[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

1 files changed, 77 insertions, 0 deletions

diff --git a/internal/gtsmodel/conversation.go b/internal/gtsmodel/conversation.go
new file mode 100644
index 000000000..f03f27458
--- /dev/null
+++ b/internal/gtsmodel/conversation.go
@@ -0,0 +1,77 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package gtsmodel
+
+import (
+	"slices"
+	"strings"
+	"time"
+
+	"github.com/superseriousbusiness/gotosocial/internal/util"
+)
+
+// Conversation represents direct messages between the owner account and a set of other accounts.
+type Conversation struct {
+	// ID of this item in the database.
+	ID string `bun:"type:CHAR(26),pk,nullzero,notnull,unique"`
+
+	// When was this item created?
+	CreatedAt time.Time `bun:"type:timestamptz,nullzero,notnull,default:current_timestamp"`
+
+	// When was this item last updated?
+	UpdatedAt time.Time `bun:"type:timestamptz,nullzero,notnull,default:current_timestamp"`
+
+	// Account that owns the conversation.
+	AccountID string   `bun:"type:CHAR(26),nullzero,notnull,unique:conversations_thread_id_account_id_other_accounts_key_uniq,unique:conversations_account_id_last_status_id_uniq"`
+	Account   *Account `bun:"-"`
+
+	// Other accounts participating in the conversation.
+	// Doesn't include the owner. May be empty in the case of a DM to yourself.
+	OtherAccountIDs []string   `bun:"other_account_ids,array"`
+	OtherAccounts   []*Account `bun:"-"`
+
+	// Denormalized lookup key derived from unique OtherAccountIDs, sorted and concatenated with commas.
+	// May be empty in the case of a DM to yourself.
+	OtherAccountsKey string `bun:",notnull,unique:conversations_thread_id_account_id_other_accounts_key_uniq"`
+
+	// Thread that the conversation is part of.
+	ThreadID string `bun:"type:CHAR(26),nullzero,notnull,unique:conversations_thread_id_account_id_other_accounts_key_uniq"`
+
+	// ID of the last status in this conversation.
+	LastStatusID string  `bun:"type:CHAR(26),nullzero,notnull,unique:conversations_account_id_last_status_id_uniq"`
+	LastStatus   *Status `bun:"-"`
+
+	// Has the owner read all statuses in this conversation?
+	Read *bool `bun:",default:false"`
+}
+
+// ConversationOtherAccountsKey creates an OtherAccountsKey from a list of OtherAccountIDs.
+func ConversationOtherAccountsKey(otherAccountIDs []string) string {
+	otherAccountIDs = util.UniqueStrings(otherAccountIDs)
+	slices.Sort(otherAccountIDs)
+	return strings.Join(otherAccountIDs, ",")
+}
+
+// ConversationToStatus is an intermediate struct to facilitate the many2many relationship between a conversation and its statuses,
+// including but not limited to the last status. These are used only when deleting a status from a conversation.
+type ConversationToStatus struct {
+	ConversationID string        `bun:"type:CHAR(26),unique:conversation_to_statuses_conversation_id_status_id_uniq,nullzero,notnull"`
+	Conversation   *Conversation `bun:"rel:belongs-to"`
+	StatusID       string        `bun:"type:CHAR(26),unique:conversation_to_statuses_conversation_id_status_id_uniq,nullzero,notnull"`
+	Status         *Status       `bun:"rel:belongs-to"`
+}