/*
Copyright 2019 The Kubernetes Authors.

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 discovery

import (
	"crypto/sha256"
	"encoding/base64"
)

// StorageVersionHash calculates the storage version hash for a
// <group/version/kind> tuple.
// WARNING: this function is subject to change. Clients shouldn't depend on
// this function.
func StorageVersionHash(group, version, kind string) string {
	gvk := group + "/" + version + "/" + kind
	if gvk == "" {
		return ""
	}
	bytes := sha256.Sum256([]byte(gvk))
	// Assuming there are N kinds in the cluster, and the hash is X-byte long,
	// the chance of colliding hash P(N,X) approximates to 1-e^(-(N^2)/2^(8X+1)).
	// P(10,000, 8) ~= 2.7*10^(-12), which is low enough.
	// See https://en.wikipedia.org/wiki/Birthday_problem#Approximations.
	return base64.StdEncoding.EncodeToString(
		bytes[:8])
}