package pwhash

import (
	"crypto/hkdf"
	"crypto/pbkdf2"
	"crypto/sha256"
	"crypto/sha512"
	"fmt"
)

const SaltLen = sha256.Size + sha512.Size

const defaultIterations = 3670016 // from cmd/finditers

func HashIter(password string, salt []byte, iter int) ([]byte, error) {
	return pbkdf2.Key(sha256.New, password, salt, iter, sha256.Size)
}

func Hash(password string, salt []byte) (key, pwHash []byte, err error) {
	if len(salt) != SaltLen {
		return nil, nil, fmt.Errorf("bad salt size")
	}
	hashedPassword, err := HashIter(password, salt[:sha256.Size], defaultIterations)
	if err != nil {
		return nil, nil, err
	}
	key, err = hkdf.Extract(sha512.New, hashedPassword, salt[sha256.Size:])
	if err != nil {
		return nil, nil, err
	}
	pwHash, err = hkdf.Expand(sha512.New, key, "auth", sha512.Size)
	if err != nil {
		return nil, nil, err
	}
	return key, pwHash, nil
}