package assetcache

import (
	"crypto/sha256"
	"encoding/binary"
	"encoding/hex"
)

// Key identifies one cached response: which app generation served it, on
// which host, for which path and query.
type Key struct {
	Account, App, Gen, Host, Path, RawQuery string
}

// ID is the hex sha256 over the six fields. Each field is written with its
// length first, so no two distinct keys hash the same input.
func (k Key) ID() string {
	h := sha256.New()
	var n [8]byte
	for _, f := range [...]string{k.Account, k.App, k.Gen, k.Host, k.Path, k.RawQuery} {
		binary.BigEndian.PutUint64(n[:], uint64(len(f)))
		h.Write(n[:])
		h.Write([]byte(f))
	}
	return hex.EncodeToString(h.Sum(nil))
}

// AppScope names the app this key belongs to, for per-app accounting.
func (k Key) AppScope() string {
	return k.Account + "/" + k.App
}