exp-feat: allow theme to be inherited from terminal

When using a modern terminal emulator such as kitty or ghostty, a new
theme called `terminal-derived-theme` can be selected. This theme will
infer the appropriate theme from the terminal palette colors. When an
unsupported terminal emulator is used, a notification will be raised and
the default selected.

This feature is EXPERIMENTAL. But it seems to be working nicely with
`ghostty` and `kitty`. Though in `kitty` there seems to be some
flickering.

Author: kainctl

demo.tape

@@ -82,7 +82,7 @@ Type@10ms "systemctl start --user '0-isd-example-unit-01.service' '0-isd-example
 # do not full refresh during recording -> Set it to a very large value
 # normal refresh should use the default value!
 # `my_asciinema` is simply `asciinema_3` wrapped in a bash script, where a custom `config.toml` is utilized.
-Type@10ms "ISD_CACHE_INPUT=false ISD_STARTUP_MODE=user ISD_JOURNAL_PAGER=lnav ISD_DEFAULT_PAGER=moar ISD_FULL_REFRESH_INTERVAL_SEC=1000 my_asciinema rec --overwrite --quiet --command isd ./docs/assets/images/isd.cast"
+Type@10ms "XDG_CACHE_HOME=$(mktemp -d) XDG_CONFIG_HOME=$(mktemp -d) ISD_STARTUP_MODE=user ISD_JOURNAL_PAGER=lnav ISD_DEFAULT_PAGER=moar ISD_FULL_REFRESH_INTERVAL_SEC=1000 my_asciinema rec --overwrite --quiet --command isd ./docs/assets/images/isd.cast"
 Enter
 
 # # Sleep 2s

src/isd_tui/derive_terminal_theme.py

@@ -0,0 +1,127 @@
+import re
+import sys
+import tty
+import termios
+import select
+from typing import Optional
+from textual.theme import Theme
+
+# OSC Codes:
+# https://chromium.googlesource.com/apps/libapps/+/a5fb83c190aa9d74f4a9bca233dac6be2664e9e9/hterm/doc/ControlSequences.md#OSC
+
+
+def send_osc_query(seq) -> str:
+    """
+    Send an OSC query. To avoid locking up when something
+    unexpected happens, the terminal has 1 second to respond
+    and cannot write more than 1024 characters.
+    If there is any issue, an empty string is returned.
+    """
+    fd = sys.stdin.fileno()
+    old_settings = termios.tcgetattr(fd)
+    response = ""
+    try:
+        tty.setcbreak(fd)
+
+        # tty.setraw(fd)
+        sys.stdout.write(seq)
+        sys.stdout.flush()
+        timeout_s = 1
+        # I am using a timeout when reading from `stdin`
+        # to ensure that this won't block forever if the terminal
+        # behaves oddly. This may only work on `UNIX` but
+        # that should be fine for now.
+        ready, _, _ = select.select([fd], [], [], timeout_s)
+        last_char_was_esc = False
+        if ready:
+            for _ in range(1024):
+                c = sys.stdin.read(1)
+                if c == "\a" or (c == "\x5c" and last_char_was_esc):
+                    break
+
+                if c == "\x1b":
+                    last_char_was_esc = True
+                    continue
+                else:
+                    last_char_was_esc = False
+                response += c
+            else:
+                response = ""
+
+    finally:
+        termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
+    return response
+
+
+def parse_rgb(resp: str) -> Optional[str]:
+    match = re.search(r"rgb:([0-9a-fA-F]+)/([0-9a-fA-F]+)/([0-9a-fA-F]+)", resp)
+    if match:
+        # TODO: At some point figure out why ghostty return RR
+        # -> Seems to be the spec
+        rgb = "".join(m[:2] for m in match.groups())
+        return "#" + rgb
+    else:
+        return None
+
+
+def query_palette_color(index: int) -> Optional[str]:
+    """Send OSC 4 query and parse reply."""
+    seq = f"\033]4;{index};?\a"
+    response = send_osc_query(seq)
+    return parse_rgb(response)
+
+
+def query_background_color() -> Optional[str]:
+    seq = "\033]11;?\a"
+    response = send_osc_query(seq)
+    return parse_rgb(response)
+
+
+def query_foreground_color() -> Optional[str]:
+    seq = "\033]10;?\a"
+    response = send_osc_query(seq)
+    return parse_rgb(response)
+
+
+def derive_textual_theme() -> Optional[Theme]:
+    """
+    Derive a textual theme by quering the current terminal
+    via OSC escape codes.
+
+    Here, we assume that an iTerm2 color scheme (https://github.com/mbadolato/iTerm2-Color-Schemes) is used.
+    This function may return `None` if the theme could not be derived.
+    This may happen if the terminal emulator does not support the `OSC 4` query extension
+    to retrieve the current palette.
+    If this is the case, use a modern terminal emulator such as `ghostty` or `kitty`.
+
+    This function REQUIRES textual to suspend the current application!
+    """
+    fg = query_foreground_color()
+    if fg is None:
+        return None
+    bg = query_background_color()
+
+    if bg is None:
+        return None
+
+    iterm_colors = []
+    for i in range(15):
+        iterm_color = query_palette_color(i)
+        if iterm_color is None:
+            return None
+        iterm_colors.append(iterm_color)
+
+    return Theme(
+        name="terminal-derived-theme",
+        primary=iterm_colors[4],
+        secondary=iterm_colors[2],
+        accent=iterm_colors[3],
+        foreground=fg,
+        background=bg,
+        success=iterm_colors[10],
+        warning=iterm_colors[11],
+        error=iterm_colors[9],
+        surface=bg,
+        panel=iterm_colors[8],
+        boost=iterm_colors[0],
+    )

src/isd_tui/isd.py

@@ -102,6 +102,7 @@
 )
 from textual.widgets.selection_list import Selection
 from textual.widgets.option_list import Option
+from .derive_terminal_theme import derive_textual_theme
 
 
 # make type checker happy.
@@ -154,8 +155,9 @@
 AUTHENTICATION_MODE = "sudo"
 # AUTHENTICATION_MODE = "polkit"
 
-# HERE: Remove this from the global scope for testing!
-Theme = StrEnum("Theme", [key for key in BUILTIN_THEMES.keys()])  # type: ignore
+Theme = StrEnum(
+    "Theme", [key for key in BUILTIN_THEMES.keys()] + ["terminal-derived-theme"]
+)  # type: ignore
 StartupMode = StrEnum("StartupMode", ["user", "system", "auto"])
 
 SETTINGS_YAML_HEADER = dedent("""\
@@ -2840,7 +2842,21 @@ def action_show_version(self) -> None:
     def on_mount(self) -> None:
         # The theme should be loaded very early,
         # as the theme change can be quite jarring.
-        self.theme = self.settings.theme
+        t = self.settings.theme
+        if t == "terminal-derived-theme":
+            with self.app.suspend():
+                derived_theme = derive_textual_theme()
+                if derived_theme is not None:
+                    self.register_theme(derived_theme)
+                    self.theme = t
+                else:
+                    self.notify(
+                        "Could not derive theme from terminal. Use a modern terminal such as ghostty or kitty instead."
+                    )
+                    self.theme = "textual-dark"
+        else:
+            self.theme = t
+
         # Always make sure to use the latest schema
         self.update_schema()
         self.install_screen(MainScreen(self.settings), "main")