// Copyright 2014 beego Author. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package rand

import (
	"crypto/rand"
	r "math/rand"
	"time"
)

var alphaNum = []byte(`0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz`)

// RandomCreateBytes generate random []byte by specify chars.
func RandomCreateBytes(n int, alphabets ...byte) []byte {
	if len(alphabets) == 0 {
		alphabets = alphaNum
	}
	var bytes = make([]byte, n)
	var randBy bool
	if num, err := rand.Read(bytes); num != n || err != nil {
		r.Seed(time.Now().UnixNano())
		randBy = true
	}
	for i, b := range bytes {
		if randBy {
			bytes[i] = alphabets[r.Intn(len(alphabets))]
		} else {
			bytes[i] = alphabets[b%byte(len(alphabets))]
		}
	}
	return bytes
}
