#' Write into or over a file
#'
#' Helpers to write into or over a new or pre-existing file. Designed mostly for
#' for internal use. File is written with UTF-8 encoding.
#'
#' @name write-this
#' @param path Path to target file. It is created if it does not exist, but the
#'   parent directory must exist.
#' @param lines Character vector of lines. For `write_union()`, these are lines
#'   to add to the target file, if not already present. For `write_over()`,
#'   these are the exact lines desired in the target file.
#' @param quiet Logical. Whether to message about what is happening.
#' @return Logical indicating whether a write occurred, invisibly.
#' @keywords internal
#'
#' @examples
#' \dontshow{
#' .old_wd <- setwd(tempdir())
#' }
#' write_union("a_file", letters[1:3])
#' readLines("a_file")
#' write_union("a_file", letters[1:5])
#' readLines("a_file")
#'
#' write_over("another_file", letters[1:3])
#' readLines("another_file")
#' write_over("another_file", letters[1:3])
#' \dontrun{
#' ## will error if user isn't present to approve the overwrite
#' write_over("another_file", letters[3:1])
#' }
#'
#' ## clean up
#' file.remove("a_file", "another_file")
#' \dontshow{
#' setwd(.old_wd)
#' }
NULL

#' @describeIn write-this writes lines to a file, taking the union of what's
#'   already there, if anything, and some new lines. Note, there is no explicit
#'   promise about the line order. Designed to modify simple config files like
#'   `.Rbuildignore` and `.gitignore`.
#' @export
write_union <- function(path, lines, quiet = FALSE) {
  stopifnot(is.character(lines))
  path <- user_path_prep(path)

  if (file_exists(path)) {
    existing_lines <- read_utf8(path)
  } else {
    existing_lines <- character()
  }

  new <- setdiff(lines, existing_lines)
  if (length(new) == 0) {
    return(invisible(FALSE))
  }

  if (!quiet) {
    ui_done("Adding {ui_value(new)} to {ui_path(proj_rel_path(path))}")
  }

  all <- c(existing_lines, new)
  write_utf8(path, all)
}

#' @describeIn write-this writes a file with specific lines, creating it if
#'   necessary or overwriting existing, if proposed contents are not identical
#'   and user is available to give permission.
#' @param contents Character vector of lines.
#' @export
write_over <- function(path, lines, quiet = FALSE) {
  stopifnot(is.character(lines), length(lines) > 0)
  path <- user_path_prep(path)

  if (same_contents(path, lines)) {
    return(invisible(FALSE))
  }

  if (can_overwrite(path)) {
    if (!quiet) {
      ui_done("Writing {ui_path(path)}")
    }
    write_utf8(path, lines)
  } else {
    if (!quiet) {
      ui_done("Leaving {ui_path(path)} unchanged")
    }
    invisible(FALSE)
  }
}

read_utf8 <- function(path, n = -1L) {
  base::readLines(path, n = n, encoding = "UTF-8", warn = FALSE)
}

write_utf8 <- function(path, lines, append = FALSE, line_ending = NULL) {
  stopifnot(is.character(path))
  stopifnot(is.character(lines))

  file_mode <- if (append) "ab" else "wb"
  con <- file(path, open = file_mode, encoding = "utf-8")
  withr::defer(close(con))

  if (is.null(line_ending)) {
    if (is_in_proj(path)) {              # path is in active project
      line_ending <- proj_line_ending()
    } else if (possibly_in_proj(path)) { # path is some other project
      line_ending <-
        with_project(proj_find(path), proj_line_ending(), quiet = TRUE)
    } else {
      line_ending <- platform_line_ending()
    }
  }

  # convert embedded newlines
  lines <- gsub("\r?\n", line_ending, lines)
  base::writeLines(enc2utf8(lines), con, sep = line_ending, useBytes = TRUE)

  invisible(TRUE)
}

same_contents <- function(path, contents) {
  if (!file_exists(path)) {
    return(FALSE)
  }

  identical(read_utf8(path), contents)
}