package generate

import (
	"crypto/rand"
	"fmt"
)

// GetRandomString 取得隨機字串
func GetRandomString(n int) (string, error) {
	const alphaNum = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
	return getRandomFromCharset(n, alphaNum)
}

// GetRandomKey 取得隨機金鑰
func GetRandomKey(n int) (string, error) {
	const alphaNum = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz~!@#$%^&*()-_=+"
	return getRandomFromCharset(n, alphaNum)
}

// getRandomFromCharset 通用隨機字串生成器
func getRandomFromCharset(n int, charset string) (string, error) {
	// 預先計算字符集的長度
	charsLen := len(charset)
	buffer := make([]byte, n)

	// 使用 crypto/rand 生成隨機數據
	_, err := rand.Read(buffer)
	if err != nil {
		return "", fmt.Errorf("failed to generate random data: %w", err)
	}

	// 從字元集選擇字符
	for i := 0; i < n; i++ {
		buffer[i] = charset[int(buffer[i])%charsLen]
	}

	return string(buffer), nil
}