Timeline manager (#40)

* start messing about with timeline manager

* i have no idea what i'm doing

* i continue to not know what i'm doing

* it's coming along

* bit more progress

* update timeline with new posts as they come in

* lint and fmt

* Select accounts where empty string

* restructure a bunch, get unfaves working

* moving stuff around

* federate status deletes properly

* mention regex better but not 100% there

* fix regex

* some more hacking away at the timeline code phew

* fix up some little things

* i can't even

* more timeline stuff

* move to ulid

* fiddley

* some lil fixes for kibou compatibility

* timelines working pretty alright!

* tidy + lint

internal/timeline/preparedposts.go

@@ -0,0 +1,60 @@
+package timeline
+
+import (
+	"container/list"
+	"errors"
+
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+)
+
+type preparedPosts struct {
+	data *list.List
+}
+
+type preparedPostsEntry struct {
+	statusID string
+	prepared *apimodel.Status
+}
+
+func (p *preparedPosts) insertPrepared(i *preparedPostsEntry) error {
+	if p.data == nil {
+		p.data = &list.List{}
+	}
+
+	// if we have no entries yet, this is both the newest and oldest entry, so just put it in the front
+	if p.data.Len() == 0 {
+		p.data.PushFront(i)
+		return nil
+	}
+
+	var insertMark *list.Element
+	// We need to iterate through the index to make sure we put this post in the appropriate place according to when it was created.
+	// We also need to make sure we're not inserting a duplicate post -- this can happen sometimes and it's not nice UX (*shudder*).
+	for e := p.data.Front(); e != nil; e = e.Next() {
+		entry, ok := e.Value.(*preparedPostsEntry)
+		if !ok {
+			return errors.New("index: could not parse e as a preparedPostsEntry")
+		}
+
+		// if the post to index is newer than e, insert it before e in the list
+		if insertMark == nil {
+			if i.statusID > entry.statusID {
+				insertMark = e
+			}
+		}
+
+		// make sure we don't insert a duplicate
+		if entry.statusID == i.statusID {
+			return nil
+		}
+	}
+
+	if insertMark != nil {
+		p.data.InsertBefore(i, insertMark)
+		return nil
+	}
+
+	// if we reach this point it's the oldest post we've seen so put it at the back
+	p.data.PushBack(i)
+	return nil
+}