// Package crypto 提供口令哈希原语（argon2id，与 opsx-loki 同参数）。
package crypto

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/base64"
	"math/big"

	"golang.org/x/crypto/argon2"
)

// HashPassword 生成 argon2id 口令哈希（salt+hash base64 编码）
func HashPassword(password string) (string, error) {
	salt := make([]byte, 16)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}
	hash := argon2.IDKey([]byte(password), salt, 3, 64*1024, 4, 32)
	combined := append(salt, hash...)
	return base64.StdEncoding.EncodeToString(combined), nil
}

// VerifyPassword 常数时间比对口令哈希
func VerifyPassword(password, hashStr string) bool {
	combined, err := base64.StdEncoding.DecodeString(hashStr)
	if err != nil || len(combined) < 16 {
		return false
	}
	salt := combined[:16]
	hash := combined[16:]
	newHash := argon2.IDKey([]byte(password), salt, 3, 64*1024, 4, 32)
	return subtle.ConstantTimeCompare(hash, newHash) == 1
}

// passwordAlphabet 去掉易混淆字符（0O1lI）的密码字母表
const passwordAlphabet = "23456789abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ"

// RandomPassword 生成 n 位随机密码（crypto/rand，无易混淆字符）
func RandomPassword(n int) (string, error) {
	max := big.NewInt(int64(len(passwordAlphabet)))
	buf := make([]byte, n)
	for i := range buf {
		idx, err := rand.Int(rand.Reader, max)
		if err != nil {
			return "", err
		}
		buf[i] = passwordAlphabet[idx.Int64()]
	}
	return string(buf), nil
}