some r code i made to dredge up older git versions of a file into a tibble

file-history.R

#' @param path current path of format
#' @param date_format date format to request from git. This format is given to
#'   git to set the format of the dates it returns and then given to readr to
#'   tell it how to parse the dates into date-times.
#' @param f_split optional function to help reduce `system()` calls. By default
#'   (`NULL`), one `system()` call is made for each version of the file.
#'   Alternatively, we can ask git to give the contents of the all files at once
#'   with one `system()` call. Then `f_split()` creates a list of file contents.
#' @return a tibble with one row commit with commit, commit date, historical
#'   file path, and historical file contents for the desired file.
get_file_history <- function(path, date_format = "%Y%m%d%H%M", f_split = NULL) {
  if (!file.exists(path)) cli::cli_abort("{.path {path}} does not exist")

  # Gameplan: Get lines with format:
  #
  # {commit1} {commit_msg1}
  # {path_at_commit1}
  # {commit2} {commit_msg2}
  # {path_at_commit2}
  # ...
  #
  # Parse this output to create further commands that retrieve file contents.

  results <- glue::glue("git log --oneline --name-only --follow -- {path}") |>
    system(intern = TRUE)

  data <- tibble::tibble(
    path_current = path,
    commit = results |>
      vec_odds() |>
      stringr::str_split_i(" ", 1),
    commit_date = get_commit_date(commit, date_format),
    commit_msg = results |>
      vec_odds() |>
      stringr::str_split_fixed(" ", 2) |>
      _[, 2],
    path_at_commit = vec_evens(results),
    contents = get_historical_file_content(commit, path_at_commit, f_split)
  )

  data
}

get_commit_date <- function(commit, date_format = "%Y%m%d%H%M") {
  xs <- paste0(commit, collapse = " ")
  glue::glue("git show -s --date=format:{date_format} --format=%cd {xs}") |>
    system(intern = TRUE) |>
    readr::parse_datetime(format = date_format)
}

# Avoid multiple system() calls by using a split function
get_historical_file_content <- function(commit, path_at_commit, f_split = NULL) {
  xs <- paste0(commit, ":", path_at_commit, collapse = " ")

  if (is.null(f_split)) {
    l <- glue::glue("git show {commit}:{path_at_commit}") |>
      lapply(system, intern = TRUE)
  } else {
    l <- glue::glue("git show {xs}") |>
      system(intern = TRUE) |>
      f_split()
  }
  stats::setNames(l, xs)
}

vec_odds  <- function(xs) xs[seq(1, length(xs), by = 2)]
vec_evens <- function(xs) xs[seq(2, length(xs), by = 2)]