defmodule Mix.Tasks.Dialup.Gen.Auth do
  @moduledoc """
  Generates authentication scaffolding for a Dialup application.

      mix dialup.gen.auth Accounts User users

  ## Options

    * `--app` — OTP application name (defaults to `Mix.Project` app)
    * `--force` — overwrite existing files
  """

  use Mix.Task

  @shortdoc "Generates authentication scaffolding"

  @switches [app: :string, force: :boolean]
  @aliases [f: :force]

  @impl Mix.Task
  def run(args) do
    Mix.Task.run("compile")

    {opts, positional} = OptionParser.parse!(args, strict: @switches, aliases: @aliases)

    case positional do
      [context, schema, table] ->
        generate(context, schema, table, opts)

      _ ->
        Mix.raise("""
        mix dialup.gen.auth expects:

            mix dialup.gen.auth Context Schema table

        Example:

            mix dialup.gen.auth Accounts User users
        """)
    end
  end

  defp generate(context, schema, table, opts) do
    otp_app = opts[:app] || app_name!()
    app_module = otp_app |> to_string() |> Macro.camelize()
    context_module = Module.concat([app_module, context])
    schema_module = Module.concat([context_module, schema])
    force? = Keyword.get(opts, :force, false)

    bindings = [
      otp_app: otp_app,
      app_module: app_module,
      context: context,
      context_module: context_module,
      context_mod: module_str(context_module),
      schema: schema,
      schema_module: schema_module,
      schema_mod: module_str(schema_module),
      schema_underscore: Macro.underscore(schema),
      table: table,
      migration_timestamp: next_migration_timestamp()
    ]

    files = [
      {"accounts.ex",
       "lib/#{otp_app}/#{Macro.underscore(context)}/#{Macro.underscore(context)}.ex"},
      {"user.ex", "lib/#{otp_app}/#{Macro.underscore(context)}/#{Macro.underscore(schema)}.ex"},
      {"user_token.ex",
       "lib/#{otp_app}/#{Macro.underscore(context)}/#{Macro.underscore(schema)}_token.ex"},
      {"notifier.ex", "lib/#{otp_app}/#{Macro.underscore(context)}/notifier.ex"},
      {"migration.ex",
       "priv/repo/migrations/#{bindings[:migration_timestamp]}_create_#{table}_auth.exs"},
      {"log_in_page.ex", "lib/app/log_in/page.ex"},
      {"register_page.ex", "lib/app/register/page.ex"},
      {"settings_page.ex", "lib/app/settings/page.ex"},
      {"reset_password_request_page.ex", "lib/app/reset_password/page.ex"},
      {"reset_password_page.ex", "lib/app/reset_password/[token]/page.ex"},
      {"auth_snippet.ex", "lib/#{otp_app}_auth_snippet.ex"}
    ]

    for {template, dest} <- files do
      write_template(template, dest, bindings, force?)
    end

    Mix.shell().info("""
    Add to your app module:

        use Dialup,
          auth_accounts: #{inspect(context_module)},
          plugs: [{Dialup.Auth.Plug, accounts: #{inspect(context_module)}}]

    Run migrations and configure your Repo before using auth pages.
    """)

    :ok
  end

  defp write_template(template, dest, bindings, force?) do
    if File.exists?(dest) and not force? do
      Mix.raise("Refusing to overwrite #{dest}. Pass --force to overwrite.")
    else
      source = template_path(template)
      content = EEx.eval_file(source, bindings, trim: true)
      File.mkdir_p!(Path.dirname(dest))
      File.write!(dest, content)
      Mix.shell().info("* creating #{dest}")
    end
  end

  defp app_name! do
    Mix.Project.config()[:app] ||
      Mix.raise("Could not determine OTP app. Pass --app APP_NAME.")
  end

  defp next_migration_timestamp do
    migrations_dir = Path.join(File.cwd!(), "priv/repo/migrations")
    base = utc_timestamp()

    if File.exists?(migrations_dir) do
      max_existing =
        migrations_dir
        |> File.ls!()
        |> Enum.filter(&String.match?(&1, ~r/^\d{14}_/))
        |> Enum.map(&String.slice(&1, 0, 14))
        |> Enum.max(fn -> base end)

      if max_existing >= base, do: increment_timestamp(max_existing), else: base
    else
      base
    end
  end

  defp utc_timestamp do
    {{y, m, d}, {h, min, s}} = :calendar.universal_time()
    Enum.map([y, m, d, h, min, s], &pad/1) |> Enum.join()
  end

  defp increment_timestamp(ts), do: ts |> String.to_integer() |> Kernel.+(1) |> pad_number()

  defp pad_number(n), do: n |> Integer.to_string() |> String.pad_leading(14, "0")
  defp pad(n) when n < 10, do: "0#{n}"
  defp pad(n), do: to_string(n)

  defp module_str(module), do: module |> inspect() |> String.replace_prefix("Elixir.", "")

  defp template_path(name) do
    priv_dir =
      case :code.priv_dir(:dialup) do
        {:error, :bad_name} ->
          __ENV__.file |> Path.dirname() |> Path.join("../../../priv") |> Path.expand()

        dir ->
          dir
      end

    Path.join(priv_dir, "templates/dialup.gen.auth/#{name}.eex")
  end
end