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

warning_threshold=80
critical_threshold=90
top_count=10

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

Detect inode exhaustion using df -i.
USAGE
}

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

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
if ! command -v df >/dev/null 2>&1; then
  printf 'CRITICAL: required command not found: df\n'
  exit 2
fi

tmp_df="$(mktemp)"
tmp_alerts="$(mktemp)"
trap 'rm -f "$tmp_df" "$tmp_alerts"' EXIT

df -Pi > "$tmp_df"
awk -v warn="$warning_threshold" '
  NR > 1 {
    pct=$5
    gsub(/%/, "", pct)
    if (pct >= warn) {
      print $0
    }
  }
' "$tmp_df" > "$tmp_alerts"

max_pct="$(awk 'NR > 1 { pct=$5; gsub(/%/, "", pct); if (pct > max) max=pct } END { printf "%d", max }' "$tmp_df")"
status="OK"
exit_code=0
if ((max_pct >= critical_threshold)); then
  status="CRITICAL"
  exit_code=3
elif ((max_pct >= warning_threshold)); then
  status="WARNING"
  exit_code=1
fi

printf '%s: Highest inode usage is %s%%\n\n' "$status" "$max_pct"

printf 'Filesystems above threshold:\n'
if [[ -s "$tmp_alerts" ]]; then
  cat "$tmp_alerts"
else
  printf 'OK: no filesystems above warning threshold\n'
fi
printf '\n'

printf 'Inode usage table:\n'
cat "$tmp_df"
printf '\n'

printf 'Top affected mount points:\n'
awk 'NR > 1 { pct=$5; gsub(/%/, "", pct); print pct, $6, $1, $2, $3, $4 }' "$tmp_df" \
  | sort -rn | head -n "$top_count" \
  | awk '{ printf "%s%% %s %s inodes=%s used=%s free=%s\n", $1, $2, $3, $4, $5, $6 }'
printf '\n'

printf 'Evidence:\n'
printf 'Thresholds: warning=%s%% critical=%s%%\n\n' "$warning_threshold" "$critical_threshold"

printf 'Recommended next steps:\n'
printf -- '- Find directories with many small files under affected mount points\n'
printf -- '- Check logs, cache, spool, session, and temporary directories\n'
printf -- '- Avoid deleting blindly; confirm ownership and application impact first\n'
printf -- '- Confirm whether inode exhaustion is causing write or deploy failures\n'
printf -- '- Attach this output to incident ticket\n'

exit "$exit_code"