# Pure helpers for local/rebuild-missing.R, kept separate so local/tests can
# source them without executing a rebuild.

# Interleaved slice of the rebuild list.
#
# The list is alphabetical and build cost clusters by name (Rcpp*, Bioc*,
# rstan*), so contiguous thirds would be badly unbalanced. Interleaving also
# makes each shard's progress counter representative of the slot as a whole.
shard_slice <- function(pkgs, split_into, split_index) {
  split_into <- as.integer(split_into)
  split_index <- as.integer(split_index)
  if (is.na(split_into) || is.na(split_index)) {
    stop("shard_slice(): split_into and split_index must be integers")
  }
  if (split_into < 1L || split_index < 1L || split_index > split_into) {
    stop(sprintf(
      "shard_slice(): need 1 <= split_index <= split_into, got %s of %s",
      split_index,
      split_into
    ))
  }
  # seq() errors on a descending range, which is what an empty list or a shard
  # index past the end would produce.
  if (length(pkgs) < split_index) {
    return(pkgs[0L])
  }
  pkgs[seq.int(split_index, length(pkgs), by = split_into)]
}

# Packages that still need building, decided from the bucket rather than from
# remembered progress.
#
# This is bincraft's `check_s3_root_package()` evaluated in bulk: an object
# whose ETag equals CRAN's published MD5sum is byte-identical to CRAN's source,
# so the build that was supposed to replace it has not happened yet.
#
# `etag_by_file`  named by `<pkg>_<ver>.tar.gz`, values are unquoted ETags
# `cran_version`  named by package
# `cran_md5`      named by `<pkg>_<ver>`
#
# Unknown always means "already a binary", never "rebuild it", so an unreadable
# CRAN index or a multipart ETag can never mass-schedule work.
outstanding_packages <- function(pkgs, etag_by_file, cran_version, cran_md5) {
  if (length(pkgs) == 0L) {
    return(pkgs)
  }

  # An empty table indexes to zero length rather than to NA, which would
  # recycle the whole result away and silently report "nothing to build".
  lookup <- function(table, key) {
    if (length(table) == 0L) {
      return(rep(NA_character_, length(key)))
    }
    unname(as.character(table[key]))
  }

  version <- lookup(cran_version, pkgs)
  file <- sprintf("%s_%s.tar.gz", pkgs, version)
  etag <- lookup(etag_by_file, file)
  md5 <- lookup(cran_md5, paste(pkgs, version, sep = "_"))

  # No CRAN version means the package cannot be resolved to a tarball at all;
  # leave it in and let bincraft report why.
  unresolved <- is.na(version)
  # No object at the key: never built, so it is outstanding by definition.
  absent <- !unresolved & is.na(etag)
  # A multipart upload carries a compound ETag rather than an MD5.
  unknown <- !is.na(etag) & grepl("-", etag, fixed = TRUE)

  is_source <- !unresolved &
    !is.na(etag) &
    !unknown &
    !is.na(md5) &
    etag == md5

  pkgs[unresolved | absent | is_source]
}

parse_rebuild_args <- function(args) {
  pos <- args[!startsWith(args, "--")]
  budget <- as.numeric(pos[3L])
  list(
    split_into = as.integer(pos[1L]),
    split_index = as.integer(pos[2L]),
    budget_hours = if (is.na(budget)) 20 else budget
  )
}