#' Scales for shapes, aka glyphs
#'
#' `scale_shape()` maps discrete variables to six easily discernible shapes.
#' If you have more than six levels, you will get a warning message, and the
#' seventh and subsequent levels will not appear on the plot. Use
#' [scale_shape_manual()] to supply your own values. You can not map
#' a continuous variable to shape unless `scale_shape_binned()` is used. Still,
#' as shape has no inherent order, this use is not advised.
#'
#' @param solid Should the shapes be solid, `TRUE`, or hollow,
#'   `FALSE`?
#' @inheritParams scale_x_discrete
#' @inheritDotParams discrete_scale -expand -position
#' @rdname scale_shape
#' @export
#' @examples
#' dsmall <- diamonds[sample(nrow(diamonds), 100), ]
#'
#' (d <- ggplot(dsmall, aes(carat, price)) + geom_point(aes(shape = cut)))
#' d + scale_shape(solid = TRUE) # the default
#' d + scale_shape(solid = FALSE)
#' d + scale_shape(name = "Cut of diamond")
#'
#' # To change order of levels, change order of
#' # underlying factor
#' levels(dsmall$cut) <- c("Fair", "Good", "Very Good", "Premium", "Ideal")
#'
#' # Need to recreate plot to pick up new data
#' ggplot(dsmall, aes(price, carat)) + geom_point(aes(shape = cut))
#'
#' # Show a list of available shapes
#' df_shapes <- data.frame(shape = 0:24)
#' ggplot(df_shapes, aes(0, 0, shape = shape)) +
#'   geom_point(aes(shape = shape), size = 5, fill = 'red') +
#'   scale_shape_identity() +
#'   facet_wrap(~shape) +
#'   theme_void()
scale_shape <- function(..., solid = TRUE) {
  discrete_scale("shape", "shape_d", shape_pal(solid), ...)
}

#' @rdname scale_shape
#' @export
scale_shape_binned <- function(..., solid = TRUE) {
  binned_scale("shape", "shape_b", binned_pal(shape_pal(solid)), ...)
}

#' @rdname scale_shape
#' @export
#' @usage NULL
scale_shape_discrete <- scale_shape

#' @rdname scale_shape
#' @export
#' @usage NULL
scale_shape_ordinal <- function(...) {
  warn("Using shapes for an ordinal variable is not advised")
  scale_shape(...)
}

#' @rdname scale_shape
#' @export
#' @usage NULL
scale_shape_continuous <- function(...) {
  abort("A continuous variable can not be mapped to shape")
}