#!/usr/bin/env bash
# Print one frame of the top CPU-consuming processes, then exit.
#
# Single-shot by design: SysStats re-runs it every procInterval while the CPU
# drawer is open (Process.running re-armed by a Timer, like dfProc). Exiting
# per frame guarantees stdout is flushed — a long-running loop kept its frame
# delimiter stuck in bash's block buffer and the QML side never saw a full
# frame. discover.sh is the reference for the bash-script + parse pattern.
#
# IMPORTANT: the flake wrapper only puts bash + coreutils on PATH, so this uses
# ONLY bash builtins and coreutils (nproc, sort, head, sleep, cat) — no awk, no
# getconf. Keep it that way or add the tool to runtimeInputs in flake.nix.
#
# Output: one "P <cpu%> <mem%> <name>" line per process, highest CPU first.
# cpu% is top-style: 100 == one fully-used core.

intv="${1:-2}"
n="${2:-6}"
ncpu="$(nproc 2>/dev/null || echo 1)"
pg_kb=4         # page size is 4096B on all targeted arches (x86_64/aarch64)

# MemTotal in kB, read without awk.
memkb=0
while read -r key val _; do
    if [ "$key" = "MemTotal:" ]; then memkb="$val"; break; fi
done < /proc/meminfo

# Aggregate CPU jiffies: sum of the fields on the leading "cpu" line.
cpu_total() {
    local line f s=0
    read -r line < /proc/stat
    # shellcheck disable=SC2086
    set -- $line            # collapses the double space; $1 == "cpu"
    shift
    for f in "$@"; do s=$(( s + f )); done
    echo "$s"
}

# Read pid -> (utime+stime) jiffies and rss pages into the given assoc arrays.
# /proc/<pid>/stat is "PID (comm) STATE ...": strip through ") " so comm spaces
# and parens can't shift field positions, then utime=14, stime=15, rss=24.
snapshot() {
    local -n _jif="$1" _rss="$2"
    local f l pid rest
    for f in /proc/[0-9]*/stat; do
        # 2>/dev/null first so a process vanishing mid-scan is silent.
        IFS= read -r l 2>/dev/null < "$f" || continue
        pid="${l%% *}"
        rest="${l#*) }"
        # shellcheck disable=SC2086
        set -- $rest
        _jif["$pid"]=$(( ${12:-0} + ${13:-0} ))
        _rss["$pid"]="${22:-0}"
    done
}

declare -A j1 j2 rss
t1="$(cpu_total)"
snapshot j1 rss
sleep "$intv"
t2="$(cpu_total)"
snapshot j2 rss
dt=$(( t2 - t1 ))
[ "$dt" -gt 0 ] || exit 0

# Emit "<cpu> <pid> <rss>" for each process seen in both snapshots, sort by cpu
# desc, take the top n, then resolve name + mem% for just those.
for pid in "${!j2[@]}"; do
    [ -n "${j1[$pid]:-}" ] || continue
    d=$(( ${j2[$pid]} - ${j1[$pid]} ))
    cpu=$(( 100 * ncpu * d / dt ))
    printf '%d %s %s\n' "$cpu" "$pid" "${rss[$pid]:-0}"
done | sort -rn | head -n "$n" | while read -r cpu pid r; do
    name="$(cat "/proc/$pid/comm" 2>/dev/null)"
    [ -n "$name" ] || name="$pid"
    mem=0
    [ "$memkb" -gt 0 ] && mem=$(( r * pg_kb * 100 / memkb ))
    printf 'P %s %s %s\n' "$cpu" "$mem" "$name"
done