add paste functionality

Backend/paste/expiry.go

@@ -0,0 +1,42 @@
+package paste
+
+import (
+	"context"
+	"log/slog"
+	"time"
+)
+
+func StartExpiryWorker(ctx context.Context, s *Store, interval time.Duration) {
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			deleteExpired(s)
+		}
+	}
+}
+
+func deleteExpired(s *Store) {
+	var expired []string
+	err := s.ForEach(func(p *Paste) error {
+		if p.ExpiresAt != nil && time.Now().After(*p.ExpiresAt) {
+			expired = append(expired, p.ID)
+		}
+		return nil
+	})
+	if err != nil {
+		slog.Error("expiry scan error", "err", err)
+		return
+	}
+	for _, id := range expired {
+		if err := s.Delete(id); err != nil {
+			slog.Error("expiry delete error", "id", id, "err", err)
+		}
+	}
+	if len(expired) > 0 {
+		slog.Info("deleted expired pastes", "count", len(expired))
+	}
+}