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

host="$(hostname)"
timestamp="$(date '+%Y-%m-%d_%H%M%S')"
report="/tmp/system_report_${host}_${timestamp}.txt"

section() {
  printf '\n== %s ==\n' "$1"
}

run_or_warn() {
  local description="$1"
  shift

  if command -v "$1" >/dev/null 2>&1; then
    "$@" || printf 'WARNING: %s command failed\n' "$description"
  else
    printf 'WARNING: %s command not available\n' "$1"
  fi
}

{
  section "Host"
  hostname

  section "Date"
  date

  section "Uptime"
  uptime

  section "OS"
  if [[ -r /etc/os-release ]]; then
    . /etc/os-release
    printf '%s\n' "${PRETTY_NAME:-Unknown Linux}"
  else
    printf 'WARNING: /etc/os-release not readable\n'
  fi

  section "Kernel"
  uname -r

  section "CPU Load"
  if [[ -r /proc/loadavg ]]; then
    awk '{print "1m="$1, "5m="$2, "15m="$3}' /proc/loadavg
  else
    uptime
  fi

  section "Memory"
  run_or_warn "memory usage" free -h

  section "Disk"
  run_or_warn "disk usage" df -h -x tmpfs -x devtmpfs

  section "Failed systemd Services"
  if command -v systemctl >/dev/null 2>&1; then
    systemctl --failed --no-pager || true
  else
    printf 'WARNING: systemctl command not available\n'
  fi

  section "Listening Ports"
  if command -v ss >/dev/null 2>&1; then
    ss -tuln || printf 'WARNING: ss command failed\n'
  else
    printf 'WARNING: ss command not available\n'
  fi

  section "Recent Kernel Messages"
  if command -v journalctl >/dev/null 2>&1; then
    journalctl -k -n 50 --no-pager || printf 'WARNING: journalctl kernel log query failed\n'
  else
    printf 'WARNING: journalctl command not available\n'
  fi
} > "$report"

printf 'System report written to: %s\n' "$report"