Get rid of stringi dependency

[petrbouchal]

unescape_unicode <- function(x) {
  # Extract all unicode escape sequences
  matches <- gregexpr("\\\\u([0-9a-fA-F]{4})", x, perl = TRUE)
  
  if (matches[[1]][1] == -1) {
    return(x)  # No matches found
  }
  
  # Get the matched strings
  matched_strings <- regmatches(x, matches)[[1]]
  
  # Convert each match to its unicode character
  replacements <- sapply(matched_strings, function(match) {
    hex_code <- sub("\\\\u", "", match)
    intToUtf8(strtoi(hex_code, 16))
  })
  
  # Replace all matches
  for (i in seq_along(matched_strings)) {
    x <- gsub(matched_strings[i], replacements[i], x, fixed = TRUE)
  }
  
  return(x)
}