"""VolumeMeter — a single-channel volume control styled as a segmented meter
bar (a Gtk.Scale dressed up via CSS, see .sb-meter in style/style.css) rather
than a bare slider, since the user asked for "an audio meter" per channel.

Two guards keep it usable against a live, event-driven backend:
  - commits are debounced (COMMIT_DEBOUNCE_MS) so dragging doesn't spawn a
    `pactl set-*-volume` per pixel of motion:
  - `set_value_quiet()` (called when a `pactl subscribe` refresh reports the
    authoritative value) is a no-op while the user has the handle pressed, so
    an in-flight drag never gets yanked back by its own not-yet-applied change.
"""

from __future__ import annotations

from typing import Callable

import gi

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

COMMIT_DEBOUNCE_MS = 80


class VolumeMeter(Gtk.Box):
    def __init__(self, label: str, value: int, on_change: Callable[[int], None],
                 muted: bool = False) -> None:
        super().__init__(orientation=Gtk.Orientation.HORIZONTAL, spacing=6)
        self.add_css_class("sb-meter-row")
        self._on_change = on_change
        self._dragging = False
        self._commit_id: int | None = None
        self._pending: int | None = None

        if label:
            tag = Gtk.Label(label=label)
            tag.add_css_class("sb-meter-label")
            self.append(tag)

        self.scale = Gtk.Scale.new_with_range(Gtk.Orientation.HORIZONTAL, 0, 150, 1)
        self.scale.set_value(value)
        self.scale.set_draw_value(True)
        self.scale.set_value_pos(Gtk.PositionType.RIGHT)
        self.scale.set_hexpand(True)
        self.scale.set_size_request(120, -1)
        self.scale.add_css_class("sb-meter")
        self.scale.add_mark(100, Gtk.PositionType.BOTTOM, None)
        self.scale.connect("value-changed", self._on_value_changed)
        self.set_muted(muted)

        click = Gtk.GestureClick()
        click.set_propagation_phase(Gtk.PropagationPhase.CAPTURE)
        click.connect("pressed", lambda *_a: setattr(self, "_dragging", True))
        click.connect("released", lambda *_a: setattr(self, "_dragging", False))
        self.scale.add_controller(click)

        self.append(self.scale)

    def _on_value_changed(self, _scale) -> None:
        self._pending = int(self.scale.get_value())
        if self._commit_id is not None:
            GLib.source_remove(self._commit_id)
        self._commit_id = GLib.timeout_add(COMMIT_DEBOUNCE_MS, self._commit)

    def _commit(self) -> bool:
        self._commit_id = None
        if self._pending is not None:
            self._on_change(self._pending)
        return False

    def set_value_quiet(self, value: int) -> None:
        """Reflect a backend-reported value without re-triggering on_change."""
        if self._dragging or self._commit_id is not None:
            return   # user (or our own not-yet-applied commit) owns the value right now
        if int(self.scale.get_value()) != value:
            self.scale.handler_block_by_func(self._on_value_changed)
            self.scale.set_value(value)
            self.scale.handler_unblock_by_func(self._on_value_changed)

    def set_muted(self, muted: bool) -> None:
        if muted:
            self.scale.add_css_class("sb-meter-muted")
        else:
            self.scale.remove_css_class("sb-meter-muted")