package aprs

import (
	"fmt"
	"strings"
)

func base91Decode(s string) (n int, err error) {
	for i, l := 0, len(s); i < l; i++ {
		c := s[i]
		if c < 33 || c > 122 {
			return 0, fmt.Errorf("aprs: invalid base-91 encoding char %q (%d)", c, c)
		}

		n *= 91
		n += int(c) - 33
	}
	return
}

func base91Encode(n int) string {
	var s []string
	for n > 0 {
		c := n % 91
		n /= 91
		s = append([]string{string(byte(c) + 33)}, s...)
	}
	return strings.Join(s, "")
}