package mysqlserver

import (
	"crypto/sha1"
	"crypto/subtle"
)

func nativePasswordToken(password string, scramble []byte) []byte {
	if password == "" {
		return []byte{}
	}
	if len(scramble) > 20 {
		scramble = scramble[:20]
	}
	hash1 := sha1.Sum([]byte(password))
	hash2 := sha1.Sum(hash1[:])
	h := sha1.New()
	h.Write(scramble)
	h.Write(hash2[:])
	hash3 := h.Sum(nil)
	out := make([]byte, 20)
	for i := 0; i < 20; i++ {
		out[i] = hash1[i] ^ hash3[i]
	}
	return out
}

func verifyNativePassword(password string, scramble, auth []byte) bool {
	if password == "" {
		return len(auth) == 0
	}
	want := nativePasswordToken(password, scramble)
	if len(auth) != len(want) {
		return false
	}
	return subtle.ConstantTimeCompare(auth, want) == 1
}

func usernamesEqual(a, b string) bool {
	if len(a) != len(b) {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(a), []byte(b)) == 1
}