package auth

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

	"golang.org/x/crypto/bcrypt"
)

// saltedInput mixes the login into the password material before bcrypt hashing, using
// the login as a per-user salt: a leaked hash can't be replayed against a different
// login, and pre-hashing keeps the input short regardless of login/password length
// (bcrypt only considers the first 72 bytes of its input).
func saltedInput(login, password string) []byte {
	sum := sha256.Sum256([]byte(login + "\x00" + password))
	return []byte(base64.StdEncoding.EncodeToString(sum[:]))
}

// dummyHash is compared against on unknown logins so that a failed lookup takes
// roughly the same time as a real password comparison, avoiding user enumeration.
var dummyHash, _ = bcrypt.GenerateFromPassword(saltedInput("dummy-login", "dummy-password"), bcrypt.DefaultCost)

func Hash(login, password string) (string, error) {
	hash, err := bcrypt.GenerateFromPassword(saltedInput(login, password), bcrypt.DefaultCost)
	if err != nil {
		return "", err
	}
	return string(hash), nil
}

func Compare(login, hash, password string) bool {
	return bcrypt.CompareHashAndPassword([]byte(hash), saltedInput(login, password)) == nil
}

func CompareDummy() {
	_ = bcrypt.CompareHashAndPassword(dummyHash, saltedInput("dummy-login", "dummy-password"))
}