defmodule Mix.Tasks.Texas.Ify do
  use Mix.Task

  @shortdoc "Take an existing Phoenix project and Texasify it"

  @moduledoc """
  Adds Texas hooks into the current Phoenix application (assumed to be create with `mix phx.new`).
  This will modify the following files as described, so it is wise to commit your changes prior to
  running this command:
  - `./assets/js/app.js` - (adds `texasjs` dependency and instantiates a new Texas socket)
  - `./lib/<your_app>_web/channels/user_socket.ex` - adds `use Texas.Socket` after `use Phoenix.Socket`
  - `./config/config.exs` -  Specifies endpoint and router modules and configures templating engine to compile .texas files
  - `./lib/<your_app>_web/router.ex` - Adds the `Texas.Plug` to your browser pipeline
  - `./lib/<your_app>_web.ex/` - imports `Texas.Controller` into your app's controller template
  # - `./lib/<your_app>_web/controllers/page_controller.ex` - Renders views with `texas_render`
  # - Renames `index.html.eex` to `index.html.texas`

  Usage:
      mix texas.ify
  """

  @impl true
  def run(_args) do


    # TODO: Check for Phoenix version?

    Mix.shell().info("Texasifying this project")
    app = Mix.Project.config()[:app]
    app_js = "./assets/js/app.js"
    [user_socket] = Path.wildcard("./lib/*_web/channels/user_socket.ex")
    config = "./config/config.exs"
    [router] = Path.wildcard("./lib/*_web/router.ex")
    app_name =
      config
      |> File.stream!()
      |> Enum.find(& String.contains?(&1, "Endpoint") && String.contains?(&1, inspect app))
      |> String.split(",")
      |> Enum.at(1)
      |> String.trim()
    [web_templates] = Path.wildcard("./lib/#{to_string(app)}_web.ex")

    Mix.shell().info("- Adding texasjs socket to app.js")
    # If user hasn't uncommented the socket import in app.js, do it for them
    replace_in_file(app_js, "// import socket", "import socket", false)
    insert_into_file(app_js, "import socket from \"./socket\"", "import Texas from \"texasjs\"\nnew Texas(socket)")

    Mix.shell().info("Adding Texas into the backend socket")
    insert_into_file(user_socket, "use Phoenix.Socket", "  use Texas.Socket")

    Mix.shell().info("Added Texas stuff to config.exs")
    insert_into_file(config, "use Mix.Config", """
config :phoenix, :template_engines,
  texas:  Texas.TemplateEngine
config :texas, pubsub: #{app_name}.Endpoint
config :texas, router: #{app_name}.Router
""")

    Mix.shell().info("Adding Texas to the browser pipeline")
    insert_into_file(router, "  pipeline :browser do", "  end", "    plug Texas.Plug")

    Mix.shell().info("Adding Texas to the controller template")
    insert_into_file(web_templates, "use Phoenix.Controller", "import", "      import Texas.Controller")

    Mix.shell().info("Done!")
  end

  defp replace_in_file(path, text, replacement_text, check? \\ true) do
    input = File.read!(path)
    unless String.contains?(input, replacement_text) and check? do
      text = String.replace(input, text, replacement_text)
      File.write!(path, text)
    end
  end

  defp insert_into_file(path, previous_line, text_to_add) do
    replace_in_file(path, previous_line, "#{previous_line}\n#{text_to_add}")
  end

  defp insert_into_file(path, section_start, section_end, text_to_add) do
    unless String.contains?(File.read!(path), text_to_add) do
      f = File.stream!(path)
      {pre, rest} = Enum.split_while(f, & not String.contains?(&1, section_start))
      {section, end_and_beyond} = Enum.split_while(rest, & not String.contains?(&1, section_end))
      out = pre ++ [section] ++ [text_to_add] ++ ["\n"] ++ [end_and_beyond] |> Enum.join()
      File.write!(path, out)
    end
  end

end