#' String matching engines from stringr
#'
#' @details CoRC makes use of the string matching engines from the \pkg{stringr} package.
#' 
#' The functions are described at \link[stringr]{modifiers}.
#' By default, matching is done with \code{coll}.
#' 
#' @name regex
NULL

#' @export
#' @rdname regex
stringr::fixed

#' @export
#' @rdname regex
stringr::coll

#' @export
#' @rdname regex
stringr::regex

# checks if a stringr engine is applied
# this function depends on the version of the stringr package. If an old version is detected, this is overwritten in .onLoad
has_engine <- function(x) inherits(x, c("stringr_fixed", "stringr_coll", "stringr_regex"))

# apply an engine for a character vector
# do nothing if engine is already applied
apply_engine <- function(x, engine = coll) {
  if (!has_engine(x))
    x <- engine(x)
  x
}

# Subsetting vectors with engine attribute (x[1]) usually clears all attributes
# This method prevents that
subset_engine <- function(x, i) {
  attrs <- attributes(x)
  x <- x[i]
  attributes(x) <- attrs
  x
}