defmodule Mix.Tasks.Totp.TimeCheck do
  @shortdoc "Check server time and TOTP time synchronization"

  @moduledoc """
  Diagnostic tool to check if the server's clock is correct.

  Usage:
      mix totp.time_check

  This will:
  1. Show the server's current time (BEAM VM time)
  2. Show the system's current time
  3. Calculate what TOTP codes should be valid right now for a test secret
  """

  use Mix.Task

  require Logger

  def run(_args) do
    Mix.Task.run("app.start")

    IO.puts("\n=== Time Synchronization Check ===\n")

    # Get different time sources
    system_time = System.system_time(:second)
    os_time = :os.system_time(:second)
    datetime_now = DateTime.utc_now()

    IO.puts("System.system_time(:second): #{system_time}")
    IO.puts("  → #{DateTime.from_unix!(system_time)}")
    IO.puts("")
    IO.puts(":os.system_time(:second): #{os_time}")
    IO.puts("  → #{DateTime.from_unix!(os_time)}")
    IO.puts("")
    IO.puts("DateTime.utc_now(): #{datetime_now}")
    IO.puts("  → unix: #{DateTime.to_unix(datetime_now)}")
    IO.puts("")

    # Check if they match
    if system_time == os_time and system_time == DateTime.to_unix(datetime_now) do
      IO.puts("✓ All time sources agree")
    else
      IO.puts("⚠️  WARNING: Time sources disagree!")
      IO.puts("  System vs OS diff: #{system_time - os_time} seconds")
      IO.puts("  System vs DateTime diff: #{system_time - DateTime.to_unix(datetime_now)} seconds")
    end

    IO.puts("")

    # Show what TOTP codes would be generated now
    test_secret = NimbleTOTP.secret()
    current_code = NimbleTOTP.verification_code(test_secret, time: system_time)
    prev_code = NimbleTOTP.verification_code(test_secret, time: system_time - 30)
    next_code = NimbleTOTP.verification_code(test_secret, time: system_time + 30)

    IO.puts("Test TOTP codes (with random secret):")
    IO.puts("  Current window: #{current_code}")
    IO.puts("  Previous (-30s): #{prev_code}")
    IO.puts("  Next (+30s): #{next_code}")
    IO.puts("")

    # Recommend action
    IO.puts("=== Recommendations ===")
    IO.puts("")
    IO.puts("Compare the server time above with actual UTC time:")
    IO.puts("  Current actual UTC: Run 'date -u' on your local machine")
    IO.puts("")
    IO.puts("If the server time is wrong:")
    IO.puts("  1. Check K8s node time: kubectl exec -it <pod> -- date -u")
    IO.puts("  2. Check if NTP is running on the node")
    IO.puts("  3. Restart the pod to resync time")
    IO.puts("")
  end
end