---
title: "Making Banner Comments for R Scripts"
author: "Bill Venables"
date: "`r Sys.Date()`"
output:
  pdf_document:
    includes:
      in_header: header.tex
    toc: yes
    toc_depth: 3
vignette: >
  %\VignetteIndexEntry{Making Banner Comments for R Scripts}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include=FALSE}
knitr::opts_chunk$set(comment = "", echo = FALSE)
library(bannerCommenter)
```

## Rationale

This tiny package is for the convenience of `R` script authors 
who wish to document their code with the occasional block of clearly 
marked comment lines in order to make the code more easily navigable
by others, or even by the same author at some later date.

A common practice is to use comment lines enclosed in some kind of
band, or box of display characters.  We call such a block of comments
a __banner comment__, and by using them sparingly and judiciously code
can be made much easier to navigate visually and hence to maintain.

Examples might include blocks such as the following to initiate a
major code section:

```{r}
section("Section 1", "Data input and initialization")
```
Subsections might be flagged by less prominent comments such as
one like this
```{r}
boxup("Primary data input", bandChar = "-", center = TRUE)
```
or a more minor one like
```{r}
open_box("Some minor glitches in the data\nneed special treatment here", 
      bandChar = ".", snug = TRUE)
```

Banner comments look much better if there is a consistent formatting
throughout the script so that sections and sub-sections can be readily
identified.  This is quite easy to do, but to do it properly can take
some editing and drafting time.

The simple tool we offer here aims to make the formatting tasks
essentially no more work than typing the text itself.  It presumes
that while the R script is being drafted there will be a console
window open as well, but this is almost _de rigeur_ these days.

## How to use it

The package `bannerCommenter` provides a single main function,
`banner`, along with a few helpers.

To make a banner such as the first one above you could simply type the
text into the console window via a call to the main function:

```{r, echo = TRUE}
library(bannerCommenter)
banner("Section 1:", "Data input and initialization", emph = TRUE)
```

This provides a formatted comment that can be copy-and-pasted into the
script.  However, if the operating system allows it, as well as
displaying the comment in the console window the result is _also
copied onto a_ `clipboard` _file or pipe_, so the "copy" part of the
copy-and-paste should not be required.

Two other conveniences are also provided.

1. Since this is likely to be a common form of banner comment, a
   simple front-end function `section()` is provided which simply
   called `banner(..., emph = TRUE)`, that is with the `emph` argument
   having a different default value.

2. Rather than typing strings with quote delimiters separated by
   commas, if the function is called with no string arguments, 
   the strings are read from the console, line by line, with prompts 
   issued as with the `scan` function.  An empty line indicates 
   the text input complete.
   
The process is particularly simple when working in `RStudio`.  The
script will be composed in the `Source` pane.  When a banner comment
is desired, the process is:

* Place the cursor at the beginning of the line where you want the comment
  to appear.

* Press `Ctrl-1` to move the focus to the console pane.

* Type `banner()` or one of the alternatives.

* Enter the text of your comment, one line per line, terminated by a blank line.

* Press `Ctrl-2` to shift the focus back to the `Source` pane, followed by
  either `Ctrl-v` or `Ctrl-y` (both seem to work!) to transfer the complete
  comment to the script.
  
* If for some reason you make a slip and lose the clipboard contents, the
  full comment remains available in the console window for copy-and-paste.
  

An example, again with the same banner comment, is as follows

```
> section()
1: Section 1
2: Data input and initialization
3: 

###########################################################################
###########################################################################
###                                                                     ###
###                              SECTION 1                              ###
###                    DATA INPUT AND INITIALIZATION                    ###
###                                                                     ###
###########################################################################
###########################################################################

> 
```
At this point the user should be able to paste the banner comment into the script in the
usual way.  If the automatic clipboard facility is not available the band displayed in
the console window, essentially for checking, can easily be used for manual copy-and-paste.

In a series of similar comment banners the function would normally be invoked by
command line recall making only the typing of the text itself necessary.

## Arguments

At first sight `banner` seems to have a bewildering number of arguments, but most have sensible
defaults and there are four front-end functions like `section` that handle simple 
special cases where the default values are slightly different.

The full list of arguments to `banner` and their default values are listed in the 
table below.  Note that some argument defaults refer to the values of other arguments.


```{r, results = "asis"}
txt <- structure(c("`x, ...`", "",
                   "`emph`", 
                   "`snug`", 
                   "`upper`", 
                   "`centre`", 
                   "`leftSideHashes`", 
                   "`rightSideHashes`",
                   "`minHashes`", 
                   "`numLines`", 
                   "`bandChar`", 
                   "`center`", 
                   "`fold`",
                   "`maxChar`",
                   "One or more strings, which may be missing.", 
                   "(Single strings may be further broken by '`\\n`'.)",
                   "Do you want emphasis, i.e. a bigger, bolder banner?", 
                   "Do you want any box to be close fitting?", 
                   "Do you want the text to be in upper case?", 
                   "Do you want the text lines to be centred?", 
                   "How many hash characters to the left?", 
                   "How many hash characters to the right", 
                   "How long do you want the bands (at least)?", 
                   "How many lines above and below do you want?", 
                   "What character do you want to use for the bands?", 
                   "Alternative (foreign) spelling of '`centre`'", 
                   "Do you want `banner` to find suitable line breaks?",
                   "Maximum number of characters in any one line, (if `fold`).",
                   "`<none>`", "",
                   "`FALSE`", 
                   "`FALSE`", 
                   "`emph`", 
                   "`!fold`", 
                   "`2 + emph`", 
                   "`leftSideHashes`", 
                   "`(!snug) * (65 + 10 * emph)`", 
                   "`1 + emph`", 
                   "`\"#\"`", 
                   "`centre`",
                   "`FALSE`",
                   "75"), 
                 .Dim = c(14L, 3L), 
                 .Dimnames = list(NULL, c("Argument", "Meaning", "Default")))
knitr::kable(txt)
```

## Examples

As well as `section` there are three other front-end functions that
simply act as a call to `banner` with different default values for
some of the arguments.  Rather than describe them in detail it
suffices simply to provide a few example, beginning with the primary
function itself.

```{r, echo = TRUE}
txt <- "This is the text of a comment"

banner(txt)  ## default heavy style

banner(txt, centre = TRUE, bandChar = "-")

boxup(txt, snug = TRUE, bandChar = "=")

open_box(txt, bandChar = ":")

block(paste("This is a chatty comment.  Entering it this way just",
            "saves a tiny bit of typing but it can be useful if",
            "you need multiple initial hash marks, as you may when",
            "using editors in RStudio or Emacs/ESS, for example.",
            "Or if you want the lines folded to make things more compact.",
            collapse = " "),
      fold = TRUE)

boxup("")  ## short lines of uniform length, for use as a separator

section("")  ## heavier, longer double lines to separate bigger things
```

## Notes

### The number of leading hash characters

In some editing systems, where a comment has only white space before it on a 
single line, the number of leading comment characters is significant.  It affects
how the line is changed under automatic reformatting.  For example, `Emacs/ESS` 
adopts this convention by default:

* A line with a single leading comment character, only, is aligned so that it begins
  near the middle of the line.  (I have no explanation as to why!)

* A line with two leading comment characters, only, is aligned as if it were an
  active code line.  This is often useful.
  
* A line with three or more leading comment characters is aligned so that it
  begins in the first column and so occupies the whole line.

Some commentators recommend using a single leading comment character for all comments,
and `RStudio`, for example, facilitates this choice.  However if the same code is handled
by `Emacs/Ess` the comments are liable to be right shifted to start in the middle of the
line (unless the default is changed, of course, which is not initially very clear).

This may be useful to keep in mind when two or more systems may be used to maintain
the same `R` scripts.

### Sending text strings to the clipboard

A helper function used in this package may be useful in its own right.
The function `copy_to_clipboard` allows text strings to be copied to a
clipboard file (or pipe) in a reasonably cross platform way, at least
for `Linux`, `Windows` and `Mac OS`.

A call such as
```{r, eval = FALSE, echo = TRUE}
copy_to_clipboard(txt)
```
will return `txt` invisibly, but will have the side effect of
transferring any strings in the `txt` object to a clipboard device.
In effect it behaves like a `print` method, but with the "printing"
going on to a clipboard device rather than on to `stdout`.

To work on `Linux` the system command `xclip` has to be installed and
visible on the `PATH` and on `Mac OS` the system command `pbcopy` has
similarly to be installed and visible.  On `Windows` it should work
universally.

Note that this is _not_ a file or pipe connection in itself, but a
_function_ which transfers strings to an appropriate clipboard
device. Thus, for example, to write a short data frame onto a
clipboard device in a way that works across the three platforms, you
may need to do something like the following:

```{r, eval=FALSE, echo = TRUE, message = FALSE}
library(dplyr)
mtcarsText <- datasets::mtcars   %>% 
  capture.output(write.table(.)) %>% 
  copy_to_clipboard(sep = "\n")
```
At this point `mrcarsText` is a character string vector with the lines
of `datasets::mtcars` as its elements, and the information would be
available on the clipboard for a paste operation.

### Gratuitous advice

Use sparingly and judiciously.  Most comments will simply be done by
typing the `#` character and proceeding.  They will usually _not_
require fancy banners.  A potential danger of providing this simple
facility is that some authors may be tempted to overdo their script
decoration.  Comments are important, but _excessive_ fancy comments will
detract from the aesthetics and waste a lot of otherwise productive
coding time.

People who find the package useful but would like to suggest other
tweaks or front-ends are welcome to contact the author at the email
address given in the package itself.

.
