err := yaml2.YAMLToJSON(patchData)
+			if err != nil {
+				return nil, err
+			}
+			patchData = jsonData
+		}
+		jsonPatch, err := jsonpatch.DecodePatch(patchData)
+		if err != nil {
+			return nil, err
+		}
+
+		// This is going to butcher the YAML ordering/comments/etc.
+		jsonData, err := node.MarshalJSON()
+		if err != nil {
+			return nil, err
+		}
+		jsonData, err = jsonPatch.Apply(jsonData)
+		if err != nil {
+			return nil, err
+		}
+		err = node.UnmarshalJSON(jsonData)
+		if err != nil {
+			return nil, err
+		}
+		return node, nil
+
+	default:
+		// This patch type is not supported
+		return nil, &UnsupportedPatchError{PatchType: f.PatchType}
+	}
+}
+
+// resetNodeStyle clears out the node style, this is useful to discard JSON formatting.
+func (f *PatchFilter) resetNodeStyle(node *yaml.Node) {
+	node.Style = 0
+	for _, node := range node.Content {
+		f.resetNodeStyle(node)
+	}
+}