# tui/events.py

Thread-safe event bus between the bot backend thread and the Textual TUI.  
The bot thread calls `post()`. The TUI drains the queue every 100ms via `_drain_bus()`.

## Public API

```python
from tui import events as bus   # from core/ and tui/app.py
from tui.events import post, init_bus, get_bus, tui_active
```

### `init_bus() -> queue.Queue`
Creates the `queue.Queue`. Called inside `MonitorApp.on_mount()` — **must run on Textual's event loop**, not before `App.run()`.

### `post(event: Any) -> None`
Fire-and-forget from any thread. Silently drops if bus not initialised.  
Uses `queue.Queue.put_nowait()` — never blocks.

### `get_bus() -> queue.Queue | None`
Returns the queue for the TUI consumer to drain.

### `tui_active: bool`
Set to `True` by `init_bus()`. Checked by `core/tdl_downloader.py` to decide whether to pipe tdl output or inherit the terminal.

---

## Event types

| Class | Fields | Posted by | Consumed by |
|-------|--------|-----------|-------------|
| `EvDownloadQueued` | `batch_id, filename, size_mb, source, password` | `tdl_downloader`, `scraper` | `DownloadPanel.queued()` |
| `EvDownloadStarted` | `batch_id, filename` | `tdl_downloader`, `scraper` | `DownloadPanel.status("downloading")` |
| `EvDownloadDone` | `batch_id, filename, via` | `tdl_downloader`, `scraper` | `DownloadPanel.status("done_tdl"\|"done_tel")` |
| `EvDownloadFailed` | `batch_id, filename, reason` | `tdl_downloader`, `scraper` | `DownloadPanel.status("failed")` |
| `EvTdlOutput` | `line` | `tdl_downloader._relay()` | `DownloadPanel.tdl_line()` |
| `EvHit` | `severity, raw, source, filename, reasons` | `notifier.notify()` | `HitsPanel.add_hit()` + `StatsPanel.refresh_stats()` |
| `EvChannelAdded` | `channel` | `ChannelPanel.on_button_pressed()` | `_drain_bus` → `_signal_channel_changed()` |
| `EvChannelRemoved` | `channel` | `ChannelPanel.on_button_pressed()` | `_drain_bus` → `_signal_channel_changed()` |
| `EvStatus` | `text, level` | everywhere | `MonitorApp.notify()` toast |

`level` on `EvStatus`: `"info"` (default) · `"warning"` · `"error"`

---

## Threading model

```
Bot thread (own asyncio loop)
  └─ bus.post(event)          ← queue.Queue.put_nowait() [thread-safe]
        ↓
  queue.Queue
        ↓
Textual thread (Textual's loop)
  └─ _drain_bus() [set_interval 100ms]
       └─ q.get_nowait() loop
            └─ dispatch to widgets [safe, same thread as Textual]
```

Channel changes flow the other way:
```
_drain_bus sees EvChannelAdded/Removed
  → _signal_channel_changed()
       → loop.call_soon_threadsafe(asyncio.Event.set)
            → bot thread's _watch_channels() wakes
```