namer.go

package namer

import (
	"fmt"
	"hash/fnv"

	kvalidation "k8s.io/apimachinery/pkg/util/validation"
)

// GetName returns a name given a base ("deployment-5") and a suffix ("deploy")
// It will first attempt to join them with a dash. If the resulting name is longer
// than maxLength: if the suffix is too long, it will truncate the base name and add
// an 8-character hash of the [base]-[suffix] string.  If the suffix is not too long,
// it will truncate the base, add the hash of the base and return [base]-[hash]-[suffix]
func GetName(base, suffix string, maxLength int) string {
	if maxLength <= 0 {
		return ""
	}
	name := fmt.Sprintf("%s-%s", base, suffix)
	if len(name) <= maxLength {
		return name
	}

	baseLength := maxLength - 10 /*length of -hash-*/ - len(suffix)

	// if the suffix is too long, ignore it
	if baseLength < 0 {
		prefix := base[0:min(len(base), max(0, maxLength-9))]
		// Calculate hash on initial base-suffix string
		shortName := fmt.Sprintf("%s-%s", prefix, hash(name))
		return shortName[:min(maxLength, len(shortName))]
	}

	prefix := base[0:baseLength]
	// Calculate hash on initial base-suffix string
	return fmt.Sprintf("%s-%s-%s", prefix, hash(base), suffix)
}

// GetPodName calls GetName with the length restriction for pods
func GetPodName(base, suffix string) string {
	return GetName(base, suffix, kvalidation.DNS1123SubdomainMaxLength)
}

// max returns the greater of its 2 inputs
func max(a, b int) int {
	if b > a {
		return b
	}
	return a
}

// min returns the lesser of its 2 inputs
func min(a, b int) int {
	if b < a {
		return b
	}
	return a
}

// hash calculates the hexadecimal representation (8-chars)
// of the hash of the passed in string using the FNV-a algorithm
func hash(s string) string {
	hash := fnv.New32a()
	hash.Write([]byte(s))
	intHash := hash.Sum32()
	result := fmt.Sprintf("%08x", intHash)
	return result
}