#!/usr/bin/env bash
set -euo pipefail

usage() {
    cat <<'EOF'
usage: memgraph PID [LOG_FILE]

Live-graph the resident memory usage of a running process.

Arguments:
  PID       Process id to monitor.
  LOG_FILE  Optional output log file. Defaults to mem-PID.log.

Examples:
  memgraph 817723
  memgraph 817723 ./mem.log

The log format is:
  unix_timestamp rss_mb
EOF
}

missing_dependency() {
    local name="$1"
    local hint="$2"

    printf 'missing dependency: %s\n' "$name" >&2
    printf 'install hint: %s\n' "$hint" >&2
}

require_command() {
    local name="$1"
    local hint="$2"

    if ! command -v "$name" >/dev/null 2>&1; then
        missing_dependency "$name" "$hint"
        return 1
    fi
}

if [[ "${1:-}" == "-h" || "${1:-}" == "--help" ]]; then
    usage
    exit 0
fi

if [[ $# -lt 1 || $# -gt 2 ]]; then
    usage >&2
    exit 2
fi

pid="$1"
log_file="${2:-mem-${pid}.log}"

if [[ ! "$pid" =~ ^[0-9]+$ ]]; then
    printf 'error: PID must be a number, got: %s\n' "$pid" >&2
    exit 2
fi

missing=0
require_command date "install GNU coreutils; on most Linux systems this is already installed" || missing=1
require_command awk "install awk/gawk; for example: sudo apt install gawk" || missing=1
require_command ps "install procps; for example: sudo apt install procps" || missing=1
require_command gnuplot "install gnuplot; for example: sudo apt install gnuplot" || missing=1

if [[ "$missing" -ne 0 ]]; then
    exit 1
fi

if ! ps -p "$pid" >/dev/null 2>&1; then
    printf 'error: no process found with PID %s\n' "$pid" >&2
    exit 1
fi

gnuplot_script="$(mktemp "${TMPDIR:-/tmp}/memgraph.XXXXXX.gnuplot")"
logger_pid=""

cleanup() {
    if [[ -n "$logger_pid" ]] && kill -0 "$logger_pid" >/dev/null 2>&1; then
        kill "$logger_pid" >/dev/null 2>&1 || true
    fi

    rm -f "$gnuplot_script"
}

trap cleanup EXIT INT TERM

cat > "$gnuplot_script" <<EOF
set xdata time
set timefmt "%s"
set format x "%H:%M:%S"
set xlabel "time"
set ylabel "RSS MB"
set title "Process $pid RSS"
set grid

while (1) {
    plot "$log_file" using 1:2 with lines title "RSS MB"
    pause 1
}
EOF

: > "$log_file"

(
    while true; do
        rss_kb="$(ps -o rss= -p "$pid" | awk '{print $1}')"

        if [[ -z "$rss_kb" ]]; then
            printf 'process %s ended; stopped logging\n' "$pid" >&2
            break
        fi

        awk -v t="$(date +%s)" -v r="$rss_kb" 'BEGIN { printf "%s %.1f\n", t, r / 1024 }' >> "$log_file"
        sleep 1
    done
) &
logger_pid="$!"

printf 'logging PID %s RSS to %s\n' "$pid" "$log_file"
printf 'close the gnuplot window or press Ctrl-C here to stop\n'

gnuplot -p "$gnuplot_script"