#!/bin/sh

set -ue

LC_ALL=C
DEFAULT_PASSWORD_LENGTH=20

simple() {
    PASSWORD_LENGTH="${1:-$DEFAULT_PASSWORD_LENGTH}"
    tr -dc 'A-Za-z0-9@#%^&*()_+=-{}[]:;<>,.?/' < /dev/urandom | head -c "${PASSWORD_LENGTH}" | xargs echo
}

_shuf_line() {
    fold -w1 | shuf | tr -d '\n'
}

_gen_random_by_charset() {
    length="${1}"
    charset="${2}"

    tr -dc "${charset}" < /dev/random | head -c "${length}"
}

_gen_random_lower() {
    length="${1}"
    _gen_random_by_charset "${length}" '[:lower:]'
}

_gen_random_upper() {
    length="${1}"
    _gen_random_by_charset "${length}" '[:upper:]'
}

_gen_random_digits() {
    length="${1}"
    _gen_random_by_charset "${length}" '[:digit:]'
}

_gen_random_special() {
    length="${1}"
    _gen_random_by_charset "${length}" '!"#$%&()*+,-./:;<=>?@[\\]^_`{|}~'\'''
}

protected() {
    readonly symbols_count_of_each_type=5

    password=""

    password="${password}$(_gen_random_lower "${symbols_count_of_each_type}")"
    password="${password}$(_gen_random_upper "${symbols_count_of_each_type}")"
    password="${password}$(_gen_random_digits "${symbols_count_of_each_type}")"
    password="${password}$(_gen_random_special "${symbols_count_of_each_type}")"

    echo "${password}" | _shuf_line
}

if [ -z "${1+x}" ]; then
    simple "${DEFAULT_PASSWORD_LENGTH}"
    exit 0
fi

main() {
    if [ "${1}" = "-p" ]; then
        protected
        exit 0
    fi

    simple "${1}"
    exit 0
}

main "${@}"