1 files changed, 43 insertions, 0 deletions
diff --git a/resources/internal/key.go b/resources/internal/key.go
new file mode 100644
index 000000000..d67d4a7e1
--- /dev/null
+++ b/resources/internal/key.go
@@ -0,0 +1,43 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import "github.com/gohugoio/hugo/helpers"
+
+// ResourceTransformationKey are provided by the different transformation implementations.
+// It identifies the transformation (name) and its configuration (elements).
+// We combine this in a chain with the rest of the transformations
+// with the target filename and a content hash of the origin to use as cache key.
+type ResourceTransformationKey struct {
+	Name     string
+	elements []interface{}
+}
+
+// NewResourceTransformationKey creates a new ResourceTransformationKey from the transformation
+// name and elements. We will create a 64 bit FNV hash from the elements, which when combined
+// with the other key elements should be unique for all practical applications.
+func NewResourceTransformationKey(name string, elements ...interface{}) ResourceTransformationKey {
+	return ResourceTransformationKey{Name: name, elements: elements}
+}
+
+// Value returns the Key as a string.
+// Do not change this without good reasons.
+func (k ResourceTransformationKey) Value() string {
+	if len(k.elements) == 0 {
+		return k.Name
+	}
+
+	return k.Name + "_" + helpers.HashString(k.elements...)
+
+}