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package common

import (
	"bytes"
	"crypto/rand"
	"fmt"
)

func RandomIdent(entropy int) (string, error) {
	randID := make([]byte, entropy)
	n, err := rand.Read(randID)
	if n != entropy || err != nil {
		return "", fmt.Errorf("couldn't generate randomness. something went very wrong")
	}
	return Encode(randID[:]), nil
}

var (
	alphabet = []byte{'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'}
	base     int
)

func init() {
	base = len(alphabet)
}

func Encode(source []byte) string {
	if len(source) == 0 {
		return ""
	}

	digits := []int{0}

	for i := 0; i < len(source); i++ {
		carry := int(source[i])

		for j := 0; j < len(digits); j++ {
			carry += digits[j] << 8
			digits[j] = carry % base
			carry = carry / base
		}

		for carry > 0 {
			digits = append(digits, carry%base)
			carry = carry / base
		}
	}

	var res bytes.Buffer

	for k := 0; source[k] == 0 && k < len(source)-1; k++ {
		res.WriteByte(alphabet[0])
	}

	for q := len(digits) - 1; q >= 0; q-- {
		res.WriteByte(alphabet[digits[q]])
	}

	return res.String()
}