#' Make a Google Sheets API request
#'
#' Low-level function to execute a Sheets API request. Most users should,
#' instead, use higher-level wrappers that facilitate common tasks, such as
#' reading or writing worksheets or cell ranges. The functions here are intended
#' for internal use and for programming around the Sheets API.
#'
#' `make_request()` is a very thin wrapper around [gargle::request_retry()],
#' only adding the googlesheets4 user agent. Typically the input has been
#' created with [request_generate()] or [gargle::request_build()] and the output
#' is processed with `process_response()`.
#'
#' [gargle::request_retry()] retries requests that error with `429
#' RESOURCE_EXHAUSTED`. Its basic scheme is exponential backoff, with one tweak
#' that is very specific to the Sheets API, which has documented [usage
#' limits](https://developers.google.com/sheets/api/limits):
#'
#' "a limit of 500 requests per 100 seconds per project and 100 requests per 100
#' seconds per user"
#'
#' Note that the "project" here means everyone using googlesheets4 who hasn't
#' configured their own OAuth client. This is potentially a lot of users, all
#' acting independently.
#'
#' If you hit the "100 requests per 100 seconds per **user**" limit (which
#' really does mean YOU), the first wait time is a bit more than 100 seconds,
#' then we revert to exponential backoff.
#'
#' If you experience lots of retries, especially with 100 second delays, it
#' means your use of googlesheets4 is more than casual and **it's time for you
#' to get your own OAuth client or use a service account token**. This is explained
#' in the gargle vignette `vignette("get-api-credentials", package = "gargle")`.
#'
#' @param x List. Holds the components for an HTTP request, presumably created
#'   with [request_generate()] or [gargle::request_build()]. Must contain a
#'   `method` and `url`. If present, `body` and `token` are used.
#' @param ... Optional arguments passed through to the HTTP method.
#' @param encode If the body is a named list, how should it be encoded? This has
#'   the same meaning as `encode` in all the [httr::VERB()]s, such as
#'   [httr::POST()]. Note, however, that we default to `encode = "json"`, which
#'   is what you want most of the time when calling the Sheets API. The httr
#'   default is `"multipart"`. Other acceptable values are `"form"` and `"raw"`.
#'
#' @return Object of class `response` from [httr].
#' @export
#' @family low-level API functions
request_make <- function(x, ..., encode = "json") {
  gargle::request_retry(
    x,
    ...,
    encode = encode,
    user_agent = gs4_user_agent()
  )
}

gs4_user_agent <- function() {
  httr::user_agent(paste0(
    "googlesheets4/",
    utils::packageVersion("googlesheets4"),
    " ",
    "(GPN:RStudio; )",
    " ",
    "gargle/",
    utils::packageVersion("gargle"),
    " ",
    "httr/",
    utils::packageVersion("httr")
  ))
}
