defmodule AiDebug.PortFinder do
  @moduledoc """
  Dynamically finds available ports to avoid conflicts with user applications.
  
  This was implemented after dogfooding revealed port 4000 conflicts with
  many development servers.
  """

  # AI-Debug reserved port range: 8200-8299 (safe from common dev ports)
  @default_port 8200
  @max_attempts 100

  @doc """
  Find an available port starting from the default port.
  
  ## Examples
  
      iex> AiDebug.PortFinder.find_available_port()
      {:ok, 8200}
      
      iex> AiDebug.PortFinder.find_available_port(8250)
      {:ok, 8250}
  """
  def find_available_port(start_port \\ @default_port) do
    find_port(start_port, 0)
  end

  defp find_port(_port, attempts) when attempts >= @max_attempts do
    {:error, :no_available_port}
  end

  defp find_port(port, attempts) do
    case port_available?(port) do
      true -> {:ok, port}
      false -> find_port(port + 1, attempts + 1)
    end
  end

  @doc """
  Check if a specific port is available.
  """
  def port_available?(port) do
    case :gen_tcp.listen(port, [:binary, {:active, false}, {:reuseaddr, true}]) do
      {:ok, socket} ->
        :gen_tcp.close(socket)
        true
      {:error, :eaddrinuse} ->
        false
      {:error, _} ->
        false
    end
  end

  @doc """
  Get a configuration-friendly port setting.
  
  Returns a port configuration that can be used in Phoenix endpoint config.
  """
  def get_phoenix_port_config() do
    case find_available_port() do
      {:ok, port} -> 
        [ip: {127, 0, 0, 1}, port: port]
      {:error, _} -> 
        # Fallback to default
        [ip: {127, 0, 0, 1}, port: @default_port]
    end
  end

  @doc """
  Print available port information for debugging.
  """
  def debug_ports(range \\ 8200..8210) do
    IO.puts("Port availability check:")
    
    Enum.each(range, fn port ->
      status = if port_available?(port), do: "✅ Available", else: "❌ In use"
      IO.puts("  Port #{port}: #{status}")
    end)
  end
end