R/read_pgn.R

In D-Se/xiangqi: Chinese Chess Utilities

#' load a PGN file.
#'
#' @param path filepath.
#' @param keep boolean. Should metadata be kept?
#' @description
#' A convenience function exists to read in multiple files, see `read_bulk_pgn()`.
#' No checking of formatting is performed so as to support multiple writing styles.
#'
#' @section PGN formats
#' No checking of formatting is performed so as to support multiple writing styles.
#' The most common writing styles are to first list metadata tags, followed by
#' a move list.
#'
#' @section Encoding
#' Encoding of files is a common source for problems in reading and writing data.
#' 1. Check if the source file is in UTF-8 or ASCII encoding.
#'
#' @export
#' @returns list of length 2, 1 element with metadata, one with moves.
### TODO: add keep utility
read_pgn <- function(path, keep = TRUE){
  ll <- vector(mode = "list", length = 2) ; names(ll) <- c("Metadata", "Moves")
  game <- readLines(path)
  # start of move list
  ind <- which(stringi::stri_detect_regex(game,
                                          pattern = "^  \\d.",
                                          max_count = 1, negate = FALSE))
  ll[[1]] <- game[1:ind-1]
  ll[[2]] <- game[ind:length(game)] %>% clean_moves()
  ll
}

#' Read a dense PGN game file that has moves of multiple games in a single file.
#'
#' @param filepath filepath to .PGN file
#'
#' @description
#' The `read_bulk_pgn()` function expects a file that is **uniform** in its formatting.
#' That is, each game contains the same metadata headers, same move_list formatting,
#' commenting style et cetera.
#'
#' @return List of length n games, split by metadata and move list.
#' TODO add parallel support ?
#' TODO arbitrary metadata length support
read_pgn_bulk <- function(path){
  game <- readLines(path)
  game <- stringi::stri_remove_empty(game)
  ll <- vector(mode = "list", length = length(game) / 14L)
  ll <- split(game, cut(seq_along(game), (length(game) / 14L), labels = FALSE))
  ll <- lapply(ll, function(x){
    ind <- which(stringi::stri_detect_regex(x,
                                            pattern = "^? \\d.",
                                            max_count = 1, negate = FALSE))
    l <- vector(mode = "list", length = 2L)
    names(l) <- c("Metadata", "Moves")
    tryCatch({ # might be some parsing errors in the metadata or move list
      l[[1]] <- x[1:(ind-1)]
      l[[2]] <- x[ind:length(x)] %>%
        clean_moves() %>%
        stringi::stri_remove_empty()
    }, error = function(e) e )
    l
  })
  ll
}