mkenvrc.nix

# This script lives in my home manager home.packages. I also have:
#
#   programs.direnv.enable = true;
#   programs.direnv.nix-direnv.enable = true;
#
# To enable a language, I use e.g.:
#
#    nix registry add rust-direnv ~/code/dev-templates/rust
#
# where the directory is my local fork of https://github.com/the-nix-way/dev-templates

(writeShellScriptBin "mkenvrc" ''
  set -e

  # construct a regex that matches languages supported in the nix registry
  # which is any user flake that named "<language>-direnv".
  known_langs_re="$(
    ${pkgs.nix}/bin/nix registry list |
    ${pkgs.perl}/bin/perl -nE 'push @l,$1 if /^user\s+flake:([\w-]+)-direnv/; END { say join("|", map quotemeta, @l) }' )";

  # construct a string of use flake directives to append to .envrc based on
  # the languages tokei found under the current directory all tokei language
  # names are normalized to lowercase with \W+ runs replaced with dashes
  # TODO sort by .code? tokei outputs an object, not a list, kinda annoying
  # to sort
  append="$(
    (for lang in $(
      ${pkgs.tokei}/bin/tokei -o json |
      ${pkgs.jq}/bin/jq --raw-output 'to_entries | sort_by(-.value.code) | .[] | .key | ascii_downcase' |
      ${pkgs.gnused}/bin/sed 's/\W+/-/'
    ); do
      if echo "$lang" | ${pkgs.gnugrep}/bin/egrep "$known_langs_re" >/dev/null; then
       [ -e .envrc ] && ${pkgs.gnugrep}/bin/grep "$lang" .envrc >/dev/null || echo "use flake $lang-direnv"
        # else
        # TODO echo "$lang in project but direnv support not in nix registry...";
      fi
    done)|
    ${pkgs.skim}/bin/sk --no-sort --multi --query "$*"
  )";

  # if we made it this far something was selected, we can append and enable,
  # interrupting sk or selecting nothing in sk will leave .envrc unmodified
  # due to the set -e above
  echo "$append" >> .envrc
  direnv allow
'')