#! /bin/bash

set -e
#set -u  # Error on unset var
set -o pipefail

# commands:
# - log (to stdout or file):
#       run arp-scan and convert output to our log format
#       - options
#           - interval
#           - file
# - status (from stdin or file):
#       read log and report
#           - seen devices, sorted by last-seen
#           - ip changes?
#       - options
#           - file
#
# TODO
# - [ ] Gather more info on each device. How? nmap?
# ...
#

_debug=''

_log() {
    local -r level="$1"; shift
    local -r fmt="$1\n"; shift
    local -r args="$*"

    printf '%s [%s] ' "$(date '+%Y-%m-%d %H:%M:%S')" "$level" >&2
    printf "$fmt" $args >&2
}

error() {
    _log 'error' "$@"
}

debug() {
    if [[ -n "$_debug" ]]; then
        _log 'debug' "$@"
    fi
}

log() {
    local -r interval_init="$1"
    local -r log_file="$2"
    local    interval_curr="$interval_init"

    while :; do
        debug '(>) scan'
        if sudo arp-scan --localnet; then
            debug '(.) scan ok'
            interval_curr="$interval_init"
        else
            error '(.) scan failure'
            interval_curr=$(( interval_curr * 2 ))
        fi
        debug '(>) sleep for %d seconds' "$interval_curr"
        sleep "$interval_curr";
        debug '(.) sleep'
    done \
    | stdbuf -o L awk '
        /^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+/ {
            ip = $1
            mac = $2
            print mac, ip
        }' \
    | ts '%.s' \
    >> "$log_file"
}

status() {
    local -r log_file="$1"

    (
        echo 'mac ip staleness_cur staleness_avg age freq dist'
        echo '--- -- ------------- ------------- --- ---- ----'
        sort -n -k 1 "$log_file" \
        | awk -v now="$(date '+%s')" \
            '
                {
                    ts = $1
                    mac = $2
                    ip = $3

                    interval[mac, ip, intervals[mac, ip]++] = ts - seen_last[mac, ip]
                    freq[mac, ip]++
                    if (!seen_last[mac, ip]  || ts > seen_last[mac, ip] ) seen_last[mac, ip]  = ts
                    if (!seen_first[mac, ip] || ts < seen_first[mac, ip]) seen_first[mac, ip] = ts
                }

                END {
                    for (key in freq) {
                        split(key, macip, SUBSEP)
                        mac = macip[1]
                        ip  = macip[2]
                        staleness_cur = now - seen_last[mac, ip]
                        age = now - seen_first[mac, ip]
                        dist = 100 * (freq[mac, ip] / NR)
                        intervals_sum = 0
                        for (i=1; i<=intervals[mac, ip]; i++)
                            intervals_sum += interval[mac, ip, i]
                        staleness_avg = intervals_sum / intervals[mac, ip]
                        print \
                            mac, \
                            ip, \
                            sprintf("%d", staleness_cur), \
                            sprintf("%d", staleness_avg), \
                            sprintf("%d", age), \
                            freq[mac, ip], \
                            sprintf("%d", dist)
                    }
                }
            ' \
        | sort -n -k 3 \
    ) \
    | column -t
}

main() {
    local cmd
    local interval
    local log_file

    case "$1" in
        '-d')
            _debug='yes'
            shift
            ;;
    esac
    cmd="$1"
    case "$cmd" in
        'log')
            interval=60
            log_file='/dev/stdout'

            if [[ -n "$2" ]]; then
                interval="$2"
                if [[ -n "$3" ]]; then
                    log_file="$3"
                fi
            fi
            debug '(>) log | interval:"%s" log_file:"%s"' "$interval" "$log_file"
            log "$interval" "$log_file"
            debug '(.) log | interval:"%s" log_file:"%s"' "$interval" "$log_file"
            ;;
        'status')
            log_file='/dev/stdin'
            if [[ -n "$2" ]]; then
                log_file="$2"
            fi
            debug '(>) status | log_file:"%s"' "$log_file"
            status "$log_file"
            debug '(.) status | log_file:"%s"' "$log_file"
            ;;
        *)
            error 'Unknown command: "%s"' "$cmd"
            exit 1
            ;;
    esac
}

main "$@"