[feature] Conversations API (#3013)

* Implement conversations API

* Sort and page conversations by last status ID

* Appease linter

* Fix deleting conversations and statuses

* Refactor to make migrations automatic

* Lint

* Update tests post-merge

* Fixes from live-fire testing

* Linter caught a format problem

* Refactor tests, fix cache

* Negative test for non-DMs

* Run conversations advanced migration on testrig startup as well as regular server startup

* Document (lack of) side effects of API method for deleting a conversation

* Make not-found check less nested for readability

* Rename PutConversation to UpsertConversation

* Use util.Ptr instead of IIFE

* Reduce cache used by conversations

* Remove unnecessary TableExpr/ColumnExpr

* Use struct tags for both unique constraints on Conversation

* Make it clear how paging with GetDirectStatusIDsBatch should be used

* Let conversation paging skip conversations it can't render

* Use Bun NewDropTable

* Convert delete raw query to Bun

* Convert update raw query to Bun

* Convert latestConversationStatusesTempTable raw query partially to Bun

* Convert conversationStatusesTempTable raw query partially to Bun

* Rename field used to store result of MaxDirectStatusID

* Move advanced migrations to their own tiny processor

* Catch up util function name with main

* Remove json.… wrappers

* Remove redundant check

* Combine error checks

* Replace map with slice of structs

* Address processor/type converter comments

- Add context info for errors
- Extract some common processor code into shared methods
- Move conversation eligibility check ahead of populating conversation

* Add error context when dropping temp tables

internal/cache/db.go

@@ -56,6 +56,12 @@ type GTSCaches struct {
 	// Client provides access to the gtsmodel Client database cache.
 	Client StructCache[*gtsmodel.Client]
 
+	// Conversation provides access to the gtsmodel Conversation database cache.
+	Conversation StructCache[*gtsmodel.Conversation]
+
+	// ConversationLastStatusIDs provides access to the conversation last status IDs database cache.
+	ConversationLastStatusIDs SliceCache[string]
+
 	// DomainAllow provides access to the domain allow database cache.
 	DomainAllow *domain.Cache
 
@@ -426,6 +432,52 @@ func (c *Caches) initClient() {
 	})
 }
 
+func (c *Caches) initConversation() {
+	cap := calculateResultCacheMax(
+		sizeofConversation(), // model in-mem size.
+		config.GetCacheConversationMemRatio(),
+	)
+
+	log.Infof(nil, "cache size = %d", cap)
+
+	copyF := func(c1 *gtsmodel.Conversation) *gtsmodel.Conversation {
+		c2 := new(gtsmodel.Conversation)
+		*c2 = *c1
+
+		// Don't include ptr fields that
+		// will be populated separately.
+		// See internal/db/bundb/conversation.go.
+		c2.Account = nil
+		c2.OtherAccounts = nil
+		c2.LastStatus = nil
+
+		return c2
+	}
+
+	c.GTS.Conversation.Init(structr.CacheConfig[*gtsmodel.Conversation]{
+		Indices: []structr.IndexConfig{
+			{Fields: "ID"},
+			{Fields: "ThreadID,AccountID,OtherAccountsKey"},
+			{Fields: "AccountID,LastStatusID"},
+			{Fields: "AccountID", Multiple: true},
+		},
+		MaxSize:    cap,
+		IgnoreErr:  ignoreErrors,
+		Copy:       copyF,
+		Invalidate: c.OnInvalidateConversation,
+	})
+}
+
+func (c *Caches) initConversationLastStatusIDs() {
+	cap := calculateSliceCacheMax(
+		config.GetCacheConversationLastStatusIDsMemRatio(),
+	)
+
+	log.Infof(nil, "cache size = %d", cap)
+
+	c.GTS.ConversationLastStatusIDs.Init(0, cap)
+}
+
 func (c *Caches) initDomainAllow() {
 	c.GTS.DomainAllow = new(domain.Cache)
 }