zng_ext_fs_watcher/
lib.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
#![doc(html_favicon_url = "https://raw.githubusercontent.com/zng-ui/zng/main/examples/image/res/zng-logo-icon.png")]
#![doc(html_logo_url = "https://raw.githubusercontent.com/zng-ui/zng/main/examples/image/res/zng-logo.png")]
//!
//! File system events and service.
//!
//! # Crate
//!
#![doc = include_str!(concat!("../", std::env!("CARGO_PKG_README")))]
// suppress nag about very simple boxed closure signatures.
#![expect(clippy::type_complexity)]
#![warn(unused_extern_crates)]
#![warn(missing_docs)]

use std::{
    fmt, fs,
    io::{self, Write as _},
    ops,
    path::{Path, PathBuf},
    sync::Arc,
    time::Duration,
};

use path_absolutize::Absolutize;
use zng_app::{
    event::{event, event_args, EventHandle},
    handler::{AppHandler, FilterAppHandler},
    update::EventUpdate,
    view_process::raw_events::LOW_MEMORY_EVENT,
    AppExtension,
};
use zng_handle::Handle;
use zng_txt::Txt;
use zng_unit::TimeUnits;
use zng_var::{ArcVar, ReadOnlyArcVar, VarValue};

mod service;
use service::*;

mod lock;
use lock::*;

/// Application extension that provides file system change events and service.
///
/// # Events
///
/// Events this extension provides.
///
/// * [`FS_CHANGES_EVENT`]
///
/// # Services
///
/// Services this extension provides.
///
/// * [`WATCHER`]
#[derive(Default)]
pub struct FsWatcherManager {}
impl AppExtension for FsWatcherManager {
    fn init(&mut self) {
        WATCHER_SV.write().init_watcher();
    }

    fn event_preview(&mut self, update: &mut EventUpdate) {
        if let Some(args) = FS_CHANGES_EVENT.on(update) {
            WATCHER_SV.write().event(args);
        } else if LOW_MEMORY_EVENT.on(update).is_some() {
            WATCHER_SV.write().low_memory();
        }
    }

    fn update_preview(&mut self) {
        WATCHER_SV.write().update();
    }

    fn deinit(&mut self) {
        let mut flush = WATCHER_SV.write().shutdown();
        for v in &mut flush {
            v.flush_shutdown();
        }
    }
}

/// File system watcher service.
///
/// This is mostly a wrapper around the [`notify`](https://docs.rs/notify) crate, integrating it with events and variables.
pub struct WATCHER;
impl WATCHER {
    /// Gets a read-write variable that defines interval awaited between each [`FS_CHANGES_EVENT`]. If
    /// a watched path is constantly changing an event will be emitted every elapse of this interval,
    /// the event args will contain a list of all the changes observed during the interval.
    ///
    /// Note that the first event notifies immediately, only subsequent events within this interval are debounced.
    ///
    /// Is `100.ms()` by default.
    pub fn debounce(&self) -> ArcVar<Duration> {
        WATCHER_SV.read().debounce.clone()
    }

    /// Gets a read-write variable that defines interval awaited between each [`sync`] write.
    ///
    /// Is `100.ms()` by default.
    ///
    /// [`sync`]: WATCHER::sync
    pub fn sync_debounce(&self) -> ArcVar<Duration> {
        WATCHER_SV.read().debounce.clone()
    }

    /// Gets a read-write variable that defines the fallback poll watcher interval.
    ///
    /// When an efficient watcher cannot be used a poll watcher fallback is used, the poll watcher reads
    /// the directory or path every elapse of this interval. The poll watcher is also used for paths that
    /// do not exist yet, that is also affected by this interval.
    ///
    /// Is `1.secs()` by default.
    pub fn poll_interval(&self) -> ArcVar<Duration> {
        WATCHER_SV.read().poll_interval.clone()
    }

    /// Maximum time the service keeps the process alive to process pending IO operations when the app shuts down.
    ///
    /// Is 1 minute by default.
    pub fn shutdown_timeout(&self) -> ArcVar<Duration> {
        WATCHER_SV.read().shutdown_timeout.clone()
    }

    /// Enable file change events for the `file`.
    ///
    /// Returns a handle that will stop the file watch when dropped, if there is no other active handler for the same file.
    ///
    /// Note that this is implemented by actually watching the parent directory and filtering the events, this is done
    /// to ensure the watcher survives operations that remove the file and then move another file to the same path.
    ///
    /// See [`watch_dir`] for more details.
    ///
    /// [`watch_dir`]: WATCHER::watch_dir
    pub fn watch(&self, file: impl Into<PathBuf>) -> WatcherHandle {
        WATCHER_SV.write().watch(file.into())
    }

    /// Enable file change events for files inside `dir`, also include inner directories if `recursive` is `true`.
    ///
    /// Returns a handle that will stop the dir watch when dropped, if there is no other active handler for the same directory.
    ///
    /// The directory will be watched using an OS specific efficient watcher provided by the [`notify`](https://docs.rs/notify) crate. If there is
    /// any error creating the watcher, such as if the directory does not exist yet a slower polling watcher will retry periodically    
    /// until the efficient watcher can be created or the handle is dropped.
    pub fn watch_dir(&self, dir: impl Into<PathBuf>, recursive: bool) -> WatcherHandle {
        WATCHER_SV.write().watch_dir(dir.into(), recursive)
    }

    /// Read a file into a variable, the `init` value will start the variable and the `read` closure will be called
    /// once immediately and every time the file changes, if the closure returns `Some(O)` the variable updates with the new value.
    ///
    /// Dropping the variable drops the read watch. The `read` closure is non-blocking, it is called in a [`task::wait`]
    /// background thread.
    ///
    /// [`task::wait`]: zng_task::wait
    pub fn read<O: VarValue>(
        &self,
        file: impl Into<PathBuf>,
        init: O,
        read: impl FnMut(io::Result<WatchFile>) -> Option<O> + Send + 'static,
    ) -> ReadOnlyArcVar<O> {
        WATCHER_SV.write().read(file.into(), init, read)
    }

    /// Same operation as [`read`] but also tracks the operation status in a second var.
    ///
    /// The status variable is set to [`WatcherReadStatus::reading`] as soon as `read` starts and
    /// is set to [`WatcherReadStatus::idle`] when read returns. If read returns a value the status
    /// only updates to idle  when the new value is available on the var, or because read the same value.
    ///
    /// [`read`]: Self::read
    pub fn read_status<O, S, E>(
        &self,
        file: impl Into<PathBuf>,
        init: O,
        read: impl FnMut(io::Result<WatchFile>) -> Result<Option<O>, E> + Send + 'static,
    ) -> (ReadOnlyArcVar<O>, ReadOnlyArcVar<S>)
    where
        O: VarValue,
        S: WatcherReadStatus<E>,
    {
        WATCHER_SV.write().read_status(file.into(), init, read)
    }

    /// Read a directory into a variable, the `init` value will start the variable and the `read` closure will be called
    /// once immediately and every time any changes happen inside the dir, if the closure returns `Some(O)` the variable updates with the new value.
    ///
    /// The `read` closure parameter is a directory walker from the [`walkdir`](https://docs.rs/walkdir) crate.
    ///
    /// The directory walker is pre-configured to skip the `dir` itself and to have a max-depth of 1 if not `recursive`, these configs can.
    ///
    /// Dropping the variable drops the read watch. The `read` closure is non-blocking, it is called in a [`task::wait`]
    /// background thread.
    ///
    /// [`task::wait`]: zng_task::wait
    pub fn read_dir<O: VarValue>(
        &self,
        dir: impl Into<PathBuf>,
        recursive: bool,
        init: O,
        read: impl FnMut(walkdir::WalkDir) -> Option<O> + Send + 'static,
    ) -> ReadOnlyArcVar<O> {
        WATCHER_SV.write().read_dir(dir.into(), recursive, init, read)
    }

    /// Same operation as [`read_dir`] but also tracks the operation status in a second var.
    ///
    /// The status variable is set to [`WatcherReadStatus::reading`] as soon as `read` starts and
    /// is set to [`WatcherReadStatus::idle`] when read returns. If read returns a value the status
    /// only updates to idle when the new value is available on the var, or because read the same value.
    ///
    /// [`read_dir`]: Self::read_dir
    pub fn read_dir_status<O, S, E>(
        &self,
        dir: impl Into<PathBuf>,
        recursive: bool,
        init: O,
        read: impl FnMut(walkdir::WalkDir) -> Result<Option<O>, E> + Send + 'static,
    ) -> (ReadOnlyArcVar<O>, ReadOnlyArcVar<S>)
    where
        O: VarValue,
        S: WatcherReadStatus<E>,
    {
        WATCHER_SV.write().read_dir_status(dir.into(), recursive, init, read)
    }

    /// Bind a file with a variable, the `file` will be `read` when it changes and be `write` when the variable changes,
    /// writes are only applied on success and will not cause a `read` on the same sync task. The `init` value is used to
    /// create the variable, if the `file` exists it will be `read` once at the beginning.
    ///
    /// Dropping the variable drops the read watch. The `read` and `write` closures are non-blocking, they are called in a [`task::wait`]
    /// background thread.
    ///
    /// # Sync
    ///
    /// The file synchronization ensures that the file is only actually modified when writing is finished by writing
    /// to a temporary file and committing a replace only if the write succeeded. The file is write-locked for the duration
    /// of `write` call, but the contents are not touched until commit. See [`WriteFile`] for more details.
    ///
    /// The [`FsWatcherManager`] blocks on app exit until all writes commit or cancel.
    ///
    /// ## Read Errors
    ///
    /// Not-found errors are handled by the watcher by calling `write` using the current variable value, other read errors
    /// are passed to `read`. If `read` returns a value for an error the `write` closure is called to override the file,
    /// otherwise only the variable is set and this variable update does not cause a `write`.
    ///
    /// ## Write Errors
    ///
    /// If `write` fails the file is not touched and the temporary file is removed, if the file path
    /// does not exit all missing parent folders and the file will be created automatically before the `write`
    /// call.
    ///
    /// Note that [`WriteFile::commit`] must be called to flush the temporary file and attempt to rename
    /// it, if the file is dropped without commit it will cancel and log an error, you must call [`WriteFile::cancel`]
    /// to correctly avoid writing.
    ///
    /// If the cleanup after commit fails the error is logged and ignored.
    ///
    /// If write fails to even create the file and/or acquire a write lock on it this error is the input for
    /// the `write` closure.
    ///
    /// ## Error Handling
    ///
    /// You can call services or set other variables from inside the `read` and `write` closures, this can be
    /// used to get a signal out that perhaps drops the sync var (to stop watching), alert the user that the
    /// file is out of sync and initiate some sort of recovery routine.
    ///
    /// If the file synchronization is not important you can just ignore it, the watcher will try again
    /// on the next variable or file update.
    ///
    /// ## Status
    ///
    /// Note that `read` and `write` run in background task threads, so if you are tracking the operation
    /// status in a separate variable you may end-up with synchronization bugs between th status variable
    /// and the actual result variable, you can use [`sync_status`] to implement racing-free status tracking.
    ///
    /// [`sync_status`]: Self::sync_status
    /// [`task::wait`]: zng_task::wait
    pub fn sync<O: VarValue>(
        &self,
        file: impl Into<PathBuf>,
        init: O,
        read: impl FnMut(io::Result<WatchFile>) -> Option<O> + Send + 'static,
        write: impl FnMut(O, io::Result<WriteFile>) + Send + 'static,
    ) -> ArcVar<O> {
        WATCHER_SV.write().sync(file.into(), init, read, write)
    }

    /// Same operation as [`sync`] but also tracks the operation status in a second var.
    ///
    /// The status variable is set to [`WatcherReadStatus::reading`] as soon as `read` starts and
    /// is set to [`WatcherReadStatus::idle`] when read returns. If read returns a value the status
    /// only updates to idle when the new sync value is available, or because read the same value.
    ///
    /// The status variable is set to [`WatcherSyncStatus::writing`] as soon as it updates and
    /// is set to [`WatcherReadStatus::idle`] only when the new sync value is available, either
    /// by update or because read the same value.
    ///
    /// [`sync`]: Self::sync
    pub fn sync_status<O, S, ER, EW>(
        &self,
        file: impl Into<PathBuf>,
        init: O,
        read: impl FnMut(io::Result<WatchFile>) -> Result<Option<O>, ER> + Send + 'static,
        write: impl FnMut(O, io::Result<WriteFile>) -> Result<(), EW> + Send + 'static,
    ) -> (ArcVar<O>, ReadOnlyArcVar<S>)
    where
        O: VarValue,
        S: WatcherSyncStatus<ER, EW>,
    {
        WATCHER_SV.write().sync_status(file.into(), init, read, write)
    }

    /// Watch `file` and calls `handler` every time it changes.
    ///
    /// Note that the `handler` is blocking, use [`async_app_hn!`] and [`task::wait`] to run IO without
    /// blocking the app.
    ///
    /// [`async_app_hn!`]: macro@zng_app::handler::async_app_hn
    /// [`task::wait`]: zng_task::wait
    pub fn on_file_changed(&self, file: impl Into<PathBuf>, handler: impl AppHandler<FsChangesArgs>) -> EventHandle {
        let file = file.into();
        let handle = self.watch(file.clone());
        FS_CHANGES_EVENT.on_event(FilterAppHandler::new(handler, move |args| {
            let _handle = &handle;
            args.events_for_path(&file).next().is_some()
        }))
    }

    /// Watch `dir` and calls `handler` every time something inside it changes.
    ///
    /// Note that the `handler` is blocking, use [`async_app_hn!`] and [`task::wait`] to run IO without
    /// blocking the app.
    ///
    /// [`async_app_hn!`]: macro@zng_app::handler::async_app_hn
    /// [`task::wait`]: zng_task::wait
    pub fn on_dir_changed(&self, dir: impl Into<PathBuf>, recursive: bool, handler: impl AppHandler<FsChangesArgs>) -> EventHandle {
        let dir = dir.into();
        let handle = self.watch_dir(dir.clone(), recursive);
        FS_CHANGES_EVENT.on_event(FilterAppHandler::new(handler, move |args| {
            let _handle = &handle;
            args.events_for_path(&dir).next().is_some()
        }))
    }

    /// Push a `note` that will be cloned on all subsequent change events until it the returned handle is dropped.
    ///
    /// This can be used to tag all events that happened over a period of time, something you can't do just
    /// by receiving the events due to async delays caused by debounce.
    ///
    /// Note that the underlying system events the [`notify`](https://docs.rs/notify) crate uses are not guaranteed to be synchronous.
    pub fn annotate(&self, note: Arc<dyn FsChangeNote>) -> FsChangeNoteHandle {
        WATCHER_SV.write().annotate(note)
    }
}

/// Represents a status type for [`WATCHER.sync_status`].
///
/// [`WATCHER.sync_status`]: WATCHER::sync_status
pub trait WatcherSyncStatus<ER = io::Error, EW = io::Error>: WatcherReadStatus<ER> {
    /// New writing value.
    fn writing() -> Self;
    /// New write error value.
    fn write_error(e: EW) -> Self;
}

/// Represents a status type for [`WATCHER`] read-only operations.
pub trait WatcherReadStatus<ER = io::Error>: VarValue + PartialEq {
    /// New idle value.
    fn idle() -> Self;
    /// New reading value.
    fn reading() -> Self;
    /// New read error value.
    fn read_error(e: ER) -> Self;
}

/// Represents an open read-only file provided by [`WATCHER.read`].
///
/// This type is a thin wrapper around the [`std::fs::File`] with some convenience parsing methods.
///
/// [`WATCHER.read`]: WATCHER::read
#[derive(Debug)]
pub struct WatchFile(fs::File);
impl WatchFile {
    /// Open read the file.
    pub fn open(file: impl AsRef<Path>) -> io::Result<Self> {
        Self::try_open_non_empty(file.as_ref(), true)
    }
    fn try_open_non_empty(path: &Path, retry: bool) -> io::Result<Self> {
        let file = fs::File::open(path)?;

        if retry && file.metadata()?.len() == 0 {
            // some apps create an empty file unlocked, then write.
            let _ = file;
            std::thread::sleep(5.ms());
            return Self::try_open_non_empty(path, false);
        }

        lock_shared(&file, Duration::from_secs(10))?;
        Ok(Self(file))
    }

    /// Read the file contents as a text string.
    pub fn text(&mut self) -> io::Result<Txt> {
        self.string().map(Txt::from)
    }

    /// Read the file contents as a string.
    pub fn string(&mut self) -> io::Result<String> {
        use std::io::Read;
        let mut s = String::new();
        self.0.read_to_string(&mut s)?;
        Ok(s)
    }

    /// Deserialize the file contents as JSON.
    #[cfg(feature = "json")]
    pub fn json<O>(&mut self) -> serde_json::Result<O>
    where
        O: serde::de::DeserializeOwned,
    {
        serde_json::from_reader(io::BufReader::new(&mut self.0))
    }

    /// Deserialize the file contents as TOML.
    #[cfg(feature = "toml")]
    pub fn toml<O>(&mut self) -> io::Result<O>
    where
        O: serde::de::DeserializeOwned,
    {
        use std::io::Read;
        let mut buf = io::BufReader::new(&mut self.0);

        let mut toml_str = String::new();
        buf.read_to_string(&mut toml_str)?;

        toml::de::from_str(&toml_str).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))
    }

    /// Deserialize the file content as RON.
    #[cfg(feature = "ron")]
    pub fn ron<O>(&mut self) -> Result<O, ron::de::SpannedError>
    where
        O: serde::de::DeserializeOwned,
    {
        ron::de::from_reader(io::BufReader::new(&mut self.0))
    }

    /// Deserialize the file content as YAML.
    #[cfg(feature = "yaml")]
    pub fn yaml<O>(&mut self) -> serde_yaml::Result<O>
    where
        O: serde::de::DeserializeOwned,
    {
        serde_yaml::from_reader(io::BufReader::new(&mut self.0))
    }

    /// Read file and parse it.
    pub fn parse<O: std::str::FromStr>(&mut self) -> Result<O, WatchFileParseError<O::Err>> {
        use std::io::Read;
        let mut s = String::new();
        self.0.read_to_string(&mut s)?;
        O::from_str(&s).map_err(WatchFileParseError::Parse)
    }
}
impl ops::Deref for WatchFile {
    type Target = fs::File;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}
impl ops::DerefMut for WatchFile {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}
impl Drop for WatchFile {
    fn drop(&mut self) {
        let _ = FileExt::unlock(&self.0);
    }
}

const TRANSACTION_GUID: &str = "6eIw3bYMS0uKaQMkTIQacQ";
const TRANSACTION_LOCK_EXT: &str = "6eIw3bYMS0uKaQMkTIQacQ-lock.tmp";

/// Represents an open write file provided by [`WATCHER.sync`].
///
/// This type actually writes to a temporary file and rename it over the actual file on commit only.
/// The dereferenced [`fs::File`] is the temporary file, not the actual one.
///
/// # Transaction
///
/// To minimize the risk of file corruption exclusive locks are used, both the target file and the temp file
/// are locked. An empty lock file is also used to cover the moment when both files are unlocked for the rename operation
/// and the moment the temp file is acquired.
///
/// The temp file is the actual file path with file extension replaced with `{path/.file-name.ext}.{GUID}-{n}.tmp`, the `n` is a
/// number from 0 to 999, if a temp file exists unlocked it will be reused.
///
/// The lock file is `{path/.file-name.ext}.{GUID}-lock.tmp`. Note that this
/// lock file only helps for apps that use [`WriteFile`], but even without it the risk is minimal as the slow
/// write operations are already flushed when it is time to commit.
///
/// [`WATCHER.sync`]: WATCHER::sync
pub struct WriteFile {
    temp_file: Option<fs::File>,
    actual_file: Option<fs::File>,
    transaction_lock: Option<fs::File>,

    actual_path: PathBuf,
    temp_path: PathBuf,
    transaction_path: PathBuf,

    cleaned: bool,
}
impl Drop for WriteFile {
    fn drop(&mut self) {
        if !self.cleaned {
            tracing::error!("dropped sync write file without commit or cancel");
            self.clean();
        }
    }
}
impl ops::Deref for WriteFile {
    type Target = fs::File;

    fn deref(&self) -> &Self::Target {
        self.temp_file.as_ref().unwrap()
    }
}
impl ops::DerefMut for WriteFile {
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.temp_file.as_mut().unwrap()
    }
}
impl WriteFile {
    /// Open or create the file.
    pub fn open(path: PathBuf) -> io::Result<Self> {
        let actual_path = path.absolutize()?.into_owned();
        if !actual_path.exists() {
            if let Some(parent) = actual_path.parent() {
                std::fs::create_dir_all(parent)?;
            }
        }

        let hidden_name = match actual_path.file_name() {
            Some(n) => format!(".{}", n.to_string_lossy()),
            None => return Err(io::Error::new(io::ErrorKind::InvalidInput, "expected file name")),
        };

        let transaction_path = actual_path.with_file_name(format!("{hidden_name}.{TRANSACTION_LOCK_EXT}"));
        let transaction_lock = fs::OpenOptions::new()
            .create(true)
            .truncate(true)
            .write(true)
            .open(&transaction_path)?;

        const TIMEOUT: Duration = Duration::from_secs(10);

        lock_exclusive(&transaction_lock, TIMEOUT)?;

        let actual_file = fs::OpenOptions::new().write(true).create(true).truncate(false).open(&actual_path)?;
        lock_exclusive(&actual_file, TIMEOUT)?;

        let mut n = 0;
        let mut temp_path = actual_path.with_file_name(format!("{hidden_name}.{TRANSACTION_GUID}-{n}.tmp"));
        let temp_file = loop {
            if let Ok(f) = fs::OpenOptions::new().write(true).create(true).truncate(true).open(&temp_path) {
                if f.try_lock_exclusive().is_ok() {
                    break f;
                }
            }

            n += 1;
            temp_path = actual_path.with_file_name(format!("{hidden_name}.{TRANSACTION_GUID}-{n}.tmp"));
            n += 1;
            if n > 1000 {
                return Err(io::Error::new(io::ErrorKind::AlreadyExists, "cannot create temporary file"));
            }
        };

        Ok(Self {
            actual_file: Some(actual_file),
            temp_file: Some(temp_file),
            transaction_lock: Some(transaction_lock),
            actual_path,
            temp_path,
            transaction_path,
            cleaned: false,
        })
    }

    /// Write the text string.
    pub fn write_text(&mut self, txt: &str) -> io::Result<()> {
        self.write_all(txt.as_bytes())
    }

    /// Serialize and write.
    ///
    /// If `pretty` is `true` the JSON is formatted for human reading.
    #[cfg(feature = "json")]
    pub fn write_json<O: serde::Serialize>(&mut self, value: &O, pretty: bool) -> io::Result<()> {
        let mut buf = io::BufWriter::new(ops::DerefMut::deref_mut(self));
        if pretty {
            serde_json::to_writer_pretty(&mut buf, value)?;
        } else {
            serde_json::to_writer(&mut buf, value)?;
        }
        buf.flush()
    }

    /// Serialize and write.
    ///
    /// If `pretty` is `true` the TOML is formatted for human reading.
    #[cfg(feature = "toml")]
    pub fn write_toml<O: serde::Serialize>(&mut self, value: &O, pretty: bool) -> io::Result<()> {
        let toml = if pretty {
            toml::ser::to_string_pretty(value)
        } else {
            toml::ser::to_string(value)
        }
        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;

        self.write_all(toml.as_bytes())
    }

    /// Serialize and write.
    ///
    /// If `pretty` is `true` the RON if formatted for human reading using the default pretty config.
    #[cfg(feature = "ron")]
    pub fn write_ron<O: serde::Serialize>(&mut self, value: &O, pretty: bool) -> io::Result<()> {
        let mut buf = io::BufWriter::new(ops::DerefMut::deref_mut(self));
        if pretty {
            ron::ser::to_writer_pretty(&mut buf, value, Default::default()).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        } else {
            ron::ser::to_writer(&mut buf, value).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        }
        buf.flush()
    }

    /// Serialize and write.
    #[cfg(feature = "yaml")]
    pub fn write_yaml<O: serde::Serialize>(&mut self, value: &O) -> io::Result<()> {
        let mut buf = io::BufWriter::new(ops::DerefMut::deref_mut(self));
        serde_yaml::to_writer(&mut buf, value).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))?;
        buf.flush()
    }

    /// Commit write, flush and replace the actual file with the new one.
    pub fn commit(mut self) -> io::Result<()> {
        let r = self.replace_actual();
        self.clean();
        r
    }

    /// Cancel write, the file will not be updated.
    pub fn cancel(mut self) {
        self.clean();
    }

    fn replace_actual(&mut self) -> io::Result<()> {
        let mut temp_file = self.temp_file.take().unwrap();
        temp_file.flush()?;
        temp_file.sync_all()?;

        unlock_ok(&temp_file).unwrap();
        drop(temp_file);

        let actual_file = self.actual_file.take().unwrap();
        unlock_ok(&actual_file)?;
        drop(actual_file);

        let mut retries = 0;
        loop {
            // commit by replacing the actual_path with already on disk temp_path file.
            match fs::rename(&self.temp_path, &self.actual_path) {
                Ok(()) => {
                    break;
                }
                Err(e) => match e.kind() {
                    io::ErrorKind::PermissionDenied => {
                        if retries == 5 {
                            // Give-up, we manage to write lock both temp and actual just
                            // before this, but now we can't replace actual and remove temp.
                            // Hardware issue? Or another process holding a lock for 1s+50ms*5.
                            return Err(e);
                        } else if retries > 0 {
                            // Second+ retries:
                            //
                            // probably a system issue.
                            //
                            // Windows sporadically returns ACCESS_DENIED for kernel!SetRenameInformationFile in
                            // other apps that use the same save pattern (write-tmp -> close-tmp -> rename).
                            // see GIMP issue: https://gitlab.gnome.org/GNOME/gimp/-/issues/1370
                            //
                            // I used procmon to trace all file operations, there is no other app trying to use
                            // the temp and actual files when the ACCESS_DENIED occurs, both files are unlocked and
                            // closed before the rename calls start. This might be a Windows bug.
                            std::thread::sleep(30.ms());
                        } else {
                            // first retry:
                            //
                            // probably another process reading the `actual_path`.
                            //
                            // Reacquire a write lock and unlock, just to wait the external app.
                            match std::fs::File::options().write(true).open(&self.actual_path) {
                                Ok(f) => {
                                    if lock_exclusive(&f, 10.secs()).is_ok() {
                                        // acquired actual ok, retry
                                        let _ = unlock_ok(&f);
                                    }
                                }
                                Err(e) => match e.kind() {
                                    io::ErrorKind::NotFound => {
                                        // all good, rename will create actual
                                        continue;
                                    }
                                    _ => {
                                        // unknown error, let retry handle it
                                        std::thread::sleep(30.ms());
                                    }
                                },
                            }
                        }

                        retries += 1;
                    }
                    _ => return Err(e),
                },
            }
        }

        Ok(())
    }

    fn clean(&mut self) {
        self.cleaned = true;

        if let Some(tmp) = self.temp_file.take() {
            let _ = FileExt::unlock(&tmp);
        }
        if let Err(e) = fs::remove_file(&self.temp_path) {
            tracing::debug!("failed to cleanup temp file, {e}")
        }

        if let Some(file) = self.actual_file.take() {
            let _ = FileExt::unlock(&file);
        }

        let transaction = self.transaction_lock.take().unwrap();
        let _ = FileExt::unlock(&transaction);
        let _ = fs::remove_file(&self.transaction_path);
    }
}

/// Error for [`WatchFile::parse`].
#[derive(Debug)]
pub enum WatchFileParseError<E> {
    /// Error reading the file.
    Io(io::Error),
    /// Error parsing the file.
    Parse(E),
}
impl<E> From<io::Error> for WatchFileParseError<E> {
    fn from(value: io::Error) -> Self {
        Self::Io(value)
    }
}
impl<E: fmt::Display> fmt::Display for WatchFileParseError<E> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            WatchFileParseError::Io(e) => write!(f, "read error, {e}"),
            WatchFileParseError::Parse(e) => write!(f, "parse error, {e}"),
        }
    }
}
impl<E: std::error::Error + 'static> std::error::Error for WatchFileParseError<E> {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            WatchFileParseError::Io(e) => Some(e),
            WatchFileParseError::Parse(e) => Some(e),
        }
    }
}

/// Represents a [`FsChange`] note.
///
/// This trait is already implemented for types it applies.
#[diagnostic::on_unimplemented(note = "`FsChangeNote` is implemented for all `T: Debug + Any + Send + Sync`")]
pub trait FsChangeNote: fmt::Debug + std::any::Any + Send + Sync {
    /// Access any.
    fn as_any(&self) -> &dyn std::any::Any;
}
impl<T: fmt::Debug + std::any::Any + Send + Sync> FsChangeNote for T {
    fn as_any(&self) -> &dyn std::any::Any {
        self
    }
}

/// Handle that holds a [`WATCHER.annotate`] note.
///
/// [`WATCHER.annotate`]: WATCHER::annotate
#[derive(Clone)]
#[must_use = "the note is removed when the handle is dropped"]
pub struct FsChangeNoteHandle(#[expect(dead_code)] Arc<Arc<dyn FsChangeNote>>);

/// Annotation for file watcher events and var update tags.
///
/// Identifies the [`WATCHER.sync`] file that is currently being written to.
///
/// [`WATCHER.sync`]: WATCHER::sync
#[derive(Debug, PartialEq, Eq)]
pub struct WatcherSyncWriteNote(PathBuf);
impl WatcherSyncWriteNote {
    /// Deref.
    pub fn as_path(&self) -> &Path {
        self
    }
}
impl ops::Deref for WatcherSyncWriteNote {
    type Target = Path;

    fn deref(&self) -> &Self::Target {
        self.0.as_path()
    }
}

/// File system change event types.
///
/// The event for each change is available in [`FsChange::event`].
///
/// This module re-exports types from the [`notify`](https://docs.rs/notify) crate.
pub mod fs_event {
    pub use notify::event::{
        AccessKind, AccessMode, CreateKind, DataChange, Event, EventKind, MetadataKind, ModifyKind, RemoveKind, RenameMode,
    };
    pub use notify::{Error, ErrorKind};
}

/// Represents a single file system change, annotated.
#[derive(Debug)]
pub struct FsChange {
    /// All [`WATCHER.annotate`] that where set when this event happened.
    ///
    /// [`WATCHER.annotate`]: WATCHER::annotate
    pub notes: Vec<Arc<dyn FsChangeNote>>,

    /// The actual notify event or error.
    pub event: Result<fs_event::Event, fs_event::Error>,
}
impl FsChange {
    /// If the change affects the `path`.
    pub fn is_for_path(&self, path: &Path) -> bool {
        if let Ok(ev) = &self.event {
            return ev.paths.iter().any(|p| p.starts_with(path));
        }
        false
    }

    /// If the change affects any path matched by the glob pattern.
    pub fn is_for_glob(&self, pattern: &glob::Pattern) -> bool {
        if let Ok(ev) = &self.event {
            return ev.paths.iter().any(|p| pattern.matches_path(p));
        }
        false
    }

    /// Iterate over all notes of the type `T`.
    pub fn notes<T: FsChangeNote>(&self) -> impl Iterator<Item = &T> {
        self.notes.iter().filter_map(|n| FsChangeNote::as_any(&**n).downcast_ref::<T>())
    }
}

event_args! {
    /// [`FS_CHANGES_EVENT`] arguments.
    pub struct FsChangesArgs {
        /// All notify changes since the last event.
        pub changes: Arc<Vec<FsChange>>,

        ..

        /// None, only app level handlers receive this event.
        fn delivery_list(&self, list: &mut UpdateDeliveryList) {
            let _ = list;
        }
    }
}
impl FsChangesArgs {
    /// Iterate over all change events.
    pub fn events(&self) -> impl Iterator<Item = &fs_event::Event> + '_ {
        self.changes.iter().filter_map(|r| r.event.as_ref().ok())
    }

    /// Iterate over all file watcher errors.
    pub fn errors(&self) -> impl Iterator<Item = &notify::Error> + '_ {
        self.changes.iter().filter_map(|r| r.event.as_ref().err())
    }

    /// Returns `true` is some events where lost.
    ///
    /// This indicates either a lapse in the events or a change in the filesystem such that events
    /// received so far can no longer be relied on to represent the state of the filesystem now.
    ///
    /// An application that simply reacts to file changes may not care about this. An application
    /// that keeps an in-memory representation of the filesystem will need to care, and will need
    /// to refresh that representation directly from the filesystem.
    pub fn rescan(&self) -> bool {
        self.events().any(|e| e.need_rescan())
    }

    /// Iterate over all changes that affects paths selected by the `glob` pattern.
    pub fn changes_for(&self, glob: &str) -> Result<impl Iterator<Item = &FsChange> + '_, glob::PatternError> {
        let glob = glob::Pattern::new(glob)?;
        Ok(self.changes.iter().filter(move |c| c.is_for_glob(&glob)))
    }

    /// Iterate over all changes that affects paths that are equal to `path` or inside it.
    pub fn changes_for_path<'a>(&'a self, path: &'a Path) -> impl Iterator<Item = &'a FsChange> + 'a {
        self.changes.iter().filter(move |c| c.is_for_path(path))
    }

    /// Iterate over all change events that affects that are equal to `path` or inside it.
    pub fn events_for(&self, glob: &str) -> Result<impl Iterator<Item = &fs_event::Event> + '_, glob::PatternError> {
        let glob = glob::Pattern::new(glob)?;
        Ok(self.events().filter(move |ev| ev.paths.iter().any(|p| glob.matches_path(p))))
    }

    /// Iterate over all change events that affects paths that are equal to `path` or inside it.
    pub fn events_for_path<'a>(&'a self, path: &'a Path) -> impl Iterator<Item = &'a fs_event::Event> + 'a {
        self.events().filter(move |ev| ev.paths.iter().any(|p| p.starts_with(path)))
    }
}

event! {
    /// Event sent by the [`WATCHER`] service on directories or files that are watched.
    pub static FS_CHANGES_EVENT: FsChangesArgs;
}

/// Represents an active file or directory watcher in [`WATCHER`].
#[derive(Clone)]
#[must_use = "the watcher is dropped if the handle is dropped"]
pub struct WatcherHandle(Handle<()>);

impl WatcherHandle {
    /// Handle to no watcher.
    pub fn dummy() -> Self {
        Self(Handle::dummy(()))
    }

    /// If [`perm`](Self::perm) was called in another clone of this handle.
    ///
    /// If `true` the resource will stay in memory for the duration of the app, unless [`force_drop`](Self::force_drop)
    /// is also called.
    pub fn is_permanent(&self) -> bool {
        self.0.is_permanent()
    }

    /// Force drops the watcher, meaning it will be dropped even if there are other handles active.
    pub fn force_drop(self) {
        self.0.force_drop()
    }

    /// If the watcher is dropped.
    pub fn is_dropped(&self) -> bool {
        self.0.is_dropped()
    }

    /// Drop the handle without dropping the watcher, the watcher will stay active for the
    /// duration of the app process.
    pub fn perm(self) {
        self.0.perm()
    }
}