#! /bin/bash

RED="\e[31m"
GREEN="\e[32m"
YELLOW="\e[33m"
CYAN="\e[36m"
NC="\e[0m"

trap "echo -e '${CYAN}System Monitor interrupted.${NC}'; exit 1" SIGINT SIGTERM

for i in {0..3}; do
  echo
done

# Cache in tmpfs to improve speed and reduce SSD load
cache=/tmp/cpu-script-cache
rm /tmp/cpu-script-cache 2>/dev/null
while true; do
  # CPU
  cpu_stats=$(awk '/^cpu / {print $2 + $3 + $4 + $5, $5}' /proc/stat)
  if [ ! -f "$cache" ]; then
    echo "$cpu_stats" >"$cache"
    cpu_color=$CYAN
    usage="--"
  else
    prev_stats=$(cat "$cache")
    total=$(echo "$prev_stats" | awk '{print $1}')
    prev_idle=$(echo "$prev_stats" | awk '{print $2}')
    curr_total=$(echo "$cpu_stats" | awk '{print $1}')
    curr_idle=$(echo "$cpu_stats" | awk '{print $2}')
    total_diff=$((curr_total - total))
    idle_diff=$((curr_idle - prev_idle))

    if [ "$total_diff" -eq 0 ]; then
      usage=0 # Avoid division by zero
    else
      usage=$((100 * (total_diff - idle_diff) / total_diff))
    fi

    if [ "$usage" -lt 50 ]; then
      cpu_color=$GREEN
    elif [ "$usage" -lt 70 ]; then
      cpu_color=$YELLOW
    else
      cpu_color=$RED
    fi
  fi

  # MEMORY
  mem_info=$(free | awk '/Mem:/ {print $2, $3}')
  read total used <<<"$mem_info"
  percent=$(awk "BEGIN {printf \"%.0f\", ($used/$total)*100}")

  mem_total=$(free -h | awk '/Mem:/ {print $2}')
  mem_used=$(free -h | awk '/Mem:/ {print $3}')

  if [ "$percent" -le 60 ]; then
    mem_color=$GREEN
  elif [ "$percent" -le 80 ]; then
    mem_color=$YELLOW
  else
    mem_color=$RED
  fi

  echo -ne "\033[4A"
  echo -e "============================="
  echo -e "  ${cpu_color}${usage}%${NC}     "
  echo -e "  ${mem_used} / ${mem_total} (${mem_color}${percent}%${NC})      "
  echo -e "============================="

  echo "$cpu_stats" >"$cache"
  sleep 2
done