defmodule Bypass do
  @moduledoc """
  Bypass provides a quick way to create a custom Plug that can be put in place
  instead of an actual HTTP server to return prebaked responses to client
  requests.

  This module is the main interface to the library.
  """

  defstruct pid: nil, port: nil

  @typedoc """
  Represents a Bypass server process.
  """
  @type t :: %__MODULE__{pid: pid, port: non_neg_integer}

  import Bypass.Utils
  require Logger

  @doc """
  Starts an Elixir process running a minimal Plug app. The process is a HTTP
  handler and listens to requests on a TCP port on localhost.

  Use the other functions in this module to declare which requests are handled
  and set expectations on the calls.
  """
  def open(opts \\ []) do
    case DynamicSupervisor.start_child(Bypass.Supervisor, Bypass.Instance.child_spec(opts)) do
      {:ok, pid} ->
        port = Bypass.Instance.call(pid, :port)
        debug_log("Did open connection #{inspect(pid)} on port #{inspect(port)}")
        bypass = %Bypass{pid: pid, port: port}
        setup_framework_integration(test_framework(), bypass)
        bypass

      other ->
        other
    end
  end

  defp setup_framework_integration(:ex_unit, bypass = %{pid: pid}) do
    ExUnit.Callbacks.on_exit({Bypass, pid}, fn ->
      do_verify_expectations(bypass.pid, ExUnit.AssertionError)
    end)
  end

  defp setup_framework_integration(:espec, _bypass) do
  end

  @doc """
  Can be called to immediately verify if the declared request expectations have
  been met.

  Returns `:ok` on success and raises an error on failure.
  """
  def verify_expectations!(bypass) do
    verify_expectations!(test_framework(), bypass)
  end

  defp verify_expectations!(:ex_unit, _bypass) do
    raise "Not available in ExUnit, as it's configured automatically."
  end

  if Code.ensure_loaded?(ESpec) do
    defp verify_expectations!(:espec, bypass) do
      do_verify_expectations(bypass.pid, ESpec.AssertionError)
    end
  end

  defp do_verify_expectations(bypass_pid, error_module) do
    case Bypass.Instance.call(bypass_pid, :on_exit) do
      :ok ->
        :ok

      :ok_call ->
        :ok

      {:error, :too_many_requests, {:any, :any}} ->
        raise error_module, "Expected only one HTTP request for Bypass"

      {:error, :too_many_requests, {method, path}} ->
        raise error_module, "Expected only one HTTP request for Bypass at #{method} #{path}"

      {:error, :unexpected_request, {:any, :any}} ->
        raise error_module, "Bypass got an HTTP request but wasn't expecting one"

      {:error, :unexpected_request, {method, path}} ->
        raise error_module,
              "Bypass got an HTTP request but wasn't expecting one at #{method} #{path}"

      {:error, :not_called, {:any, :any}} ->
        raise error_module, "No HTTP request arrived at Bypass"

      {:error, :not_called, {method, path}} ->
        raise error_module,
              "No HTTP request arrived at Bypass at #{method} #{path}"

      {:exit, {class, reason, stacktrace}} ->
        :erlang.raise(class, reason, stacktrace)
    end
  end

  @doc """
  Re-opens the TCP socket on the same port. Blocks until the operation is
  complete.
  """
  @spec up(Bypass.t()) :: :ok | {:error, :already_up}
  def up(%Bypass{pid: pid}),
    do: Bypass.Instance.call(pid, :up)

  @doc """
  Closes the TCP socket. Blocks until the operation is complete.
  """
  @spec down(Bypass.t()) :: :ok | {:error, :already_down}
  def down(%Bypass{pid: pid}),
    do: Bypass.Instance.call(pid, :down)

  def expect(%Bypass{pid: pid}, fun),
    do: Bypass.Instance.call(pid, {:expect, fun})

  def expect(%Bypass{pid: pid}, methods, paths, fun),
    do: Bypass.Instance.call(pid, {:expect, methods, paths, fun})

  def expect_once(%Bypass{pid: pid}, fun),
    do: Bypass.Instance.call(pid, {:expect_once, fun})

  def expect_once(%Bypass{pid: pid}, methods, paths, fun),
    do: Bypass.Instance.call(pid, {:expect_once, methods, paths, fun})

  def stub(%Bypass{pid: pid}, methods, paths, fun),
    do: Bypass.Instance.call(pid, {:stub, methods, paths, fun})

  def pass(%Bypass{pid: pid}),
    do: Bypass.Instance.call(pid, :pass)

  defp test_framework do
    Application.get_env(:bypass, :test_framework, :ex_unit)
  end
end