i have no idea what i'm doing

internal/processing/timeline/sharedcache.go

@@ -0,0 +1,56 @@
+package timeline
+
+import (
+	"sort"
+	"sync"
+)
+
+type sharedCache struct {
+	data      map[string]*post
+	maxLength int
+	*sync.Mutex
+}
+
+func newSharedCache(maxLength int) *sharedCache {
+	return &sharedCache{
+		data:      make(map[string]*post),
+		maxLength: maxLength,
+	}
+}
+
+func (s *sharedCache) shrink() {
+	// check if the length is longer than max size
+	toRemove := len(s.data) - s.maxLength
+
+	if toRemove > 0 {
+		// we have stuff to remove so lock the map while we work
+		s.Lock()
+		defer s.Unlock()
+
+		// we need to time-sort the map to remove the oldest entries
+		// the below code gives us a slice of keys, arranged from newest to oldest
+		postSlice := make([]*post, 0, len(s.data))
+		for _, v := range s.data {
+			postSlice = append(postSlice, v)
+		}
+		sort.Slice(postSlice, func(i int, j int) bool {
+			return postSlice[i].createdAt.After(postSlice[j].createdAt)
+		})
+
+		// now for each entry we have to remove, delete the entry from the map by its status ID
+		for i := 0; i < toRemove; i = i + 1 {
+			statusID := postSlice[i].statusID
+			delete(s.data, statusID)
+		}
+	}
+}
+
+func (s *sharedCache) put(post *post) {
+	s.Lock()
+	defer s.Unlock()
+	s.data[post.statusID] = post
+}
+
+func (s *sharedCache) get(statusID string) *post {
+	return s.data[statusID]
+}