iTerm 2 - script to change theme depending on Mac OS dark mode

README.md

My fork of https://gist.github.com/jamesmacfie/2061023e5365e8b6bfbbc20792ac90f8 , adapted to also switch Emacs.

How to use

Copy the Python script to the following location:

$HOME/Library/Application Support/iTerm2/Scripts/AutoLaunch/

Create the directory if it doesn't exist. Reboot iTerm2, and say "Yes" if it asks you to download a Python runtime.

Emacs

This will automatically update Emacs themes, as well, through emacsclient. Make sure you have Emacs running as a server in your init.el ((server-start)).

If Emacs isn't running, this script will skip it silently, no problem. But the emacsclient binary must exist.

For context, here's what I use for my init.el:

;; Start emacs in server mode, unless there already is one
(when (and (require 'server nil :noerror)
           (not (server-running-p)))
  (server-start))

(defun hly/disable-themes ()
  (mapc 'disable-theme custom-enabled-themes))

(defun hly/light-mode ()
  (interactive)
  ;; I like the default theme.
  (hly/disable-themes))

(defun hly/dark-mode ()
  (interactive)
  (hly/disable-themes)
  (load-theme 'tango-dark))

Changing what themes this uses

Note the constants at the top of the file. These are iTerm2 colour profiles, and Emacs functions (which you must define in your Emacs config) to actually switch the theme.

auto_dark_mode.py

#!/usr/bin/env python3

# Originally from:
# https://gist.github.com/jamesmacfie/2061023e5365e8b6bfbbc20792ac90f8

import asyncio
import iterm2

EMACSCLIENT_BINARY = '/Applications/Emacs.app/Contents/MacOS/bin/emacsclient'
EMACS_DARK_THEME = 'hly/dark-mode'
EMACS_LIGHT_THEME = 'hly/light-mode'
ITERM_DARK_THEME = "Dark Background"
ITERM_LIGHT_THEME = "Tango Light"

def is_dark(theme: str) -> bool:
    # Themes have space-delimited attributes, one of which will be light or dark.
    return "dark" in theme.split(" ")

async def sync_to_theme_iterm(connection, dark_mode: bool):
    itheme = ITERM_DARK_THEME if dark_mode else ITERM_LIGHT_THEME
    preset = await iterm2.ColorPreset.async_get(connection, itheme)

    # Update the list of all profiles and iterate over them.
    profiles=await iterm2.PartialProfile.async_query(connection)
    for partial in profiles:
        # Fetch the full profile and then set the color preset in it.
        profile = await partial.async_get_full_profile()
        await profile.async_set_color_preset(preset)

async def sync_to_theme_emacs(dark_mode: bool):
    etheme = EMACS_DARK_THEME if dark_mode else EMACS_LIGHT_THEME
    proc = await asyncio.create_subprocess_exec(
        EMACSCLIENT_BINARY,
        '--eval', f'({etheme})',
        '--quiet',
        '--no-wait',
        '--suppress-output',
        '-a', 'true')
    await proc.communicate()
    # Ignore return code

async def sync_to_theme(connection, theme: str):
    dark_mode = is_dark(theme)
    await asyncio.gather(
        sync_to_theme_iterm(connection, dark_mode),
        sync_to_theme_emacs(dark_mode))

async def main(connection):
    app = await iterm2.async_get_app(connection)
    initial_theme = await app.async_get_theme()
    await sync_to_theme(connection, initial_theme[0])

    async with iterm2.VariableMonitor(connection, iterm2.VariableScopes.APP, "effectiveTheme", None) as mon:
        while True:
            # Block until theme changes
            await sync_to_theme(connection, await mon.async_get())

iterm2.run_forever(main)

I appreciate the iTerm script refactoring in this! 👌🙏