# Watching Directory Trees

Monitor an entire directory hierarchy for filesystem events.

## Overview

The Linux inotify API watches individual directories — it does not descend into subdirectories automatically. The ``Inotify/Inotify`` actor offers two convenience methods that handle the recursion for you.

### Recursive Watch

Call ``Inotify/Inotify/addRecursiveWatch(forDirectory:mask:)`` to walk the directory tree once and install a watch on every subdirectory that exists at the time of the call:

```swift
let inotify = try Inotify()
let descriptors = try await inotify.addRecursiveWatch(
    forDirectory: "/home/user/project",
    mask: [.create, .modify, .delete]
)
```

The returned array contains one watch descriptor per directory. Subdirectories created **after** this call are not covered. When one of the directories cannot be watched, for instance because the user's watch limit is reached, the call throws and removes the watches it had added, so the instance is left as it was.

### Automatic Subtree Watching

When you also want future subdirectories to be picked up, use ``Inotify/Inotify/addWatchWithAutomaticSubtreeWatching(forDirectory:mask:)`` instead:

```swift
let descriptors = try await inotify.addWatchWithAutomaticSubtreeWatching(
    forDirectory: "/home/user/project",
    mask: [.create, .modify, .delete]
)
```

Internally this listens for `CREATE` and `MOVED_TO` events carrying the ``InotifyEventMask/isDir`` flag and installs new watches with the same mask on the subdirectory and its subtree whenever one appears. Items that already exist inside such a subdirectory are reported with ``FileSystemEvent/synthesized`` set to `true`, since the kernel never produces events for them; a synthesized event may duplicate a kernel event for the same item.

When a directory is moved out of the watched tree, the watches on it and on its subdirectories are removed, so no events are reported under the stale path.

### Excluding Directories

When watching large trees you often want to skip certain subdirectories entirely — version-control metadata, build artefacts, dependency caches, and so on. Call ``Inotify/Inotify/exclude(names:)`` or ``Inotify/Inotify/exclude(patterns:)`` **before** adding a recursive or automatic-subtree watch:

```swift
let inotify = try Inotify()
await inotify.exclude(names: ".git", "node_modules", ".build")
await inotify.exclude(patterns: ".*", "*.tmp")

try await inotify.addWatchWithAutomaticSubtreeWatching(
    forDirectory: "/home/user/project",
    mask: .allEvents
)
```

Excluded names and patterns are matched against the last path component of each directory during resolution, against a directory that appears later before a watch is extended to it, and against every event, so you never receive events for excluded items. A pattern is matched the way the shell matches file names: `*` and `?` stand for any characters and `[…]` for a set of characters; a leading dot needs no special treatment.

### Choosing the Right Method

| Method | Covers existing subdirectories | Covers new subdirectories |
|--------|:----:|:----:|
| ``Inotify/Inotify/addWatch(path:mask:)`` | No | No |
| ``Inotify/Inotify/addRecursiveWatch(forDirectory:mask:)`` | Yes | No |
| ``Inotify/Inotify/addWatchWithAutomaticSubtreeWatching(forDirectory:mask:)`` | Yes | Yes |