"""TabSwitcher — a row of mutually-exclusive toggle buttons driving a
Gtk.Stack, styled as a segmented control (see .sb-tabbar/.sb-tab in
style/style.css). Plain manual mutual exclusion rather than Gtk.CheckButton
grouping, since that's simplest for a small fixed set of tabs."""

from __future__ import annotations

from typing import Callable

import gi

gi.require_version("Gtk", "4.0")
from gi.repository import Gtk  # noqa: E402


class TabSwitcher(Gtk.Box):
    def __init__(self, tabs: list[tuple[str, str, Gtk.Widget]], stack: Gtk.Stack,
                 on_changed: Callable[[str], None]) -> None:
        super().__init__(orientation=Gtk.Orientation.HORIZONTAL, spacing=4)
        self.add_css_class("sb-tabbar")
        self._stack = stack
        self._on_changed = on_changed
        self._buttons: dict[str, Gtk.ToggleButton] = {}

        first = None
        for name, label, _widget in tabs:
            btn = Gtk.ToggleButton(label=label)
            btn.add_css_class("sb-tab")
            btn.connect("toggled", self._make_handler(name))
            self.append(btn)
            self._buttons[name] = btn
            if first is None:
                first = name
        if first is not None:
            self._buttons[first].set_active(True)

    def _make_handler(self, name: str):
        def handler(btn: Gtk.ToggleButton) -> None:
            if not btn.get_active():
                if not any(b.get_active() for b in self._buttons.values()):
                    btn.set_active(True)   # one tab must always stay selected
                return
            for other_name, other_btn in self._buttons.items():
                if other_name != name and other_btn.get_active():
                    other_btn.set_active(False)
            self._stack.set_visible_child_name(name)
            self._on_changed(name)
        return handler