prose/watcher/watcher.go

package watcher

import (
	"iter"
	"log"
	"os"
	"runtime"
	"strings"

	"github.com/rjeczalik/notify"
)

type WatchEventKind int

const (
	Update WatchEventKind = iota
	Clean
)

// WatchEvent represents a change to a watched folder. It notes which file
// changed and what change happened to it.
type WatchEvent struct {
	File string
	Kind WatchEventKind
}

func updated(f string) *WatchEvent {
	return &WatchEvent{
		File: f,
		Kind: Update,
	}
}

func cleaned(f string) *WatchEvent {
	return &WatchEvent{
		File: f,
		Kind: Clean,
	}
}

// Watcher classifies notify.Events into updates and deletes, and calls the
// respective functions for a file when those events happen to that file.
func Watch(folder string, up Updater[string]) {
	cwd, err := os.Getwd()
	if err != nil {
		log.Fatal("could not get current working directory for listener!")
	}
	cwd = cwd + "/"

	c := make(chan notify.EventInfo, 1)

	var events []notify.Event

	// inotify events prevent double-firing of
	// certain events in Linux.
	if runtime.GOOS == "linux" {
		events = []notify.Event{
			notify.InCloseWrite,
			notify.InMovedFrom,
			notify.InMovedTo,
			notify.InDelete,
		}
	} else {
		events = []notify.Event{
			notify.Create,
			notify.Remove,
			notify.Rename,
			notify.Write,
		}
	}

	err = notify.Watch(folder, c, events...)

	if err != nil {
		log.Fatalf("could not setup watcher for folder %s: %s", folder, err)
	}

	defer notify.Stop(c)
	for {
		ei := <-c
		log.Printf("event: %s", ei.Event())
		switch ei.Event() {
		case notify.InCloseWrite, notify.InMovedTo, notify.Create, notify.Rename, notify.Write:
			filePath := strings.TrimPrefix(ei.Path(), cwd)
			log.Printf("updating file %s", filePath)
			err := up.Fetch(strings.TrimPrefix(filePath, folder))
			if err != nil {
				log.Printf("up.Fetch(%q): %v", filePath, err)
			}
		case notify.InMovedFrom, notify.InDelete, notify.Remove:
			filePath := strings.TrimPrefix(ei.Path(), cwd)
			log.Printf("cleaning file %s", filePath)
			err := up.Delete(strings.TrimPrefix(filePath, folder))
			if err != nil {
				log.Printf("up.Delete(%q): %v", filePath, err)
			}
		}
	}
}

// Updater is a key-value store which can be informed when to recompute values
// for a particular key. Updaters are normally also AutoMaps.
type Updater[K any] interface {
	Fetch(K) error
	Delete(K) error
}

// AutoMap is a key-value store where the values are automatically computed by
// the store itself, based on the key.
type AutoMap[K, V any] interface {
	Get(K) (V, bool)
}

// OrderedAutoMap is an AutoMap that provides an iterator over its
// currently-existing keys in a known order.
type OrderedAutoMap[K, V any] interface {
	AutoMap[K, V]
	All() iter.Seq2[K, V]
}