Crawler performance improvements, better structure

Refactored the crawler implementation to make the whole thing more
testable. Added a document interface to make the crawler generic.
This will be useful for collecting plugins, and other documents.

internal/tools/doc/kustomize_util.go

@@ -0,0 +1,51 @@
+package doc
+
+import (
+	"fmt"
+	"regexp"
+
+	"sigs.k8s.io/yaml"
+)
+
+func FixKustomizationPreUnmarshallingNonFatal(data []byte) ([]byte, error) {
+	deprecateFieldsMap := map[string]string{
+		"imageTags:": "images:",
+	}
+	for oldname, newname := range deprecateFieldsMap {
+		pattern := regexp.MustCompile(oldname)
+		data = pattern.ReplaceAll(data, []byte(newname))
+	}
+
+	found, err := useLegacyPatch(data)
+	if err == nil && found {
+		pattern := regexp.MustCompile("patches:")
+		data = pattern.ReplaceAll(data, []byte("patchesStrategicMerge:"))
+	}
+
+	return data, err
+}
+
+func useLegacyPatch(data []byte) (bool, error) {
+	found := false
+
+	var object map[string]interface{}
+	err := yaml.Unmarshal(data, &object)
+	if err != nil {
+		return false, fmt.Errorf("invalid content from %s",
+			string(data))
+	}
+	if rawPatches, ok := object["patches"]; ok {
+		patches, ok := rawPatches.([]interface{})
+		if !ok {
+			return false, fmt.Errorf("invalid patches from %v",
+				rawPatches)
+		}
+		for _, p := range patches {
+			_, ok := p.(string)
+			if ok {
+				found = true
+			}
+		}
+	}
+	return found, nil
+}