defmodule Mix.Tasks.Log.Tail do
  @moduledoc """
  Watch a log file in real-time with parsed, color-coded, filtered output.

  ## Usage

      mix log.tail <path> [options]

  ## Options

      --level    Only show entries matching this level (error, warn, info, debug)
      --format   Only show entries matching this format (morgan, java, elixir, nginx)
      --grep     Only show entries whose message contains this text (case-insensitive)
      --history  Show N existing lines from end of file before tailing (default: 0)

  ## Examples

      mix log.tail logs/app.log
      mix log.tail logs/app.log --level error
      mix log.tail logs/app.log --grep "timeout" --level error
      mix log.tail logs/app.log --format java --history 20

  Press Ctrl+C to stop.
  """
  @shortdoc "Watch a log file in real-time"

  use Mix.Task

  alias TelemetryData.LogTail

  @impl Mix.Task
  def run(args) do
    {opts, positional, _} =
      OptionParser.parse(args,
        strict: [level: :string, format: :string, grep: :string, history: :integer]
      )

    path = List.first(positional) || "logs/app.log"
    history = Keyword.get(opts, :history, 0)

    unless File.exists?(path) do
      Mix.raise("File not found: #{path}")
    end

    filters =
      opts
      |> Keyword.take([:level, :format, :grep])
      |> Enum.filter(fn {_k, v} -> v != nil end)

    # Print header
    Mix.shell().info("")
    Mix.shell().info(IO.ANSI.bright() <> "  Tailing: #{path}" <> IO.ANSI.reset())

    if filters != [] do
      filter_desc =
        filters
        |> Enum.map(fn {k, v} -> "#{k}=#{v}" end)
        |> Enum.join(", ")

      Mix.shell().info(IO.ANSI.faint() <> "  Filters: #{filter_desc}" <> IO.ANSI.reset())
    end

    Mix.shell().info(IO.ANSI.faint() <> "  Press Ctrl+C to stop" <> IO.ANSI.reset())
    Mix.shell().info("")

    # Show history if requested
    if history > 0, do: show_history(path, history, filters)

    # Start tailing
    {:ok, _pid} =
      LogTail.start_link(path,
        callback: &print_entry/1,
        filters: filters
      )

    # Block forever (until Ctrl+C)
    Process.sleep(:infinity)
  end

  defp show_history(path, n, filters) do
    alias TelemetryData.LogParser

    case File.read(path) do
      {:ok, content} ->
        entries = LogParser.parse_lines(content)

        filtered =
          Enum.filter(entries, fn entry ->
            Enum.all?(filters, fn
              {:level, level} -> entry.level == String.downcase(level)
              {:format, format} -> entry.format == String.to_existing_atom(format)
              {:grep, pattern} -> String.contains?(String.downcase(entry.message), String.downcase(pattern))
              _ -> true
            end)
          end)

        history_entries = Enum.take(filtered, -n)

        if history_entries != [] do
          Mix.shell().info(IO.ANSI.faint() <> "  --- history (last #{length(history_entries)}) ---" <> IO.ANSI.reset())

          Enum.each(history_entries, &print_entry/1)

          Mix.shell().info(IO.ANSI.faint() <> "  --- live tail ---" <> IO.ANSI.reset())
          Mix.shell().info("")
        end

      _ ->
        :ok
    end
  end

  defp print_entry(entry) do
    level_tag = colorize_level(entry.level)
    format_tag = IO.ANSI.cyan() <> "[#{entry.format}]" <> IO.ANSI.reset()

    source =
      if entry.source,
        do: IO.ANSI.faint() <> " #{entry.source}" <> IO.ANSI.reset(),
        else: ""

    time = IO.ANSI.faint() <> entry.timestamp <> IO.ANSI.reset()

    IO.puts("#{level_tag} #{format_tag}#{source} #{time}  #{entry.message}")
  end

  defp colorize_level("error"), do: IO.ANSI.red() <> "[ERROR]" <> IO.ANSI.reset()
  defp colorize_level("warn"), do: IO.ANSI.yellow() <> "[WARN] " <> IO.ANSI.reset()
  defp colorize_level("info"), do: IO.ANSI.green() <> "[INFO] " <> IO.ANSI.reset()
  defp colorize_level("debug"), do: IO.ANSI.faint() <> "[DEBUG]" <> IO.ANSI.reset()
  defp colorize_level(other), do: "[#{String.upcase(other)}]"
end