hugo/resources/internal/key.go

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// 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 (
"strconv"
"github.com/mitchellh/hashstructure"
)
// 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 + "_" + HashString(k.elements...)
}
// HashString returns a hash from the given elements.
// It will panic if the hash cannot be calculated.
func HashString(elements ...interface{}) string {
var o interface{}
if len(elements) == 1 {
o = elements[0]
} else {
o = elements
}
hash, err := hashstructure.Hash(o, nil)
if err != nil {
panic(err)
}
return strconv.FormatUint(hash, 10)
}