#!/usr/bin/env bash
set -o errexit
set -o nounset
set -o pipefail

warning_threshold=75
critical_threshold=90
top_count=10

usage() {
  cat <<'USAGE'
Usage: check_high_cpu.sh [--warning PERCENT] [--critical PERCENT] [--top N] [--help]

Detect high CPU load and show top CPU-consuming processes.

Exit codes:
  0 OK
  1 WARNING / operational issue detected
  2 invalid input / missing required dependency
  3 CRITICAL issue detected
USAGE
}

is_number() {
  [[ "$1" =~ ^[0-9]+$ ]]
}

require_cmd() {
  if ! command -v "$1" >/dev/null 2>&1; then
    printf 'CRITICAL: required command not found: %s\n' "$1"
    exit 2
  fi
}

while (($# > 0)); do
  case "$1" in
    --warning)
      [[ $# -ge 2 ]] || { printf 'CRITICAL: --warning requires a value\n'; exit 2; }
      warning_threshold="$2"
      shift 2
      ;;
    --critical)
      [[ $# -ge 2 ]] || { printf 'CRITICAL: --critical requires a value\n'; exit 2; }
      critical_threshold="$2"
      shift 2
      ;;
    --top)
      [[ $# -ge 2 ]] || { printf 'CRITICAL: --top requires a value\n'; exit 2; }
      top_count="$2"
      shift 2
      ;;
    --help|-h)
      usage
      exit 0
      ;;
    *)
      printf 'CRITICAL: unknown option: %s\n' "$1"
      usage
      exit 2
      ;;
  esac
done

for value in "$warning_threshold" "$critical_threshold" "$top_count"; do
  if ! is_number "$value"; then
    printf 'CRITICAL: numeric option expected, got: %s\n' "$value"
    exit 2
  fi
done

if ((warning_threshold >= critical_threshold)); then
  printf 'CRITICAL: --warning must be lower than --critical\n'
  exit 2
fi

require_cmd ps
require_cmd awk
require_cmd head

cpu_count=1
if command -v getconf >/dev/null 2>&1; then
  cpu_count="$(getconf _NPROCESSORS_ONLN 2>/dev/null || printf '1')"
elif [[ -r /proc/cpuinfo ]]; then
  cpu_count="$(grep -c '^processor' /proc/cpuinfo 2>/dev/null || printf '1')"
fi
[[ "$cpu_count" =~ ^[0-9]+$ ]] || cpu_count=1
((cpu_count > 0)) || cpu_count=1

load_1m="unavailable"
load_5m="unavailable"
load_15m="unavailable"
load_per_cpu_pct=0
if [[ -r /proc/loadavg ]]; then
  read -r load_1m load_5m load_15m _ < /proc/loadavg
  load_per_cpu_pct="$(awk -v load="$load_1m" -v cpus="$cpu_count" 'BEGIN { printf "%d", (load / cpus) * 100 }')"
elif command -v uptime >/dev/null 2>&1; then
  load_line="$(uptime 2>/dev/null || true)"
  load_1m="$(printf '%s\n' "$load_line" | sed -n 's/.*load average[s]*: *\([^,]*\).*/\1/p')"
fi

status="OK"
exit_code=0
if ((load_per_cpu_pct >= critical_threshold)); then
  status="CRITICAL"
  exit_code=3
elif ((load_per_cpu_pct >= warning_threshold)); then
  status="WARNING"
  exit_code=1
fi

printf '%s: 1-minute load is %s across %s CPU(s) (%s%% of CPU count)\n\n' "$status" "$load_1m" "$cpu_count" "$load_per_cpu_pct"

printf 'Load average:\n'
printf '1m=%s 5m=%s 15m=%s\n\n' "$load_1m" "$load_5m" "$load_15m"

printf 'CPU count:\n'
printf '%s\n\n' "$cpu_count"

printf 'Top CPU processes:\n'
ps -eo pid,ppid,user,pcpu,pmem,comm,args --sort=-pcpu | head -n "$((top_count + 1))"
printf '\n'

printf 'Evidence:\n'
if command -v uptime >/dev/null 2>&1; then
  uptime || true
else
  printf 'WARNING: uptime command not available; used /proc/loadavg where possible\n'
fi
if ((load_per_cpu_pct >= 100)); then
  printf 'WARNING: load is higher than online CPU count; runnable task saturation is possible\n'
else
  printf 'OK: load is not above online CPU count at collection time\n'
fi
if [[ "${EUID:-$(id -u 2>/dev/null || printf '1')}" != "0" ]]; then
  printf 'WARNING: running without root; process ownership details are usually available, but some command lines may be limited\n'
fi
printf '\n'

printf 'Recommended next steps:\n'
printf -- '- Check process ownership and whether the top process is expected\n'
printf -- '- Check recent deployments, cron jobs, batch jobs, or maintenance activity\n'
printf -- '- Review logs for the top CPU-consuming process\n'
printf -- '- Compare with longer trend data from monitoring before taking action\n'
printf -- '- Attach this output to the incident ticket\n'

exit "$exit_code"