# Only used for test/testthat
# https://github.com/n-s-f/mockery/blob/master/R/stub.R
# COPYRIGHT HOLDER: Noam Finkelstein, Lukasz Bartnik

#' Replace a function with a stub.
#'
#' The result of calling \code{stub} is that, when \code{where}
#' is invoked and when it internally makes a call to \code{what},
#' \code{how} is going to be called instead.
#'
#' This is much more limited in scope in comparison to
#' \code{\link[testthat]{with_mock}} which effectively replaces
#' \code{what} everywhere. In other words, when using \code{with_mock}
#' and regardless of the number of intermediate calls, \code{how} is
#' always called instead of \code{what}. However, using this API,
#' the replacement takes place only for a single function \code{where}
#' and only for calls originating in that function.
#'
#'
#' @name stub
#' @rdname stub
NULL

# \code{remote_stub} reverses the effect of \code{stub}.


#' @param where Function to be called that will in turn call
#'        \code{what}.
#' @param what Name of the function you want to stub out (a
#'        \code{character} string).
#' @param how Replacement function (also a \code{mock} function)
#'        or a return value for which a function will be created
#'        automatically.
#'
#' @export
#' @rdname stub
#'
#' @examples
#' f <- function () TRUE
#' g <- function () f ()
#' stub (g, "f", FALSE)
#'
#' # now g() returns FALSE because f() has been stubbed out
#' g ()
#'
`stub` <- function (where, what, how) {

    # `where` needs to be a function
    where_name <- deparse (substitute (where))
    stopifnot (is.function (where))

    # `what` needs to be a character value
    stopifnot (is.character (what), length (what) == 1)

    # this is where a stub is going to be assigned in
    env <- new.env (parent = environment (where))

    if (grepl ("::", what)) {
        elements <- strsplit (what, "::")
        what <- paste (elements [[1]] [1], elements [[1]] [2], sep = "XXX")

        stub_list <- c (what)
        if ("stub_list" %in% names (attributes (get ("::", env)))) {
            stub_list <- c (
                stub_list,
                attributes (get ("::", env)) [["stub_list"]]
            )
        }

        create_new_name <- create_create_new_name_function (stub_list, env)
        assign ("::", create_new_name, env)
    }

    if (!is.function (how)) {
        assign (what, function (...) how, env)
    } else {
        assign (what, how, env)
    }

    environment (where) <- env
    assign (where_name, where, parent.frame ())
}


create_create_new_name_function <- function (stub_list, env) { # nolint

    create_new_name <- function (pkg, func) {

        pkg_name <- deparse (substitute (pkg))
        func_name <- deparse (substitute (func))
        for (stub in stub_list) {
            if (paste (pkg_name, func_name, sep = "XXX") == stub) {
                return (eval (parse (text = stub), env))
            }
        }
        return (eval (parse (text = paste (pkg_name, func_name, sep = "::"))))
    }
    attributes (create_new_name) <- list (stub_list = stub_list)
    return (create_new_name)
}