#!/usr/bin/env bash
# ------------------------------------------------------------------------------
# Copyright (c) 2013-2026 Geoffray Levasseur <fatalerrors@geoffray-levasseur.org>
# Protected by the BSD3 license. Please read bellow for details.
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# ------------------------------------------------------------------------------

# Private helpers of profile.d/pwd.sh, loaded by the module itself.

# Pool of random words read from /dev/urandom, refilled by _pwd_rand.
_PWD_POOL=()

# Internal helper: put in _PWD_RAND an integer uniformly distributed in
# [0, $1), for 1 <= $1 <= 2^32. $RANDOM is NOT usable for passwords: it only
# has 15 bits, a state seeded from the time and the PID, and is predictable.
# The source is $SRANDOM (bash >= 5.1, from the kernel's random generator), or
# else /dev/urandom read through od, 256 words at a time to limit the number
# of processes. Values above the largest multiple of $1 are rejected, so that
# "% $1" introduces no bias.
# Usage: _pwd_rand <max>
_pwd_rand()
{
    local max="$1" limit r
    limit=$(( 4294967296 - 4294967296 % max ))
    while :; do
        if [[ -n "${SRANDOM+x}" ]]; then
            r="$SRANDOM"
        else
            if (( ${#_PWD_POOL[@]} == 0 )); then
                # shellcheck disable=SC2207 # whitespace-separated numbers
                _PWD_POOL=( $(od -An -v -N1024 -tu4 /dev/urandom 2>/dev/null) )
                if (( ${#_PWD_POOL[@]} == 0 )); then
                    disp E "No source of random numbers available (/dev/urandom)."
                    return 1
                fi
            fi
            r="${_PWD_POOL[-1]}"
            unset '_PWD_POOL[-1]'
        fi
        if (( r < limit )); then
            _PWD_RAND=$(( r % max ))
            return 0
        fi
    done
}