Keeping Terminal & Vim Colors in Sync

#!/usr/bin/env bash

# modus: switch between modus light (operandi) & dark (vivendi)
# themes.

# This script makes a few assumptions:
# 1. You are using kitty as your terminal <https://sw.kovidgoyal.net/kitty/>
# 2. You have a light & dark theme for kitty stored in kitty's config
#    dir (which is $XDG_CONFIG_HOME/kitty by default)
# 3. You exclusively use the wonderful modus themes by Protesilaos
#    Stravrou for your shell <https://protesilaos.com/emacs/modus-themes>
# 4. You have some plumbing on the vim side to automatically update
#    the `background' setting using autocommands. See
#    <https://github.com/arumoy-shome/dotfiles/blob/c3b172dc05446aff20a5660f09699ffcc89e0379/vim/autoload/aru.vim#L95>
#    and
#    <https://github.com/arumoy-shome/dotfiles/blob/c3b172dc05446aff20a5660f09699ffcc89e0379/vim/plugin/autocmds.vim#L27>
#    for examples.

# Usage: modus [COLOR]
# This script is meant to be called from the command line. Without any
# arguments, modus switches between the light & dark themes. It does
# so by looking at the first line of the
# $XDG_DATA_HOME/modus/background file which should contain the word
# `light' or `dark'.
# With the optional argument COLOR---which can be `light' or
# `dark'---it switches to the specified colorscheme.

[[ ! -d "$XDG_DATA_HOME/modus" ]] && mkdir -p "$XDG_DATA_HOME/modus"
MODUS_CURRENT_BG_FILE="$XDG_DATA_HOME/modus/background"
KITTY_LIGHT_THEME="$XDG_CONFIG_HOME/kitty/light-theme.conf"
KITTY_DARK_THEME="$XDG_CONFIG_HOME/kitty/dark-theme.conf"
KITTY_CURRENT_THEME="$XDG_CONFIG_HOME/kitty/current-theme.conf"

__update_emacs() {
  # update the colorscheme in Emacs. Assumes that the modus-themes
  # package <https://github.com/protesilaos/modus-themes> is installed
  # and in the load-path. The output is redirected to /dev/null to
  # avoid printing error messages if no emacs server is running.

  if [[ "$1" == "light" ]]; then
    emacsclient --eval '(modus-themes-load-operandi)' > /dev/null
  else
    emacsclient --eval '(modus-themes-load-vivendi)' > /dev/null
  fi
}

__update_kitty() {
  # Update the colorscheme in kitty. Assumes that you are using
  # a recent version of kitty with the `themes' kitten available & the
  # colorschemes are installed.
  # Note that we use a temp file to redirect the config output. This
  # is to avoid changing the kitty.conf file (causes false positive in
  # the vcs). Your kitty.conf should contain the following line:
  #
  #     include current-theme.conf

  TMPFILE="$(mktemp)"

  if [[ "$1" == "light" ]]; then
    kitty +kitten themes --config-file-name="$TMPFILE" Modus Operandi
  else
    kitty +kitten themes --config-file-name="$TMPFILE" Modus Vivendi
  fi

  rm -f "$TMPFILE" # cleanup
}

__light() {
  # Switch to the light (operandi) theme. Some preliminary error
  # handling is done when $KITTY_LIGHT_THEME does not exist.

  if [[ ! -f $KITTY_LIGHT_THEME ]]; then
    echo "Error: $KITTY_LIGHT_THEME does not exist."
    echo "Info: Use kitty +kitten themes to save the theme first."
    return 1
  fi

  ln -sf "$KITTY_LIGHT_THEME" "$KITTY_CURRENT_THEME"
  __update_kitty light
  __update_emacs light
  echo light > "$MODUS_CURRENT_BG_FILE"
}

__dark() {
  # Switch to the dark (vivendi) theme. Some preliminary error
  # handling is done when $KITTY_DARK_THEME does not exist.

  if [[ ! -f $KITTY_DARK_THEME ]]; then
    echo "Error: $KITTY_DARK_THEME does not exist."
    echo "Info: Use kitty +kitten themes to save the theme first."
    return 1
  fi

  ln -sf "$KITTY_DARK_THEME" "$KITTY_CURRENT_THEME"
  __update_kitty dark
  __update_emacs dark
  echo dark > "$MODUS_CURRENT_BG_FILE"
}

__toggle() {
  # Toggle between light and dark themes. Some preliminary error
  # handling is done when $MODUS_CURRENT_BG_FILE does not exist or is
  # not in the expected format.

  if [[ ! -f $MODUS_CURRENT_BG_FILE ]]; then
    echo "Error: $MODUS_CURRENT_BG_FILE does not exist."
    echo "Info: set a colorscheme using modus {light,dark} first."
    return 1
  fi

  if [[ ! -r $MODUS_CURRENT_BG_FILE || ! -s $MODUS_CURRENT_BG_FILE ]]; then
    echo "Error: Something is not right with $MODUS_CURRENT_BG_FILE."
    echo "Info: Make sure that it is readable & not empty."
    return 1
  fi

  local CURRENT_BG="$(head -n 1 "$MODUS_CURRENT_BG_FILE")"
  case "$CURRENT_BG" in
    light)
      __dark
      ;;
    dark)
      __light
      ;;
    *)
      echo "Error: Something is not right with $MODUS_CURRENT_BG_FILE."
      echo "Info: Make sure it is valid & try again."
      ;;
  esac
}

main() {
  if [[ "$#" -eq 0 ]]; then
    __toggle
  else
    case "$1" in
      light)
        __light
        ;;
      dark)
        __dark
        ;;
      *)
        # Do nothing
        ;;
    esac
  fi
}

main "$@"