defmodule ToweropsWeb.Api.V1.ResourceController do
  @moduledoc """
  Shared helpers for standard API v1 CRUD resource operations.

  Eliminates the repetitive `ScopedResource.fetch` + case + changeset
  error handling pattern that appears in every resource controller.

  ## Usage

      defmodule ToweropsWeb.Api.V1.SitesController do
        use ToweropsWeb, :controller

        alias ToweropsWeb.Api.V1.ResourceController, as: Resources

        def show(conn, %{"id" => id}) do
          org_id = conn.assigns.current_organization_id
          Resources.fetch_and_render(conn, Site, id, org_id, &format_site/1, "Site not found")
        end
      end
  """

  alias Phoenix.Controller
  alias Plug.Conn
  alias ToweropsWeb.Api.ErrorHelpers
  alias ToweropsWeb.ScopedResource

  @doc """
  Fetch a resource by id and org scope, render JSON or 404.

  ## Examples

      Resources.fetch_and_render(conn, Site, id, org_id, &format_site/1, "Site not found")
  """
  def fetch_and_render(conn, schema, id, org_id, format_fn, not_found_msg) do
    case ScopedResource.fetch(schema, id, org_id) do
      {:ok, resource} ->
        Controller.json(conn, format_fn.(resource))

      {:error, :not_found} ->
        not_found(conn, not_found_msg)
    end
  end

  @doc """
  Fetch a resource by id and org scope with preloads, render JSON or 404.
  """
  def fetch_and_render(conn, schema, id, org_id, preloads, format_fn, not_found_msg) do
    case ScopedResource.fetch_preload(schema, id, org_id, preloads) do
      {:ok, resource} ->
        Controller.json(conn, format_fn.(resource))

      {:error, :not_found} ->
        not_found(conn, not_found_msg)
    end
  end

  def update_and_render(conn, schema, id, org_id, opts) do
    context = opts[:context]
    update_fn = opts[:update_fn]
    params = opts[:params]
    format_fn = opts[:format_fn]
    not_found_msg = opts[:not_found_msg]

    case ScopedResource.fetch(schema, id, org_id) do
      {:ok, resource} ->
        case apply(context, update_fn, [resource, params]) do
          {:ok, updated} ->
            Controller.json(conn, format_fn.(updated))

          {:error, %Ecto.Changeset{} = changeset} ->
            unprocessable_entity(conn, changeset)
        end

      {:error, :not_found} ->
        not_found(conn, not_found_msg)
    end
  end

  @doc """
  Fetch a resource, apply a delete function, render success or errors.
  """
  def delete_and_render(conn, schema, id, org_id, context, delete_fn, not_found_msg) do
    case ScopedResource.fetch(schema, id, org_id) do
      {:ok, resource} ->
        case apply(context, delete_fn, [resource]) do
          {:ok, _} ->
            Controller.json(conn, %{success: true})

          {:error, %Ecto.Changeset{} = changeset} ->
            unprocessable_entity(conn, changeset)
        end

      {:error, :not_found} ->
        not_found(conn, not_found_msg)
    end
  end

  @doc """
  Render 201 created with formatted resource, or 422 with changeset errors.
  """
  def created_or_error(conn, {:ok, resource}, format_fn) do
    conn
    |> Conn.put_status(:created)
    |> Controller.json(format_fn.(resource))
  end

  def created_or_error(conn, {:error, %Ecto.Changeset{} = changeset}, _format_fn) do
    unprocessable_entity(conn, changeset)
  end

  @doc "Render 422 with changeset errors."
  def unprocessable_entity(conn, changeset) do
    conn
    |> Conn.put_status(:unprocessable_entity)
    |> Controller.json(%{errors: ErrorHelpers.translate_errors(changeset)})
  end

  @doc "Render 404 JSON error."
  def not_found(conn, message) do
    conn
    |> Conn.put_status(:not_found)
    |> Controller.json(%{error: message})
  end

  @doc "Render 400 for missing required parameter."
  def missing_param(conn, param_name) do
    conn
    |> Conn.put_status(:bad_request)
    |> Controller.json(%{error: "Missing '#{param_name}' parameter"})
  end
end