kanban_cpp/backend/sse_watcher.go

package main

import (
	"log"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/fsnotify/fsnotify"
)

// startBoardsWatcher launches a goroutine that watches dev/issues and
// dev/flows (recursively, one level deep — completed/ subdir) for .md
// changes and broadcasts ServerEvent messages via the hub. It also
// invalidates the relevant cardsCache so the next /cards GET reflects
// disk state.
//
// On fsnotify errors the watcher logs + retries every 30s.
func startBoardsWatcher(hub *Hub) {
	go func() {
		for {
			if err := runBoardsWatcher(hub); err != nil {
				log.Printf("sse_watcher: %v — retrying in 30s", err)
				time.Sleep(30 * time.Second)
			}
		}
	}()
}

func runBoardsWatcher(hub *Hub) error {
	w, err := fsnotify.NewWatcher()
	if err != nil {
		return err
	}
	defer w.Close()

	roots := map[string]string{
		"issues": issuesDir(),
		"flows":  flowsDir(),
	}
	for board, dir := range roots {
		if err := addRecursive(w, dir); err != nil {
			log.Printf("sse_watcher: watch %s (%s): %v", board, dir, err)
		} else {
			log.Printf("sse_watcher: watching %s -> %s", board, dir)
		}
	}

	for {
		select {
		case ev, ok := <-w.Events:
			if !ok {
				return nil
			}
			handleFsEvent(hub, ev)
		case err, ok := <-w.Errors:
			if !ok {
				return nil
			}
			log.Printf("sse_watcher: fsnotify error: %v", err)
		}
	}
}

// addRecursive adds dir and its immediate subdirectories (e.g.
// dev/issues/completed/) to the watcher. We do NOT follow symlinks.
func addRecursive(w *fsnotify.Watcher, root string) error {
	if err := w.Add(root); err != nil {
		return err
	}
	entries, err := readDirNoSymlink(root)
	if err != nil {
		return nil // root added, subdirs best-effort
	}
	for _, name := range entries {
		full := filepath.Join(root, name)
		// best-effort, ignore errors on subdirs
		_ = w.Add(full)
	}
	return nil
}

// handleFsEvent translates an fsnotify event into a ServerEvent (if
// applicable) and broadcasts it. Non-md files and skipped names
// (README/INDEX/...) are ignored.
func handleFsEvent(hub *Hub, ev fsnotify.Event) {
	board, cardID, action := classifyEvent(ev)
	if board == "" {
		return
	}
	// Invalidate the right cache so the next GET re-scans disk.
	switch board {
	case "issues":
		if issuesCache != nil {
			issuesCache.invalidate()
		}
	case "flows":
		if flowsCache != nil {
			flowsCache.invalidate()
		}
	}
	if hub == nil {
		return
	}
	hub.Broadcast(ServerEvent{
		Board:     board,
		CardID:    cardID,
		Action:    action,
		EventType: sseEventForAction(action),
	})
}

// classifyEvent inspects a raw fsnotify event and returns
// (board, cardID, action) — board is "" if the event is irrelevant.
func classifyEvent(ev fsnotify.Event) (board, cardID, action string) {
	name := filepath.Base(ev.Name)
	if !strings.HasSuffix(strings.ToLower(name), ".md") {
		return "", "", ""
	}
	if isSkippedMarkdown(name) {
		return "", "", ""
	}
	// Determine board from the path.
	lower := strings.ToLower(filepath.ToSlash(ev.Name))
	switch {
	case strings.Contains(lower, "/dev/issues/"):
		board = "issues"
	case strings.Contains(lower, "/dev/flows/"):
		board = "flows"
	default:
		return "", "", ""
	}
	cardID = deriveIDFromFilename(name)
	switch {
	case ev.Op&fsnotify.Create != 0:
		action = "created"
	case ev.Op&fsnotify.Remove != 0:
		action = "deleted"
	case ev.Op&fsnotify.Rename != 0:
		// Treat rename as updated — the file likely moved between
		// canonical dir and completed/.
		action = "updated"
	case ev.Op&fsnotify.Write != 0:
		action = "updated"
	default:
		return "", "", ""
	}
	return board, cardID, action
}

func sseEventForAction(action string) string {
	switch action {
	case "created":
		return "card_added"
	case "deleted":
		return "card_removed"
	default:
		return "card_changed"
	}
}

// readDirNoSymlink lists subdirectory names under root, skipping symlinks
// and hidden entries.
func readDirNoSymlink(root string) ([]string, error) {
	entries, err := os.ReadDir(root)
	if err != nil {
		return nil, err
	}
	out := []string{}
	for _, e := range entries {
		if !e.IsDir() {
			continue
		}
		name := e.Name()
		if strings.HasPrefix(name, ".") {
			continue
		}
		// Detect symlinks: lstat the full path.
		full := filepath.Join(root, name)
		info, err := os.Lstat(full)
		if err != nil {
			continue
		}
		if info.Mode()&os.ModeSymlink != 0 {
			continue
		}
		out = append(out, name)
	}
	return out, nil
}