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#' Watch a directory for changes (additions, deletions & modifications).
#'
#' This is used to power the [auto_test()] and
#' [auto_test_package()] functions which are used to rerun tests
#' whenever source code changes.
#'
#' Use Ctrl + break (windows), Esc (mac gui) or Ctrl + C (command line) to
#' stop the watcher.
#'
#' @param path character vector of paths to watch. Omit trailing backslash.
#' @param pattern file pattern passed to [dir()]
#' @param callback function called everytime a change occurs. It should
#' have three parameters: added, deleted, modified, and should return
#' TRUE to keep watching, or FALSE to stop.
#' @param hash hashes are more accurate at detecting changes, but are slower
#' for large files. When FALSE, uses modification time stamps
#' @export
#' @keywords internal
watch <- function(path, callback, pattern = NULL, hash = TRUE) {
prev <- dir_state(path, pattern, hash = hash)
repeat {
Sys.sleep(1)
curr <- dir_state(path, pattern, hash = hash)
changes <- compare_state(prev, curr)
if (changes$n > 0) {
# cat("C")
keep_going <- TRUE
try(keep_going <- callback(changes$added, changes$deleted, changes$modified))
if (!isTRUE(keep_going)) return(invisible())
} else {
# cat(".")
}
prev <- curr
}
}
#' Compute a digest of a filename, returning NA if the file doesn't
#' exist.
#'
#' @param filename filename to compute digest on
#' @return a digest of the file, or NA if it doesn't exist.
#' @keywords internal
safe_digest <- function(path) {
if (!file.exists(path)) return(NA_character_)
if (is_directory(path)) return(NA_character_)
if (!is_readable(path)) return(NA_character_)
digest::digest(path, file = TRUE)
}
#' Capture the state of a directory.
#'
#' @param path path to directory
#' @param pattern regular expression with which to filter files
#' @param hash use hash (slow but accurate) or time stamp (fast but less
#' accurate)
#' @keywords internal
dir_state <- function(path, pattern = NULL, hash = TRUE) {
files <- dir(path, pattern, full.names = TRUE)
# It's possible for any of the files to be deleted between the dir()
# call above and the calls below; `file.info` handles this
# gracefully, but digest::digest doesn't -- so we wrap it. Both
# cases will return NA for files that have gone missing.
if (hash) {
file_states <- vapply(files, safe_digest, character(1))
} else {
file_states <- stats::setNames(file.info(files)$mtime, files)
}
file_states[!is.na(file_states)]
}
#' Compare two directory states.
#'
#' @param old previous state
#' @param new current state
#' @return list containing number of changes and files which have been
#' `added`, `deleted` and `modified`
#' @keywords internal
compare_state <- function(old, new) {
added <- setdiff(names(new), names(old))
deleted <- setdiff(names(old), names(new))
same <- intersect(names(old), names(new))
modified <- names(new[same])[new[same] != old[same]]
n <- length(added) + length(deleted) + length(modified)
list(n = n, added = added, deleted = deleted, modified = modified)
}
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