[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

4 files changed, 230 insertions, 12 deletions

diff --git a/internal/api/client/conversations/conversationdelete.go b/internal/api/client/conversations/conversationdelete.go
new file mode 100644
index 000000000..6f8f43a94
--- /dev/null
+++ b/internal/api/client/conversations/conversationdelete.go
@@ -0,0 +1,93 @@
+// 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 conversations
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+)
+
+// ConversationDELETEHandler swagger:operation DELETE /api/v1/conversations/{id} conversationDelete
+//
+// Delete a single conversation with the given ID.
+//
+// This doesn't delete the actual statuses in the conversation,
+// nor does it prevent a new conversation from being created later from the same thread and participants.
+//
+//	---
+//	tags:
+//	- conversations
+//
+//	produces:
+//	- application/json
+//
+//	parameters:
+//	-
+//		name: id
+//		type: string
+//		description: ID of the conversation
+//		in: path
+//		required: true
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- write:conversations
+//
+//	responses:
+//		'200':
+//			description: conversation deleted
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'404':
+//			description: not found
+//		'406':
+//			description: not acceptable
+//		'500':
+//			description: internal server error
+func (m *Module) ConversationDELETEHandler(c *gin.Context) {
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorUnauthorized(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	id, errWithCode := apiutil.ParseID(c.Param(apiutil.IDKey))
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	errWithCode = m.processor.Conversations().Delete(c.Request.Context(), authed.Account, id)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	c.JSON(http.StatusOK, apiutil.EmptyJSONObject)
+}
diff --git a/internal/api/client/conversations/conversationread.go b/internal/api/client/conversations/conversationread.go
new file mode 100644
index 000000000..7f68a2a33
--- /dev/null
+++ b/internal/api/client/conversations/conversationread.go
@@ -0,0 +1,95 @@
+// 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 conversations
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+)
+
+// ConversationReadPOSTHandler swagger:operation POST /api/v1/conversation/{id}/read conversationRead
+//
+// Mark a conversation with the given ID as read.
+//
+//	---
+//	tags:
+//	- conversations
+//
+//	produces:
+//	- application/json
+//
+//	parameters:
+//	-
+//		name: id
+//		in: path
+//		type: string
+//		required: true
+//		description: ID of the conversation.
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- write:conversations
+//
+//	responses:
+//		'200':
+//			name: conversation
+//			description: Updated conversation.
+//			schema:
+//				"$ref": "#/definitions/conversation"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'404':
+//			description: not found
+//		'406':
+//			description: not acceptable
+//		'422':
+//			description: unprocessable content
+//		'500':
+//			description: internal server error
+func (m *Module) ConversationReadPOSTHandler(c *gin.Context) {
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorUnauthorized(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
+		apiutil.ErrorHandler(c, gtserror.NewErrorNotAcceptable(err, err.Error()), m.processor.InstanceGetV1)
+		return
+	}
+
+	id, errWithCode := apiutil.ParseID(c.Param(apiutil.IDKey))
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	apiConversation, errWithCode := m.processor.Conversations().Read(c.Request.Context(), authed.Account, id)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	apiutil.JSON(c, http.StatusOK, apiConversation)
+}
diff --git a/internal/api/client/conversations/conversations.go b/internal/api/client/conversations/conversations.go
index be19a9cdc..e742c8d3d 100644
--- a/internal/api/client/conversations/conversations.go
+++ b/internal/api/client/conversations/conversations.go
@@ -21,13 +21,17 @@ import (
 	"net/http"
 
 	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 	"github.com/superseriousbusiness/gotosocial/internal/processing"
 )
 
 const (
-	// BasePath is the base URI path for serving
-	// conversations, minus the api prefix.
+	// BasePath is the base path for serving the conversations API, minus the 'api' prefix.
 	BasePath = "/v1/conversations"
+	// BasePathWithID is the base path with the ID key in it, for operations on an existing conversation.
+	BasePathWithID = BasePath + "/:" + apiutil.IDKey
+	// ReadPathWithID is the path for marking an existing conversation as read.
+	ReadPathWithID = BasePathWithID + "/read"
 )
 
 type Module struct {
@@ -42,4 +46,6 @@ func New(processor *processing.Processor) *Module {
 
 func (m *Module) Route(attachHandler func(method string, path string, f ...gin.HandlerFunc) gin.IRoutes) {
 	attachHandler(http.MethodGet, BasePath, m.ConversationsGETHandler)
+	attachHandler(http.MethodDelete, BasePathWithID, m.ConversationDELETEHandler)
+	attachHandler(http.MethodPost, ReadPathWithID, m.ConversationReadPOSTHandler)
 }
diff --git a/internal/api/client/conversations/conversationsget.go b/internal/api/client/conversations/conversationsget.go
index 11bddb1ce..663b9a707 100644
--- a/internal/api/client/conversations/conversationsget.go
+++ b/internal/api/client/conversations/conversationsget.go
@@ -24,14 +24,13 @@ import (
 	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
 )
 
 // ConversationsGETHandler swagger:operation GET /api/v1/conversations conversationsGet
 //
 // Get an array of (direct message) conversations that requesting account is involved in.
 //
-// NOT IMPLEMENTED YET: Will currently always return an array of length 0.
-//
 // The next and previous queries can be parsed from the returned Link header.
 // Example:
 //
@@ -51,26 +50,26 @@ import (
 //		name: max_id
 //		type: string
 //		description: >-
-//			Return only conversations *OLDER* than the given max ID.
+//			Return only conversations with last statuses *OLDER* than the given max ID.
 //			The conversation with the specified ID will not be included in the response.
-//			NOTE: the ID is of the internal conversation, use the Link header for pagination.
+//			NOTE: The ID is a status ID. Use the Link header for pagination.
 //		in: query
 //		required: false
 //	-
 //		name: since_id
 //		type: string
 //		description: >-
-//			Return only conversations *NEWER* than the given since ID.
+//			Return only conversations with last statuses *NEWER* than the given since ID.
 //			The conversation with the specified ID will not be included in the response.
-//			NOTE: the ID is of the internal conversation, use the Link header for pagination.
+//			NOTE: The ID is a status ID. Use the Link header for pagination.
 //		in: query
 //	-
 //		name: min_id
 //		type: string
 //		description: >-
-//			Return only conversations *IMMEDIATELY NEWER* than the given min ID.
+//			Return only conversations with last statuses *IMMEDIATELY NEWER* than the given min ID.
 //			The conversation with the specified ID will not be included in the response.
-//			NOTE: the ID is of the internal conversation, use the Link header for pagination.
+//			NOTE: The ID is a status ID. Use the Link header for pagination.
 //		in: query
 //		required: false
 //	-
@@ -108,7 +107,8 @@ import (
 //		'500':
 //			description: internal server error
 func (m *Module) ConversationsGETHandler(c *gin.Context) {
-	if _, err := oauth.Authed(c, true, true, true, true); err != nil {
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
 		apiutil.ErrorHandler(c, gtserror.NewErrorUnauthorized(err, err.Error()), m.processor.InstanceGetV1)
 		return
 	}
@@ -118,5 +118,29 @@ func (m *Module) ConversationsGETHandler(c *gin.Context) {
 		return
 	}
 
-	apiutil.Data(c, http.StatusOK, apiutil.AppJSON, apiutil.EmptyJSONArray)
+	page, errWithCode := paging.ParseIDPage(c,
+		1,  // min limit
+		80, // max limit
+		40, // default limit
+	)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	resp, errWithCode := m.processor.Conversations().GetAll(
+		c.Request.Context(),
+		authed.Account,
+		page,
+	)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if resp.LinkHeader != "" {
+		c.Header("Link", resp.LinkHeader)
+	}
+
+	apiutil.JSON(c, http.StatusOK, resp.Items)
 }