#!/usr/bin/env zsh

# I don't believe the interface for Nix's utility scripts are very good. Guix's,
# on the other hand, is excellent. Management of your OS is done by a single
# program with simpler, more intuitive commands. This script is a rudimentary
# attempt at giving me that.
#
#   dots cd|check      -> nix flake check $DOTFILES
#   dots sh|show       -> nix flake show $DOTFILES
#   dots u|update      -> nix flake update --recreate-lock-file $DOTFILES
#   dots re|rebuild    -> nixos-rebuild --flake $DOTFILES#$HOSTNAME ${1:-build}
#   dots rollback      -> dots rebuild --rollback switch
#   dots vm            -> dots rebuild vm
#   dots up|upgrade    -> dots update && dots rebuild switch
#   dots gc            -> GC user profile, optimise nix store
#   sudo dots gc       -> GC, optimise nix store, & delete old boot entries
#   dots push REMOTE   -> push flake to remote (over SSH) and rebuild remotely
#   dots gen|generations -> explore, manage, diff across generations (WIP)
#
# dots (with no sub-command) can also be used as an alternative to nix-env:
#
#   dots -q
#   dots -iA nixos.htop
#   dots -e htop

set -e
REMOTE=${REMOTE:-"~/.config/dotfiles"}
DOTFILES="${0:a:h}/.."

#
function main {
  function _do { [[ $DRYRUN ]] && echo "$@" || "$@" }

  ### Helpers
  function _usage {
    echo "Usage: dots COMMAND [FLAGS...] [ARGS...]"
    echo
    echo "Available commands:"
    echo "  init               TODO"
    echo "  env (e)            TODO"
    echo "  shell (sh)         TODO"
    echo "  build (b)          TODO"
    echo "  upgrade (up)       TODO"
    echo "  rebuild (re)       TODO"
    echo "  rollback           TODO"
    echo "  gc                 TODO"
    echo "  vm                 TODO"
    echo "  repl               TODO"
    echo "  push               Push thie config to a remote NixOS system and rebuild it"
    echo "  generations (gen)  TODO"
  }

  function _rebuild {
    # Move to $DOTFILES to prevent polluting the system with result links
    pushd $DOTFILES >/dev/null
    _do sudo nixos-rebuild --flake ".#$HOSTNAME" ${@:-build}
    popd >/dev/null
  }

  function _update {
    echo "Updating NixOS flake"
    _do nix flake update --recreate-lock-file "$DOTFILES"
  }

  function _gc {
    if [[ $EUID == 0 ]]; then
      echo "Cleaning up your system..."
      _do sudo nix-collect-garbage ${@:--d}
      # nix-collect-garbage is a Nix tool, not a NixOS tool. It won't delete old
      # boot entries until you do a nixos-rebuild (which means we'll always have
      # 2 boot entries at any time). Instead, we properly delete them by
      # reloading the current environment.
      _do sudo nix-env --delete-generations old --profile /nix/var/nix/profiles/system
      _do sudo /nix/var/nix/profiles/system/bin/switch-to-configuration switch
    else
      echo "Cleaning up your user profile..."
      _do nix-collect-garbage ${@:--d}
    fi
    _do nix-store --optimise
  }

  ###
  cmd="$1"
  [[ $# > 0 ]] && shift
  case "$cmd" in
    # TODO Repl/shell for nixos+dotfiles
    # sh|shell)    _do nix-shell "$@"             ;;
    # repl)        _do nix develop "$@"           ;;

    ch|check)    _do nix flake check "$DOTFILES";;
    sh|show)     _do nix flake show "$DOTFILES" ;;

    re|rebuild)  _rebuild "${@:-switch}"        ;;
    rollback)    _rebuild --rollback switch     ;;
    vm)          _rebuild "$@" vm               ;;

    u|update)    _update "$@"                  ;;
    up|upgrade)  _update && _rebuild switch    ;;

    gc)          _gc "$@"                       ;;
    push)
      rsync -avzh ./ "$1:$REMOTE/"
      ssh -t -l "$USERNAME" "$1" "$REMOTE/dots re" "${@[2,-1]}"
      ;;

    gen|generations)
      profile=/nix/var/nix/profiles/system
      case "$1" in
        switch) >&2 echo "Targeted rollback not supported yet" ;;  # TODO Is this true?
        diff)
          to=/nix/var/nix/profiles/system-${2}-link
          diff \
            <(nix-store -q --references $profile) \
            <(nix-store -q --references $to)
          ;;
        remove)
          shift
          _do sudo nix-env --delete-generations --profile $profile $@
          ;;
        "")
          _do sudo nix-env --list-generations --profile $profile
          ;;
      esac
      ;;

    h|help|-h|--help) _usage ;;
    -*) _do nix-env "$cmd" "$@" ;;
    "") _usage ;;
    *)  echo "Couldn't find command: $cmd" 1>&2
        exit 1
        ;;
  esac
}

main "$@"