alexandria/2024/nix/lib/indexByCourse.nix

{
  pkgs,
  indexByName,
  ...
}:
baseDirectory:
let
  inherit (pkgs) lib;
  inherit (lib.attrsets)
    mapAttrs
    mapAttrsToList
    mergeAttrsList
    ;
  inherit (builtins) readDir;
in
let
  # Package files for a single shard
  # Type: String -> String -> AttrsOf Path
  namesForShard =
    shard: type:
    if type != "directory" then
      # Ignore all non-directories. Technically only README.md is allowed as a file in the base directory, so we could alternatively:
      # - Assume that README.md is the only file and change the condition to `shard == "README.md"` for a minor performance improvement.
      #   This would however cause very poor error messages if there's other files.
      # - Ensure that README.md is the only file, throwing a better error message if that's not the case.
      #   However this would make for a poor code architecture, because one type of error would have to be duplicated in the validity checks and here.
      # Additionally in either of those alternatives, we would have to duplicate the hardcoding of "README.md"
      { }
    else
      mapAttrs (a: b: indexByName (baseDirectory + "/${a}")) (readDir baseDirectory);

in
# mapAttrs (a: b: builtins.trace (builtins.tryEval a) b) (
#   mergeAttrsList (mapAttrsToList namesForShard (readDir baseDirectory))
# )
mergeAttrsList (mapAttrsToList namesForShard (readDir baseDirectory))