#!/usr/bin/env bash

set -euo pipefail

R='\033[0m' B='\033[1m' D='\033[2m' RED='\033[31m' BLU='\033[38;5;33m' YLW='\033[38;5;179m'

die() { printf "${RED}${B}error:${R} %s\n" "$1" >&2; exit 1; }

usage() { die "usage: $0 [-w] [-i interval] <PID>"; }

WATCH=0 INTERVAL=1

while getopts "wi:" opt; do
    case "$opt" in
        w) WATCH=1 ;; i) INTERVAL="$OPTARG" ;; *) usage ;;
    esac
done
shift $((OPTIND - 1))

PID="${1:-}"

if [ -z "$PID" ]; then
    command -v fzf >/dev/null 2>&1 || usage
    PID=$(ps -eo pid,user,%mem,comm --sort=-%mem | fzf --header-lines=1 | awk '{print $1}')
    [ -z "$PID" ] && exit 0
fi

ps -p "$PID" >/dev/null 2>&1 || die "process $PID does not exist"

COMM=$(cat /proc/"$PID"/comm 2>/dev/null || echo "?")

print_rss() {
    read -r rss peak size swap < <(awk '
        /^VmRSS:/  { rss=$2 }
        /^VmPeak:/ { peak=$2 }
        /^VmSize:/ { size=$2 }
        /^VmSwap:/ { swap=$2 }
        END { print rss, peak, size, swap }
    ' /proc/"$PID"/status 2>/dev/null) || die "could not read memory for PID $PID"

    fmt() { awk -v kb="$1" 'BEGIN { printf "%.1f MB", kb/1024 }'; }

    printf "${B}%s${R} ${D}(PID %s)${R}\n" "$COMM" "$PID"
    printf "  ${YLW}${B}RSS:${R}  ${BLU}%s${R}  ${D}Peak:${R} %s  ${D}Size:${R} %s  ${D}Swap:${R} %s\n" \
        "$(fmt "$rss")" "$(fmt "$peak")" "$(fmt "$size")" "$(fmt "$swap")"
}

if [ "$WATCH" -eq 1 ]; then
    printf '\033[?25l'
    trap 'printf "\033[?25h"; exit' INT TERM
    first=1
    while ps -p "$PID" >/dev/null 2>&1; do
        [ "$first" -eq 0 ] && printf '\033[2A'
        first=0
        print_rss
        sleep "$INTERVAL"
    done
    printf '\033[?25h'
    die "process $PID exited"
else
    print_rss
fi