Make it easy to send a plot (#37)

And include an example using it to generate some alt-text.

Fixes #6

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method(print,Chat)
 export(content_image_file)
+export(content_image_plot)
 export(content_image_url)
 export(create_tool_metadata)
 export(new_chat_openai)

R/content.R

@@ -21,6 +21,15 @@
 #'   content_image_url("https://www.r-project.org/Rlogo.png"),
 #'   content_image_file(system.file("httr2.png", package = "elmer"))
 #' )
+#'
+#' plot(waiting ~ eruptions, data = faithful)
+#' chat <- new_chat_openai(echo = TRUE)
+#' chat$chat(
+#'   "Describe this plot in one paragraph, as suitable for inclusion in
+#'    alt-text. You should briefly describe the plot type, the axes, and
+#'    2-5 major visual patterns.",
+#'    content_image_plot()
+#' )
 content_image_url <- function(url, detail = c("auto", "low", "high")) {
   # TODO: Allow vector input?
   check_string(url)
@@ -106,6 +115,24 @@ content_image_file <- function(path, content_type = "auto", resize = "low") {
   content_image_url(data_uri)
 }
 
+#' @rdname content_image_url
+#' @export
+#' @param width,height Width and height in pixels.
+content_image_plot <- function(width = 768, height = 768) {
+  plot <- recordPlot()
+  old <- dev.cur()
+
+  path <- tempfile("elmer-plot-", fileext = ".png")
+  defer(unlink(path))
+
+  png(path, width = width, height = height)
+  replayPlot(plot)
+  dev.off()
+
+  dev.set(old)
+
+  content_image_file(path, "image/png", resize = "high")
+}
 
 # Define allowed types - add new types here in the future
 allowed_input_types <- c("text", "image_url")

R/utils.R

@@ -18,3 +18,8 @@ key_get <- function(name, error_call = caller_env()) {
 key_exists <- function(name) {
   !identical(Sys.getenv(name), "")
 }
+
+defer <- function(expr, env = caller_env(), after = FALSE) {
+  thunk <- as.call(list(function() expr))
+  do.call(on.exit, list(thunk, TRUE, after), envir = env)
+}