phase3: HTTP server with converter, one-shot preview store, and middleware

internal/server/preview_store.go

@@ -0,0 +1,91 @@
+package server
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+const janitorInterval = 5 * time.Minute
+
+type PreviewStore struct {
+	mu    sync.Mutex
+	items map[string]previewItem
+	ttl   time.Duration
+	now   func() time.Time
+}
+
+type previewItem struct {
+	html     []byte
+	mime     string
+	filename string
+	expires  time.Time
+}
+
+func NewPreviewStore(ttl time.Duration) *PreviewStore {
+	return &PreviewStore{
+		items: make(map[string]previewItem),
+		ttl:   ttl,
+		now:   time.Now,
+	}
+}
+
+func (s *PreviewStore) Put(html []byte, mime, filename string) string {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	id := uuid.NewString()
+	s.items[id] = previewItem{
+		html:     append([]byte(nil), html...),
+		mime:     mime,
+		filename: filename,
+		expires:  s.now().Add(s.ttl),
+	}
+
+	return id
+}
+
+func (s *PreviewStore) Take(id string) (previewItem, bool) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	item, ok := s.items[id]
+	if !ok {
+		return previewItem{}, false
+	}
+
+	delete(s.items, id)
+	if s.now().After(item.expires) {
+		return previewItem{}, false
+	}
+
+	item.html = append([]byte(nil), item.html...)
+	return item, true
+}
+
+func (s *PreviewStore) janitor(ctx context.Context) {
+	ticker := time.NewTicker(janitorInterval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case now := <-ticker.C:
+			s.cleanupExpired(now)
+		}
+	}
+}
+
+func (s *PreviewStore) cleanupExpired(now time.Time) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	for id, item := range s.items {
+		if now.After(item.expires) {
+			delete(s.items, id)
+		}
+	}
+}