package provider

import (
	"crypto/sha256"
	"encoding/base32"
	"strings"

	"k8s.io/apimachinery/pkg/types"
)

const namePrefix = "proxy-"

// NameFromUID derives a deterministic instance name from a Proxy CR's UID.
// Provider.Create implementations key idempotency on this name: a repeat
// call after a crash must find the existing instance by this name rather
// than create a duplicate, and the reconciler relies on that to recover
// providerID after a crash even if status was wiped.
//
// SHA-256 of the UID, truncated to the first 10 bytes, RFC 4648 base32
// (no padding), lowercased: exactly 16 characters, for 22 total with the
// "proxy-" prefix. That gives 80 bits of collision resistance — a birthday
// collision only becomes likely around 2^40 objects, against a fleet of
// tens — while satisfying GCP's instance name rules
// (^[a-z]([-a-z0-9]{0,61}[a-z0-9])?$, <=63 chars) with headroom, since GCP
// auto-names some resources (e.g. the boot disk) after the instance name.
// base32's alphabet (A-Z2-7) is entirely legal once lowercased; base64 is
// not (has '+', '/', and uppercase), and hex would need 20 characters for
// the same 80 bits.
func NameFromUID(uid types.UID) string {
	sum := sha256.Sum256([]byte(uid))
	enc := base32.StdEncoding.WithPadding(base32.NoPadding)
	return namePrefix + strings.ToLower(enc.EncodeToString(sum[:10]))
}