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#' Create a printer callback function
#'
#' A printer callback function is a function can performs the actual
#' printing. It has a number of subcommands, that are called by
#' the `printer` package, in a form \preformatted{
#' printer_callback("subcommand", argument1, argument2, ...)
#' } See the examples below.
#'
#' The subcommands:
#'
#' \describe{
#' \item{`length`}{The length of the data to print, the number of
#' items, in natural units. E.g. for a list of objects, it is the
#' number of objects.}
#' \item{`min_width`}{TODO}
#' \item{`width`}{Width of one item, if `no` items will be
#' printed. TODO}
#' \item{`print`}{Argument: `no`. Do the actual printing,
#' print `no` items.}
#' \item{`done`}{TODO}
#' }
#'
#' @param fun The function to use as a printer callback function.
#' @family printer callbacks
#' @export
printer_callback <- function(fun) {
if (!is.function(fun)) warning("'fun' is not a function")
add_class(fun, "printer_callback")
}
#' Is this a printer callback?
#'
#' @param x An R object.
#' @family printer callbacks
#' @export
is_printer_callback <- function(x) {
inherits(x, "printer_callback")
}
print_header <- function(header) {
print_head_foot(header)
}
print_footer <- function(footer) {
print_head_foot(footer)
}
print_head_foot <- function(head_foot) {
if (is.function(head_foot)) head_foot() else cat(head_foot)
}
#' Print the only the head of an R object
#'
#' @param x The object to print, or a callback function. See
#' [printer_callback()] for details.
#' @param max_lines Maximum number of lines to print, *not*
#' including the header and the footer.
#' @param header The header, if a function, then it will be called,
#' otherwise printed using `cat`.
#' @param footer The footer, if a function, then it will be called,
#' otherwise printed using `cat`.
#' @param omitted_footer Footer that is only printed if anything
#' is omitted from the printout. If a function, then it will be called,
#' otherwise printed using `cat`.
#' @param ... Extra arguments to pass to `print()`.
#' @return `x`, invisibly.
#'
#' @export
head_print <- function(x, max_lines = 20, header = "", footer = "",
omitted_footer = "", ...) {
if (is_printer_callback(x)) {
head_print_callback(x, max_lines, header, footer, omitted_footer, ...)
} else {
head_print_object(x, max_lines, header, footer, omitted_footer, ...)
}
invisible(x)
}
head_print_object <- function(x, max_lines, header, footer, omitted_footer,
print_fun = print, ...) {
print_header(header)
cout <- capture.output(print_fun(x, ...))
cout_no <- min(length(cout), max_lines)
cat(cout[seq_len(cout_no)], sep = "\n")
print_footer(footer)
if (cout_no < length(cout)) print_footer(omitted_footer)
invisible(c(lines = length(cout), printed = cout_no))
}
#' @importFrom utils tail
head_print_callback <- function(x, max_lines, header, footer,
omitted_footer, ...) {
## Header
print_header(header)
len <- x("length")
minw <- x("min_width")
ow <- getOption("width", 80)
## Max number of items we can print. This is an upper bound.
can_max <- min(floor(ow / minw) * max_lines, len)
if (can_max == 0) {
return()
}
## Width of item if we print up to this
cm <- x("width", no = can_max)
## How many rows we need if we print up to a certain point
no_rows <- ceiling(cm * seq_along(cm) / (ow - 4))
## So how many items should we print?
no <- tail(which(no_rows <= max_lines), 1)
if (is.null(no) || length(no) < 1 || is.na(no)) no <- can_max
cat_pern <- function(..., sep = "\n") cat(..., sep = sep)
## Format them, and print
out_lines <- head_print_object(
x("print", no = no, ...),
print_fun = cat_pern, max_lines = max_lines,
header = "", footer = "", omitted_footer = ""
)
done_stat <- c(
tried_items = no, tried_lines = out_lines[["lines"]],
printed_lines = out_lines[["printed"]]
)
if (done_stat["tried_items"] < len ||
done_stat["printed_lines"] < done_stat["tried_lines"]) {
print_footer(omitted_footer)
}
x("done", done_stat)
## Footer
print_footer(footer)
}
#' Indent a printout
#'
#' @param ... Passed to the printing function.
#' @param .indent Character scalar, indent the printout with this.
#' @param .printer The printing function, defaults to [print].
#' @return The first element in `...`, invisibly.
#'
#' @export
indent_print <- function(..., .indent = " ", .printer = print) {
if (length(.indent) != 1) stop(".indent must be a scalar")
opt <- options(width = getOption("width") - nchar(.indent))
on.exit(options(opt), add = TRUE)
cout <- capture.output(.printer(...))
if (length(cout)) {
cout <- paste0(.indent, cout)
cat(cout, sep = "\n")
}
invisible(list(...)[[1]])
}
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