defmodule Mix.Tasks.Phia.Install do
  @moduledoc """
  Sets up PhiaUI in the current Phoenix project.

  Injects the PhiaUI TailwindCSS v4 `@theme` block into `assets/css/app.css`,
  creates `assets/js/phia_hooks/index.js`, and registers PhiaUI hooks in
  `assets/js/app.js`.

  ## Usage

      mix phia.install

  ## Behaviour

  - Detects the current app name via `Mix.Project.config()[:app]`.
  - Prepends the `@theme { ... }` block from `priv/templates/theme/theme.css`
    into `assets/css/app.css`.
  - Creates `assets/js/phia_hooks/index.js` with PhiaHooks export.
  - Adds PhiaHooks import and registration to `assets/js/app.js`.
  - **Idempotent**: all steps are safe to run multiple times.
  - Prints confirmation messages via `Mix.shell().info/1`.

  ## Options

      --help    Print this help message
  """

  use Mix.Task

  @shortdoc "Installs PhiaUI theme tokens, hooks, and app.js wiring"

  @css_marker "/* PhiaUI Theme — do not remove this line */"
  @js_marker "// phia_hooks_registered"

  @hooks_content """
  // PhiaUI JS Hooks — auto-generated by mix phia.install
  // Add your custom PhiaUI hooks here or import from sub-modules.

  const PhiaHooks = {}

  export default PhiaHooks
  """

  @impl Mix.Task
  def run(["--help"]) do
    Mix.shell().info(@moduledoc)
  end

  def run(_args) do
    name = app_name()
    root = File.cwd!()
    css_path = Path.join([root, "assets/css/app.css"])

    if File.exists?(css_path) do
      inject_theme(css_path)
      Mix.shell().info([:green, "* inject ", :reset, css_path])
    else
      Mix.shell().error("Could not find #{css_path}. Run from your Phoenix project root.")
    end

    inject_hooks(root)
    Mix.shell().info([:green, "* create ", :reset, "assets/js/phia_hooks/index.js"])

    inject_app_js(root)
    Mix.shell().info([:green, "* update ", :reset, "assets/js/app.js"])

    Mix.shell().info([:green, "✓ PhiaUI installed for ", :reset, inspect(name)])
  end

  @doc """
  Returns the current Mix project's application name.

  ## Example

      iex> Mix.Tasks.Phia.Install.app_name()
      :phia_ui
  """
  @spec app_name() :: atom()
  def app_name, do: Mix.Project.config()[:app]

  @doc """
  Injects the PhiaUI theme block into the CSS file at `path`.

  Skips silently if the marker is already present (idempotent).
  """
  @spec inject_theme(Path.t()) :: :ok | :already_installed
  def inject_theme(path) do
    current = File.read!(path)

    if String.contains?(current, @css_marker) do
      :already_installed
    else
      theme_block = build_theme_block()
      File.write!(path, theme_block <> current)
      :ok
    end
  end

  @doc """
  Creates `assets/js/phia_hooks/index.js` under `root` with PhiaHooks export.

  Uses `Mix.Generator.create_file/3` for interactive conflict handling: if the
  file already exists, the user is prompted before any overwrite.
  """
  @spec inject_hooks(Path.t()) :: :ok | nil
  def inject_hooks(root) do
    hooks_dir = Path.join([root, "assets", "js", "phia_hooks"])
    hooks_path = Path.join(hooks_dir, "index.js")
    File.mkdir_p!(hooks_dir)
    Mix.Generator.create_file(hooks_path, @hooks_content)
  end

  @doc """
  Adds PhiaHooks import and registration to `assets/js/app.js` under `root`.

  Skips if the idempotency marker is already present.
  """
  @spec inject_app_js(Path.t()) :: :ok | :already_installed | :not_found
  def inject_app_js(root) do
    app_js = Path.join([root, "assets", "js", "app.js"])

    if File.exists?(app_js) do
      current = File.read!(app_js)

      if String.contains?(current, @js_marker) do
        :already_installed
      else
        injection =
          "#{@js_marker}\n" <>
            "import PhiaHooks from './phia_hooks/index.js'\n\n"

        File.write!(app_js, injection <> current)
        :ok
      end
    else
      :not_found
    end
  end

  # ---------------------------------------------------------------------------
  # Private helpers
  # ---------------------------------------------------------------------------

  defp build_theme_block do
    template_path = template_path()
    theme_css = File.read!(template_path)
    @css_marker <> "\n" <> theme_css <> "\n"
  end

  defp template_path do
    # When running inside the phia_ui library itself, use priv/ directly.
    # When installed as a dep, use Application.app_dir/2.
    local = Path.join([File.cwd!(), "priv/templates/theme/theme.css"])

    if File.exists?(local) do
      local
    else
      Application.app_dir(:phia_ui, "priv/templates/theme/theme.css")
    end
  end
end