package seeds

import (
	"crypto/sha256"
	"crypto/subtle"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"io"
)

// ClosedGate is the import gate a rollback installs (spec §5.6 step 1): a
// value no token's hash can equal, so the edge refuses even verify requests.
const ClosedGate = "closed"

// NewVerifyToken mints an import's verify token (spec §5.1): 32 random
// bytes, base64url without padding. The record and the box keep only hash.
func NewVerifyToken() (token, hash string, err error) {
	var b [32]byte
	if _, err := io.ReadFull(randReader, b[:]); err != nil {
		return "", "", fmt.Errorf("seeds: mint a verify token: %w", err)
	}
	token = base64.RawURLEncoding.EncodeToString(b[:])
	return token, HashToken(token), nil
}

// HashToken is the hex sha256 the record's verify_hash and the row's
// import_gate hold.
func HashToken(token string) string {
	sum := sha256.Sum256([]byte(token))
	return hex.EncodeToString(sum[:])
}

// TokenMatches reports whether token's hash is hash, in constant time. An
// empty token, an empty hash and ClosedGate match nothing.
func TokenMatches(hash, token string) bool {
	if token == "" || len(hash) != sha256.Size*2 {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(HashToken(token)), []byte(hash)) == 1
}