// Copyright © 2016 Abcum Ltd
//
// 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"
)

var chars = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")

// New produces a random string of length n
func New(l int) []byte {

	if l == 0 {
		return nil
	}

	i := 0
	t := len(chars)
	m := 255 - (256 % t)
	b := make([]byte, l)
	r := make([]byte, l+(l/4))

	for {

		rand.Read(r)

		for _, rb := range r {
			c := int(rb)
			if c > m {
				continue
			}
			b[i] = chars[c%t]
			i++
			if i == l {
				return b
			}
		}

	}

}