watch.go RawHistoryFolder

1package config
2
3import (
4	"context"
5	"errors"
6	"log/slog"
7	"os"
8	"reflect"
9	"time"
10
11	"github.com/bnema/neferbar/internal/fswatch"
12)
13
14// debounce waits for a save to finish before the file is read.
15const debounce = 100 * time.Millisecond
16
17// Watch reloads the file at path whenever it changes and sends each valid,
18// different Config to out. last is the Config the caller already runs, so a
19// save that changes nothing sends nothing. A broken file or a deleted file is
20// logged and the caller keeps its current configuration. It blocks until ctx
21// ends.
22func Watch(ctx context.Context, path string, last Config, out chan<- Config, log *slog.Logger) error {
23	changed := make(chan struct{}, 1)
24	wctx, cancel := context.WithCancel(ctx)
25	defer cancel()
26	errc := make(chan error, 1)
27	go func() { errc <- fswatch.Watch(wctx, path, debounce, changed) }()
28
29	for {
30		select {
31		case <-ctx.Done():
32			return nil
33		case err := <-errc:
34			return err
35		case <-changed:
36		}
37		next, err := Load(path, true)
38		switch {
39		case errors.Is(err, os.ErrNotExist):
40			log.Warn("config file removed; keeping the current config", "path", path)
41		case err != nil:
42			log.Warn("config reload failed; keeping the current config", "err", err)
43		case reflect.DeepEqual(next, last):
44			log.Debug("config unchanged")
45		default:
46			last = next
47			select {
48			case <-ctx.Done():
49				return nil
50			case out <- next:
51			}
52		}
53	}
54}