defmodule MicrowavepropWeb.Api.ErrorJSON do
  @moduledoc """
  RFC 9457 problem+json error responses for `/api/v1`.

  All error bodies share the shape:

      {
        "type": "about:blank",
        "title": "<short slug>",
        "status": <int>,
        "detail": "<human-readable explanation>",
        "errors": <optional changeset error map>
      }
  """

  import Plug.Conn

  alias Ecto.Changeset
  alias Plug.Conn.Status

  @content_type "application/problem+json"

  @doc "Halts the connection with a problem+json body."
  @spec send_problem(Plug.Conn.t(), pos_integer(), String.t(), String.t(), map()) :: Plug.Conn.t()
  def send_problem(conn, status, title, detail, extra \\ %{}) do
    body =
      %{
        type: "about:blank",
        title: title,
        status: status,
        detail: detail
      }
      |> Map.merge(extra)
      |> Jason.encode!()

    conn
    |> put_resp_content_type(@content_type)
    |> send_resp(status, body)
    |> halt()
  end

  @doc "Halts with a 422 problem+json including a flattened changeset error map."
  @spec send_changeset(Plug.Conn.t(), Changeset.t()) :: Plug.Conn.t()
  def send_changeset(conn, %Changeset{} = changeset) do
    send_problem(
      conn,
      422,
      "validation_failed",
      "One or more fields are invalid.",
      %{errors: translate_errors(changeset)}
    )
  end

  @doc "Translates a changeset's errors into a flat map of field -> [messages]."
  @spec translate_errors(Changeset.t()) :: map()
  def translate_errors(%Changeset{} = changeset) do
    Changeset.traverse_errors(changeset, fn {msg, opts} ->
      Enum.reduce(opts, msg, fn {key, value}, acc ->
        String.replace(acc, "%{#{key}}", to_string(value))
      end)
    end)
  end

  ## Default Phoenix error renderer hooks ----------------------------

  @doc false
  @spec render(String.t(), map()) :: map()
  def render("400.json", _assigns), do: error_body(400, "bad_request", "Malformed request.")
  def render("401.json", _assigns), do: error_body(401, "unauthorized", "Authentication is required.")
  def render("403.json", _assigns), do: error_body(403, "forbidden", "You may not access this resource.")
  def render("404.json", _assigns), do: error_body(404, "not_found", "Resource not found.")
  def render("405.json", _assigns), do: error_body(405, "method_not_allowed", "HTTP method not allowed.")
  def render("415.json", _assigns), do: error_body(415, "unsupported_media_type", "Unsupported media type.")
  def render("429.json", _assigns), do: error_body(429, "too_many_requests", "Rate limit exceeded.")
  def render("500.json", _assigns), do: error_body(500, "internal_server_error", "Something went wrong.")

  def render(template, _assigns) do
    [code | _] = String.split(template, ".")
    status = String.to_integer(code)
    error_body(status, status |> Status.reason_atom() |> Atom.to_string(), "")
  end

  defp error_body(status, title, detail) do
    %{type: "about:blank", title: title, status: status, detail: detail}
  end
end